Patent Application
20180076168
Embodiments are related to systems and methods for fluidic assembly, and more particularly to systems and methods for forming contacts during fluidic assembly.
LED displays, LED display components, and arrayed LED devices include a large number of diodes formed or placed at defined locations across the surface of the display or device. Fluidic assembly may be used for assembling diodes in relation to a substrate for use in manufacturing LED devices. Such assembly can result in excessive resistance between the diodes and electrical contacts formed on the substrate. Using a metallic contact integrally connecting the diodes with the electrical contacts formed on the substrate would reduce resistances. However, such integral connectivity using a metallic contact is not easily formed using conventional technologies resulting in high costs and low reliability.
Hence, for at least the aforementioned reasons, there exists a need in the art for advanced systems and methods for manufacturing LED displays, LED display components, and LED devices.
A further understanding of the various embodiments of the present invention may be realized by reference to the figures which are described in remaining portions of the specification. In the figures, like reference numerals are used throughout several figures to refer to similar components. In some instances, a sub-label consisting of a lower case letter is associated with a reference numeral to denote one of multiple similar components. When reference is made to a reference numeral without specification to an existing sub-label, it is intended to refer to all such multiple similar components.
Embodiments are related to systems and methods for fluidic assembly, and more particularly to systems and methods for forming contacts during fluidic assembly.
Various embodiments provide electronic assembly systems that include a suspension having a carrier liquid and a plurality of solder particles. In some instances of the aforementioned embodiments, the solder particles are formed of eutectic solder material and/or non-eutectic solder material. In some cases, the solder particles are formed from an Au/Ge solder material. In other cases, the solder particles are formed from an Au/Sn solder material. In one or more instances of the aforementioned embodiments, the systems further include a substrate. The substrate has a well including one or more of the solder particles settled out from the suspension near a corner of the well. In some such cases, an object is deposited in the well on top of the one or more of the solder particles settled out from the suspension near the corner of the well. In particular cases, the object is a diode. In some instances of the aforementioned embodiments, the solder particles are formed in part by directing ultrasonic waves at a solder material.
In various instances of the aforementioned embodiments, the system further includes: a substrate and a suspension moving device. The substrate includes a well, and the suspension is deposited on the well. The suspension movement device is operable to move the suspension over the substrate such that a first flow rate near a corner of the well is less than a second flow rate outside the well. The difference between the first flow rate and the second flow rate encourages a first subset of the plurality of the solder particles to settle out in the first flow rate, but a second subset of the plurality of particles to remain in suspension in the second flow rate.
Other embodiments provide methods for device assembly that include: depositing a suspension on a substrate including a non-planar structure where the suspension includes a carrier liquid and a plurality of solder particles; agitating the suspension relative to the substrate such that a first flow rate of the suspension at a first location relative to the non-planar structure is less than a second flow rate of the suspension at a second location relative to the non-planar structure, where a difference between the first flow rate and the second flow rate encourages a first subset of the plurality of the solder particles to settle out near the first location, but a second subset of the plurality of particles to remain in the suspension near the second location. The solder particles may be formed of either a eutectic solder material or a non-eutectic solder material.
In some instances of the aforementioned embodiments, the non-planar structure may be, but is not limited to, a trench or a well. In various instances of the aforementioned embodiments, the non-planar structure is a well, the first location is in a corner of the well, and the second location is near a center of the well. In one or more instances of the aforementioned embodiments, the methods further include: forming the plurality of solder particles; and adding the plurality of solder particles to the carrier liquid to make the suspension. In some instances of the aforementioned embodiments, the methods further include draining the suspension from the substrate, where the first subset of the plurality of the solder particles remain on the substrate. In some cases, the methods additionally include sintering the first subset of the solder particles. In some cases, the methods further include: depositing an object in the non-planar structure on the first subset of the solder particles, and annealing the substrate such that the first subset of the solder particles connect the object to the substrate.
