US20070004088A1 - Laser separation of encapsulated submount - Google Patents

Abstract

In a light emitting package fabrication process, a plurality of light emitting chips (10) are attached on a sub-mount wafer (14). The attached light emitting chips (10) are encapsulated. Fracture-initiating trenches (30, 32) are laser cut into the sub-mount wafer (14) between the attached light emitting chips (10) using a laser. The sub-mount wafer (14) is fractured along the fracture initiating trenches (30, 32).

Description

• This application is a continuation of prior Application Ser. No. 10/911,052 filed Aug. 4, 2004. Application Ser. No. 10/911,052 is incorporated herein by reference in its entirety.
BACKGROUND
• The following relates to the lighting arts. It especially relates to high intensity light emitting diode chip packages, components, apparatuses, and so forth, and to methods for producing such packages, and will be described with particular reference thereto. However, the following will also find application in conjunction with other solid state light emitting chip packages such as vertical cavity surface emitting laser packages, and in conjunction with methods for producing such other packages.
• The use of sub-mounts in packaging light emitting diode chips, semiconductor laser chips, and other light emitting chips is well known. The light emitting chip or chips are attached to the sub-mount by soldering, thermosonic bonding, thermocompressive bonding, or another thermally conductive attachment. The light emitting chips are electrically connected to bonding pads or other electrical terminals disposed on the sub-mount by wire bonding, flip-chip bonding, or another suitable technique. In some approaches, the light emitting chip is attached to the sub-mount and in thermal contact with the sub-mount, but is electrically connected by wire bonds to a circuit such that the sub-mount is not part of the electrical circuit.
• In a manufacturing setting, a plurality of light emitting chips are typically attached in parallel rows, or in another layout, to a large-area sub-mount wafer. The attached light emitting chips are transfer molded or otherwise encapsulated on the sub-mount wafer. Optionally, the encapsulant includes a dispersed phosphor for performing a selected wavelength conversion. For example, a group-III nitride based light emitting diode chip emits light in the blue to ultraviolet range, and a suitable phosphor can be incorporated into the encapsulant to convert the blue or ultraviolet emission into white light. The sub-mount wafer is then diced to separate individual light emitting packages, each including one or more of the attached and encapsulated light emitting chips along with a supporting portion of the sub-mount wafer.
• Typically, the dicing of the sub-mount wafer is performed by mechanical sawing or scribing. Such mechanical separation processes are readily automated, and are advantageously relatively independent of material characteristics; hence, the mechanical sawing or scribing can simultaneously cut through the transfer-molded encapsulant and the sub-mount. However, mechanical separation processes are problematic in the case of sub-mounts of harder materials, such as aluminum nitride, sapphire, and the like. For these materials, a diamond-coated saw blade or a diamond-tipped scribe is used. Diamond-coated saw blades are relatively thick and generally produce cut widths or kerfs of 150 microns or wider, which adversely impacts device density on the sub-mount wafer. Diamond tipped scribes may produce narrower cut widths or kerfs; however, the scribe depth is limited. Hence, thicker sub-mounts cannot be diced by scribing unless the sub-mount is substantially thinned.
• Both sawing and scribing effectively cut through any encapsulant material disposed in the dicing lanes. However, both techniques can produce roughened, striated, or otherwise damaged sidewalls that reduce light extraction efficiency. Moreover, mechanical sawing or scribing produces shear forces that tend to delaminate the encapsulant, which can adversely impact device yield.
• The following contemplates improved apparatuses and methods that overcome the above-mentioned limitations and others.
BRIEF SUMMARY
• According to one aspect, a method is provided. A plurality of light emitting chips are attached on a sub-mount wafer. The attached light emitting chips are encapsulated. Fracture-initiating trenches are laser cut into the sub-mount wafer between the attached light emitting chips using a laser. The sub-mount wafer is fractured along the fracture initiating trenches.
• According to another aspect, a method is provided. A plurality of light emitting chips are attached on a sub-mount wafer. Fracture-initiating trenches are laser ablated into the sub-mount wafer between the attached light emitting chips using a laser. The sub-mount wafer is fractured along the fracture initiating trenches.
