WO2025024924A1

WO2025024924A1 - Backplane pad

Info

Publication number: WO2025024924A1
Application number: PCT/CA2024/050997
Authority: WO
Inventors: Gholamreza Chaji; Hossein Zamani Siboni; John Cronin; Dana Saud Yousef AYYASH; Long PU; Ting CHENG
Original assignee: Vuereal Inc
Current assignee: Vuereal Inc
Priority date: 2023-07-28
Filing date: 2024-07-26
Publication date: 2025-02-06
Anticipated expiration: 2026-01-28
Also published as: TW202524666A; CN121420662A

Abstract

The present invention discloses the transfer of a selected set of microdevices from a donor substrate to a receiver/system substrate. It further discloses shorting challenges in microdevice integration into the system substrate (or backplane) by providing a novel method and apparatus for integrating flip-chip devices into backplanes that minimize the risk of pad shorting. The invention further discloses a method for correcting non-flatness of a cartridge during integration of microdevices to the system substrates.

Description

Backplane Pad

Field of the invention

[001] The present disclosure relates to transferring a selected set of micro devices from a donor substrate to a receiver/system substrate. At the same time, microdevices can already be transferred in the system substrate. The present invention further relates to microdevice integration and, more particularly, to a method and apparatus for integrating flip-chip microdevices into backplanes while mitigating the risks of pad shorting due to pressure and heat during the assembly process. The present invention further relates to correcting the cartridge flatness during the integration of microdevices into system substrate.

Summary

[002] The present invention relates to a method comprising, having a backplane comprising of circuit layers to control microdevices, forming pads on the backplane and the microdevices, and applying heat or pressure to the backplane and or the microdevice after aligning microdevices with the backplane to bond the pads to each other and secure the microdevice to the backplane mechanically and electrically.

[003] The present invention relates to a method for integration of microdevices into a cartridge substrate with a corrected cartridge flatness the method comprising, having a deformable (or elastic) layer in between the cartridge substrate and a tool head, wherein the tool head holds the cartridge substrate during a microdevices transfer, applying pressure or heat to the cartridge substrate and reducing a non-flatness effect by deforming the elastic or the deformable layer under pressure.

[004] The present invention relates to a transfer method for integration of microdevices into a system substrate, aligning a donor substrate with an array of microdevices is aligned with a system substrate, and having the system substrate with an array of pads for selective bonding of microdevices, wherein the pads perform two functions: loosening the microdevices from the donor substrate and bonding the microdevices to the system substrate.

Brief description of the Drawings

[005] The foregoing and other advantages of the disclosure will become apparent upon reading the following detailed description and upon reference to the drawings.

[006] Figure 1(a) shows the non-flatness of the donor/cartridge substrate or system substrate.

[007] Figure 1(b) shows selected microdevices touching or getting close to the selected pads.

[008] Figure 2(a) shows the donor substrate has a buffer layer.

[009] Figure 3(a) and 3(b) show the pads on the system substrate are formed on a stage.

[0010] Figure 4 shows the highlights of the pad-to-pad short.

[0011] Figures 5(a) and 5(b) show the use of tapered spacers.

[0012] Figure 5(c) shows the backplane after the microdevice is integrated into the substrate.

[0013] Figure 6 shows integration of micro devices into system substrates.

[0014] While the present disclosure is susceptible to various modifications and alternative forms, specific embodiments or implementations have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the disclosure is not intended to be limited to the particular forms disclosed. Rather, the disclosure is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of an invention as defined by the appended claims. Detailed Description

[0015] The invention relates to transferring a selected set of microdevices from a donor substrate to a receiver/system substrate while there are already microdevices transferred to the system substrate.

[0016] Receiver, target or system substrate are used interchangeably.

[0017] A donor material would typically be a temporary substrate that serves as a carrier for microLEDs during the transfer process to transfer microLEDs from a donor substrate to a system substrate. The donor material should have good mechanical and thermal stability. The donor material should be easily separable from the transferred microLEDs or transparent or translucent to the emitted light from microLED.

[0018] Some common materials used as donor substrates for microLED transfer include silicon, glass, and sapphire. Silicon is widely used due to its availability, low cost, and compatibility with semiconductor processing techniques. Glass and sapphire are also used as donor substrates, especially for high-performance applications, due to their excellent optical and mechanical properties. Other materials, such as polymers and metals, may also be used as donor substrates depending on the specific requirements of the transfer process and the desired performance of the microLEDs.

[0019] Pick-and-place transfer: This method involves picking up individual microLEDs with a tool and placing them onto the target substrate.

[0020] In one case, the tool can be a stamp. This transfer method uses a stamp or mold to pick up the microLEDs from the donor substrate and transfer them to the target substrate. The stamp/mold is typically made of a soft, elastomeric material, which conforms to the microLEDs and allows for high-precision placement.

[0021] In another pick-and-place case, the tool can be electrostatic force-assisted transfer (EFAT): This transfer method uses an electric field to attract and transfer microLEDs from the donor substrate to the target substrate. The donor substrate is typically coated with a conductive layer, and a voltage is applied to the target substrate to induce the transfer.