Turning to
During fluidic assembly a liquid flow (indicated by arrows 160) results in drag forces on diode objects 110 traversing the surface of substrate 190. As shown in a cross-sectional view 102 of
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As shown, substrate 290 is composed of a polymer material 215 laminated to the surface of a glass layer 205. It should be noted that materials other than glass may be used in place of glass layer 205. Additionally, other conductive or non-conductive layers may exist between material 215 and layer 205. Further, it should be noted that in some cases polymer material 215 may be replaced by glass or another suitable material. In some embodiments, substrate 215 is made by forming an electric contact layer on the surface of glass layer 205, and etching the electric contact layer to yield an electrical contact 235 at a location corresponding to a future well. It should be noted that while electrical contact 235 is shown as covering only a portion of the base of well 212, that it may cover the entire base of well 212 as there is not a through-hole via. Polymer material 215 is then laminated over glass layer 205 and electrical contact 235, followed by an etch of polymer material 215 to open well 212 defined by a sidewall 214 and expose a portion of electrical contact 235. Electrical contact 235 may be formed of any material capable of forming an electrical junction with bottom surface 275 of a diode object 110. In some cases, electrical contact 235 is formed of a metal that when annealed with a diode object 110 disposed within well 212 forms an electrically conductive location between a signal connected to electrical contact 235 and electrically conductive material 270 of a diode object 110. In some embodiments, the depth of well 212 is substantially equal to the height (Hd) of diode object 110 such that only one diode object 110 deposits in well 212. It should be noted that while specifics of the substrate, wells and diode objects are discussed herein, that the processes discussed herein may be used in relation to different substrates, wells and other objects.
During fluidic assembly a liquid flow (indicated by arrows 260) results in drag forces on diode objects 110 traversing the surface of substrate 290. As shown in a cross-sectional view 202 of
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In some embodiments, carrier liquid 315 is isopropanol. Based upon the disclosure provided herein, one of ordinary skill in the art will recognize a variety of liquids, gasses, and/or liquid and gas combinations that may be used as the carrier liquid. It should be noted that various analysis provided herein is based upon flow in a single, continuous direction or in other cases a relatively simple back-forth motion, but that the flow may be more complex where both the direction and magnitude of fluid velocity can vary over time.
The solder particles may be made of any material capable of reducing resistance between electrodes 335 along the bottom of wells 342 and a diode object (not shown) deposited in a given one of wells 342. In some embodiments, the solder particles are eutectic solder particles that are not neutrally buoyant and will tend to settle out of carrier liquid 315 in lower velocity regions and remain suspended in the carrier liquid 315 in higher velocity regions. Examples of such lower velocity regions and higher velocity regions are discussed in detail below in relation to
In some embodiments, solder particles are formed by depositing a solder particle material on top of a base structure. In some embodiments, the solder particle material is a mixture of Gold and Germanium formed as an Au/Ge metallized layer on the top of the base structure. This deposition of the solder particle material includes evaporating solder material layers with poor adhesion, and cycling through proportional layering. The base structure may be, but is not limited to, a photoresist layer formed on top of a silicon layer. Once the solder particle material is deposited on top of the base structure, layer peeling may be enhanced by mechanical grinding or other manipulation. Then, the overall structure is exposed to ultrasonic waves and additional mechanical milling to reduces the solder particle size. Larger solder particles are filtered out, and the remaining smaller solder particles are introduced into carrier fluid 315 to yield suspension 310.
As shown in
The remaining neat liquid is allowed to evaporate leaving the solder particles deposited near the corners of wells 342. In some cases, to improve the mechanical stability of the remaining solder particles, the deposited solder particles are sintered together by heating substrate 340.
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As shown in
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A depositing device 550 deposits suspension 510 over the surface of substrate 540 with suspension 510 held on top of substrate 540 by sides 520 of a dam structure. In some embodiments, depositing device 550 is a pump with access to a reservoir of suspension 510. A suspension movement device 560 agitates suspension 510 deposited on substrate 540 such that diode objects 530 move relative to the surface of substrate 540. As diode objects 530 move relative to the surface of substrate 540 they deposit into wells 542 in either a non-inverted orientation or an inverted orientation. In some embodiments, suspension movement device 560 is a brush that moves in three dimensions. Based upon the disclosure provided herein, one of ordinary skill in the art will recognize a variety of devices that may be used to perform the function of suspension movement device 560 including, but not limited to, a pump.
A capture device 570 includes an inlet extending into suspension 510 and capable of recovering a portion of suspension 510 including a portion of carrier liquid 515 and non-deposited diode objects 530, and returning the recovered material for reuse. In some embodiments, capture device 570 is a pump.
It should be noted that while
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Further, the solder particles may be made of a number of different materials including both eutectic materials and non-eutectic materials. As just some examples, the solder particles may be made of Au/Ge or Au/Sn. Based upon the disclosure provided herein, one of ordinary skill in the art will recognize a variety of materials that may be used to form the solder particles.