• According to yet another aspect, an apparatus is disclosed, including a plurality of light emitting chips and a sub-mount wafer. The sub-mount wafer has a front principal surface on which the light emitting chips are attached, a back principal surface opposite the front principal surface, and one or more fracture-initiating trenches disposed between the attached light emitting chips. The fracture-initiating trenches have widths less than about 75 microns.
• Numerous advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the present specification.
BRIEF DESCRIPTION OF THE DRAWINGS
• The invention may take form in various components and arrangements of components, and in various process operations and arrangements of process operations. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention. Except where indicated, layer thicknesses and other dimensions are not drawn to scale.
• FIGS. 1A-1D show a sub-mount wafer with attached light emitting chips at various stages of a light emitting package fabrication process.FIG. 1A shows the sub-mount wafer with the chips attached;FIG. 1B shows the sub-mount wafer after transfer-molded encapsulation;FIG. 1C shows the sub-mount wafer after laser cutting of fracture-initiating trenches; andFIG. 1D shows one of the light emitting packages after sub-mount fracturing.
• FIG. 2 shows a flow chart of an example light emitting package fabrication process.
• FIG. 3 shows a flow chart of an example laser cutting process.
• FIG. 4 diagrammatically shows an approach for shaping the encapsulant sidewall geometry during laser cutting. The top ofFIG. 4 plots a Gaussian laser beam intensity distribution at the sub-mount; the bottom ofFIG. 4 diagrammatically shows the resulting encapsulant sidewall geometry.
• FIG. 5 shows a microscope image of the sidewall of a sub-mount with encapsulant after laser cutting and sub-mount fracturing.
• FIG. 6 shows a more magnified microscope image of an encapsulant sidewall after laser cutting and sub-mount fracturing.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
• With reference toFIGS. 1A-1D andFIG. 2, a plurality oflight emitting chips10 are bonded to afrontside12 of asub-mount wafer14 in aprocess operation100. In typical embodiments, thechips10 are attached arranged in rows; however, substantially any layout of chip attachments can be used. Thelight emitting chips10 can be light emitting diodes, semiconductor lasers, or the like. In some embodiments, the chips are attached by flip-chip bonding thechips10 to electrical bonding pads disposed on thefrontside12 of thesub-mount wafer14, which also makes electrical connection of thechips10 with thesub-mount wafer14. In other embodiments, thechips10 are soldered or otherwise thermally attached to the frontside12 of thesub-mount wafer14, and wire bonds are used to make electrical connection of thechips10 with electrically conductive traces disposed on or in thesub-mount wafer14. In yet other embodiments, thechips10 are soldered or otherwise thermally attached to the frontside12 of thesub-mount wafer14, and wire bonds are used to make electrical connection of thechips10 with an external circuit, such that the sub-mount is not part of the electrical path. Optionally, thesub-mount wafer14 can have an array of electrostatic discharge (ESD) protection devices or other electrical circuitry disposed on or in thesub-mount wafer14, and eachchip10 is electrically connected with such circuitry during the chip attachprocess100.
• Because thesub-mount wafer14 will subsequently be separated by laser cutting (described infra), thechips10 can be attached with a relatively high density. The heat-affected zone of laser ablation for typical cutting lasers and typical sub-mount materials can be focused to about 25 microns; hence, corresponding gaps between adjacent attachedchips10 can be as small as about 25 microns. In contrast, separation by sawing using a diamond-coated blade usually dictates larger gaps between adjacent chips, for example gaps of about 150-250 microns, in order to accommodate the larger widths or kerfs of the diamond-coated blade. Thus, although for illustrative purposes only twelve relatively widely spacedchips10 are illustrated inFIGS. 1A-1D, it is to be understood that the device packing densities can be substantially higher.
