US20050173790A1 - Protective structures for bond wires - Google Patents

Abstract

Protective structures for bond wires or other intermediate conductive elements of a semiconductor device assembly cover the intermediate conductive elements without covering a substantial portion of a semiconductor device from which the intermediate conductive elements extend. In addition to coating at least portions of one or more intermediate conductive elements, the protective structure may include a fence which is configured to receive a semiconductor device. Such a fence may be formed integrally with the remainder of the protective structure or a separately formed member. The protective structures may be formed from a photopolymer material which has been at least partially cured, for example, by stereolithography processes. Accordingly, the protective structures may include a single layer or a plurality of superimposed, contiguous, mutually adhered layers.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a continuation of application Ser. No. 10/641,471, filed Aug. 14, 2003, pending, which is a continuation of application Ser. No. 09/841,923, filed Aug. 16, 2001, now U.S. Pat. No. 6,611,053, issued Aug. 26, 2003, which is a divisional of application Ser. No. 09/590,419, filed Jun. 8, 2000, abandoned.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The present invention relates generally to stereolithography and, more specifically, to the use of stereolithography to fabricate structures on, or components of, semiconductor testing apparatus and to the resulting structures.
• 2. Background of Related Art
• 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. 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. This is followed by selective consolidation or fixation of the material to at least a semisolid 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. The unconsolidated material employed to build an object may be supplied in particulate or liquid form and the material itself may be consolidated, fixed or cured, 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. When a liquid is employed, resolution is highly dependent upon the minimum surface area of the liquid which can be fixed (cured) and the minimum thickness of a layer which can be generated given the viscosity of the liquid and other parameters, such as transparency to radiation or particle bombardment (see below) used to effect at least a partial cure of the liquid to a structurally stable state. 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 enabled rapid fabrication of molds and prototypes of objects from CAD files. Thus, either male or female forms on which mold material might be disposed could be rapidly generated. Prototypes of objects could 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 was 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, 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.
• 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 pre-existing 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 the electronics industry, computer chips are typically manufactured by configuring a large number of integrated circuits on a wafer and subdividing the wafer to form singulated devices or dice. Such dice, including so-called “flip-chip” dice, have “solder bumps” or other conductors, or conductive structures, for electrically connecting each die to circuitry external thereto. These conductors are also useful for temporary connection of a die to a test circuit to determine its fitness for the intended use. Tests may be conducted before or after the die has been packaged.
• One type of conventional test apparatus that is used to test the electrical characteristics of semiconductor devices includes a carrier substrate, a test substrate positioned on the carrier substrate, and a fence disposed over the test substrate. The carrier substrate includes terminals and electrical traces that lead from the terminals to communicate with test equipment. Terminals of the carrier substrate are wire bonded to contact pads on the test substrate. The contact pads of the test substrate communicate with test pads thereof. The test pads are arranged to correspond to a pattern of conductors, such as solder balls, conductive pillars, bond pads, or other conductive structures of a semiconductor device to be tested. The fence forms an aperture over the test substrate to facilitate alignment of the semiconductor device to be tested relative to the substrate. As a die to be tested is aligned with a test substrate, test pads of the test substrate temporarily mate or contact the conductors of the semiconductor device. Such test apparatus can be configured to test bare or minimally packaged semiconductor dice or packaged semiconductor devices, such as ball grid array (BGA) packages and chip-scale packages (CSPs).
• Conventionally, the bond wires of a test apparatus have been covered with a silicone gel or a nonconductive epoxy “glob-top” material. As such materials can flow, the use of such materials typically also requires that external fences or walls be used to contain such materials in the desired locations. Internal fences or walls may also be required to prevent such glob top, silicone, and other materials from flowing onto the test pads of a test substrate, which can prevent the electrical connection of tested semiconductor devices to the test substrate. Otherwise, if flowable materials are used to cover wire bonds, these materials may have to be removed from the test pads or from the conductors of the tested semiconductor device to ensure adequate electrical connections between the test substrate and the semiconductor device assembled therewith.
• In other test apparatus, a photoresist material is used to cover the bond wires that connect a test substrate to a carrier substrate. When photoresist materials are used to protect bond wires, the use of a mask and several exposure and developing steps are required.
• Accordingly, there is a need for a method of efficiently and effectively protecting the bond wires of semiconductor device test apparatus, as well as protective structures and test apparatus formed by such a method.
SUMMARY OF THE INVENTION
• The present invention includes a method of fabricating a protective structure over the bond wires of a semiconductor device assembly, such as the bond wires of the semiconductor device test apparatus that connect test pads of a test substrate to a carrier substrate and, thereby, to the semiconductor device test apparatus. The present invention also includes semiconductor device assemblies so formed.
• A test apparatus embodying teachings of the present invention includes a silicon or other known test substrate with test pads on a surface thereof for receiving complementarily arranged conductors, or conductive structures, of a semiconductor device and electrical traces leading from the test pads to peripheral portions of the test substrate. The test pads may be substantially flush with the surface of the test substrate, recessed relative to the surface, or protrude from the surface, depending upon the types of conductors on the semiconductor devices to be tested with the test substrate or upon the configurations of components of the test apparatus that overlie the test substrate.