[0022] Transfer by dissolution: This method involves dissolving the sacrificial layer that holds the microLEDs on the donor substrate. Once the sacrificial layer is dissolved, the microLEDs are free to transfer onto the target substrate due to adhesive forces.

[0023] In another case, other structures exist in the receiver substrate that can interfere with the transfer. In this invention, we use the previously transferred microdevice to explain the invention; however, similar topics can be applied to the other structures.

[0024] In the microSolid Printing process, the microLEDs are directly transferred from a cartridge into the target substrate. Here, a bonding force between microLED and the target substrate is formed that is stronger than the force holding microdevices to the donor substrate structures, which could be, for example, surface roughness. If the surface of the receiver substrate is rough, it can cause poor adhesion and incomplete transfer of the microLEDs. The roughness can also cause damage to the microLEDs during transfer. Other structures could be, for example, surface contaminants: Any contaminants, such as dust, oils, or fingerprints, on the surface of the receiver substrate, can interfere with adhesion and cause incomplete transfer of the microLEDs. Other structures could be, for example, caused by thermal expansion coefficient mismatch. Suppose the thermal expansion coefficient of the receiver substrate is significantly different from that of the donor substrate. In that case, it can cause mechanical stress during transfer, leading to cracking or delamination of the microLEDs. Microdevices can be microLED, OLED, microsensors, MEMs, and other devices.

[0025] For another example, devices could be micro actuators. These devices convert electrical or other forms of energy into motion or mechanical work on a microscale. Examples include microvalves, micropumps, and microgrippers.

[0026] Another example could be Microfluidic devices. These systems manipulate small amounts of fluids or gasses on a microscale, typically within channels or chambers with dimensions less than 1 mm. Examples include microreactors, lab-on-a-chip devices, and microfluidic chips.

[0027] Another example of a device could be micro-optics. These are devices that manipulate light on a microscale, typically through the use of lenses, prisms, or diffraction gratings. Examples include micro spectrometers, micro-lenses, and micro prisms.

[0028] Another example is micro batteries. These devices store energy on a microscale, typically through thin-film or microfabrication techniques. Examples include micro-supercapacitors, micro fuel cells, and micro batteries.

[0029] For another example, devices could be microarrays, Which allow for high-throughput analysis of biological or chemical samples on a microscale, typically through small spots or features arranged in a grid pattern. Examples include DNA microarrays, protein microarrays, and chemical microarrays.

[0030] In one case, the microdevice has a functional body and contacts, which can be electrical, optical, or mechanical.

[0031] For example, contacts may be adhesive layers. Thin films of adhesive materials, such as polymers or metal oxides, can be applied to the donor substrate to promote adhesion between the microLEDs and the target substrate during transfer.

[0032] For example, contacts may be sacrificial layers. These temporary layers hold the microLEDs in place on the donor substrate but can be dissolved or removed after transfer to release the microLEDs onto the target substrate. Examples of sacrificial materials include polymers and oxides.

[0033] For example, contacts may be release layers. These layers facilitate the separation of the donor substrate from the transferred microLEDs after transfer. Release layers can be made of materials such as silicon oxide or metal.

[0034] For example, contacts may be conductive layers. These layers provide electrical contact between the transferred microLEDs and the target substrate. Examples of conductive materials include metals such as gold or indium tin oxide (ITO).

[0035] For example, contacts may be anti-stiction layers. These layers are used to prevent the microLEDs from sticking to the donor substrate during transfer, which can cause damage to the microLEDs or reduce transfer yield. Anti-stiction layers can be made of materials such as fluorocarbons or self-assembled monolayers.

[0036] In the case of an optoelectronic microdevice, the device can have functional layers and charge-carrying layers. Where charge-carrying layers (doped layers, ohmic and contacts) transfer the charges (electrons of the hole) between the functional layers and contacts outside the device. The functional layers can generate electromagnetic signals (e.g., lights) or absorb electromagnetic signals. [0037] For example, functional layers may be multi-quantum well (MQW) with barrier layers. MQW functional layers can be used in sensors, LEDs, lasers, and other microdevices that convert electrical energy into light or vice versa through the use of MQW. They typically consist of several other layers, including an anode, a hole transport layer, an electron transport layer, and a cathode.

[0038] For example, functional layers may be heterojunction or homojunction semiconductor layers. These structures are used in emissive sensors or photovoltaic devices. They typically comprise several other layers, including an anode, a hole transport layer, an active layer, an electron transport layer, and a cathode.

[0039] For example, functional layers may be Photodetectors. Photodetectors are microdevices that detect light by converting photons into electrical current. They typically consist of several layers, including a substrate, a photoactive layer, and an electrode.

[0040] For example, functional layers may be Micro-optoelectromechanical systems (MOEMS). MOEMS are microdevices that integrate optical and mechanical components with electrical circuits. They typically consist of several layers, including a substrate, an actuation layer, an optical layer, and a sensing layer.

[0041] System substrates can have pixels and pixel circuits, each controlling at least one microdevice. Pixel circuits can be made of electrodes, transistors, or other components. The transistors can be fabricated with a thin-film process, CMOS, or organic materials.

