US20070062033A1 - Selective consolidation methods for fabricating semiconductor device components and conductive features thereof - Google Patents

Abstract

Methods for forming conductive elements of substrates of components that are configured for use in electronic devices includes providing unconsolidated material over at least a portion of such a substrate and at least partially consolidating the material selectively or in accordance with a program. Such consolidation may be effected by directing consolidating energy, in the form of focused (e.g., laser) radiation or otherwise, toward the unconsolidated material. Additionally, all or part of a substrate may be formed by programmed material consolidation processes.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a divisional of application Ser. No. 10/896,271, filed Jul. 20, 2004, now U.S. Pat. No. 7,137,193, issued Nov. 21, 2006, which is a continuation of application Ser. No. 10/108,959, filed Mar. 28, 2002, now U.S. Pat. No. 6,764,933 issued Jul. 20, 2004, which is a divisional of application Ser. No. 09/843,118, filed Apr. 26, 2001, now U.S. Pat. No. 6,468,891, issued Oct. 22, 2002, which is a divisional of Ser. No. 09/511,986, filed Feb. 24, 2000, pending.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The present invention relates to conductive elements for electrically connecting different semiconductor device components to one another. Particularly, the present invention relates to conductive elements that are carried by semiconductor devices. More particularly, the present invention relates to stereolithographically fabricated conductive elements. The present invention also relates to the conductive lines of carrier substrates, such as circuit boards, and to methods of fabricating such carrier substrates.
• 2. State of the Art
• Intermediate Conductive Elements. An electronic device typically includes one or more semiconductor devices. The semiconductor devices of an electronic device are electrically connected to a carrier substrate, which, in turn, electrically connects each semiconductor device to other components of the electronic device. In order to fulfill the demands for electronic devices of ever-decreasing size and ever-increasing capability, much of the large, space-consuming circuitry components of conventional electronic devices have been incorporated into semiconductor devices. As a result, many state of the art electronic devices include semiconductor devices that are directly connected to one another.
• Conventionally, electrical connections between a semiconductor device and a carrier substrate or another semiconductor device are made by way of wire bonds between bond pads of the semiconductor device and contact pads of the carrier substrate. Wire bonding is somewhat undesirable, however, in that the wire bonds are separately and sequentially formed. As state of the art semiconductor devices typically include large numbers of bond pads positioned closely to one another, wire bonding these semiconductor devices to carrier substrates or other semiconductor devices can be a very time-consuming process.
• The semiconductor devices of many state of the art electronic devices are connected to carrier substrates or other semiconductor devices with alternative types of intermediate conductive elements. For example, semiconductor devices can be flip-chip bonded, or bonded by way of a controlled collapse chip connection (C-4) to a substrate or another semiconductor device with conductive structures, such as solder balls. When flip-chip type bonds are used, a minimal amount of the real estate on a carrier substrate or other semiconductor device component is consumed.
• Tape automated bonding (TAB) processes, which employ a tape including a dielectric film with conductive traces extending thereacross, have also been used to electrically connect semiconductor devices to other semiconductor device components. Tape automated bonding is useful for forming very thin assemblies of semiconductor devices and substrates.
• While all of the bond pads of a semiconductor device may be simultaneously connected with a carrier substrate or another semiconductor device when both flip-chip type bonding and TAB are used, neither of these techniques addresses the need for assemblies of both minimal lateral dimensions and minimal thickness.
• Circuit Boards: Circuit boards are often assembled with semiconductor devices to electrically connect different semiconductor devices to one another or to other components of an electronic device. Typically, circuit boards have one or more layers of metal circuitry carried by the insulating, or dielectric, substrates thereof. When circuit boards have conductive circuits extending across more than one plane thereof, the circuits may be electrically connected by way of through holes that are metal plated or filled.
• Typically, reinforced polymeric materials are employed as the dielectric substrates of rigid circuit boards. The most commonly used dielectric substrate material is glass-reinforced epoxy. Some circuit boards are made from polyimide resins so as to withstand higher temperatures. Other dielectric materials have also been developed and used to fabricate the dielectric substrates of circuit boards.
• Some applications require that the dielectric substrate of the circuit board bend or flex during assembly of the circuit board with semiconductor or other electronic devices or while a device including the circuit board is being used. While some flexible circuit boards have substrates fabricated from flexible dielectric materials that are reinforced with woven or random fibers, unsupported polymeric films may also be used to form the substrates of flexible circuit boards.
• Conventional printed circuit boards having a single-layered substrate are machined to define the edges thereof, to bevel the edges thereof, and to form through holes at desired locations. Metal conductive circuits are then formed on one or both surfaces of the printed circuit boards, in communication with metal plating or vias located in the through holes. Originally, conductive materials, such as silver, were printed onto the substrate to form the metal conductive circuits and to plate the through holes or to form vias therein.
• Copper-clad laminates, which include a layer of copper secured to a dielectric substrate, can also be used to fabricate circuit boards. Copper is removed from regions of the surface of the substrate where conductive circuits are not desired. Accordingly, the process is referred to as a “subtractive” technique.
• Other conventional techniques for forming metal conductive circuits and plating or filling the through holes include electroless plating, electrolytic plating, and plasma-assisted chemical vapor deposition (“CVD”) processes. Etching processes may also be used to pattern the conductive circuits of printed circuit boards. As the metal circuits, plating, or vias are formed on the substrate, these processes are referred to as “additive” techniques.
• The substrates of state of the art circuit boards have multiple, laminated layers. The conductive circuits of these circuit boards laterally traverse the surfaces of the boards, as well as several different planes through the interior of the substrate to accommodate the increasingly complex semiconductor devices connected to the substrate while maintaining or decreasing the size of the circuit board. In manufacturing such boards, circuit traces are fabricated, as noted above, on one layer of the substrate prior to laminating the next layer of the substrate thereto. Thus, laminated circuit boards are built up, layer by layer. The use of conventional processes to fabricate multilayer circuit boards is, however, somewhat undesirable since each new layer must be aligned with every previously formed layer of the circuit board to provide the desired functionality.
• Completed circuit boards may then be tested. Optical or electrical testing may be conducted to determine whether the circuit boards will function properly.
• Circuit boards are typically fabricated on a very large scale, with sheets of several circuit boards typically being supplied to semiconductor device manufacturers or electronic device manufacturers for assembly with semiconductor devices and other electronic components. Conventional, large scale circuit board fabrication processes are typically not useful for fabricating prototype circuit boards.
• When a new circuit board design is needed, a prototype circuit board is usually fabricated. Due to the complexity of state of the art semiconductor devices and electronic devices, the fabrication of prototype circuit boards is a very time-consuming process. Moreover, production scale circuit boards based on a certain prototype circuit board design may not provide the same electrical performance as intended.
• Accordingly, there is a need for a method that can be employed to quickly fabricate simple and multilayered circuit boards in either very small numbers or very large numbers. There is also a need for a process for fabricating multilayered circuit boards that does not require repeated alignment of each of the new layers of the circuit board with the previously fabricated layers thereof.
• Stereolithography. In the past decade, a manufacturing technique termed “stereolithography,” also known as “layered manufacturing,” has evolved to a degree where it is employed in many industries.
• Essentially, stereolithography as conventionally practiced involves utilizing a computer to generate a three-dimensional (3-D) mathematical simulation or model of an object to be fabricated, such generation usually effected with 3-D computer-aided design (CAD) software. The model or simulation is mathematically separated or “sliced” into a large number of relatively thin, parallel, usually vertically superimposed layers, each layer having defined boundaries and other features associated with the model (and thus the actual object to be fabricated) at the level of that layer within the exterior boundaries of the object. A complete assembly or stack of all of the layers defines the entire object, and surface resolution of the object is, in part, dependent upon the thickness of the layers.