• The test substrate is secured to a carrier substrate and electrical connections are formed between terminals of the carrier substrate and the traces and test pads of the test substrate. Preferably, bond wires are used to establish the electrical connections between the electrical traces of the test substrate and their corresponding terminals of the carrier substrate. The terminals of the carrier substrate are configured to communicate with known semiconductor device testing equipment.
• The test apparatus also has protective structures located over the bond wires. The structures formed in accordance with teachings of the present invention may be used to physically protect, seal, and isolate the bond wires of a test apparatus so as to prevent physical damage to and shorting of the bond wires.
• A so-called “fence,” which has a large opening therethrough, is positioned over the test substrate. The fence and the opening therethrough are configured to seat a semiconductor device face down over the test substrate, aligning the conductors on the semiconductor device with their corresponding test pads of the test substrate. The opening through the fence may substantially expose a contact surface of the test substrate. The opening through the fence may have a plurality of vertically extending slots spaced about the periphery thereof, which provide additional tolerances at the periphery of the opening to facilitate the insertion of semiconductor devices into, and their removal from, the fence.
• As another alternative, the fence or the protective structure may include a relatively thin layer that is positionable over the test substrate so as to protect the test substrate from damage during the repeated testing of semiconductor devices. Apertures formed through the thin protective layer of the fence over at least test pads of the test substrate allow for contact between the test pads and corresponding conductors of a die to be tested and may be used to facilitate alignment of the semiconductor device relative to the test substrate.
• The present invention employs computer-controlled, 3-D computer-assisted drafting (CAD) initiated, stereolithographic techniques to rapidly form precision layers of material to specific surfaces of a test substrate and carrier substrate of a test apparatus.
• In the stereolithographic processes that are useful in the present invention, one or more layers of a photo-curable liquid, referred to herein as a photopolymer, are sequentially placed on or laterally adjacent to the item to be covered, and the liquid photopolymer of each layer is cured to at least a semisolid state by a precisely directed beam of laser radiation at substantially ambient temperature. Multiple superimposed, contiguous, mutually adhered layers, each separately cured, form one or more precision three-dimensional structures of desired dimensions.
• For example, a substrate may be covered with a layer of liquid polyimide or other photopolymer which is cured only in particular locations to an at least semisolid state by precisely directed laser radiation at a substantially ambient temperature. As the regions of the layer that are cured by the laser may be selected, photopolymer located over certain regions of the substrate, such as the contact pads thereof, may be left uncured. Thus, apertures may be formed through the protective layer substantially simultaneously with formation of solid regions of a structure. A single layer having a uniform thickness of, for example, about 25 μm (1 mil) may be formed on the surface of the wafer. Single layers having thicknesses of up to about 10 mil or more may be formed, the maximum possible thickness of each layer being limited only by the maximum depth into the liquid photopolymer that the laser beam can penetrate. Multiple superimposed layers, each separately cured, may be formed to create structure layers of even greater thickness while maintaining a thickness accuracy not achievable by conventional techniques.
• In one embodiment of the method, the bond wire protectors and the fence are fabricated on a substrate using precisely focused electromagnetic radiation in the form of an ultraviolet (UV) wavelength laser to fix or cure a liquid material in the form of a photopolymer. However, the invention is not so limited and other stereolithographically applicable materials may be employed in the present invention. The apparatus used in the present invention may also incorporate a machine vision system to locate substrates and features on the substrates, such as bond wires and test pads. The method of the present invention encompasses the use of all stereolithographic apparatus and the application of any and all materials thereby, including both metallic and nonmetallic materials applied in any state and cured or otherwise fixed to at least a semisolid state to define a three-dimensional layer or layers having identifiable boundaries.
• The highly precise stereolithographic process provides accurate alignment of the conductors of a semiconductor device to be tested with the test pads of the test substrate, providing good electrical connection without bump deformation.
• The bond wire protectors and the fence may be fabricated separately by use of individual CAD programs. In another embodiment, the fence is formed stereolithographically to be integral with the bond wire protectors.
• Alternatively, a fence can be fabricated on the test and carrier substrates by other known processes or fabricated separately from the test apparatus by known processes and subsequently assembled with the test substrate and carrier substrate assembly. As another alternative, a stereolithographically formed fence can be formed separately from the remainder of the test apparatus and then assembled therewith.
• 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
• The figures of the application illustrate exemplary embodiments of the invention, wherein the drawings are not necessarily to scale, wherein like indicia are used for like and similar elements, and wherein:
• FIG. 1 is a schematic elevation of an exemplary stereolithography apparatus suitable for use in practicing the method of the present invention;
• FIG. 1A is an enlarged portion ofFIG. 1 showing a structure of the invention being formed in a stereolithographic method of the invention;
• FIG. 2 is a perspective view of an exemplary test substrate useful for forming a test apparatus of the invention for testing a semiconductor flip-chip die;
• FIG. 3 is a perspective view of an exemplary test substrate joined to a carrier substrate for forming a semiconductor device test apparatus of the invention;
• FIG. 4 is a side cross-sectional view of a test substrate joined to a carrier substrate for forming a semiconductor device test apparatus of the invention, as taken along line4-4 ofFIG. 3;
• FIG. 5 is a perspective view of a test apparatus of the invention as formed by the method of the invention;