[0042] Figure 1 shows an embodiment for transferring microdevices from the donor substrate 102 to the receiver substrate 150. Here, a buffer layer 104 can be formed on the donor substrate 102 and microdevices 106 are located on top of the buffer layer. The buffer layer can be formed by patterning or etching processes. The buffer layer can be a polymer, dielectric, or other materials such as metals. Due to the use of semiconductor processes to develop the buffer layer, it can be aligned to the edge of the last microdevices on the substrate. The System substrate 150 has pads 152 associated with the current microdevices to be transferred to the system substrate 150 from the donor substrate 102. System substrate 150 also has pads 154 that have already been populated with microdevices 156, and some of these pads may be adjacent to the current location for the transfer.

[0043] As shown in Figure 1(b), when the donor substrate 102 and system substrate 152 get close, the selected microdevices touch (or get close to) the selected pads 152. The pads 152 can be soft materials (adhesive, polymers, Indium, and so on).

[0044] Soft materials can be adhesive materials, for example. Adhesive materials are substances that can stick two surfaces together. Examples include pressure-sensitive adhesives (PSAs), epoxy adhesives, cyanoacrylate adhesives, and silicone adhesives.

[0045] Soft materials can be, for example, polymers. Polymers are large molecules composed of repeating units. They are commonly used in various applications due to their unique properties, such as flexibility, toughness, and resistance to chemicals and temperature. Examples include polyethylene, polypropylene, polystyrene, and polyvinyl chloride (PVC).

[0046] Soft materials can be, for example, elastomers. Elastomers are polymers with elastic properties, such as high resilience and deformability. They are commonly used in seals, gaskets, and shock absorbers. Examples include natural rubber, silicone rubber, and polyurethane elastomers.

[0047] Soft materials include indium. Indium is a soft, malleable metal with a low melting point and is commonly used in various applications such as soldering, plating, and sealing. It can be easily formed into thin films or sheets, making it useful for flexible electronics and displays.

[0048] As a result, under pressure, the pads can deform. If the pressure is not uniform, the pads can deform differently, damaging the backplane or some of the existing microdevices in the backplane. In another case, the pads 152 are made of hard material. As a result, the pads will not deform. This can result in a weak connection for some of the devices due to surface non-uniformity or deviation in parallelism between two substrates.

[0049] Hard materials, such as silicon, are hard and brittle. Silicon has excellent mechanical and thermal stability and can be easily patterned using microfabrication techniques.

[0050] Hard materials, such as metals, are hard and ductile materials that can be used as pads. Metals have good thermal and electrical conductivity and can be easily patterned and etched using microfabrication techniques.

[0051] Polymers can be soft materials, but cured polymers can also be hard materials. In some cases, polymers can be doped with nanoparticles for conductivity.

[0052] Some metals, such as In and Tin, can be soft materials. [0053] Figure 2(a) shows an embodiment for transferring microdevices from the donor substrate 102 to the receiver substrate 150. Here, a buffer layer 104 can be formed on the donor substrate 102 and microdevices 106 are located on top of the buffer layer. The buffer layer can be formed by patterning or etching processes. The buffer layer can be a polymer, a dielectric, or other materials such as metals. Due to the use of semiconductor processes to develop the buffer layer, it can be aligned to the edge of the last microdevices on the substrate. The system substrate 150 has pads 152 associated with the current microdevices to be transferred to the system substrate 150 from the donor substrate 102. System substrate 150 also has pads 154 that have already been populated with microdevices 156, and some of these pads may be adjacent to the current location for the transfer. When the donor substrate 102 and system substrate 152 get close to each other, the selected microdevices are touching (or getting close to) the selected pads 152. The pads have a hard material base 152-a and a soft shell 152-b in one related case. As seen, the transferred microdevice 156 can deform the soft material 154-b over a hard base 154 -a.

[0054] Figure 2(b) shows a pad structure with hard core 152-a and soft shell 152-b. The shell 152- b can cover only the top surface of the core 152-a or at least one sidewall. Electrodes 202 can connect the pads to the system sub strate/b ackplane 150. The pads can have different shapes. The hard core can be hard metals such as Al, Gold, dielectric such as silicon oxide or silicon nitride, or polymers such as BCB, SU8, etc. The soft shell can be indium, other soft metals, or soft adhesive (PI, PMMA, or PSA). The adhesive can have conductive particles embedded in it. In one related case, the soft shell covers a part of the top surface of the hard core. The height of the hard core is designed to be taller than the surface difference between the highest point in the system substrate and the location of pads in the system substrate. Other parameters, such as the surface nonuniformity of the two substrates and the error in parallelism between the donor and the system substrates, can be used to adjust the height of the hard core of the pad. In this case, the height is designed to prevent the microdevices from touching the unwanted areas in the system substrate as it stops the donor substrate from moving toward the system substrate. The height of the soft shell is designed to provide enough adhesion force connection to the pads across the donor substrate. To achieve this, the soft material should be taller than the distance difference between pads on the system substrate and microdevices on the donor substrate. The distance difference can come from the error in the parallelism between two substrates and surface non-uniformities of the system substrate and donor substrate. [0055] In another related embodiment, shown in Figure 2(c) , a post 154 can be developed on the backplane 150 to prevent nonuniform pressure further. Here, the post gets in touch with the donor substrate 102 during the transfer and eliminates damage to the pads, microdevices, and backplane. The post can be distributed in different parts of the backplane. In one related embodiment, the posts flatten the donor substrate. The donor substrate is first in touch with the post under low pressure. The flatness of the donor substrate and/or the transfer setup is adjusted until the donor substrate is in touch with the post underneath it. Then, the pressure can increase to transfer the devices to the pads on the system substrate.