In some embodiments, solder particles are formed by depositing a solder particle material on top of a base structure. In some embodiments, the solder particle material is a mixture of Gold and Germanium formed as an Au/Ge metallized layer on the top of the base structure. This deposition of the solder particle material includes evaporating solder material layers with poor adhesion, and cycling through proportional layering. The base structure may be, but is not limited to, a photoresist layer formed on top of a silicon layer. Once the solder particle material is deposited on top of the base structure, layer peeling may be enhanced by mechanical grinding or other manipulation. Then, the overall structure is exposed to ultrasonic waves and additional mechanical milling to reduces the solder particle size. Larger solder particles are then filtered out to leave a group of solder particles that may be used in processing.
The group of solder particles are added to a carrier liquid to make a suspension (block 710). Any liquid capable of moving solder particles at high flow rate regions, and allowing the solder particles to settle out in lower flow rate regions may be used in accordance with different embodiments of the present inventions. In some embodiments, the carrier liquid is isopropanol. Based upon the disclosure provided herein, one of ordinary skill in the art will recognize a variety of liquids, gasses, and/or liquid and gas combinations that may be used as the carrier liquid.
The suspension is deposited on the surface of a substrate including a number of wells (block 715). In some embodiments the wells include through-hole vias extending from the bottom of the wells to the bottom of the substrate. In other embodiments, the wells do not exhibit through-hole vias. The suspension is agitated in relation to the surface of the substrate such that areas of higher flow rates and areas of lower flow rates are created (block 720). Examples of areas with differential flow rates are shown in
The suspension is then drained from the surface of the substrate (block 725). In embodiments where the wells do not include through-hole vias, the draining may include pumping the remaining suspension from the surface of the substrate or titling the substrate to drain the excess material. In embodiments where the wells do include through-hole vias, the excess suspension may simply be allowed to drain through the through-hole vias. In either case, as the excess suspension is drained, it is replaced by neat liquid (i.e., the carrier liquid without solder particles) such that solder particles do not settle out during the draining process. Once the draining process is complete, the remaining neat liquid is allowed to dry (block 735).
It is then determined whether a sintering process is to be completed (block 740). Where sintering is to be completed (block 740), the deposited solder particles are sintered together by heating the substrate (block 745). Such sintering enhances the mechanical stability of the remaining solder particles. Objects are then fluidically assembled into the wells on top of the solder particles (block 750). Once the fluidic assembly of the objects is complete (block 750), the substrate is annealed such that the solder particles integrally connect the object to the substrate within the wells (block 755).
One of ordinary skill in the art will recognize various advantages achievable through use of different embodiments of the inventions. As just some of many advantages, lower display costs are possible as a significant cost of manufacturing a microLED display is the material cost of the microLEDs themselves. As some embodiments of the present inventions allow for reducing redundancy otherwise necessary to assure an operable display, the overall number of microLEDs may be reduced resulting in a corresponding reduction in costs. Various embodiments of the present inventions do not require lock-n-key type interaction between post enhanced diodes and wells which allow diodes to deposit in only a single orientation. As such, manufacturing tolerances may be reduced leading to greater yields and/or lower costs. Based upon the disclosure provided herein, one of ordinary skill in the art will recognize a variety of other advantages achievable through use of one or more embodiments of the present inventions.
Additionally, while the inventions have been discussed in relation to assembling diode objects into cylindrical wells, it should be noted that the inventions discussed herein may be used, for example, to deposit solder particles into a trench formed on a substrate surface. All such surface features in the substrate including, but not limited to, wells and trenches are referred to herein as “non-planar structures”. As used herein, a “non-planar structure” is any feature on or in the substrate which causes differential flow rates in a suspension being agitated relative to the surface of the substrate. By flowing a suspension including solder particles perpendicular to the trench, some of the solder particles will settle out in the trench. The substrate may then be heated resulting in the formation of a metal wire on the surface of the substrate as defined by the trench. Further, some embodiments may use a carrier liquid that includes a fluxing material that remains after the neat liquid is evaporated or dried.
In conclusion, the invention provides novel systems, devices, methods and arrangements for fluidic assembly. While detailed descriptions of one or more embodiments of the invention have been given above, various alternatives, modifications, and equivalents will be apparent to those skilled in the art without varying from the spirit of the invention. For examples, while some embodiments are discussed in relation to displays, it is noted that the embodiments find applicability to devices other than displays. Therefore, the above description should not be taken as limiting the scope of the invention, which is defined by the appended claims.