• FIG. 6 is a side cross-sectional view of a test apparatus of the invention, as taken along line6-6 ofFIG. 5;
• FIG. 7 is a perspective view of one embodiment of a test apparatus of the invention as formed by the method of the invention;
• FIG. 8 is a side cross-sectional view of one embodiment of a test apparatus of the invention, as taken along line8-8 ofFIG. 7;
• FIG. 9 is a perspective view of another embodiment of a test apparatus of the invention;
• FIG. 10 is a side cross-sectional view of another embodiment of a test apparatus of the invention, as taken along line10-10 ofFIG. 9;
• FIG. 11 is a side cross-sectional view of another embodiment of a test apparatus of the invention;
• FIG. 12 is a perspective view of a further embodiment of a test apparatus of the invention;
• FIG. 13 is a side cross-sectional view of a further embodiment of a test apparatus of the invention, as taken along line13-13 ofFIG. 12;
• FIG. 14 is a perspective view of another embodiment of a test apparatus of the invention;
• FIG. 15 is a side cross-sectional view of another embodiment of a test apparatus of the invention, as taken along line15-15 ofFIG. 14;
• FIG. 16 is a perspective view of an additional embodiment of a test apparatus of the invention;
• FIG. 17 is a side cross-sectional view of an additional embodiment of a test apparatus of the invention, as taken along line17-17 ofFIG. 16;
• FIG. 18 is a perspective view of a test apparatus of the invention with a semiconductor device to be tested inserted into the test apparatus;
• FIG. 19 is a side cross-sectional view of a test apparatus of the invention with a semiconductor device therein, as taken along line19-19 ofFIG. 18; and
• FIG. 20 is a perspective view of another embodiment of a test apparatus of the invention, showing additional features.
DETAILED DESCRIPTION OF THE INVENTION
• FIG. 1 schematically depicts various components and operation of anexemplary stereolithography apparatus10 to facilitate the reader's understanding of the technology employed in implementation 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. The preferred stereolithography apparatus for implementation of the present invention, as well as operation of such apparatus, 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. 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; 5,141,680; 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; 5,344,298; 5,345,391; 5,358,673; 5,447,822; 5,481,470; 5,495,328; 5,501,824; 5,554,336; 5,556,590; 5,569,349; 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; 5,672,312; 5,676,904; 5,688,464; 5,693,144; 5,695,707; 5,711,911; 5,776,409; 5,779,967; 5,814,265; 5,850,239; 5,854,748; 5,855,718; 5,855,836; 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 reference. Improvements in the conventional stereolithographic apparatus, as described in copending application Ser. No. 09/259,143, filed Feb. 26, 1999, and of even assignment, relate to a so-called “machine vision” system in combination with suitable programming of the computer controlling the stereolithographic process. This improvement eliminates the need for accurate positioning or mechanical alignment of workpieces to which material is stereolithographically applied. Alignment of the laser beam or other fixing agent may be item specific (e.g., substrate specific) so that, for example, a plurality of micromachinedsilicon test substrates40 may be attached to acarrier substrate50 and alignment and protective structure60 (seeFIG. 1A) independently formed in selected patterns on each test substrate. Using a machine vision system, accuracy of the process is not dependent on a fiduciary mark62 (FIG. 2) on atest substrate40 or on acarrier substrate50 but on the visual recognition of specific substrate characteristics, such as the locations oftest pads42,bond wires56, or other features oftest substrate40 orcarrier substrate50.
• With reference toFIGS. 1-19 and as noted above, a 3-D CAD drawing of an object such as aprotective structure60 to be fabricated in the form of a data file is placed in the memory of acomputer12 controlling the operation ofapparatus10 ifcomputer12 is not a CAD computer in which the original structure design is effected. In other words, an object or structure 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 otherwise as known in the art tocomputer12 ofapparatus10 to fabricate aprotective structure60 or other object comprising one or more applied layers64 (seeFIG. 1A).
• Eachlayer64 is formed or consolidated from a flowable,curable material16, which is also referred to herein asliquid material16, by a pass of alaser beam28 thereinto.Test substrate40 has anactive surface38 havingtest pads42 thereon. The completedtest apparatus30 comprisestest substrate40,carrier substrate50, andprotective structure60 formed overbond wires56 that electrically connecttest substrate40 tocarrier substrate50. The invention relates specifically to the stereolithographic fabrication ofprotective structure60 to shieldbond wires56 of a semiconductor test apparatus.
• The data forprotective structure60 is preferably formatted in an STL 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 ofprotective structure60 are defined as a mesh of interconnected triangles.
• Apparatus10 also includes a reservoir14 (which may comprise a removable reservoir interchangeable with others containing different materials) ofliquid material16 to be employed in applying the intended layer(s)64 of solidified material to testsubstrate40 and/orcarrier substrate50. In a currently preferred embodiment,liquid material16 is a photo-curable polymer (hereinafter “photopolymer”) responsive to light in the UV wavelength range.Surface level18 of theliquid material16 is automatically maintained at an extremely precise, constant magnitude by devices known in the art responsive to output of sensors withinapparatus10 and preferably under control ofcomputer12. A support platform orelevator20, precisely vertically movable in fine, repeatable increments indirections46 responsive to control ofcomputer12, is located for movement downward into and upward out ofliquid material16 inreservoir14. A UV wavelength range laser plus associated optics and galvanometers (collectively identified as laser22) for controlling the scan oflaser beam26 in the X-Y plane acrossplatform20 has associated therewithmirror24 to reflectbeam26 downwardly asbeam28 towardsurface32 ofplatform20 or, more particularly, towardactive surface38 oftest substrate40 and towardsurface54 ofcarrier substrate50 positioned onsurface32.Beam28 is traversed in a selected pattern in the X-Y plane, that is to say, in a plane parallel to surface32, by initiation of the galvanometers under control ofcomputer12 to at least partially cure, by impingement thereon, selected portions ofliquid material16 disposed overactive surface38 to at least a semisolid state. The use ofmirror24 lengthens the path of thelaser beam26, effectively doubling same, and provides a morevertical beam28 than would be possible iflaser22 itself were mounted directly aboveplatform surface32, thus enhancing resolution.