[0056] In another related embodiment, the posts 120 can also be formed on the donor substrate (Figure 2(d)). The post on the donor substrate can function similarly to the post on the system substrate. The post can be made of metals, dielectric or polymer.

[0057] In another related case demonstrated in Figure 3, the pads on system substrate 150 are formed on stage 200. Here, electrode 202 is extended over stage 200 and pad 204 is formed on top of the electrode. The height of the stage can be larger than the difference between the tallest part in the system substrate and the height at which microdevices will be transferred. As a result, during transfer, as demonstrated in Figure 1, the gap between the donor substrate and system substrate will increase by the height of the stage.

[0058] In another related case, there can be a post 206 or spacer on the stage 200. The spacer 206 can prevent a short between two pads if the microdevice has more than one pad, also it can assist in the transfer of microdevice if it is adhesive.

[0059] Stage 200 is a structure that can be on system substrate 150 prior to processing spacer 206, electrodes 202 and post 206.

[0060] Stage 200 materials need to be nonconductive; one example is Polydimethylsiloxane (PDMS). PDMS is a silicone-based elastomer that is commonly used in microfabrication and soft lithography. PDMS is a transparent and flexible material that can be easily molded into various shapes, and has good chemical and thermal stability.

[0061] Stage 200 materials need to be nonconductive; another example is Polymethyl methacrylate (PMMA). PMMA is a transparent and rigid plastic that is commonly used in microfabrication and optical applications. PMMA has good mechanical and thermal stability, and can be easily patterned using photolithography or other microfabrication techniques.

[0062] Stage 200 materials need to be nonconductive; another example is Polyimide. Polyimide is a high-performance polymer that is commonly used in microfabrication and flexible electronics. Polyimide has good mechanical, electrical, and thermal properties, and can be easily patterned using photolithography or other microfabrication techniques.

[0063] Stage 200 materials need to be nonconductive; another example is Polycarbonate (PC). PC is a transparent and rigid plastic that is commonly used in microfabrication and optical applications. The PC has good mechanical and thermal stability, and can be easily molded and machined into various shapes.

[0064] Stage 200 materials are defined in a region to support electrode 202, pad 204, and spacer 206. Any of several patterning techniques may do the patterning of stage 200. For instance, it could be stamp deposited. The patterning of stage 200 may be deposited and then dry or wet etching. The patterning of stage 200 may be formed by damascene.

[0065] When using spacer, the stage 200 can be part of a substrate structure and not a separate one. The stage 200 could be the same material as system substrate 150. When system substrate 150 is formed, the system substrate 150 is patterned with mask regions that define stage 200. The system substrate 150 is etched (wet or dry) to create stage regions 200 once the masks are removed.

[0066] The stage 200, if it was the same material as receiver substrate 150 could be epitaxially grown in stage regions 200 if the received substrate was compatible with epitaxial growth.

[0067] In another related case, the stage and spacer can be the same and the stage only covers the spacer area. In this embodiment, stage 200 is defined as previously explained, but only in a region identical to spacer region 206 shown in Figure 3. Spacer 206 is formed on top of this stage region by any patterning technique, such as stamp deposited. In this case , the patterning of spacer 206 may be deposited on stage region 200 by dry or wet etching on top of stage 200. The patterning of In one related case, spacer can have a hard base and soft shell or vice versa. In one related case, the spacer gets softer under temperature. As the temperature of the donor can be higher the top surface gets softer in connection with donor substrate through the device. In another related case, the base gets soft as a result of being in contact with the system substrate and the top is harder as the temperature of the donor substrate is lower than the temperature of the donor substrate. [0068] In one related case, spacer can have a hard base and soft shell or vice versa. In one related case, the spacer gets softer under temperature. As the temperature of the donor can be higher the top surface gets softer in connection with donor substrate through the device. In another related case, the base gets soft as a result of being in contact with the system substrate and the top is harder as the temperature of the donor substrate is lower than the temperature of the donor substrate.

[0069] In another embodiment, the spacer 206 helps to reduce the microdevice contact force to the donor substrate by pushing the microdevice into the donor substrate.

[0070] In a related case, the spacer pushing the microdevice into the donor substrate mechanically breaks the contact points of the microdevice to the donor substrate.

[0071] In another related case, the mechanical push reduces the adhesion of microdevices to the donor substrate. If the spacer 206 is within a range of thickness, combined with the stage 200 thickness, the combined thickness can be such that when the donor substrate 102 is coupled with the receiver substrate 150 , the total space 206 plus stage 200 maintains and exact distance for coupling the microdevices on the receiver substrate 150 to the donor substrate 102 to allow contact pad 204 to be attached without being crushed.