• With reference toFIG. 1B andFIG. 2, anencapsulant20 is disposed over the attachedchips10 in aprocess operation102. In some embodiments, theencapsulant20 hermetically seals thelight emitting chips10 to the frontside12 of thesub-mount wafer14. In some embodiments, theencapsulant20 includes a wavelength-converting phosphor that is selected to convert light generated by thelight emitting chips10 to another wavelength. For example, in some embodiments thelight emitting chips10 are group III-nitride based light emitting diode chips emitting in the ultraviolet, and theencapsulant20 includes a white phosphor that converts the ultraviolet emission to visible white light. In other example embodiments, thelight emitting chips10 are group III-nitride based light emitting diode chips emitting blue light, and theencapsulant20 includes a yellow phosphor that converts a portion of the blue light to yellow light such that the combination of direct blue emission and wavelength-converted yellow fluorescence or phosphorescence approximates visible white light. In yet other example embodiments, thelight emitting chips10 are group III-arsenide or group III-phosphide based light emitting diode chips that emit red, orange, green, or blue light, and theencapsulant20 contains no phosphor. These are illustrative examples; more generally, thelight emitting chips10 can be substantially any type of light emitting diode, laser, organic semiconductor chip, or so forth, and theencapsulant20 may or may not contain phosphor or a blend of phosphors.
• In one suitable approach, theencapsulant20 is applied by transfer molding in which each row oflight emitting chips10 are encapsulated. In the illustrated example ofFIGS. 1A-1D, there are three such rows each containing fourchips10, and so there are three transfer molded strips ofencapsulant20. Theencapsulant20 extends over and covers the area of thesub-mount wafer14 between thechips10 in each row. In other embodiments, the light emitting chips are each individually encapsulated. In yet other embodiments, a blanket encapsulant is applied across the entire frontside12 of thesub-mount wafer14 to encapsulate all thechips10 in a single encapsulation process, and the encapsulant extends over and covers substantially the entire frontside of the sub-mount wafer. For certain applications, it is also contemplated to omit theencapsulant20, and the correspondingencapsulation process operation102, entirely.
• The encapsulated chips10 should generally be electrically accessible unless, for example, thechips10 are optically pumped, capacitively energized, or so forth, in which cases conductive electrical access to thechips10 may be omitted. In some embodiments, thesub-mount wafer14 includes electrically conductive vias passing from the frontside12 to a backside of thesub-mount wafer14. Such vias provide electrical connection between backside bonding pads of thesub-mount wafer14 and electrodes of the attachedchips10. In other embodiments, printed circuitry disposed on the frontside12 or elsewhere on or in thesub-mount wafer14 connects with chip electrodes and extends outside of the area covered by theencapsulant20 to provide electrical access to thelight emitting chips10.
• With reference toFIG. 1C andFIG. 2, thesub-mount wafer14 is secured toadhesive tape24 in aprocess operation104. Fracture-initiatingtrenches30,32 are laser cut into thesub-mount wafer14 between thelight emitting chips10 in aprocess operation106. The fracture-initiatingtrenches30,32 do not pass fully through the sub-mount14 so as to sever the sub-mount14 into pieces; rather, each fracture-initiatingtrench30,32 passes partway through the thickness of the sub-mount14. In some embodiments, the fracture-initiatingtrenches30,32 pass about half-way through the thickness of the sub-mount14. In the illustrated example, the fracture-initiatingtrenches30 run transverse to the encapsulated rows ofchips10 and cut completely through the strips ofencapsulant20, whereas the fracture-initiatingtrenches32 run parallel with the strips ofencapsulant20 and hence do not pass through theencapsulant20.
• With reference toFIG. 1D andFIG. 2, thesub-mount wafer14 is fractured in aprocess operation108 at the fracture-initiatingtrenches30,32 to produce individual packages, such as the individuallight emitting package40 shown inFIG. 1D which includes one of thelight emitting chips10 and portions of theencapsulant20 andsub-mount14. In the illustrated embodiment, each light emittingpackage40 includes a singlelight emitting chip10; hence, if the yield is 100% then thesub-mount wafer14 is diced to produce twelve light emitting packages40. Although each light emittingpackage40 in the illustrated example includes onelight emitting chip10, in other embodiments each package may include two, three, or more light emitting chips. For example, each light emitting package may include a red light emitting diode chip, a green light emitting diode chip, and a blue light emitting diode chip such that the light emitting package is a full-color light emitter.
• The lasercutting process operation106 entails certain difficulties as compared with laser cutting of silicon device wafers and other typical laser cutting applications. The sub-mount generally contains at least two very dissimilar materials: (i) the sub-mount material, and (ii) the encapsulant material. Typical epoxies, resins, and the like used for theencapsulant20 are relatively soft materials, while sub-mounts for light emitting diode chips are sometimes made of hard materials such as gallium nitride (GaN), aluminum nitride (AlN), silicon carbide (SiC), sapphire (Al₂O₃), ceramic materials, and oxide materials. These hard materials typically provide relatively higher thermal conductivity versus softer materials. The large difference in characteristics between the relativelysoft encapsulant20 and the relatively harder sub-mount14 typically leads to a large difference in cut depth for a single pass of the cutting laser. This difference in cut depth can be two orders of magnitude or larger.