• Data from the STL files resident incomputer12 is manipulated to buildprotective structure60 or another object onactive surface38, the surface of another substrate, or onsurface32 ofplatform20 one layer at a time. Accordingly, the data mathematically representingprotective structure60 is divided into subsets, each subset representing a layer or slice64 ofprotective structure60. This is effected by mathematically sectioning a 3-D CAD model into a plurality ofhorizontal layers64, a “stack” of such layers representingprotective structure60. Each slice or layer may be from about 0.0001 to about 0.0300 inches thick. As mentioned previously, a thinner slice promotes higher resolution by enabling better reproduction of fine vertical surface features ofprotective structure60. In some instances, a base support or supports34 (FIG. 1A) for the object (e.g., test apparatus30) upon whichprotective structure60 is fabricated may also be programmed as a separate STL file. Such base supports34 may be fabricated before the overlyingprotective structure60 and even prior to the disposal of an object, such astest apparatus30, onsurface32 ofplatform20. Base supports34 facilitate fabrication ofprotective structure60 with reference to a perfectly horizontal plane. Such base supports also facilitate removal of the object (e.g.,carrier substrate50 bearing one ormore test substrates40 andprotective structures60 fromsurface32 of platform20). Where a “recoater”blade85 is employed, as described below, the interposition of base supports34 precludes inadvertent contact ofrecoater blade85 withsurface32.
• Before fabrication ofprotective structure60 is initiated withapparatus10, the primary STL file forprotective structure60, the file for the object upon whichprotective structure60 is fabricated, and the file for base support(s)34 are merged. It should be recognized that, while reference has been made to the formation of asingle test apparatus30,protective structures60 may be concurrently fabricated onmultiple test apparatus30 positioned onsurface32 ofplatform20. In such an instance, the STL files forprotective structures60 and supports34, if any, are merged. Operational parameters forapparatus10 are then set, for example, to adjust the size (diameter, if circular) oflaser beam28 used to cureliquid material16.
• In the exemplary method described herein,test substrate40 orcarrier substrate50 may be precisely coated with astructural layer64 irrespective of substrate size or number oftest substrates40. Thus, current stereolithographic equipment will accommodate objects up to12 or more inches in X and Y dimensions, and it is expected that equipment size will increase as the need to produce larger groups oftest substrates40 becomes commonplace.Bond wires56 and other structures may be totally enclosed without introducing any temperature-induced or flow-induced bending stresses.
• As shown inFIG. 1A, base supports34 may be placed onplatform20 prior to the placement oftest apparatus30 ontoplatform20. In addition, lateral supports36 may be similarly fabricated to securetest apparatus30 toplatform20, preventing lateral movement during fabrication ofprotective structure60 overbond wires56 oftest apparatus30. The fabrication of lateral supports36 can be facilitated by one or more individual STL files or an STL file for lateral supports36 may be merged with the other STL files for the entire STL process. Alternative methods and apparatus for securingtest apparatus30 toplatform20 and immobilizingtest apparatus30 relative toplatform20 may also be used and are within the scope of the present invention.
• Base supports34 and lateral supports36 may be formed of an at least partially cured material whose attachment to the platform is readily releasable. Alternatively, a solvent may be used to dissolvesupports34,36 to releasetest apparatus30 fromplatform20 and supports34,36. 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.
• While the invention is described in terms of a liquid material polymerizable to a semisolid or a solid state, the process may be varied to use a finely divided, powdered material, for example. The term “unconsolidated” will be used herein to denote the unpolymerized material which becomes “altered” or “consolidated” by the laser radiation to an at least semisolid state.
• As shown inFIG. 2, atest substrate40 includes alayer41 of silicon upon whichconductive test pads42 are located.Conductive test pads42 are connected by way ofelectrical traces44 to contactpads48, which are located at or near the periphery oftest substrate40.Test pads42 may be depressed, raised, or level withactive surface38 oftest substrate40 to accommodate the particular type of semiconductor devices to be tested withtest apparatus30.
• As depicted inFIGS. 3 and 4,test substrate40 is secured on a higherlevel carrier substrate50, which hascontact pads52 on asurface54 thereof. Contactpads52 are connected by way ofbond wires56 to corresponding contact pads48 (FIG. 3) oftest substrate40. The test substrate40-carrier substrate50 assembly is secured toplatform20 ofstereolithographic apparatus10 as already described and shown inFIG. 1A. InFIG. 4, traces44 andcontact pads52 are shown to illustrate their general location. In the remaining cross-sectional views ofFIGS. 6, 8,10,11,13,15,17, and19, traces44 andcontact pads52 are not shown for the sake of clarity.
• FIGS. 5 and 6 depicttest apparatus30 ofFIGS. 3 and 4, upon which aprotective structure60 has been formed, such as by the stereolithographic process disclosed herein.
• The position and orientation of eachtest apparatus30 on whichprotective structure60 is to be formed is located by scanningplatform20 and comparing the features of thattest apparatus30 with corresponding features stored in the data file residing in memory, the locational and orientational data for eachtest apparatus30 then also being stored in memory. It should be noted that the data file representing the design size, shape and topography for one ormore test apparatus30 onplatform20 may be used at this juncture to detect thosetest apparatus30 which may be physically defective or damaged. It should also be noted that data files for more than one type (size, thickness, configuration, surface topography) oftest apparatus30 may be placed in computer memory andcomputer12 programmed to recognize the locations and orientations oftest substrates40 andcarrier substrates50, as well as oftest pads42,contact pads48,bond wires56,contact pads52, andboundaries58 which define theprotective structure60 which is to be formed, and a laser path for formingprotective structure60.
• Data from the STL files resident incomputer12 is manipulated to form onelayer64 at a time ontest apparatus30 disposed onplatform20. Accordingly, where the finalprotective structure60 is formed of a plurality of individually formedlayers64, the data mathematically representingprotective structure60 is divided into subsets, each subset representing a slice orlayer64. This is effected by mathematically sectioning the 3-D CAD model into a plurality ofhorizontal layers64, “stacks” of such layers representingprotective structures60. Slices or layers64 may each 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 ofprotective structure60.