[0072] In another related case, the spacer 206 can be in another area of receiver substrate 150 associated with the microdevice.

[0073] One example to position spacer 206 is to control the gap distance. Spacers can be used to precisely control the gap distance between the donor substrate and the receiver substrate during coupling. This can help ensure that the microdevices are transferred to the target substrate with high accuracy and uniformity.

[0074] Another example to position spacer 206 is to prevent damage. Spacers can help prevent damage to the microdevices during transfer by providing a cushioning effect and reducing the risk of collisions or scratches between the donor and receiver substrates.

[0075] Another example to position spacer 206 is to improve yield. Spacers can help improve the yield of the transfer process by reducing the likelihood of incomplete or faulty transfer of the microdevices. This is especially important for high-volume manufacturing applications where yield and efficiency are critical.

[0076] Another example to position spacer 206 is to prevent contamination. Spacers can help prevent contamination of the microdevices and the transfer equipment by creating a barrier between the donor and receiver substrates. This is especially important for applications in which cleanliness and purity are important, such as in biomedical or semiconductor manufacturing.

[0077] Another example to position spacer 206 is to accommodate different substrate thicknesses Spacers can be used to accommodate different substrate thicknesses or irregularities, ensuring that the microdevices are transferred with high accuracy and uniformity regardless of the substrate properties.

[0078] In another case, there are adhesive pads or bonds separated from spacer to hold the microdevice. For example, spacer 200 in some regions would have adhesive pads to adhere, the donor substrate 102 to receiver substrate 150.

[0079] In one example, by adding adhesive pads or bonds to the receiver substrate along with also adding spacers on the receiver substrate will allow for improved adhesion. Adhesive pads or bonds can improve the adhesion between the receiver substrate and the donor substrate, ensuring that the microdevices are securely transferred to the target substrate and reducing the risk of incomplete or faulty transfer.

[0080] In another example, adding adhesive pads or bonds to the receiver substrate along with also adding spacers on the receiver substrate will allow for additional support. Adhesive pads or bonds can provide additional support to the microdevices during transfer, reducing the likelihood of damage or deformation and improving the yield and reliability of the transfer process.

[0081] In another example, adding adhesive pads or bonds to the receiver substrate along with also adding spacers on the receiver substrate will allow for accommodating different substrate materials. Adhesive pads or bonds can be used to accommodate different substrate materials and properties, ensuring that the microdevices are transferred with high accuracy and uniformity regardless of the substrate properties.

[0082] In another example, adding adhesive pads or bonds to the receiver substrate along with also adding spacers on the receiver substrate will allow for improving precision. Adhesive pads or bonds can improve the precision of the transfer process by providing a fixed reference point for the microdevices, reducing the risk of misalignment or displacement.

[0083] In another example, by adding adhesive pads or bonds to the receiver substrate along with also adding spacers on the receiver substrate will allow for simplifying the transfer process: Adhesive pads or bonds can simplify the transfer process by reducing the need for complex alignment or registration steps, allowing for high-throughput transfer of microdevices with minimal operator intervention.

[0084] In another related embodiment, the spacer 206 first loses the force holding the microdevice to the donor substrate and it acts as the adhesive layer and holds the microdevice. As the pressure or temperature between microdevice and spacer increases the spacer transitions to adhesive and holds the device.

[0085] In one example the adhesive layer could be Pressure-sensitive adhesives (PSAs). PSAs are soft and tacky materials that can adhere to surfaces under light pressure. They are commonly used in applications such as labeling, bonding, and packaging.

[0086] In another example the adhesive layer could be Thermoplastic elastomers (TPEs). TPEs are materials that exhibit both rubber-like elasticity and thermoplastic processability. They can be easily molded or extruded into various shapes and sizes, and have good adhesion properties.

[0087] In another example the adhesive layer could be Shape memory polymers (SMPs). SMPs are materials that can change their shape in response to temperature or other external stimuli. They can be used as spacers that transition into adhesives at a specific temperature or pressure, enabling controlled transfer of microdevices.

[0088] In another example the adhesive layer could be Conductive adhesives. Conductive adhesives are materials that can provide electrical connectivity between surfaces while also acting as spacers or adhesives. They are commonly used in electronic applications, such as bonding microelectronic components to substrates.

[0089] In another example the adhesive layer could be Hydrogels. Hydrogels are soft and water- swollen materials that can be used as spacers or adhesives in microdevice transfer. They can be designed to have specific mechanical and biological properties, and can transition into an adhesive layer in response to changes in temperature or pH.

[0090] Adhesive bonds may improve adhesion. Adhesive pads or bonds can improve the adhesion between the receiver substrate and the donor substrate, ensuring that the microdevices are securely transferred to the target substrate and reducing the risk of incomplete or faulty transfer. [0091] Adhesive bonds may provide additional support. Adhesive pads or bonds can provide additional support to the microdevices during transfer, reducing the likelihood of damage or deformation and improving the yield and reliability of the transfer process.