• The mathematical simulation or model is then employed to generate an actual object by building the object, layer by superimposed layer. A wide variety of approaches to stereolithography by different companies has resulted in techniques for fabrication of objects from both metallic and nonmetallic materials. Regardless of the material employed to fabricate an object, stereolithographic techniques usually involve disposition of a layer of unconsolidated or unfixed material corresponding to each layer within the object boundaries, followed by selective consolidation or fixation of the material to at least a partially consolidated, or semi-solid, state in those areas of a given layer corresponding to portions of the object, the consolidated or fixed material also at that time being substantially concurrently bonded to a lower layer of the object being fabricated. The unconsolidated material employed to build an object may be supplied in particulate or liquid form, and the material itself may be consolidated or fixed, or a separate binder material may be employed to bond material particles to one another and to those of a previously formed layer. In some instances, thin sheets of material may be superimposed to build an object, each sheet being fixed to a next lower sheet and unwanted portions of each sheet removed, a stack of such sheets defining the completed object. When particulate materials are employed, resolution of object surfaces is highly dependent upon particle size, whereas when a liquid is employed, surface resolution is highly dependent upon the minimum surface area of the liquid which can be fixed and the minimum thickness of a layer that can be generated. Of course, in either case, resolution and accuracy of object reproduction from the CAD file is also dependent upon the ability of the apparatus used to fix the material to precisely track the mathematical instructions indicating solid areas and boundaries for each layer of material. Toward that end, and depending upon the layer being fixed, various fixation approaches have been employed, including particle bombardment (electron beams), disposing a binder or other fixative (such as by ink-jet printing techniques), or irradiation using heat or specific wavelength ranges.
• An early application of stereolithography was to enable rapid fabrication of molds and prototypes of objects from CAD files. Thus, either male or female forms on which mold material might be disposed may be rapidly generated. Prototypes of objects might be built to verify the accuracy of the CAD file defining the object and to detect any design deficiencies and possible fabrication problems before a design is committed to large-scale production.
• In more recent years, stereolithography has been employed to develop and refine object designs in relatively inexpensive materials, and has also been used to fabricate small quantities of objects where the cost of conventional fabrication techniques is prohibitive for same, such as in the case of plastic objects conventionally formed by injection molding. It is also known to employ stereolithography in the custom fabrication of products generally built in small quantities or where a product design is rendered only once. Finally, it has been appreciated in some industries that stereolithography provides a capability to fabricate products, such as those including closed interior chambers or convoluted passageways, which cannot be fabricated satisfactorily using conventional manufacturing techniques. It has also been recognized in some industries that a stereolithographic object or component may be formed or built around another, preexisting object or component to create a larger product.
• However, to the inventor's knowledge, stereolithography has yet to be applied to mass production of articles in volumes of thousands or millions, or employed to produce, augment or enhance products including other, preexisting components in large quantities, where minute component sizes are involved, and where extremely high resolution and a high degree of reproducibility of results are required. In particular, the inventor is not aware of the use of stereolithography to fabricate intermediate conductive elements between semiconductor device components or on circuit boards. Furthermore, conventional stereolithography apparatus and methods fail to address the difficulties of precisely locating and orienting a number of preexisting components for stereolithographic application of material thereto without the use of mechanical alignment techniques or to otherwise assuring precise, repeatable placement of components.
SUMMARY OF THE INVENTION
• The present invention includes stereolithographically fabricated intermediate conductive elements. Accordingly, the intermediate conductive elements of the present invention may have one or more layers of conductive material. In multilayet embodiments, the intermediate conductive elements have a plurality of superimposed, contiguous, mutually adhered layers of conductive material. Any known conductive material may be used to form the intermediate conductive elements of the present invention. Exemplary conductive materials include, without limitation, electrically conductive thermoplastic elasiomers and metals.
• The invention also includes semiconductor device assemblies with one or more semiconductor devices that are electrically connected to one or more other semiconductor device components, such as carrier substrates, leads, or other semiconductor devices, by way of the intermediate conductive elements of the present invention. These intermediate conductive elements are substantially carried upon the semiconductor device and the component to which the semiconductor device is connected. For example, when used to connect one semiconductor die to another semiconductor die, an intermediate conductive element of the present invention contacts a bond pad of the first semiconductor die, extends across a portion of the active surface of the first semiconductor die towards the second semiconductor die, extends over the active surface of the second semiconductor die, and contacts a corresponding bond pad of the second semiconductor die. As another example, when the intermediate conductive elements of the present invention are used to connect a semiconductor die to a carrier substrate, one end of an intermediate conductive element may contact a contact (e.g., a bond pad) of the semiconductor die, extend over an active surface of the semiconductor die, down a peripheral edge thereof, and over a surface of the carrier substrate, and contact a contact pad of the carrier substrate at a second end of the intermediate conductive element.
• In another aspect, the present invention includes a printed circuit board with a substrate that carries one or more stereolithographically fabricated conductive traces. Each conductive trace may have one or more layers of conductive material. The conductive material may be, for example, a thermoplastic conductive elastomer or a metal.
• According to another aspect of the present invention, the substrate of the printed circuit board has two or more superimposed, contiguous, mutually adhered layers of dielectric material. One or more of these layers of the substrate may be fabricated using stereolithography techniques. For example, each stereolithographically formed layer of the substrate may be defined by, first, forming a layer of unconsolidated (i.e., uncured or particulate) dielectric material, then consolidating (i.e., curing or bonding particles) of the dielectric material in selected regions of the layer. Alternatively, each of the layers of the substrate may be fabricated by spraying dielectric material so as to define the desired configuration of the layer, permitting the dielectric material to at least partially harden or solidify, then using the same technique to form and stack one or more additional layers of dielectric material to complete the substrate.
• When both the intermediate conductive elements and the substrate are fabricated by stereolithographic techniques, layers of the intermediate conductive elements and of the substrate residing in the same planes can be fabricated substantially simultaneously or sequentially.
• The materials of both the intermediate conductive elements and the substrate may be either rigid or flexible. Accordingly, the methods of the present invention can be used to fabricate both rigid and flexible circuit boards.
• The stereolithography, or “layered manufacturing,” processes that are used to fabricate the intermediate conductive elements or circuit board substrates of the present invention are initiated and controlled by a 3-D CAD-programmed computer.
• When stereolithography is used to fabricate intermediate conductive elements between assembled semiconductor device components, the stereolithographic method of fabricating the intermediate conductive elements of the present invention preferably includes the use of a machine vision system to locate the assembled semiconductor device components on which intermediate conductive elements are to be fabricated, as well as the various features of the semiconductor device components. The use of a machine vision system directs the alignment of a stereolithography system with each substrate or layer for material disposition purposes. Accordingly, the assembled semiconductor device components need not be precisely mechanically aligned with any component of the stereolithography system to practice the stereolithographic embodiment of the method of the present invention.
• As noted previously herein, in a preferred embodiment, the intermediate conductive elements of the present invention are preferably fabricated using three-dimensional printing techniques, wherein a conductive material having the desired properties and that is solid at ambient temperatures is heated to liquefy same. Exemplary materials that are useful for forming intermediate conductive elements according to the present invention include thermoplastic conductive elastomers and metals. The liquified conductive material is then disposed, in a precisely focused spray (e.g., through an ink jet type nozzle) under control of a computer and, preferably, responsive to input from a machine vision system, such as a pattern recognition system, to form a layer of each of the intermediate conductive elements. The conductive material is then permitted to at least partially harden.
• A circuit board substrate may be similarly manufactured, except with a dielectric material rather than a conductive material. Alternatively, other stereolithographic processes may be employed to fabricate the substrate. For example, the substrate may be fabricated using precisely focused electromagnetic radiation in the form of an ultraviolet (UV) wavelength laser to fix or cure selected regions of a layer of a liquid photopolymer material disposed on the semiconductor device or other substrate.
• Other features and advantages of the present invention will become apparent to those of skill in the art through consideration of the ensuing description, the accompanying drawings, and the appended claims.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
• FIG. 1 is a top schematic representation of a first embodiment of an assembly according to the present invention, which includes a semiconductor die with bond pads electrically connected to the contact pads of a carrier substrate by way of the intermediate conductive elements of the present invention;
• FIG. 2 is a cross-section taken along line2-2 ofFIG. 1;
• FIG. 3 is a top schematic representation of a second embodiment of an assembly according to the present invention, which includes two semiconductor dice with bond pads that are connected by way of the intermediate conductive elements of the present invention;
• FIG. 4 is a cross-section taken along line4-4 ofFIG. 3;
• FIG. 5 is a top schematic representation of a circuit board with a single substrate layer, at least the intermediate conductive elements of the circuit board having been fabricated in accordance with the method of the present invention;