• Before initiation of afirst layer64 for asupport34,36 or forprotective structure60 is commenced,computer12 automatically checks and, if necessary, adjusts by means known in the art,surface level18 ofliquid material16 inreservoir14 to maintain same at an appropriate focal length forlaser beam28. U.S. Pat. No. 5,174,931, referenced above and previously incorporated herein by reference, discloses one suitable level control system. Alternatively, the height ofmirror24 may be adjusted responsive to a detectedsurface level18 to cause the focal point oflaser beam28 to be located precisely at the surface ofliquid material16 atsurface level18 ifsurface level18 is permitted to vary, although this approach is somewhat more complex.Platform20 may then be submerged inliquid material16 inreservoir14 to a depth equal to the thickness of one layer or slice64 to be formed ontest apparatus30.Surface level18 ofliquid material16 can be readjusted as required, such as to accommodate liquid material16-displaced by submergence ofplatform20.Laser22 is then activated so thatlaser beam28 will scanliquid material16 in a defined path oversurface54 ofcarrier substrate50 oractive surface38 of eachtest substrate40 of eachtest apparatus30, in turn, to at least partially cure (e.g., at least partially polymerize)liquid material16 at selected locations on eachtest apparatus30, including around and overbond wires56.
• Boundaries58 ofprotective structure60circumscribe test substrate40 belowactive surface38 and circumscribe acentral opening66 above active surface38 (seeFIG. 5).Central opening66 has precise inner wall surfaces86 configured to accurately guide packaged semiconductor devices80 (or alternatively unpackaged semiconductor devices) (seeFIGS. 18 and 19) thereinto so that thecontact pads82 ofsemiconductor device80 precisely contacttest pads42 for testing each of the semiconductor devices without the necessity for undue pressure. The placement of theinner wall surface86 is based on the location of test pads42 (in computer memory) rather thancarrier substrate50, so that accurate positioning is achieved even whentest substrate40 is joined tocarrier substrate50 in a less accurate fashion. Theouter boundaries58A ofprotective structure60 are shown as being in agreement with theedges88 ofcarrier substrate50, but need not be.
• If arecoater blade85 is employed, the process sequence is somewhat different. In this instance,surface32 ofplatform20 is lowered intoliquid material16 belowsurface level18, then raised thereabove until it is precisely a thickness96 (seeFIG. 1A) oflayer64 belowrecoater blade85.Recoater blade85 then sweeps horizontally over the uppermost surface ofprotective structure60 on which the next layer is to be formed to remove excessliquid material16 and leave a film thereof of the precise, desired thickness on the uppermost surface.Platform20 is then lowered so that the surface of the film andsurface level18 are coplanar and the surface ofliquid material16 is still.Laser22 is then initiated to scan withlaser beam28 and define thefirst layer64 onsurface54 ofcarrier substrate50. The process is repeated, layer by layer, to define each succeedinglayer64 and simultaneously bond same to the nextlower layer64 untilprotective structure60 is 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. In general,recoater blade85 cannot be used where any portion oftest substrate40,carrier substrate50,bond wires56, or another feature oftest apparatus30 protrudes upwardly above the sweeping portion ofrecoater blade85.Recoater blade85 may generally be used for forming only an upper portion ofprotective structure60.
• As an alternative to the above approach to preparing a layer ofliquid material16 for scanning withlaser beam28, a layer ofliquid material16 may be formed ontest apparatus30 by loweringplatform20 to flood material oversurface54 or over the highest completedlayer64 ofprotective structure60, then raisingplatform20 and horizontally traversing a so-called “meniscus” blade across platform20 (or just across the formed portion of protective structure60) to form alayer64 of desired thickness thereabove, followed by initiation oflaser22 and scanning ofbeam28 to define the next higher layer ofprotective structure60.
• As yet another alternative to layer preparation ofliquid material16,platform20 can be lowered to a depth equal to that of alayer64 ofliquid material16 to be scanned and a combination flood bar and meniscus bar assembly can be horizontally traversed overplatform20 to substantially concurrently floodliquid material16 oversurface54 and define alayer64 of precisely a desired thickness ofliquid material16 for scanning.
• All of the foregoing approaches to flooding and layer definition and apparatus of initiation thereof are known in the art, so no further details relating thereto will be provided.
• Each layer ofprotective structure60 is preferably built by first defining any internal andexternal object boundaries58,58A of that layer withlaser beam28, then hatching solid areas ofprotective structure60 withlaser beam28. If a particular part of aparticular layer64 is to form aboundary58 of a void in the object above or below that layer, thenlaser beam28 is scanned in a series of closely spaced, parallel vectors so as to develop a continuous surface, or skin, with improved strength and resolution. For example,laser22 first definesboundaries58 ofprotective structure60 infirst layer64 and fills in solid portions oflayer64 withinboundaries58 to complete a layer ofprotective structure60.Platform20 is then lowered by a distance substantially equal to a desired thickness of the next,second layer64, andlaser beam28 scanned over the next,second layer64 to define boundaries ofprotective structure60 therein and to fill in the areas ofsecond layer64 withinboundaries58 while simultaneously bonding the second layer to the first.Additional layers64 are then added at least partially atop the previously formed layer as needed to completeprotective structure60. The time it takes to form eachlayer64 depends upon its geometry, surface tension and viscosity ofliquid material16, and thickness of the layer.
• Onceprotective structure60 is completed ontest apparatus30 or another substrate,platform20 is elevated abovesurface level18 ofliquid material16, andtest apparatus30 may be removed fromapparatus10. Excess, uncuredliquid material16 on the surface oftest apparatus30 may be removed, for example, by a manual removal step and solvent cleaning.Protective structure60 on eachtest apparatus30 may then require postcuring, asliquid material16 may be only partially polymerized and exhibit only a portion (typically 40% to 60%) of its fully cured strength. Partially consolidated material or unconsolidated material in contact with at least partially consolidated material will eventually cure due to the cross-linking initiated in the outwardly adjacent photopolymer. Postcuring to completely hardenprotective structure60 or portions thereof may be accelerated in another apparatus projecting UV radiation in a continuous manner overprotective structure60 and/or by thermal completion of the initial, UV-initiated partial cure.