[0092] Adhesive bonds may accommodate different substrate material.: Adhesive pads or bonds can be used to accommodate different substrate materials and properties, ensuring that the microdevices are transferred with high accuracy and uniformity regardless of the substrate properties.

[0093] Adhesive bonds may improve precision. Adhesive pads or bonds can improve the precision of the transfer process by providing a fixed reference point for the microdevices, reducing the risk of misalignment or displacement.

[0094] Adhesive bonds may simplify the transfer process. Adhesive pads or bonds can simplify the transfer process by reducing the need for complex alignment or registration steps, allowing for high-throughput transfer of microdevices with minimal operator intervention.

[0095] In another embodiment, the spacer 206 can first adhere to the microdevice and then push it to loosen the force between microdevice and donor substrate. In this case, a spacer can have a hard base and a soft layer. The soft adhesive layer will hold the device while as the pressure increases the hard base will push the microdevice will .

[0096] For example, polyurethane foam on top of a plastic substrate. The polyurethane foam can act as a soft adhesive layer to hold the microdevice, while the plastic substrate provides a hard base for pushing the microdevice to release it from the donor substrate.

[0097] In another example, materials may be silicone gel on top of a glass substrate. The silicone gel can act as a soft adhesive layer to hold the microdevice, while the glass substrate provides a hard base for pushing the microdevice to release it from the donor substrate.

[0098] In another example, materials may be rubber adhesive on top of a metal substrate: The rubber adhesive can act as a soft adhesive layer to hold the microdevice, while the metal substrate provides a hard base for pushing the microdevice to release it from the donor substrate.

[0099] In another example, materials may be Acrylic adhesive on top of a ceramic substrate. The acrylic adhesive can act as a soft adhesive layer to hold the microdevice, while the ceramic substrate provides a hard base for pushing the microdevice to release it from the donor substrate. [00100] In another example, materials may be Epoxy adhesive on top of a silicon substrate. The epoxy adhesive can act as a soft adhesive layer to hold the microdevice, while the silicon substrate provides a hard base for pushing the microdevice to release it from the donor substrate.

[00101] The space can be taller than the pads on the system substrate. In another case, the spacer height difference with the system substrate pads is less than the microdevice effective pad height. The height difference between spacer and pad height can be measured from the tip of the spacer to the tip of the pads on the system substrate. Here, the pads reach the system substrate pads first and at least part of the pads is deformed. Part of the microdevice surface reaches the spacer and the spacer facilitates the microdevice detachment from the donor substrate and attachment to the backplane. The spacer effective height from the surface of the system substrate can be between the system substrate effective pad height and the sum of the system substrate pad and microdevice pad. The height of spacer being taller than the height of the pads on system substrate can prevent the short during the transfer/bonding process and operation of the device by preventing the pads material migrating to the other side of the spacer as spacer act as a physical block by connecting to the surface of the microdevice.

[00102] The width of the spacer can be more than the pads on the system substrate pads. This will prevent the pads from being shorted during bonding or during the lifetime of the device. Here, the pads material cannot migrate from the side of the microdevice to the other edge and short with the other pad(s).

[00103] Spacer can have a bend at the edge similar to ‘L’ or ‘T’ shape (not necessarily right angle) to further prevent the migration of pad materials.

[00104] Spacer can be formed around more than one side of the pads to further assist with transfer and contain the pads materials.

[00105] Spacer can be used as a bank to form the pad material. Here, the space is formed and has an opening where the pad needs to be on the system substrate. The pads can fill the opening. The pad material can be soft (or hard) cured prior to the microdevice transfer step. The filling process can be by printing (spray, inkjet, nozzle) or spin coating, or slot coating. In one case, the spacer and bank can be different. In one case, the bank is removed prior to the transfer of microdevices. [00106] In one related case, at least part of the spacer is formed in microdevices.

[00107] In one related case, the microdevices transferred into the system substrate are pushed down after the transfer. This will deform spacer furthermore can provide further contact between microdevice and system substrate pads. Furthermore, it reduces the height of the microdevices in relation to the surface of the system substrate enabling easier integration of other microdevices.

[00108] In one related embodiment, more than one type of microdevice is transferred into substrate. Here, the first transfer is done under higher pressure or higher temperature. As a result, the pads or spacer is deformed further, and the device is moved further toward the substrate. The second set of microdevices are transferred with a pressure or temperature setting lower than the pressure or temperature of the transfer process for the first set of microdevices. As a result, the pads or spacer associated with the second set of microdevices will deform less and the microdevices will stay higher from the surface of the substrate compared to the first set of microdevices. This will prevent the transfer donor; transfer head or cartridge touch the first set of microdevices during the transfer of the second set of microdevices. Thus, preventing any damage to the first set of microdevices.

[00109] A combination of techniques and embodiments introduced here can be used. For example, in one case, stage and hard core for pads can be used together. In this case, the combination of the height of the stage and hard core pads compensate for the height difference in system substrate, non-uniformity and error in the parallelism of the two substrates.