• FIG. 6 is a cross-section taken along line6-6 ofFIG. 5;
• FIG. 6A is a cross-sectional representation of a variation of the circuit board shown inFIGS. 5 and 6, in which the conductive elements are at least partially recessed within the surrounding material;
• FIG. 7 is a schematic cross-sectional representation of a multilayered circuit board with stereolithographically fabricated intermediate conductive elements;
• FIG. 8 is a schematic representation of an assembly including a packaged semiconductor device with leads that are electrically connected to corresponding contact pads of a carrier substrate by way of the intermediate conductive elements of the present invention;
• FIG. 9 is a schematic representation of an assembly including a semiconductor die and leads connected to the bond pads thereof by way of the intermediate conductive elements of the present invention;
• FIG. 10 is a schematic cross-sectional representation of a semiconductor device including a semiconductor die, intermediate conductive elements of the present invention in communication with the bond pads of the semiconductor die to reroute same, and a dielectric layer disposed between the intermediate conductive elements and the active surface of the semiconductor die;
• FIG. 11 is a schematic representation of a first apparatus for stereolithographically fabricating structures in accordance with a first embodiment of the method of the present invention;
• FIG. 12 is a schematic representation of a second apparatus for stereolithographically fabricating structures in accordance with a second embodiment of the method of the present invention; and
• FIG. 13 is partial cross-sectional schematic representation of a semiconductor device disposed on a platform of a stereolithographic apparatus for the formation of intermediate conductive elements between contacts of the assembled semiconductor device components.
DETAILED DESCRIPTION OF THE INVENTIONStereolithography Apparatus and Methods
• FIG. 11 schematically depicts various components, and operation, ofexemplary stereolithography apparatus80 to facilitate the reader's understanding of the technology employed in implementation of the methods of the present invention, although those of ordinary skill in the art will understand and appreciate that apparatus of other designs and manufacture may be employed in practicing the method of the present invention.Apparatus80 and the operation thereof are described in great detail in U.S. Patents assigned to 3D Systems, Inc. of Valencia, Calif., such patents including, without limitation, U.S. Pat. Nos. 4,575,330; 4,929,402; 4,996,010; 4,999,143; 5,015,424; 5,058,988; 5,059,021; 5,059,359; 5,071,337; 5,076,974; 5,096,530; 5,104,592; 5,123,734; 5,130,064; 5,133,987; 5,143,663; 5,164,128; 5,174,931; 5,174,943; 5,182,055; 5,182,056; 5,182,715; 5,184,307; 5,192,469; 5,192,559; 5,209,878; 5,234,636; 5,236,637; 5,238,639; 5,248,456; 5,256,340; 5,258,146; 5,267,013; 5,273,691; 5,321,622; 5,345,391; 5,358,673; 5,447,822; 5,481,470; 5,495,328; 5,554,336; 5,556,590; 5,569,431, 5,571,471; 5,573,722; 5,609,812; 5,609,813; 5,610,824; 5,630,981; 5,637,169; 5,651,934; 5,667,820; 5,676,904; 5,688,464; 5,693,144; 5,711,911; 5,779,967; 5,814,265; 5,850,239; 5,854,748; 5,855,718; 5,885,511; 5,897,825; 5,902,537; 5,902,538; 5,904,889; 5,943,235; and 5,945,058. The disclosure of each of the foregoing patents is hereby incorporated herein by this reference.
• With continued reference toFIG. 11 and as noted above, a 3-D CAD drawing of an object to be fabricated in the form of a data file is placed in the memory of acomputer82 controlling the operation ofapparatus80 ifcomputer82 is not a CAD computer in which the original object design is effected. In other words, an object design may be effected in a first computer in an engineering or research facility and the data files transferred via wide or local area network, tape, disc, CD-ROM, or as otherwise known in the art tocomputer82 ofapparatus80 for object fabrication.
• The data is preferably formatted in an STL (for STereoLithography) file, STL being a standardized format employed by a majority of manufacturers of stereolithography equipment. Fortunately, the format has been adopted for use in many solid-modeling CAD programs, so translation from another internal geometric database format is often unnecessary. In an STL file, the boundary surfaces of an object are defined as a mesh of interconnected triangles.
• Apparatus80 also includes a reservoir84 (which may comprise a removable reservoir interchangeable with others containing different materials) of anunconsolidated material86 to be employed in fabricating the intended object.Unconsolidated material86 useful inapparatus80 is a liquid, photo-curable polymer, or “photopolymer” that cures in response to light in the UV wavelength range. Thesurface level88 ofmaterial86 is automatically maintained at an extremely precise, constant magnitude by devices known in the art responsive to output of sensors withinapparatus80 and preferably under control ofcomputer82. A support platform orelevator90, precisely vertically movable in fine, repeatable increments responsive to control ofcomputer82, is located for movement downward into and upward out ofmaterial86 inreservoir84.
• An object may be fabricated directly onplatform90, or on a substrate disposed onplatform90. When the object is to be fabricated on a substrate disposed onplatform90, the substrate may be positioned onplatform90 and secured thereto by way of one or more base supports122 (FIG. 13). Such base supports122 may be fabricated before or simultaneously with the stereolithographic fabrication of one or more objects onplatform90 or a substrate disposed thereon. These base supports122 may support, or prevent lateral movement of, the substrate relative to asurface100 ofplatform90. Base supports122 may also provide a perfectly horizontal reference plane for fabrication of one or more objects thereon, as well as facilitate the removal of a substrate fromplatform90 following the stereolithographic fabrication of one or more objects on the substrate. Moreover, where a so-called “recoater”blade102 is employed to form a layer of material onplatform90 or a substrate disposed thereon, base supports122 can preclude inadvertent contact ofrecoater blade102, to be described in greater detail below, withsurface100 ofplatform90.
• Apparatus80 has a UV wavelength range laser plus associated optics and galvanometers (collectively identified as laser92) for controlling the scan oflaser beam96 in the X-Y plane acrossplatform90.Laser92 has associated therewith amirror94 to reflectlaser beam96 downwardly aslaser beam98 towardsurface100 ofplatform90.Laser beam98 is traversed in a selected pattern in the X-Y plane, that is to say in a plane parallel tosurface100, by initiation of the galvanometers under control ofcomputer82 to at least partially cure, by impingement thereon, selected portions ofmaterial86 disposed oversurface100 to at least a partially consolidated (e.g., semisolid) state. The use ofmirror94 lengthens the path of the laser beam, effectively doubling same, and provides a morevertical laser beam98 than would be possible if thelaser92 itself were mounted directly aboveplatform surface100, thus enhancing resolution.
• Referring now toFIGS. 11 and 13, data from the STL files resident incomputer82 is manipulated to build an object, such as an intermediateconductive element 20, 20N, 20O, or 20′″, illustrated inFIGS. 1-10, or base supports122, one layer at a time. Accordingly, the data mathematically representing one or more of the objects to be fabricated are divided into subsets, each subset representing a slice or layer of the object. The division of data is effected by mathematically sectioning the 3-D CAD model into at least one layer, a single layer or a “stack” of such layers representing the object. Each slice may be from about 0.0001 to about 0.0300 inch thick. As mentioned previously, a thinner slice promotes higher resolution by enabling better reproduction of fine vertical surface features of the object or objects to be fabricated.
• When one or more base supports122 are to be stereolithographically fabricated, base supports122 may be programmed as a separate STL file from the other objects to be fabricated. The primary STL file for the object or objects to be fabricated and the STL file for base support(s)122 are merged.
• Before fabrication of a first layer for asupport122 or an object to be fabricated is commenced, the operational parameters forapparatus80 are set to adjust the size (diameter if circular) of the laser light beam used to curematerial86. In addition,computer82 automatically checks and, if necessary, adjusts by means known in the art thesurface level88 ofmaterial86 inreservoir84 to maintain same at an appropriate focal length forlaser beam98. U.S. Pat. No. 5,174,931, referenced above and previously incorporated herein by reference, discloses one suitable level control system. Alternatively, the height ofmirror94 may be adjusted responsive to a detectedsurface level88 to cause the focal point oflaser beam98 to be located precisely at thesurface level88 ofmaterial86 if thesurface level88 is permitted to vary, although this approach is more complex.Platform90 may then be submerged inmaterial86 inreservoir84 to a depth equal to the thickness of one layer or slice of the object to be formed, and theliquid surface level88 is readjusted as required to accommodatematerial86 displaced by submergence ofplatform90.Laser92 is then activated solaser beam98 will scan unconsolidated (e.g., liquid or powdered)material86 disposed oversurface100 ofplatform90 to at least partially consolidate (e.g., polymerize to at least a semisolid state)material86 at selected locations, defining the boundaries of afirst layer122A ofbase support122 and filling in solid portions thereof.Platform90 is then lowered by a distance equal to the thickness ofsecond layer122B, andlaser beam98 scanned over selected regions of the surface ofmaterial86 to define and fill in the second layer while simultaneously bonding the second layer to the first. The process may be repeated as often as necessary, layer by layer, untilbase support122 is completed.Platform90 is then moved relative to mirror94 to form any additional base supports122 onplatform90 or a substrate disposed thereon or to fabricate objects uponplatform90,base support122, or a substrate, as provided in the control software. The number of layers required to erectsupport122 or one or more other objects to be formed depends upon the height of the object or objects to be formed and the desired layer thicknesses oflayers20A,20B, etc. The layers of a stereolithographically fabricated structure may have different thicknesses.