• In the embodiment ofFIGS. 5 and 6,protective structure60 is shown as formed to encapsulate and protectbond wires56 and to provide atop surface68 to which a preformedfence member90 may be bonded. InFIGS. 7 and 8, a preformedfence member90 is shown bonded totop surface68 with athin layer92 of adhesive.Fence member90 has acentral opening67 that is generally co-aligned withcentral opening66 ofprotective structure60, althoughcentral opening66 may be larger thancentral opening67.Fence member90 is positioned to provide accurate mating of contact pads on a type of semiconductor device to be tested withcorresponding test pads42.
• Fence member90 may, by way of example and not limitation, be formed of plastic, ceramic, semiconductor material such as silicon, or glass (e.g., borophosphosilicate glass (BPSG), borosilicate glass (BSG), or phosphosilicate glass (PSG)). Alternatively, the stereolithography processes disclosed herein may be used to form afence member90 of the desired configuration. When stereolithography is used,fence member90 can be fabricated separately fromtest apparatus30 orprotective structure60, directly onprotective structure60, or integrally withprotective structure60.
• The external terminals used withtest apparatus30 may be of any type which enables reliable electrical connection with test circuitry. Thus, a wide variety of external terminals may be used, including wire-contact pads, solder bumps, tabs, pins, and the like, and are not shown in the drawings with the exception ofFIGS. 7 and 8. InFIGS. 7 and 8, external terminals are illustrated as exemplary down-formedtab conductors94.
• In practicing the present invention, a commercially available stereolithography apparatus operating generally in the manner as that described with respect toapparatus10 ofFIG. 1 is preferably employed. 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 practice of the present invention. 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 system and Cibatool SL 7510 resin for the SLA-7000 system. All of these resins are available from Ciba Specialty Chemicals Inc. Materials are selected for dielectric constant, sufficient purity (semiconductor grade), adherence to other semiconductor device materials, desirable hardness for physical protection, low shrinkage upon cure, and a coefficient of thermal expansion (CTE) sufficiently similar to that oftest substrate40 andcarrier substrate50 oftest apparatus30, to which the material is applied. By selecting a photopolymer with a CTE similar to those ofsubstrates40 and50,substrates40 and50 and the at least partially cured material thereon will not be unduly stressed during thermal cycling in initial testing at elevated temperature and subsequent normal operation as a semiconductordevice test apparatus30. One area of particular concern in determining resin suitability is the substantial absence of mobile ions and, specifically, fluorides.Layer thickness96 ofliquid material16 to be formed, for purposes of the invention, may vary widely depending upon the required apparatus height for holdingsemiconductor device80 to be tested, but will enclosebond wires56 and may be configured to apply a dielectric coating overelectrical traces44 onactive surface38 oftest substrate40 or other protective coating onactive surface38.
• The size of the laser beam “spot”78 impinging on the surface ofliquid material16 to cure same may be on the order of 0.002 inch to 0.008 inch. Resolution is preferably ±0.0003 inch in the X-Y plane (parallel to platform surface31) over at least a 0.5 inch×0.25 inch field from a center point, permitting a high resolution scan effectively across a 1.0 inch×0.5 inch area. Of course, it is desirable to have substantially this high a resolution across the entirety ofsurface54 of a large structure to be scanned bylaser beam28, such area being termed the “field of exposure.” The longer and more effectively vertical the path oflaser beam26/28, the greater the achievable resolution.
• Referring again toFIG. 1 of the drawings, improved performance of this process is achieved by certain additions toapparatus10. As depicted,apparatus10 includes acamera70 which is in communication withcomputer12 and preferably located, as shown, in close proximity to mirror24 located abovetest apparatus30.Camera70 may be any one of a number of commercially available cameras, such as capacitative-coupled discharge (CCD) cameras available from a number of vendors. Suitable circuitry as required for adapting the output ofcamera70 for use bycomputer12 may be incorporated in aboard72 installed incomputer12, which is programmed, as known in the art, to respond to images generated bycamera70 and processed byboard72.Camera70 andboard72 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. The apparatus of the exemplary Cognex BGA Inspection Package™ or SMD Placement Guidance Package™ may be adapted to the present invention, although it is believed that the MVS-8000™ product family and the Checkpoint® product 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 herein by this reference.
• In order to facilitate practice of the method of the present invention withimproved apparatus10, a data file representative of the substrate surfaces54 on which aprotective structure60 is to be formed is placed in the memory ofcomputer12. The data file will contain information, such as surface dimensions (in three dimensions) and visual features, as well as spacing and layout of features (e.g.,test pads42,contact pads48,bond wires56, and contact pads52) ontest substrate40 andcarrier substrate50. The data file will also containinformation defining boundaries58,58A ofprotective structure60 to be formed and, in addition, a defined path oflaser beam28 as controlled bymirror24 to achieve the coverage.
• Continuing with reference toFIGS. 1 and 1A of the drawings, atest apparatus30 onplatform20 may be submerged partially belowsurface level18 ofliquid material16 to a depth the same as, or greater than, the desiredthickness96 of afirst layer64 ofliquid material16 to be at least partially cured to a semisolid state. Thenplatform20 is raised to a depth equal to the layer thickness96 (if previously lowered to a greater depth than a layer thickness) andsurface level18 ofliquid material16 is allowed to stabilize.Liquid material16 selected for use in applyinglayer64 to testapparatus30 may be one of the above-referenced resins from Ciba Specialty Chemicals Inc. Inasmuch as the stereolithography process is conducted without appreciable temperature rise, the need to compensate boundary location (as constructed) for subsequent temperature drop to match semiconductor device dimensions is generally insignificant.
• Camera70 is initiated to locate the position and orientation of eachtest apparatus30 on which one or moreprotective structures60 are to be formed by scanningplatform20 and comparing the features oftest apparatus30 with those in the data file residing in memory, the locational and orientational data for eachtest apparatus30 then also being stored in memory.