• Additionally, characteristics of the sidewalls produced by the laser cutting can be important. The sidewall geometry can impact the light extraction efficiency of thelight emitting package40. For example, sideways-directed light may pass through the sidewall of theencapsulant20, or may be internally reflected at the sidewall, depending upon the laser-cut geometry of the sidewall. Moreover, it may be advantageous to generate sloped sidewalls that can act as reflectors (either through internal reflection at the encapsulant sidewall/air interface or by applying a reflective coating to the encapsulant sidewall). The geometry of the sloped sidewalls impacts the efficiency of such light reflection.
• With reference toFIG. 3, some preferred embodiments of the lasercutting process operation106 are described. The laser cutting processes106 use a suitable cutting laser, such as a krypton-fluoride (KrF) excimer laser operating at 248 nm, a diode-pumped solid state laser, a copper ion (Cu-ion) laser, or the like, which is configured to perform multiple passes to form each fracture-initiating trench. In aprocess operation200, laser operating parameters are selected for producing laser ablation, melting, or other removal of encapsulant material. These parameters may include, for example: laser power or fluence, laser pulse frequency, beam scan speed along the trench, laser wavelength (in the case of a wavelength-selectable cutting laser), laser beam angle respective to the sub-mount14, the focused laser beam spot size on the sub-mount14, and so forth. Typically, a relatively low power is used for cutting theencapsulant20 in view of the relative softness of the encapsulant material.
• In a firstcutting process operation202, one or more passes of the laser are applied to thesub-mount wafer14 to remove theencapsulant20 in the area of the trench, and optionally to shape the sidewalls of theencapsulant20 adjacent the trench. These passes are principally intended to remove theencapsulant20; however, thecutting process202 typically also removes some material from the sub-mount14 as well. However, because the cutting efficiency for the encapsulant material is generally much higher than the cutting efficiency for the sub-mount material, thesefirst passes202 typically remove mostly encapsulant material.
• Optionally, theprocess operation200 selected laser parameters which impart a selected sidewall geometry to the sidewalls of theencapsulant20 formed adjacent the fracture-initiatingtrench30 by the lasercutting process operation202. That is, the encapsulant sidewall geometry is optionally formed simultaneously with the laser cutting of theencapsulant20. For example, by arranging the laser beam at a selected angle with respect to thefrontside surface12 of the sub-mount14 (or, equivalently, by tilting the sample relative to the laser beam) during thecutting process operation202, a selected slope can be imparted to the encapsulant material sidewalls along the fracture-initiatingtrenches30. To produce a selected slanted sidewall on both sides of eachtrench30, the beam can be used with a selected tilt relative to the sub-mount14 during a first set of laser passes to form one sidewall, followed by a 180° rotation of the sub-mount14 (thus effectively reversing the tilt relative to the sub-mount14), followed by a second set of laser passes to form the other sidewall. Depending upon the tilt of the laser beam relative to the sub-mount30 during the encapsulant lasercutting process operation202, the sidewalls can be slanted away from thetrench30 or toward the trench30 (the latter being an “undercut” encapsulant with slanted sidewalls). Moreover, by varying the laser tilt during thecutting process operation202, a varying tilt can be produced, such as a sidewall that starts out vertical adjacent the sub-mount30 and then slants toward or away from thetrench30.
• With reference toFIG. 4, in yet another approach for producing shaped encapsulant sidewalls, the laser beam can be defocused to produce a broader spot on the sub-mount14 with a substantialGaussian intensity variation300. TheGaussian intensity variation300 produces a highest intensity in the center of thetrench30, with gradually lower intensities approaching the edges of thetrench30. Thisintensity variation300 imparts a spatial variation in cutting rate of theencapsulant20 that provides sloped encapsulant sidewalls. In a central region of the trench, denoted “W” inFIG. 4, the laser intensity is high enough that the one or more laser passes202 completely remove theencapsulant20, and additionally cut slightly into thefrontside surface12 of the sub-mount14. However, because of the much lower laser ablation rate of the sub-mount material as compared with the ablation rate of the encapsulant material, the removal of sub-mount material in the region “W” is limited, so that only ashallow depression302 is formed in thefrontside surface12 of the sub-mount14. Outside the region “W”, the laser intensity is too low for the one or more laser passes202 to completely remove theencapsulant20. The gradual decrease in laser intensity outside of the region “W” thus produces slopedencapsulant sidewalls304,306 adjacent thetrench30.