• If arecoater blade102 is employed, the process sequence is somewhat different. In this instance,surface100 ofplatform90 is lowered into unconsolidated (e.g., liquid)material86 below surface level88 a distance greater than a thickness of a single layer ofmaterial86 to be cured, then raised abovesurface level88 untilplatform90, a substrate disposed thereon, or a structure being formed onplatform90 or a substrate thereon is precisely one layer's thickness belowblade102.Blade102 then sweeps horizontally overplatform90 or (to save time) at least over a portion thereof on which one or more objects are to be fabricated to removeexcess material86 and leave a film of precisely the desired thickness. Platform.90 is then lowered so that the surface of the film andsurface level88 are coplanar and the surface of theunconsolidated material86 is still.Laser92 is then initiated to scan withlaser beam98 and define thefirst layer20A. The process is repeated, layer by layer, to define each succeeding layer and simultaneously bond same to the next lower layer until all of the layers of the object or objects to be fabricated are completed. A more detailed discussion of this sequence and apparatus for performing same is disclosed in U.S. Pat. No. 5,174,931, previously incorporated herein by reference.
• As an alternative to the above approach to preparing a layer ofmaterial86 for scanning withlaser beam98, a layer of unconsolidated (e.g., liquid)material86 may be formed onsurface100 ofsupport platform90, on a substrate disposed onplatform90, or on one or more objects being fabricated by loweringplatform90 toflood material86 oversurface100, over a substrate disposed thereon, or over the highest completed layer of the object or objects being formed, then raisingplatform90 and horizontally traversing a so-called “meniscus” blade horizontally overplatform90 to form a layer of unconsolidated material having the desired thickness overplatform90, the substrate, or each of the objects being formed.Laser92 is then initiated and alaser beam98 scanned over the layer of unconsolidated material to define at least the boundaries of the solid regions of the next higher layer of the object or objects being fabricated.
• Yet another alternative to layer preparation of unconsolidated (e.g., liquid) material86.is to merelylower platform90 to a depth equal to that of a layer ofmaterial86 to be scanned, and to then traverse a combination flood bar and meniscus bar assembly horizontally overplatform90, a substrate disposed onplatform90, or one or more objects being formed to substantially concurrentlyflood material86 thereover and to define a precise layer thickness ofmaterial86 for scanning.
• All of the foregoing approaches to liquid material flooding and layer definition and apparatus for initiation thereof are known in the art and are not material to practice of the present invention, so no further details relating thereto will be provided herein.
• In practicing the present invention, a commercially available stereolithography apparatus operating generally in the manner as that described above with respect toapparatus80 ofFIG. 11 may be employed, but with further additions and modifications as hereinafter described for practicing the method of the present invention. For example and not by way of limitation, the SLA-250/50HR, SLA-5000 and SLA-7000 stereolithography systems, each offered by 3D Systems, Inc., of Valencia, Calif., are suitable for modification. Photopolymers believed to be suitable for use in practicing the present invention include Cibatool SL 5170 and SL 5210 resins for the SLA-250/50HR system, Cibatool SL 5530 resin for the SLA-5000 and 7000 systems, and Cibatool SL 7510 resin for the SLA-7000 system. All of these photopolymers are available from Ciba Specialty Chemicals Inc.
• By way of example and not limitation, the layer thickness ofmaterial86 to be formed, for purposes of the invention, may be on the order of about 0.0001 to 0.0300 inch, with a high degree of uniformity. It should be noted that different material layers may have different heights, so as to form a structure of a precise, intended total height or to provide different material thicknesses for different portions of the structure. The size of the laser beam “spot” impinging on the surface ofmaterial86 to cure same may be on the order of 0.001 inch to 0.008 inch. Resolution is preferably ∀0.0003 inch in the X-Y plane (parallel to surface100) over at least a 0.5 inch H 0.25 inch field from a center point, permitting a high resolution scan effectively across a 1.0 inch H 0.5 inch area. Of course, it is desirable to have substantially this high a resolution across the entirety ofsurface100 ofplatform90 to be scanned bylaser beam98, such area being termed the “field of exposure,” such area being substantially coextensive with the vision field of a machine vision system employed in the apparatus of the invention as explained in more detail below. The longer and more effectively vertical the path oflaser beam96/98, the greater the achievable resolution.
• Anotherapparatus180 useful in implementing the methods of the present invention, referred to as a thermal stereolithography apparatus, is schematically illustrated inFIG. 12.Apparatus180 and the operation ofapparatus180 are described in great detail in United States Patents assigned to 3D Systems, Inc. of Valencia, Calif., such patents including, without limitation, U.S. Pat. Nos. 5,141,680; 5,344,298; 5,501,824; 5,569,349; 5,672,312; 5,695,707; 5,776,409; 5,855,836. The disclosure of each of the foregoing patents is hereby incorporated herein by this reference.
• As noted above, a 3-D CAD drawing of an object to be fabricated in the form of a data file may be placed in the memory of acomputer182 controlling the operation ofapparatus180 ifcomputer182 is not a CAD computer in which the original object design is effected. Preferably, the data is formatted in an STL file.
• Apparatus180 includes a support platform orelevator190, precisely vertically movable in fine, repeatable increments responsive to control ofcomputer182. An object may be fabricated directly onplatform190, or on a substrate disposed onplatform190. When the object is to be fabricated on a substrate disposed onplatform190, the substrate may be positioned onplatform190 and secured thereto by way of one or more base supports (seeFIG. 13). Such base supports122 may be fabricated before or simultaneously with the stereolithographic fabrication of one or more objects onplatform190 or a substrate disposed thereon. These base supports122 may support, or prevent lateral movement of, the substrate relative to asurface200 ofplatform190. Base supports122 may also provide a perfectly horizontal reference plane for fabrication of one or more objects thereon, as well as facilitate the removal of a substrate fromplatform190 following the stereolithographic fabrication of one or more objects on the substrate.
• Apparatus180 also includes a reservoir184 (which may comprise a removable reservoir interchangeable with others containing different materials) of anunconsolidated material186 to be employed in fabricating the intended object.Unconsolidated material186 useful withapparatus180 is a heated, flowable material that is typically solid at the operating temperatures of a semiconductor device.
• One or more spray heads192 ofapparatus180 communicate with and receiveunconsolidated material186 fromreservoir184. Eachspray head192, under control ofcomputer182, effects the deposition ofunconsolidated material186 in the X-Y plane ofplatform190, on a substrate disposed onplatform190, or on an object being formed.
• Data from the STL files resident incomputer182 is manipulated to build an object, such as intermediateconductive element20, illustrated inFIGS. 1-10, or base supports122, illustrated inFIG. 13, one layer at a time. Accordingly, the data mathematically representing one or more of the objects to be fabricated are divided into subsets, each subset representing a slice or layer of the object. The division of data is effected by mathematically sectioning the 3-D CAD model into at least one layer, a single layer or a “stack” of such layers representing the object. Each slice may be from about 0.003 to about 0.030 inch thick. As mentioned previously, a thinner slice promotes higher resolution by enabling better reproduction of fine vertical surface features of the object or objects to be fabricated.
• When one or more base supports122 are to be stereolithographically fabricated, base supports122 may be programmed as an STL file separate from the STL files for other objects to be fabricated. The primary STL file for the object or objects to be fabricated and the STL file for base support(s)122 are merged.
• Before fabrication of a first layer for asupport122 or an object to be fabricated is commenced, the operational parameters forapparatus180 are set to adjust the size (diameter if circular) of the stream ofunconsolidated material186 to be ejected from eachspray head192. In addition,computer182 automatically checks and, if necessary, adjusts by means known in the art thesurface level188 ofplatform190 to maintain same at an appropriate length from spray heads192 to obtain an object having the desired resolution. U.S. Pat. No. 5,174,931, referenced above and previously incorporated herein by reference, discloses one suitable level control system.
• Eachspray head192 is then activated so as to depositunconsolidated material186 oversurface200 ofplatform190 to form at least the boundaries of afirst layer122A of base support122 (FIG. 13) and to fill in solid portions thereof. The depositedmaterial186 is then permitted to at least partially harden, or consolidate, prior to forming another layer thereon. Each layer of the object being fabricated may be laterally supported by a material that remains substantially unconsolidated at ambient temperatures and that, preferably, will not adhere to the just-formed layer ofmaterial186.
• After a layer is formed,platform190 may be lowered a distance substantially equal to the thickness of the just-formed layer so as to maintain a substantially constant distance between spray heads192 and the surface on which the next layer ofunconsolidated material186 is to be disposed. Spray heads192 may then be scanned over selected regions ofsurface200 or the surface of the previously formed layer to define and fill in the second layer while simultaneously bonding the second layer to the first. The process may be then repeated, as often as necessary, layer by layer, untilbase support122 is completed. The number of layers required to erectsupport122 or one or more other objects to be formed depends upon the height of the object or objects to be formed and the desired thicknesses oflayers20A,20B, etc. The layers of a stereolithographically fabricated structure may have different thicknesses.
• Exemplary commercially available thermal stereolithography apparatus operating generally in the manner as that described above with respect toapparatus180 ofFIG. 12 include, but are not limited to, the THERMOJET™ printer offered by 3D Systems, Inc., of Valencia, Calif. Of course, as withapparatus80 depicted inFIG. 11,apparatus180 may be employed with further additions and modifications as hereinafter described. Thermoplastic materials, or “thermopolymers,” believed to be suitable for use in practicing the method of the present invention in combination withapparatus180 includeThermoJet 88 Thermopolymer, available from 3D Systems, Inc., as well as other nonconductive and electrically conductive thermopolymers known in the art.