• Laser22 is then activated and scanned to directbeam28, under control ofcomputer12, across the desired portion ofcarrier substrate50 to effect the partial cure ofliquid material16 to formfirst layer64. For forming a second andsubsequent layers64,platform20 is lowered intoreservoir14 and raised as before, and the laser activated to form the next layer atoplayer64, for example. It should be noted thatlayer thickness96 ofliquid material16 in a selected portion of a givenprotective structure60 may be altered layer by layer, again responsive to output ofcamera70 or one or moreadditional cameras74 and76 shown in broken lines, which detect particular features ofcertain test apparatus30.
• It should be noted that the laser treatment may be carried out to form aboundary58 which adheres tosubstrate surface54 or the surface ofprevious layer64 and the layer within the boundary is lightly cured to form a semisolid “skin” which enclosesliquid material16. The final cure ofprotective structure60 may be effected subsequently by broad-source UV radiation in a chamber or by thermal cure in an oven. In this manner, an extremely preciseprotective structure60 may be formed in minimal time withinapparatus10.
• As illustrated inFIGS. 9, 10 and11,fence member90 may be configured withportions100 having reduced elevation. These portions may have any shape, includingsloped portions100A (FIGS. 9 and 10) and slottedportions100B (FIG. 11).Sloped portions100A and slottedportions100B may be useful for manipulation of a semiconductor device (not shown) inserted intocentral opening66 ofprotective structure60. Use of such portions also reduces the quantity of material used to constructfence member90.
• In another embodiment of the invention, atest apparatus30 is formed without the use of a preformedfence member90. Thus, as illustrated inFIGS. 12 through 15, the formation ofprotective structure60 previously shown inFIGS. 5 and 6 is continued to a desirable higher elevation to provide a guide forsemiconductor devices80 inserted intocentral opening66. In this embodiment, use of a separately formedfence member90 is unnecessary.
• InFIGS. 14 and 15, atest apparatus30 is shown with cut-outwall portions100 as previously described.
• As depicted inFIGS. 16 and 17,protective structure60 may include athin layer104 of dielectric material formed over an inner portion ofactive surface38 oftest substrate40 to protectactive surface38, including electrical traces44 (not shown) from damage or shorts under repeated use.Layer104 may also be useful for protecting a semiconductor device during assembly thereof withtest apparatus30. Whilelayer104 may be formed by conventional methods, this invention encompasses the incorporation of its construction as a part of the stereolithography process.Layer104 can have one or two sublayers of material that are at least partially cured to give layer104 a thickness of about 10 to about 50 μm, butlayer104 may have any thickness that will permit the formation of electrical connections betweentest substrate40 and conductive elements of a semiconductor device to be assembled therewith. As shown,test pads42 are left uncovered, eliminating any additional step to remove cured material therefrom. The methodology is incorporated as a STL file into the total stereolithography program.
• FIGS. 18 and 19 show a completed test apparatus (exterior terminals not shown) of the type illustrated inFIG. 12, with asemiconductor device80 inserted therein for testing. In addition, thegap106 betweencentral opening66 andsemiconductor device80 is precisely configured to facilitate insertion ofsemiconductor device80 intocentral opening66 and to aligncontact pads82 ofsemiconductor device80 or other conductors communicating therewith and thecorresponding test pads42. In the various embodiments of this invention, a minimum ofdownward force108 is required to maintain electrical contact between allcontact pads82 ofsemiconductor device80 and thecorresponding test pads42 oftest substrate40. If conductors, such as the illustratedsolder balls84, protrude fromcontact pads82 ofsemiconductor device80,solder balls84 or other conductors need not be deformed to provide a sufficient electrical connection.
• It should be noted that in any of the embodiments described thus far, the inner wall surfaces86 ofcentral opening66 may be vertical, sloped slightly inward, sloped slightly outward, or undercut (see, e.g.,FIG. 7). In addition, as shown inFIG. 20, inner wall surfaces86 may have vertically extendingslots98, or notches.Such slots98 reduce the frictional forces in inserting or removing asemiconductor device80 to be tested and also result in material savings, weight reduction, and reduced manufacturing time.
• Also shown inFIG. 20 are various optionalopen spaces102 inprotective structure60, which result in weight, material and time savings.Open spaces102 may be located anywhere inprotective structure60, so long as their location does not hinder the testing ofsemiconductor devices80 or reduce the useful life oftest apparatus30. Each of these features is incorporated into the STL data file.
• It is notable that the present invention provides a rapid method for forming structures of protective material precisely on specified areas oftest apparatus30. The method is frugal ofliquid material16, since all such material in which cure is not initiated bylaser beam28 remains in a liquid state inreservoir14 for continued use.
• The method of the present invention is conducted at substantially ambient temperature, the smalllaser beam spot78 size and rapid traverse oflaser beam28 ontest substrate40,carrier substrate50,bond wires56, and other features oftest apparatus30 resulting in negligible thermal stress thereon.
• Furthermore, forming aprotective structure60 on atest apparatus30 by stereolithographic processes is advantageous in that such processes enhance the precision of material placement and the precision with which structures of desired dimensions can be fabricated, reduces fabrication time, reduces subsequent packaging costs, and enables computer control of the protective structure fabrication process using commercially available equipment.
• Referring toFIGS. 1 through 20 of the drawings, it will be apparent to the reader that the present invention involves a substantial departure from prior applications of stereolithography, in that the structures of preformed electrical components are modified by forming multilayered structures thereon using computer-controlled stereolithography. Moreover, the use of stereolithography facilitates the fabrication ofprotective structures60 that have different configurations and are made from different materials than existing bond wire protective structures.
• It should be re-emphasized that the stereolithographic technique of the present invention is suitable for covering, or leaving uncovered, any desired portion of a substrate, so that electrical connections for connection to semiconductor devices and other devices may be left bare, eliminating a material removal step.
• 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 (16)