• While the removal of theencapsulant20 is typically an ablation process, it is to be understood that the laser may remove encapsulant material by another physical process or combination of processes. For example, the laser may melt material of theencapsulant20 in the vicinity of thetrench30. It is contemplated that under appropriate laser power and other operating conditions, such melted encapsulant material may “ball up” or otherwise shape itself by surface tension or other impetus to produce a slanted or other desirable sidewall characteristic.
• With returning reference toFIG. 3, once theencapsulant20 is removed by one or more first laser passes in theprocess operation202, the laser parameters are adjusted in a laseradjustment process operation204 to optimize the laser for cutting the material of the sub-mount14. Typically, a higher laser power, fluence, or energy, a slower laser scan speed, higher laser pulse frequency, or other adjustment or combination of adjustments is made to increase the laser ablation rate to more efficiently cut through the harder sub-mount material. If the first laser passes202 generated selectively shaped encapsulant sidewalls, then the laseradjustment process operation204 preferably includes more tightly focusing the laser beam on the sub-mount14 to ensure that the subsequent cutting does not continue to remove encapsulant material from the sloped sidewalls. Tradeoffs can be made between the laser power, beam focusing, beam scanning speed, number of laser passes, and other parameters to control the kerf of the laser cut.
• In some embodiments, the same laser parameters are used for cutting both theencapsulant20 and the sub-mount14. In these embodiments, the laseradjustment process operation204 is suitably omitted.
• The first laser passes202 that removed the encapsulant are applied to the frontside12 of the sub-mount14. Optionally, the sub-mount14 is flipped over in the laser cutting apparatus in aprocess operation206 before initiating substantial laser cutting into the sub-mount14, so that the subsequent laser cutting into the sub-mount14 is performed on the backside. This optionalsub-mount flipping operation206 can reduce contamination or coating of the front-side12 by laser ablated material. In other embodiments, both theencapsulant20 and the sub-mount14 are cut from the frontside12, in which case thesub-mount flipping operation206 is omitted.
• With the laser operating parameters selected for cutting the sub-mount14, and with the desired side of the sub-mount14 exposed to the laser beam, the sub-mount is cut. In acutting process operation208, one or more subsequent passes of the laser are applied to thesub-mount wafer14 to cut the fracture-initiatingtrench30 to the desired depth. In experiments performed by the inventors using aluminum nitride sub-mount wafers having about 2.5 cm×5 cm area, a depth of about 47% or greater of the total thickness of the sub-mount was found to produce high device yields in thefracturing process108. Additional laser cutting beyond that needed to achieve a high device yield in the sub-mount fracturing is generally not advantageous; hence, a trench depth of about one-half of the sub-mount thickness was considered optimal for fracturing these aluminum nitride sub-mount wafers. However, the optimal depth is expected to depend upon many factors, such as sub-mount material and quality, sub-mount thickness, the length of the fracture-initiating trenches, the overall size of the sub-mount wafer, and so forth. For example, it is expected that for thinner sub-mount wafers, such as wafers having thickness under 300 microns, trenches extending a substantially reduced percentage of the way through the sub-mount wafer may be sufficient. Trial cuts for 100 micron thick sub-mount wafers were found to facture well for trenches extending less than 40% of the total sub-mount thickness. Those skilled in the art can readily optimize the depth of the fracture-initiatingtrenches30 for specific sub-mounts.