• By way of example and not limitation, the layer thickness ofmaterial186 to be formed, for purposes of the invention, may be on the order of about 0.003 to 0.030 inch, with a high degree of uniformity. It should be noted that different material layers may have different heights, so as to form a structure of a precise, intended total height or to provide different material thicknesses for different portions of the structure. Resolution is preferably about 300 dpi (dots per inch) or about 0.003 inch in the X-Y plane (parallel to surface200). Of course, it is desirable to have substantially this high a resolution across theentire surface200 ofplatform190 to be scanned by spray heads192, such area being termed the “field of exposure,” such area being substantially coextensive with the vision field of a machine vision system employed in the apparatus of the invention as explained in more detail below. Of course, sinceapparatus180 deposits material by way of one or more spray heads192, the resolution with which an object can be formed byapparatus180 is dependent, at least in part, upon spray heads192 and the type ofmaterial186 deposited thereby.
• Referring now to bothFIGS. 11 and 12, it should be noted thatapparatus80,180 useful in the methods of the present invention includecameras140 which are in communication withcomputers82,182, respectively, and are preferably located, as shown, in close proximity to optics andmirror94 located abovesurface100,200 ofsupport platform90,190. Eachcamera140 may be any one of a number of commercially available cameras, such as capacitive-coupled discharge (CCD) cameras available from a number of vendors. Suitable circuitry as required for adapting the output ofcamera140 for use bycomputer82,182 may be incorporated in aboard142 installed incomputer82,182 which is programmed as known in the art to respond to images generated bycamera140 and processed byboard142.Camera140 andboard142 may together comprise a so-called “machine vision system” and, specifically, a “pattern recognition system” (PRS), the operation of which will be described briefly below for a better understanding of the present invention. Alternatively, a self-contained machine vision system available from a commercial vendor of such equipment may be employed. For example, and without limitation, such systems are available from Cognex Corporation of Natick, Mass. For example, the apparatus of the Cognex BGA Inspection Package™ or the SMD Placement Guidance Package™ may be adapted to the present invention, although it is believed that the MVS-8000 product family and the Checkpoint⁷product line, the latter employed in combination with Cognex PatMax™ software, may be especially suitable for use in the present invention.
• It is noted that a variety of machine vision systems are in existence, examples of which and their various structures and uses are described, without limitation, in U.S. Pat. Nos. 4,526,646; 4,543,659; 4,736,437; 4,899,921; 5,059,559; 5,113,565; 5,145,099; 5,238,174; 5,463,227; 5,288,698; 5,471,310; 5,506,684; 5,516,023; 5,516,026; and 5,644,245. The disclosure of each of the immediately foregoing patents is hereby incorporated by this reference.
Stereolithographic Fabrication of the Conductive Elements
• In order to facilitate fabrication of one or more intermediateconductive elements20 in accordance with the method of the present invention withapparatus80,180, a data file representative of the size, configuration, thickness and surface topography of, for example, a particular type and design ofsemiconductor device10 or other substrate upon which one or more intermediateconductive elements20 are to be fabricated is placed in the memory ofcomputer82,182.
• One ormore semiconductor devices10,carrier substrates30, or other semiconductor device components may be placed onsurface100,200 ofplatform90,190 for fabrication of intermediateconductive elements20 in communication with contact pads thereof (e.g.,bond pads12 ofsemiconductor device10, shown inFIGS. 1-4). One ormore semiconductor devices10,carrier substrates30, or other semiconductor device components may be held on or supported aboveplatform90,190 by stereolithographically formed base supports122. Whenapparatus80 is used, these base supports122 are formed by sequentially disposing one or more layers ofmaterial86 onsurface100 and selectively alteringmaterial86 by use oflaser92.Apparatus180 forms base supports122 by selectively depositing one or more layers ofmaterial186 from spray heads192.
• Camera140 is then activated to locate the position and orientation of eachsemiconductor device10,carrier substrate30, or other type of semiconductor device component upon which intermediateconductive elements20 are to be fabricated. The features of eachsemiconductor device10,carrier substrate30, or other type of semiconductor device component are compared with those in the data file residing in memory, the locational and orientational data for eachsemiconductor device10,carrier substrate30, or other type of semiconductor device component then also being stored in memory. It should be noted that the data file representing the design size, shape and topography for eachsemiconductor device10,carrier substrate30, or other type of semiconductor device component may be used at this juncture to detect physically defective or damagedsemiconductor devices10,carrier substrates30, or other types of semiconductor device components prior to fabricating intermediateconductive elements20 thereon or before conducting further packaging ofsemiconductor devices10,carrier substrates30, or other types of semiconductor device components. Accordingly, such damaged ordefective semiconductor devices10,carrier substrates30, or other types of semiconductor device components can be deleted from the process of fabricating intermediateconductive elements20 and from further packaging. It should also be noted that data files for more than one type (size, thickness, configuration, surface topography) of eachsemiconductor device10,carrier substrate30, or other type of semiconductor device component may be placed in computer memory andcomputer82,182 programmed to recognize not only the locations and orientations of eachsemiconductor device10,carrier substrate30, or other type of semiconductor device component, but also the type of semiconductor component at each location uponplatform90,190 so thatmaterial86 may be at least partially consolidated bylaser beam98 ormaterial186 selectively deposited byspray heads192 in the correct pattern and to the height required to define intermediateconductive elements20 in the appropriate, desired locations on eachsemiconductor device10,carrier substrate30, or other semiconductor device component.
Fabrication of the Conductive Elements by Photo-Stereolithography
• Whenapparatus80 is used, as depicted inFIGS. 11 and 13, the one ormore semiconductor devices10,carrier substrates30, or other semiconductor device components onplatform90 may then be submerged partially below thesurface level88 of unconsolidated (e.g., liquid)material86 to a depth greater than the thickness of a first layer ofmaterial86 to be at least partially consolidated (e.g., cured to at least a semisolid state) to form the lowest layer of each intermediateconductive element20 at the appropriate location or locations on eachsemiconductor device10,carrier substrate30, or other type of semiconductor device component, then raised to a depth equal to the layer thickness, thesurface level88 ofmaterial86 being allowed to become calm. Photopolymers that are useful asmaterial86 exhibit a desirable dielectric constant and low shrinkage upon cure, are of sufficient (i.e., semiconductor grade) purity, exhibit good adherence to other semiconductor device materials, and have a coefficient of thermal expansion (CTE) similar to that of the materials adjacent thereto. Preferably, the CTE ofmaterial86 is sufficiently similar to that of the adjacent materials to prevent undue stressing thereof during thermal cycling ofsemiconductor device10,carrier substrate30, or other semiconductor device component in testing, subsequent processing, and subsequent normal operation. Exemplary photopolymers exhibiting these properties are believed to include, but are not limited to, the above-referenced resins from Ciba Specialty Chemicals Inc. One area of particular concern in determining resin suitability is the substantial absence of mobile ions and, specifically, fluorides.
• Laser92 is then activated and scanned todirect laser beam98, under control ofcomputer82, toward specific locations ofsurface level88 relative to eachsemiconductor device10,carrier substrate30, or other type of semiconductor device component to effect the aforementioned partial cure ofmaterial86 to form afirst layer20A of each intermediateconductive element20.Platform90 is then lowered intoreservoir84 and raised a distance equal to the desired thickness of anotherlayer20B of each intermediateconductive element20, andlaser92 is activated to add anotherlayer20B to each intermediateconductive element20 under construction. This sequence continues, layer by layer, until each of the layers of intermediateconductive elements20 has been completed.
• InFIG. 13, the first layer of intermediateconductive element20 is identified by numeral20A, and the second layer is identified by numeral20B. Likewise, the first layer ofbase support122 is identified by numeral122A and the second layer thereof is identified by numeral122B. As illustrated,base support122 and intermediateconductive element20 have only two layers. Intermediateconductive elements20 with any number of layers are, however, within the scope of the present invention.
• In addition to being useful for fabricating intermediateconductive elements20,apparatus80 may also be used to fabricate nonconductive structures, such as dielectric layers and substrate layers, such as the nonconductive support layers of a circuit board or other carrier substrate.
• Whenapparatus80 is employed to fabricate one or more intermediateconductive elements20 or other structures (e.g., one or more layers of a carrier substrate30), eachlayer20A,20B of each intermediateconductive element20 is preferably built by first defining any internal and external object boundaries of that layer withlaser beam98, then hatching solid areas of intermediateconductive elements20 located within the object boundaries withlaser beam98. An internal boundary of a layer may comprise an aperture, a through hole, a void, or a recess incarrier substrate30, for example. If a particular layer includes a boundary of a void in the object above or below that layer, thenlaser beam98 is scanned in a series of closely spaced, parallel vectors so as to develop a continuous surface, or skin, with improved strength and resolution. The time it takes to form each layer depends upon the geometry thereof, the surface tension and viscosity ofmaterial86, and the thickness of that layer.
