Patent Publication Number: US-2022231204-A1

Title: Adhesive film transfer coating and use in the manufacture of light emitting devices

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 16/874,529 filed on May 14, 2020, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This disclosure generally relates to devices and methods used in the manufacture of light emitting devices (LEDs) for attaching phosphors to LED dies, and LEDs formed using the devices and methods. 
     BACKGROUND 
     Semiconductor light emitting diodes and laser diodes (collectively referred to herein as “LEDs”) are among the most efficient light sources currently available. The emission spectrum of an LED typically exhibits a single narrow peak at a wavelength determined by the structure of the device and by the composition of the semiconductor materials from which it is constructed. By suitable choice of device structure and material system, LEDs may be designed to operate at ultraviolet, visible, or infrared wavelengths. 
     LEDs may be combined with one or more wavelength converting materials (generally referred to herein as “phosphors”) that absorb light emitted by the LED and in response emit light of a longer wavelength. For such phosphor-converted LEDs (“pcLEDs”), the fraction of the light emitted by the LED that is absorbed by the phosphors depends on the amount of phosphor material in the optical path of the light emitted by the LED, for example on the concentration of phosphor material in a phosphor layer disposed on or around the LED and the thickness of the layer. Phosphors may be embedded in a silicone matrix that is disposed in the path of light emitted by the LED. 
     Phosphor-converted LEDs may be designed so that all of the light emitted by the LED is absorbed by one or more phosphors, in which case the emission from the pcLED is entirely from the phosphors. In such cases the phosphor may be selected, for example, to emit light in a narrow spectral region that is not efficiently generated directly by an LED. 
     Alternatively, pcLEDs may be designed so that only a portion of the light emitted by the LED is absorbed by the phosphors, in which case the emission from the pcLED is a mixture of light emitted by the LED and light emitted by the phosphors. By suitable choice of LED, phosphors, and phosphor composition, such a pcLED may be designed to emit, for example, white light having a desired color temperature and desired color-rendering properties. 
     SUMMARY 
     In one aspect, a converter layer bonding device includes a release liner and an adhesive layer coating the release liner, the adhesive layer is solid and non-adhesive at a first temperature, and is adhesive at an elevated temperature above the first temperature. The adhesive layer may have a thickness of less than 10 μm. The adhesive layer may have a thickness between 0.3 μm and 2 μm. The adhesive layer may be configured to bond to a substrate at the elevated temperature, and the release liner may be configured to be removable after the adhesive layer is bonded to the substrate. The adhesive layer may be configured to form a bond layer between the substrate and a phosphor in contact with the adhesive layer opposite the substrate. 
     In another aspect, a method for forming a converter layer bonding device includes mixing an adhesive material and a solvent to form an adhesive mixture, coating a sheet of release liner with the adhesive mixture, and drying the solvent from the adhesive mixture coated onto the release liner to form an adhesive layer, the adhesive layer being solid and non-adhesive at a first temperature, and adhesive at an elevated temperature above the first temperature. 
     In yet another aspect, a light emitting device includes a light emitting diode, a phosphor, and a bond layer between and in contact with the light emitting diode and phosphor, the bond layer configured to bond the light emitting diode to the phosphor, the bond layer having a thickness that is uniform, the thickness varying less than 10%. The thickness of the bond layer may be less than 10 μm. The thickness of the bond layer may be between 0.3 μm and 2 μm. The bond layer may be transparent. A surface of the phosphor or the light emitting diode in contact with the bond layer may have a surface roughness, and the bond layer may conform to the surface roughness while maintaining the uniform thickness. An edge of the phosphor and an edge of the bond layer may align on a same plane. The bond layer may include multiple channels, which may have openings on an edge of the bond layer. 
     In yet another aspect, a light emitting device may include a plurality of individually addressable light emitting diodes mounted on a single chip, a plurality of phosphor tiles, and a bond layer between each of the individually addressable light emitting diodes and phosphor tiles, the bond layer having a thickness that is uniform, the thickness varying less than 10% between each individually addressable light emitting diode and phosphor tile across the single chip. The thickness of the bond layer may be less than 10 μm. The thickness of the bond layer may be between 0.3 μm and 2 μm. The bond layer may be transparent. The plurality of LED die may be mounted on a tile, a portion of the plurality of LED die may have a height from the tile that varies from another portion of the plurality of LED die, the bond layer maintaining uniform thickness on the plurality of LED die. Surfaces of the plurality of phosphor tiles in contact with the bond layer may have a surface roughness, and the bond layer may conform to the surface roughness while maintaining the uniform thickness. Surfaces of the plurality of light emitting diodes in contact with the bond layer may have a surface roughness, and the bond layer may conform to the surface roughness while maintaining the uniform thickness. The bond layer may include multiple channels. The multiple channels may have openings on an edge of the bond layer. The bond layer may include a first bond layer in contact with the plurality of phosphor tiles and a second bond layer in contact with the plurality of light emitting diodes and the first bond layer. The first bond layer may have a different physical characteristic from the second bond layer. The first bond layer may include multiple channels. The first bond layer may have a different refractive index from the second bond layer. 