[00110] The present invention addresses the shorting challenges in microdevice integration into the system substrate (or backplane) by providing a novel method and apparatus for integrating flip-chip devices into backplanes that minimize the risk of pad shorting. The invention includes techniques for precise control of alignment, pressure, and heat during the bonding process to prevent the extrusion or displacement of conductive material that could lead to shorts.

[00111] Additionally, the invention involves using a negative photoresist between the bonding materials and the point susceptible to shorting.

[00112] Flip-chip technology is a method for connecting semiconductor microdevices to system substrates or backplanes. In this technique, conductive bumps placed on the chip are directly attached to corresponding pads on the substrate. This technique facilitates testing the devices after integration and eliminates the need for post-processing steps. However, integrating flip-chip microdevices into backplanes involves the application of heat and pressure to ensure the conductive bumps properly bond to the substrate pads.

[00113] A significant challenge in this process is the potential for short circuits between the pads. During the thermal and mechanical bonding process, there is a risk that the conductive material used to connect the bumps to the pads may extrude or be displaced. This displacement can cause unintended electrical connections either between adjacent pads on the microdevice itself ("pad-to-pad shorts") or between the pads and other conductive elements of the microdevice or backplane ("pad-to-backplane shorts"). These shorts can lead to device malfunction, including incorrect signaling or power distribution issues, ultimately damaging the semiconductor microdevice and compromising device functionality

[00114] In accordance with one embodiment of the present invention, a method for integrating a flip-chip device into a backplane is provided, comprising the steps of forming a spacer on the backplane with a small base on the backplane and wider top surface, aligning the semiconductor microdevice with the backplane such that the conductive bumps on the microdevice align precisely with the corresponding pads on the backplane, applying controlled heat and pressure to bond the bumps to the pads.

[00115] One related method is inspecting the bonded microdevice using electrical testing and visual inspection techniques to identify and rectify any shorts that may have formed during the bonding process. The rectifying process can be done by either laser or extensive electrical power.

[00116] Another method of reducing shorting is using a bonding material with specific rheological properties that prevent it from flowing excessively under pressure and heat.

[00117] Another related method of reducing the shorting is tapered pads on the backplane or microdevices. The top surface of the pads is much smaller than the bottom surface on the backplane. Here, the shape can reduce the displacement caused by pressure or heat.

[00118] Further embodiments may include variations in the materials used for the conductive bumps and pads, variations in the mechanical and thermal properties of the bonding equipment, and the integration of automated feedback systems to dynamically adjust pressure and heat during the bonding process based on real-time inspection results.

[00119] The invention thus provides a reliable and efficient method for integrating flip-chip devices into backplanes with reduced risk of malfunction due to pad shorting, thereby enhancing the performance and reliability of electronic devices.

[00120] Figure 4 highlights the pad-to-pad short. Backplane 402 comprises circuit layers 404, which control the microdevice 410. To connect the circuit layers 404 to the microdevice 410, pads 412 with displacement in pads 406 are formed on the backplane 402 and microdevices 410. After aligning the microdevice 410 with the substrate, pressure or heat can be applied to either the backplane or microdevice to bond the pads to each other and secure the microdevice to the backplane mechanically and electrically (electro-mechanical bonding). As highlighted, the pads on the backplane or microdevice can be squished and cut short each other, causing malfunction.

[00121] Figures 5(a)-5(c) show the use of tapered spacer 508. Here, a backplane 502 includes circuit layers 504, and pads 514 formed on the backplane coupled to the backplane circuit layers 504. A spacer 508 is formed on the top of the backplane 502. The spacer can be formed with negative photoresist, which, upon patterning, forms a tapered spacer. The taper structure has a bottom surface 508A facing the backplane 502 and a top surface 508B, facing away from the backplane. The bottom surface 508 A is smaller than the top surface 508B (demonstrated in Figures 5(a) and 5(b)).

[00122] Figure 5(c) shows the backplane after microdevice 512 is integrated into the substrate. As can be seen, the displacement in pad 506 is managed by the spacer 508, eliminating the possibility of shorting.

[00123] The materials for pads on the backplane or microdevice can be Indium, Tin, Gold, Ni, Copper, or other conductive materials.

[00124] The spacer can be patterned using lithography, nano-imprint, inkjet printing, nozzle printing, or other additive or subtractive process techniques.

[00125] The height of the spacer is optimized to eliminate the possibility of a short in the device. The spacer is generally taller than the pads on the backplane.

[00126] If the spacer is on the device, it can be taller than the pads. [00127] To integrate microdevices into a system substrate, a cartridge is formed. The cartridge includes a substrate 600, cartridge layers 602 and microdevices 604 bonded to at least one of cartridge layers. Here, the cartridge layers can be bonding material, anchors, release layers or other layers.

[00128] The cartridge is aligned with the system substrate and the microdevices are selectively bonded to the system substrate bonding areas. The microdevices bonded to the pads will remain in the system substrate after the cartridge is moved away.

[00129] The main challenge with this method is the cartridge or system substrate flatness. This issue can cause some areas in the cartridge to experience more bonding pressure while some areas have not enough pressure. As a result, some microdevices may get damaged due to excess pressure and some may not get transferred due to not proper bonding. Also, the non-flatness can cause visual non-uniformity in the devices transferred to the system substrate.