• In some embodiments, the sub-mount may include more than one material. For example, the sub-mount may include a silicon wafer and an aluminum nitride wafer which are fused or otherwise bonded together. For such composite sub-mounts, additional laser parameters adjustments may optionally be performed when the laser cutting passes from one sub-mount material into the next sub-mount material. The inventors have found that pre-calibration of the laser cutting time is adequate to reproducibly obtain the desired fracture-initiating trench depth; however, it is also contemplated to employ feedback control of the laser cutting process based on profilometry, phase contrast, or other depth measurements.
• The laser cutting process has been described with reference to the fracture-initiatingtrenches30, which pass through theencapsulant20. For forming the fracture-initiatingtrenches32 which do not pass through theencapsulant20, the encapsulantremoval process operations200,202 are suitably omitted. Moreover, it is to be appreciated that the laseradjustment process operations200,204, can include adjustments to both the laser itself and to associated optics, optical filters, beam scanning hardware, and so forth that are associated with the cutting laser and that collectively determine the cutting characteristics of the laser. Such laser adjustments can also be made during the one or more first laser passes202 and/or during the one or more subsequent laser passes208. For example, with brief reference back toFIG. 4, during the first laser passes202 that remove theencapsulant20 the laser beam spot focus may be continuously adjusted to produce a selected sidewall geometry of theencapsulant sidewalls304,306.
• An advantage of the disclosed laser cutting method for dicing the sub-mount14 is that the fracture-initiatingtrenches30,32 can be made narrower in width than can be achieved using mechanical sawing employing a diamond coated saw blade. In some embodiments, the laser cut fracture-initiatingtrenches30,32 have widths or kerfs that are less than about 75 microns. In some embodiments, the laser cut fracture-initiatingtrenches30,32 have widths or kerfs that are less than about 25 microns. In contrast, diamond coated saw blades generally produce kerfs of about 150 microns or wider. The narrower kerfs of the laser cuttrenches30,32 enables a higher packing density ofchips10 on thesub-mount wafer14.
• The inventors have applied the disclosed packaging techniques, including laser cutting of the sub-mount wafer, to aluminum nitride sub-mounts. A krypton-fluoride (KrF) excimer laser operating at 248 nm was used to separate a 380 micron thick unprocessed aluminum nitride (AlN) sub-mount. The fracture-initiating trenches were cut to a depth of 50% of the total thickness (i.e., about 190 microns), which was found to be sufficient to provide controlled fracture. Another aluminum nitride sub-mount was fully processed, including transfer molding of an encapsulant onto the sub-mount, but did not have light emitting chips attached. This processed sub-mount was similarly laser cut and run through a wafer fracture tool. Complete fracture of the sub-mount and encapsulant into individual devices was achieved. On this sub-mount, the encapsulant was molded to the sub-mount surface without using an adhesion promoter. The omitted adhesion promoter is typically used to reduce the possibility of encapsulant delamination from the sub-mount. Encapsulant delamination was observed in 5% of the devices after fracturing. This result suggests that the laser cutting does not produce substantial shear forces of the type that typically lead to encapsulant delamination, and it is expected that nearly 100% yield should be achieved when the adhesion promoter is included.
• With reference toFIGS. 5 and 6, microscopic examination of the sidewalls of the encapsulated and laser-separated aluminum nitride sub-mounts is illustrated.FIG. 5 shows a microscopic image of theencapsulant sidewall400 and thesub-mount sidewall402 after laser cutting and sub-mount fracture. Thicknesses are labeled inFIG. 5: the encapsulant has a thickness of about 427.0 microns, while the sub-mount has a thickness of about 408.3 microns. Aboundary404 is visible between the portion of thesub-mount sidewall402 that was formed by laser cutting, and the remaining portion that was formed by the fracturing. It is observed that the laser cut portion has a depth of about 146.0 microns in areas distal from the encapsulant (corresponding to about 35.7% of the 408.3 micron total sub-mount wafer thickness), and a reduced depth of about 131.4 microns under the encapsulant (corresponding to about 32.2% of the 408.3 micron total sub-mount wafer thickness). The slightly reduced sub-mount laser cutting depth under the encapsulant is due to the fact that the laser cutting had to first remove the encapsulant before reaching the sub-mount wafer itself. However, the difference in cutting depths (146.0 microns versus 131.4 microns) is too small to substantially impact device yield during fracturing.FIG. 6 shows a more magnified view of theencapsulant sidewall400, which indicates a substantially smooth encapsulant sidewall surface.
• The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims (20)