• Alternatively, intermediateconductive elements20 or other stereolithographically fabricated structures may each be formed as a partially cured outer skin extending aboveactive surface14 ofsemiconductor device10 or abovesurface34 ofcarrier substrate30 and forming a dam within whichunconsolidated material86 can be contained. This may be particularly useful where intermediateconductive elements20 or other structures protrude a relatively high distance aboveactive surface14. In this instance,support platform90 may be submerged so thatmaterial86 enters the area within the dam and raised abovesurface level88, and thenlaser beam98 activated and scanned to at least partially curematerial86 residing within the dam or, alternatively, to merely cure a “skin,” a final cure of the material of intermediateconductive elements20 or other structures under construction being effected subsequently by broad-source UV radiation in a chamber, or by thermal cure in an oven. In this manner, intermediateconductive elements20 and other structures of extremely precise dimensions may be formed ofmaterial86 byapparatus80 in minimal time.
• Once intermediateconductive elements20 or other structures, or at least the outer skins thereof, have been fabricated,platform90 is elevated abovesurface level88 ofmaterial86 andplatform90 is removed fromapparatus80, along withsemiconductor device10,carrier substrate30, or another semiconductor device component upon which intermediateconductive elements20 or other structures have been stereolithographically fabricated. Excess, unconsolidated material86 (e.g., excess uncured liquid) may be manually removed fromplatform90, from any substrate disposed thereon, and from intermediateconductive elements20 or other stereolithographically fabricated structures. Eachsemiconductor device10,carrier substrate30, or other semiconductor device component is removed fromplatform90, such as by cutting the semiconductor device component free of base supports122. Alternatively, base supports122 may be configured to readily releasesemiconductor devices10,carrier substrates30, or other semiconductor device components. As another alternative, a solvent may be employed to release base supports122 fromplatform90. Such release and solvent materials are known in the art. See, for example, U.S. Pat. No. 5,447,822 referenced above and previously incorporated herein by reference.
• The stereolithographically fabricated intermediateconductive elements20 or other structures, as well assemiconductor device10,carrier substrate30, or another semiconductor device component upon which these structures have been fabricated, may also be cleaned by use of known solvents that will not substantially degrade, deform, or damage the stereolithographically fabricated structures, such as intermediateconductive elements20, or the semiconductor device components.
• As noted previously, intermediateconductive elements20 or other stereolithographically fabricated structures may then require postcuring. Intermediateconductive elements20 or other structures may have regions of unconsolidated material contained within a boundary or skin thereof, ormaterial86 may be only partially consolidated (e.g., polymerized or cured) and exhibit only a portion (typically 40%-to 60%) of its fully consolidated strength. Postcuring to completely harden intermediateconductive elements20 or other stereolithographically fabricated structures may be effected in another apparatus projecting UV radiation in a continuous manner over the stereolithographically fabricated structures or by thermal completion of the initial, UV-initiated partial cure.
Fabrication of the Conductive Elements by Thermal Stereolithography
• Referring again toFIGS. 12 and 13, whenapparatus180 is used to fabricate intermediateconductive elements20, spray heads192 directliquified material186 onto the appropriate location or locations of the one ormore semiconductor devices10,carrier substrates30, or other semiconductor device components onplatform190,90. The material is permitted to solidify to form thelowest layer20A of each intermediateconductive element20. Thermoplastic polymers that are useful asmaterial186 exhibit desirable electrical conductivity, exhibit low shrinkage upon solidification, substantially maintain their structural integrity under normal operating conditions (e.g., operating temperatures of the semiconductor-device), are of sufficient.(i.e., semiconductor grade) purity, exhibit good adherence to other semiconductor device materials, and have a coefficient of thermal expansion (CTE) similar to that of the materials adjacent thereto. Preferably, the CTE ofmaterial186 is sufficiently similar to that of the adjacent materials to prevent undue stressing thereof during-thermal cycling ofsemiconductor device10,carrier substrate30, or another semiconductor device component in testing, subsequent processing, and subsequent normal operation.
• Platform190 is then lowered a distance substantially equal to thenext layer20B of each intermediateconductive element20 under construction. Heatedconductive material186 is then disposed byspray heads192 onto appropriate locations of the previously fabricatedlayer20A of each intermediateconductive element20 to formlayer20B. This sequence continues, layer by layer, until each of the layers of intermediateconductive elements20 have been completed.
• In addition to being useful for fabricating intermediateconductive elements20,apparatus180 may also be used to fabricate nonconductive structures, such as dielectric layers and substrate layers, such as the nonconductive support layers of a circuit board or other carrier substrate.
• Once intermediateconductive elements20 or other structures have been fabricated,platform190 is removed fromapparatus180, along withsemiconductor device10,carrier substrate30, or another semiconductor device component upon which intermediateconductive elements20 or other structures have been stereolithographically fabricated. Eachsemiconductor device10,carrier substrate30, or other semiconductor device component is removed fromplatform190, such as by cutting the semiconductor device component free of base supports122. Alternatively, base supports122 may be configured to readily releasesemiconductor devices10,carrier substrates30, or other semiconductor device components. As another alternative, a solvent may be employed to release base supports122 fromplatform190. Such release and solvent materials are known in the art. See, for example, U.S. Pat. No. 5,447,822 referenced above and previously incorporated herein by reference.
• The stereolithographically fabricated intermediateconductive elements20 or other structures, as well assemiconductor device10,carrier substrate30, or another semiconductor device component upon which these structures have been fabricated, may also be cleaned by use of known solvents that will not substantially degrade, deform, or damage the stereolithographically fabricated structures, such as intermediateconductive elements20, or the semiconductor device components.
• The use of a stereolithographic process as exemplified above to fabricate intermediateconductive elements20 is particularly advantageous since a large number of intermediateconductive elements20 may be substantially simultaneously fabricated in a short time, the positioning thereof is computer controlled and extremely precise, wastage of material is minimal, and the stereolithography method requires minimal handling ofsemiconductor devices10,carrier substrates30, or other semiconductor device components.
• Stereolithography is also an advantageous method of fabricating intermediateconductive elements20 according to the present invention since stereolithography can be conducted at temperatures that will not damage or induce significant thermal stress on the semiconductor device components during fabrication of intermediateconductive elements20 thereon. The stereolithography fabrication process may also be used to simultaneously form intermediateconductive elements20 on several semiconductor device components or assemblies, saving fabrication time and expense. As the stereolithography method of the present invention recognizesspecific semiconductor devices10,carrier substrates30, and other semiconductor device components, variations between different semiconductor device components are accommodated. Accordingly, when the stereolithography method of the present invention is employed, intermediateconductive elements20 can be simultaneously fabricated on different types of semiconductor device components or assemblies of semiconductor device components.
Semiconductor Device Components and Assemblies Including the Conductive Elements
• Referring now toFIGS. 1 and 2, an assembly1 of asemiconductor device10 and acarrier substrate30 is illustrated.Semiconductor device10 is a semiconductor die that includesbond pads12, which are also referred to herein as contact pads or contacts for simplicity, on anactive surface14 thereof. Aback side16 ofsemiconductor device10 is disposed against asurface34 ofcarrier substrate30.Bond pads12 ofsemiconductor device10 are electrically connected tocorresponding contact pads32 ofcarrier substrate30 by way of intermediateconductive elements20. For simplicity,contact pads32 are also referred to herein as contacts.
• Intermediateconductive elements20, which are fabricated by stereolithographic techniques, are formed from a conductive material, such as a conductive elastomer or a metal. Intermediateconductive elements20 may each include a single layer or a plurality of superimposed, contiguous, mutually adhered layers of conductive material.
• Each intermediateconductive element20 is substantially entirely carried along the length thereof upon eithersemiconductor device10 orcarrier substrate30. As illustrated inFIG. 2, each intermediateconductive element20 extends across a portion ofactive surface14 ofsemiconductor device10, down alateral edge18 ofsemiconductor device10, and across a portion ofsurface34 ofcarrier substrate30. Afirst end22 of each intermediateconductive element20 is in contact with abond pad12 and asecond end24 of intermediateconductive element20 is connected to acontact pad32 ofcarrier substrate30.
• FIGS. 3 and 4 illustrate anotherexemplary assembly2 with intermediateconductive elements20 of the present invention.Assembly2 includes twosemiconductor devices10,10N disposed on acarrier substrate30. As illustrated, eachsemiconductor device10,10N is a semiconductor die that includesbond pads12,12N, or contact pads or contacts, on anactive surface14,14N thereof. Back sides16,16N ofsemiconductor devices10,10N are disposed over asurface34 ofcarrier substrate30, with alateral edge18 of onesemiconductor device10 abutting a lateral edge18N of the other semiconductor device10N.Corresponding bond pads12,12N of the twosemiconductor devices10,10N are electrically connected to each other by way of intermediateconductive elements20.