[00130] In one related embodiment a deformable (or elastic) layer 606 can be used between the cartridge substrate and the tool head 608. Tool head holds the cartridge during the microdevices transfers. It can apply pressure or heat to the cartridge substrate. It has a mechanism to hold the cartridge such as vacuum, adhesive, electromagnetic, electrostatic, etc. The elastic or deformable layer 606 can reduce the non-flatness effect by deforming under pressure. As a result providing a more uniform surface and pressure to the entire surface area of the cartridge. The deformable layer can be polymer, graphite, and etc.

[00131] In one related embodiment, the deformable layer is part of the transfer head. It can be replaced after it is worn out. In this case, the layer can be a film that is added to the transfer head. The film can have adhesion property. In one related case, the film may have holes for vacuum pass through. In one related case, the head may have vacuum holes that are aligned with the holes in the film. In another related case, the tool head may have vacuum holes that are not aligned with the film holes so it can hold the film in place.

[00132] In another related embodiment, the deformable layer is part of the cartridge. The layer is formed or bonded to the cartridge substrate.

[00133] In one related case, the film is printed, spin coated or applied using other forms of coating and then cured to stay in place. [00134] In another case, a film with adhesive property is attached or laminated to the cartridge.

[00135] While particular embodiments and applications of the present invention have been illustrated and described, it is to be understood that the invention is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations can be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A transfer method for integration of microdevices into a system substrate: aligning a donor substrate with an array of microdevices is aligned with a system substrate; and having the system substrate with an array of pads for selective bonding of microdevices, wherein the pads perform two functions: loosening the microdevices from the donor substrate and bonding the microdevices to the system substrate.

2. The method of claim 1, where a stage is used to loosen the microdevices selectively from the donor substrate and bonding pads on stage are used to bond the microdevices.

3. The method of claim 1, where there is a spacer at least on one side of the pad where the spacer deforms less compared to the pads to loosen the microdevice from the donor substrate.

4. The method of claim 2, where the height of space is used to control the gap between microdevices and the system substrate

5. The method of claim 2, where the position of the spacer is between two pads to prevents a short between the two pads

6. The method of claim 2, where the stage is the same material as system substrate.

7. The method of claim 1, where the stage and the spacer are the same in the stage only region covering the spacer area.

8. The method of claim 1, where the spacer helps to loosen a microdevice in contact with the donor substrate.

9. The method of claim 1, where the spacer is in another area of the system substrate.

10. The method of claim 1, where the position spacer is used to control the gap distance.

11. The method of claim 1, where the position spacer is to prevent damage.

12. The method of claim 1, where the position spacer is to improve yield.

13. The method of claim 1, where the position of the spacer is to prevent contamination.

14. The method of claim 1, where the position spacer is to accommodate different substrate thicknesses.

15. The method of claim 1, where adhesive pads or bonds are used to separate from spacer to hold the microdevice.

16. A method comprising: having a backplane comprising of circuit layers to control microdevices; forming pads on the backplane and the microdevices; and applying heat or pressure to the backplane and or the microdevice after aligning microdevices with the backplane to bond the pads to each other and secure the microdevice to the backplane mechanically and electrically.

17. The method of claim 16, further comprising forming a tapered spacer on a top of the backplane, wherein the spacer is formed with a negative photoresist and wherein upon patterning, the spacer forms a tapered space.

18. The method of claim 17 wherein the tapered spacer has a bottom surface, facing the backplane and a top surface, facing away from the backplane.

19. The method of claim 18 where the bottom surface is smaller than the top surface.

20. The method of claim 19 wherein the backplane after integration of microdevices, tapered spacer is managing a displacement in the pads..

21. The method of claim 16 wherein the pads on the backplane are made of either conductive materials Indium, Tin, Gold, Ni, Copper.

22. The method of claim 17 wherein patterning the spacer forms a tapered spacer using either additive and subtractive process techniques.

23. The method of claim 17 wherein the tapered spacer is taller than the pads on the backplane.

24. A method for integration of microdevices into a cartridge substrate with a corrected cartridge flatness the method comprising: having a deformable (or elastic) layer in between the cartridge substrate and a tool head, wherein the tool head holds the cartridge substrate during a microdevices transfer; applying pressure or heat to the cartridge substrate; and reducing a non-flatness effect by deforming the elastic or the deformable layer under pressure.

25. The method of claim 24, wherein the deformable layer is a part of the cartridge substrate, wherein the deformable layer is formed or bonded to the cartridge substrate.

26. The method of claim 24, wherein layer is a film, that is added to the transfer head and has an adhesion property.

27. The method of claim 24, wherein layer may be one of a material from polymer, graphite.

28. The method of claim 24, wherein the layer is a part of the transfer head which is replaced after it is worn out.

29. The method of claim 24, wherein a film has holes for a vacuum pass through.

30. The tool head of claim 24, wherein the head may have vacuum holes that are aligned with the holes in the film.

31. The method of claim 26, wherein the film with adhesive property is attached or laminated to the cartridge.

32. The method of claim 26, wherein the film is printed, spin coated or applied using other forms of coating and then cured to stay in place.