1. A method comprising:

attaching a plurality of light emitting chips on a sub-mount wafer;

disposing an encapsulant over the attached light emitting chips and over at least a portion of a surface of the sub-mount wafer,

laser-cutting fracture-initiating trenches into the sub-mount wafer between the attached light emitting chips, the fracture-initiating trenches passing through the encapsulant disposed on the surface of the sub-mount wafer, the laser-cutting employing operating conditions selected such that the laser-cutting causes the encapsulant to melt and re-shape to produce a desired sidewall characteristic; and

fracturing the sub-mount wafer along the fracture-initiating trenches.

2. The method as set forth inclaim 1, wherein the laser-cutting comprises:

employing operating conditions selected such that the laser-cutting causes the encapsulant to ball up to produce the desired sidewall characteristic.

3. The method as set forth inclaim 1, wherein the laser-cutting comprises:

employing operating conditions selected such that the laser-cutting causes the encapsulant to melt and re-shape by surface tension to produce the desired sidewall characteristic.

4. The method as set forth inclaim 1, wherein the laser-cutting of fracture-initiating trenches comprises:

performing one or more first passes of laser-cutting that cut the encapsulant disposed between the light emitting chips, the one or more first passes employing the operating conditions selected such that the laser-cutting causes the encapsulant to melt and re-shape to produce a desired sidewall characteristic; and

performing one or more subsequent passes of laser-cutting that cut into the sub-mount wafer to form a trench in the sub-mount wafer, the one or more subsequent passes employing different operating conditions from the operating conditions of the one or more first passes.

5. The method as set forth inclaim 4, wherein the one or more subsequent passes employ at least one of a higher laser-cutting power, a higher laser-cutting fluence, a higher laser-cutting energy, a slower laser-cutting scan speed, and a higher laser-cutting pulse frequency respective to the one or more first passes.

6. A method comprising:

attaching a plurality of light emitting chips on a sub-mount wafer;

encapsulating the attached light emitting chips;

laser-cutting fracture-initiating trenches having kerfs of less than about 75 microns into the sub-mount wafer between the attached light emitting chips using a laser; and

fracturing the sub-mount wafer along the fracture-initiating trenches.

7. The method as set forth inclaim 6, wherein the encapsulating includes disposing encapsulant material on the sub-mount in areas between light emitting chips, and the laser-cutting of fracture-initiating trenches comprises:

removing the encapsulant disposed between the light emitting chips; and

removing a portion of the sub-mount wafer.

8. The method as set forth inclaim 7, wherein the laser-cutting of fracture-initiating trenches further comprises:

performing one or more first laser-cutting passes that cut the encapsulant disposed between the light emitting chips, the one or more first laser-cutting passes employing first operating parameters; and

performing one or more subsequent laser-cutting passes that cut into the sub-mount wafer to form a trench in the sub-mount wafer, the one or more subsequent laser-cutting passes employing second operating parameters different from the first operating parameters.

9. The method as set forth inclaim 8, wherein the encapsulant is disposed on a frontside of the sub-mount wafer, and the one or more subsequent laser-cutting passes are performed on a backside of the sub-mount wafer opposite the frontside.

10. The method as set forth inclaim 8, wherein the first operating parameters provide a relatively lower laser-cutting rate, and the second operating parameters provide a relatively higher laser-cutting rate.

11. The method as set forth inclaim 8, wherein the first operating parameters cause the encapsulant to melt and re-shape to produce a desired sidewall characteristic.

12. The method as set forth inclaim 6, wherein the laser-cutting fracture-initiating trenches pass about half-way through a thickness of the sub-mount.

13. The method as set forth inclaim 6, wherein the laser-cutting fracture-initiating trenches pass less than 40% through a thickness of the sub-mount.

14. The method as set forth inclaim 6, wherein the laser-cutting comprises:

employing feedback control of the laser-cutting based on a measurement of a depth produced by the laser-cutting.

15. A method comprising:

attaching a plurality of light emitting chips on a sub-mount wafer;

laser-cutting fracture-initiating trenches into the sub-mount wafer between the attached light emitting chips using a laser; and

fracturing the sub-mount wafer along the fracture-initiating trenches.

16. The method as set forth inclaim 15, wherein the laser-cutting of fracture-initiating trenches comprises:

removing an encapsulant material encapsulating the plurality of light emitting chips in the areas of the fracture-initiating trenches.

17. The method as set forth inclaim 16, wherein the laser-cutting of fracture-initiating trenches comprises:

employing operating conditions for the laser-cutting selected such that the laser-cutting causes the encapsulant to melt and re-shape to produce a desired sidewall characteristic.

18. The method as set forth inclaim 15, wherein the fracture-initiating trenches have kerfs of less than about 75 microns.

19. The method as set forth inclaim 15, wherein the fracture-initiating trenches have kerfs of less than about 25 microns.

20. The method as set forth inclaim 15, wherein the sub-mount wafer includes a material, or a fusion or bonding of a plurality of materials, selected from a group of materials consisting of gallium nitride, aluminum nitride, silicon carbide, sapphire, a ceramic material, an oxide material, silicon, or a semiconductor.

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