• As in assembly1 depicted inFIGS. 1 and 2, intermediateconductive elements20 ofassembly2 are stereolithographically fabricated from an electrically conductive material, such as an electrically conductive thermoplastic polymer or a metal. Since intermediateconductive elements20 are stereolithographically fabricated, each intermediateconductive element20 may include one layer or a plurality of superimposed, contiguous, mutually adhered layers of conductive material.
• With continued reference toFIGS. 3 and 4, substantially the entire lengths of intermediateconductive elements20 are carried bysemiconductor devices10,10N. As illustrated inFIG. 4, each intermediateconductive element20 extends across a portion ofactive surface14 of afirst semiconductor device10, over aninterface17 between abuttinglateral edges18,18N of the twosemiconductor devices10,10N, and across a portion of active surface14N of the second semiconductor device10N. Afirst end22 of each intermediateconductive element20 is in contact with abond pad12 of onesemiconductor device10 and asecond end24 of intermediateconductive element20 is connected to a bond pad12N of the other semiconductor device10N (FIG. 3).
• Turning now toFIGS. 5 and 6, an embodiment of acarrier substrate30, in this case a circuit board, is schematically depicted that includes stereolithographically fabricated intermediate conductive elements20N according to the present invention.Carrier substrate30 includes asingle substrate layer31, intermediate conductive elements20N carried bycarrier substrate30, and acontact pad32, or contact, at an end of each intermediate conductive element20N. Intermediate conductive elements20N that traverse more than one plane ofcarrier substrate30 include vertically extendingvias36 along the lengths thereof.Vias36 are located in throughholes38 formed throughsubstrate layer31.
• As discussed previouslyherein, intermediate conductive elements20N may be fabricated by stereolithographic techniques. Contactpads32 may also be stereolithographically fabricated. Accordingly, each intermediate conductive element20N andcontact pad32 may include one layer or a plurality of superimposed, contiguous, mutually adhered layers of conductive material. Exemplary conductive materials that may be used to form intermediate conductive elements20N andcontact pads32 include known thermoplastic conductive polymers and metals. In order to fabricate intermediate conductive elements20N on both sides ofsubstrate layer31, a first set of intermediate conductive elements20N is fabricated on a first side ofsubstrate layer31.Substrate layer31 is then inverted and a second set of intermediate conductive elements20N is fabricated on a second side ofsubstrate layer31.
• Substrate layer31 may similarly be fabricated from dielectric materials by stereolithographic processes such as those disclosed herein. As shown inFIG. 6A, whensubstrate layer31 is stereolithographically fabricated,channels33 may be recessed in one or both surfaces thereof to receive intermediate conductive elements20N. Thus, the exposed surfaces of intermediate conductive elements20N may be recessed relative to the surfaces ofsubstrate layer31 or substantially flush therewith. When stereolithography is used to fabricatesubstrate layer31, the layer or layers of material are preferably deposited onto a flexible or fibrous matrix and become integral therewith, thereby imparting strength and some flexibility to the fabricatedsubstrate layer31.
• When both intermediate conductive elements20N andsubstrate layer31 are stereolithographically fabricated,carrier substrates30 that carry intermediate conductive elements20N on both surfaces thereof may be fabricated by forming a first, bottom set of intermediate conductive elements20N on a platform of a suitable stereolithography apparatus, formingsubstrate layer31 over the first set of intermediate conductive elements20N, then forming a second, upper set of intermediate conductive elements20N onsubstrate layer31. Anyvias36 that extend vertically throughsubstrate layer31 may be fabricated before, during, or after the fabrication ofsubstrate layer31. When both intermediate conductive elements20N andsubstrate layer31 are fabricated by use of stereolithography, the same stereolithographic technique and apparatus are preferably employed to fabricate intermediate conductive elements20N andsubstrate layer31. Accordingly,carrier substrate30 need not be moved between different stereolithographic apparatus during fabrication thereof. However, the use of different stereolithographic techniques and apparatus to fabricate intermediate conductive elements20N andsubstrate layer31 are also within the scope of the present invention.
• FIG. 7 schematically illustrates a multilayer carrier substrate30N according to the present invention, which includes a plurality of superimposed, contiguous, mutually adhered layers31N of dielectric material and intermediate conductive elements20N that are each carried by one or more of layers31N. Intermediate conductive elements20N that are carried by more than one layer31N and, thus, that extend along more than one plane through carrier substrate30N includevias36 along the lengths thereof.Vias36 extend substantially vertically through through holes38N formed in one or more layers31N.
• Intermediate conductive elements20N, which are preferably fabricated by stereolithographic techniques such as those disclosed herein, each include one layer or a plurality of superimposed, contiguous, mutually adhered layers of conductive material, such as a conductive elastomer (e.g., a thermoplastic conductive elastomer or a conductive photopolymer) or a metal.
• One or more layers31N of carrier substrate30N may also be fabricated by stereolithographic techniques using a dielectric material. When stereolithography is used to fabricate layers31N of carrier substrate30N, each layer31N may be made by disposing dielectric material onto a layer of a flexible or fibrous matrix to impart strength and some flexibility to each fabricatedsubstrate layer31′.
• When both intermediate conductive elements20N andsubstrate layer31′ are stereolithographically fabricated, a first, bottom set of intermediate conductive elements20N may be formed on a platform of a suitable stereolithography apparatus, forming a first substrate layer31N over or laterally adjacent to the first set of intermediate conductive elements20N. The appropriate sequence of forming intermediate conductive elements20N and substrate layers3 IN then continues until a multilayer carrier substrate30N of desired configuration has been fabricated. Anyvias36 that extend vertically through one or more substrate layers31N may be fabricated before, during, or after the fabrication of the substrate layers31N. When both intermediate conductive elements20N and substrate layers31N are fabricated by use of stereolithography, the same stereolithographic technique and apparatus are preferably employed to fabricate intermediate conductive elements20N and substrate layers31N. Accordingly,carrier substrate30′ need not be moved between different stereolithographic apparatus during fabrication thereof However, the use of different stereolithographic techniques and apparatus to fabricate intermediate conductive elements20N and substrate layers31N are also within the scope of the present invention.
• Turning now toFIGS. 8 and 9, packaged semiconductor devices that include stereolithographically fabricated conductive elements are also within the scope of the present invention.
• FIG. 8 illustrates an exemplary semiconductor device package3 incorporating teachings of the present invention. Semiconductor device package3 includes asemiconductor device10, illustrated as a leads-over-chip (LOC) type semiconductor die, leads40 positioned over anactive surface14 ofsemiconductor device10 proximatecorresponding bond pads12 onactive surface14, and intermediateconductive elements200 disposed betweenleads40 andbond pads12 so as to establish electrical communication therebetween. Leads40 andactive surface14 are electrically isolated from one another by way of one or moredielectric layers42 disposed therebetween. Semiconductor device package3 may also include apackage50. Whilepackage50 is illustrated as covering substantially theentire semiconductor device10 and the portions ofleads40adjacent semiconductor device10,package50 may only enclosebond pads12 and intermediateconductive elements200.
• Intermediateconductive elements200 are stereolithographically fabricated structures that may include one layer or a plurality of superimposed, contiguous, mutually adhered layers of a conductive material, such as a conductive elastomer or a metal.Dielectric layers42 andpackage50 may also be fabricated by stereolithographic techniques.
• With reference toFIG. 9, another embodiment of asemiconductor device package4 that incorporates teachings of the present invention is illustrated.Semiconductor device package4 includes asemiconductor device10, illustrated as a LOC type semiconductor die, withbond pads12 on anactive surface14 thereof. Intermediateconductive elements20′″ communicate with selectedbond pads12 and extend laterally so as to reroute selectedbond pads12 to different lateral locations relative toactive surface14. The laterally extending portions of intermediateconductive elements20′″ are electrically isolated fromactive surface14 by way of adielectric layer42 positioned therebetween. Each intermediateconductive element20′″ includes acontact26′″ at an end or along the length thereof.Contacts26′″ are at least electrically exposed through aprotective layer44 and may include integralconductive structures28′″ or attachedconductive structures28′″, such as solder bumps, protruding therefrom.
• Intermediateconductive elements20′″ are stereolithographically fabricated and may each include a single layer or a plurality of superimposed, contiguous, mutually adhered layers of a conductive material, such as a conductive elastomer or a metal.Conductive structures28′″ protruding from intermediateconductive elements20′″ may also be stereolithographically fabricated from conductive material. In addition,dielectric layer42 andprotective layer44 may be fabricated from dielectric materials by use of stereolithographic techniques.
• FIG. 10 illustrates yet another use of conductive elements according to the present invention, wherein a packagedsemiconductor device60 withleads62 extending therefrom is connected to acarrier substrate30. Leads62 are electrically connected tocorresponding contact pads32 ofcarrier substrate30 by way of intermediateconductive elements200, such as those described above with reference toFIG. 8.
• Of course, other semiconductor devices and semiconductor device assemblies that include stereolithographically fabricated conductive elements are also within the scope of the present invention.
• While the present invention has been disclosed in terms of certain preferred embodiments, those of ordinary skill in the art will recognize and appreciate that the invention is not so limited. Additions, deletions and modifications to the disclosed embodiments may be effected without departing from the scope of the invention as claimed herein. Similarly, features from one embodiment may be combined with those of another while remaining within the scope of the invention.