1. A protective sheath for at least one elongate conductive element, comprising dielectric material and surrounding at least a portion of the at least one elongate conductive element without covering a substantial portion of a semiconductor device component from which the at least one elongate conductive element extends.

2. The protective sheath ofclaim 1, wherein a nonperipheral portion of the semiconductor device component remains exposed beyond or through the dielectric material.

3. The protective sheath ofclaim 2, wherein the semiconductor device component comprises an interposer, a carrier, or a test substrate.

4. The protective sheath ofclaim 3, further comprising a fence member configured to receive a semiconductor device.

5. The protective sheath ofclaim 4, wherein the fence member comprises a plurality of adjacent, mutually adhered regions.

6. The protective sheath ofclaim 5, wherein the plurality of adjacent, mutually adhered regions comprises a plurality of superimposed, contiguous, mutually adhered layers.

7. The protective sheath ofclaim 1, comprising a plurality of adjacent, mutually adhered regions.

8. The protective sheath ofclaim 7, wherein the plurality of adjacent, mutually adhered regions comprises a plurality of superimposed, contiguous, mutually adhered layers.

9. The protective sheath ofclaim 1, wherein the semiconductor device component comprises a semiconductor device.

10. The protective sheath ofclaim 1, wherein the dielectric material comprises a photopolymer.

11. The protective sheath ofclaim 1, substantially surrounding at least a portion of the at least one elongate conductive element.

12. A protective sheath for at least one elongate conductive element, comprising dielectric material surrounding an entire periphery of at least a portion of the one elongate conductive element.

13. The protective sheath ofclaim 12, wherein the dielectric material comprises at least partially cured photopolymer.

14. The protective sheath ofclaim 12, comprising at least a portion of a fence member configured to receive a semiconductor device

15. The protective sheath ofclaim 14, wherein the fence member comprises a plurality of adjacent, mutually adhered regions.

16. The protective sheath ofclaim 15, wherein the plurality of adjacent, mutually adhered regions comprise a plurality of superimposed, contiguous, mutually adhered layers.

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