Claims (20)

1. A method for fabricating a circuit board, comprising:

consolidating unconsolidated material over selected regions of a dielectric substrate in accordance with a program to fabricate at least one conductive element on at least the portion of the dielectric substrate.

2. The method ofclaim 1, further comprising:

fabricating at least the portion of the dielectric substrate by a programmed material consolidation technique.

3. The method ofclaim 2, wherein the acts of fabricating and consolidating are effected in situ.

4. The method ofclaim 1, wherein consolidating unconsolidated material comprises:

forming a first layer of the at least one conductive element from substantially unconsolidated conductive material;

forming at least one additional layer of the at least one conductive element from substantially unconsolidated conductive material; and

permitting or causing the substantially unconsolidated conductive material to at least partially consolidate.

5. A method for fabricating a component for use in an electronic device, comprising:

providing unconsolidated material over at least a portion of a substrate; and

selectively directing consolidating energy toward the unconsolidated material to at least partially consolidate the same at desired locations on the substrate.

6. The method ofclaim 5, wherein selectively consolidating comprises directing focused consolidating energy toward the unconsolidated material under control of a program.

7. The method ofclaim 5, wherein selective consolidating comprises directing focused consolidating energy toward to unconsolidated material in response to recognition of a feature of or on the substrate.

8. The method ofclaim 5, wherein providing comprises providing a layer of unconsolidated material over at least the portion of the substrate.

9. The method ofclaim 8, including:

forming a first layer of the at least one conductive element from substantially unconsolidated conductive material;

forming at least one additional layer of the at least one conductive element from substantially unconsolidated conductive material; and

permitting or causing the substantially unconsolidated conductive material to at least partially consolidate.

10. The method ofclaim 5, wherein providing comprises providing a radiation-curable polymer over at least the portion of the substrate.

11. The method ofclaim 10, wherein selectively directing consolidating energy comprises selectively directing a laser beam toward the radiation-curable polymer.

12. The method ofclaim 5, wherein the acts of providing and selectively directing are effected in situ.

13. A method of fabricating a carrier substrate, comprising:

providing at least a portion of a dielectric substrate;

providing unconsolidated conductive material over at least a portion of the dielectric substrate; and

at least partially consolidating conductive material over selected locations of the dielectric substrate in accordance with a program.

14. The method ofclaim 13, wherein providing the at least a portion of the dielectric substrate comprises fabricating at least the portion by a programmed material consolidation technique.

15. The method ofclaim 14, wherein the acts of fabricating at least the portion of the dielectric substrate, providing unconsolidated conductive material, and at least partially consolidating conductive material are effected in situ.

16. The method ofclaim 13, further comprising:

sequentially forming and at least partially consolidating a plurality of regions comprising substantially unconsolidated conductive material.

17. The method ofclaim 16, wherein sequentially forming and at least partially consolidating comprises sequentially forming and at least partially consolidating a plurality of layers comprising substantially unconsolidated conductive material.

18. The method ofclaim 16, wherein at least partially consolidating comprises permitting the substantially unconsolidated conductive material to at least partially harden.

19. The method ofclaim 13, wherein at least partially consolidating comprises exposing at least some of the unconsolidated conductive material to focused energy.

20. The method ofclaim 19, wherein exposing comprises directing a laser beam onto at least some of the unconsolidated conductive material.

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