     In yet another aspect, a method of forming a light emitting device includes aligning a converter layer bonding device over a phosphor, the converter layer bonding device including an adhesive layer adhered to a release liner, a first surface of the adhesive layer opposite the release liner facing a surface of the phosphor, bringing the first surface of the adhesive layer and the surface of the phosphor into contact at an elevated temperature, the elevated temperature being a temperature at which the adhesive layer adheres to the phosphor, cooling the adhesive layer adhered to the phosphor, removing the release liner from the adhesive layer, bringing one or more LED die into contact with a second surface of the adhesive layer opposite the first surface, and heating the adhesive layer, LED die, and phosphor to cure the adhesive layer and form a bond layer between the LED die and the phosphor. The adhesive layer may be solid and non-adhesive at a first temperature below the elevated temperature. The G* (at 1 Hz) of the adhesive layer at the first temperature may be greater than 100 KPa, and the G* (at 1 Hz) of the adhesive layer at the elevated temperature may be between 1 KPa and 100 KPa. Bringing the first surface of the adhesive layer and the surface of the phosphor into contact at an elevated temperature may include applying a vacuum to the converter layer bonding device and the phosphor. The method may further include dicing the phosphor and the bonding layer between the LED die. The method may further include, after removing the release liner, cutting the phosphor and adhesive layer into n×m arrays, and wherein bringing one or more LED die into contact with the adhesive layer opposite the phosphor comprises bringing each LED die into contact with an n×m array. The method may further include cutting channels into the adhesive layer on the converter layer bonding device. The method may further include, before bringing one or more LED die into contact with adhesive layer, aligning a second converter layer bonding device over the adhesive layer, the second converter layer bonding device comprising a second adhesive layer adhered to a second release liner, a first surface of the second adhesive layer opposite the second release liner facing the second surface of the adhesive layer, bringing the second adhesive layer and a surface of the adhesive layer opposite the phosphor into contact at an elevated temperature, the elevated temperature being a temperature at which the second adhesive layer adheres to the adhesive layer, cooling the second adhesive layer adhered to the adhesive layer, removing the second release liner from the second adhesive layer, and bringing the LED die into contact with a surface of the second adhesive layer opposite the adhesive layer. 
     In yet another aspect, a method of forming a light emitting device includes attaching a plurality of LED die to a tile, aligning a converter layer bonding device over the plurality of LED die, the converter layer bonding device comprising an adhesive layer adhered to a release liner, a first surface of the adhesive layer opposite the release liner facing surfaces of the plurality of LED die that are opposite the tile, bringing the first surface of the adhesive layer and surfaces of the plurality of LED die into contact at an elevated temperature, the elevated temperature being a temperature at which the adhesive layer adheres to the LED die, cooling the adhesive layer adhered to the plurality of LED die, removing the release liner from the adhesive layer, leaving portions of the adhesive layer adhered to each LED die and remaining portions of the adhesive layer being removed with the release liner, bringing a plurality of phosphor tiles each into contact with a portion of the adhesive layer adhered to each of the plurality of LED die, heating the adhesive layer, LED die, and phosphor to cure the adhesive layer and form a bond layer between the LED die and the phosphor. The adhesive layer is solid and non-adhesive at a first temperature below the elevated temperature, and adhesive at the elevated temperature. Bringing the first surface of the adhesive layer and surfaces of the plurality of LED die into contact at an elevated temperature may include applying a vacuum to the converter layer bonding device and the plurality of LED die. A height of each of the plurality of LED die from the tile varies, and the bond layer has a uniform thickness, the thickness varying less than 10% over the plurality of LED die. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a plan view and  FIG. 1B  a cross-sectional view illustrating an example of a micro-LED. The cross-section view in  FIG. 1B  is taken through line A-A in  FIG. 1A . 
         FIG. 2  is a cross-sectional view illustrating a converter layer bonding device according to an example embodiment. 
         FIG. 3A  shows a flow chart for, and  FIG. 3B ,  FIG. 3C  and  FIG. 3D  illustrate an example embodiment of a method for making a converter layer bonding device. 
         FIG. 4A  shows a flow chart for, and  FIG. 4B ,  FIG. 4C ,  FIG. 4D  and  FIG. 4E  illustrate an example embodiment of a method of using a converter layer bonding device according to example embodiments. 
         FIG. 5A ,  FIG. 5B ,  FIG. 5C ,  FIG. 5D  and  FIG. 5E  illustrate an example application of a converter layer bonding device as disclosed herein and resulting pcLED device. 
         FIG. 6A ,  FIG. 6B ,  FIG. 6C ,  FIG. 6D  and  FIG. 6E  illustrate another example application of a converter layer bonding device as disclosed herein and resulting pcLED device. 
         FIG. 7A ,  FIG. 7B ,  FIG. 7C  and  FIG. 7D  illustrate another example application of a converter layer bonding device as disclosed herein and resulting pcLED device. 
         FIG. 8A  is a cross-sectional view and  8 B a plan view illustrating a patterned converter layer bonding device according to an example embodiment. 
         FIG. 9A ,  FIG. 9B ,  FIG. 9C  and  FIG. 9D  illustrate an example application of a patterned converter layer bonding device as disclosed herein and resulting pcLED device. 
         FIG. 10A ,  FIG. 10B ,  FIG. 10C ,  FIG. 10D  and  FIG. 10E  illustrate an example embodiment of an application of a converter layer bonding device with stacked adhesive layers. 
         FIG. 11A ,  FIG. 11B ,  FIG. 11C ,  FIG. 11D  and  FIG. 11E  illustrate an example embodiment of a method for forming a multilayer converter layer bonding device. 
         FIG. 12A  illustrates an example of a bond layer on a substrate applied using a converter layer bonding device in accordance with an example embodiment.  FIG. 12B , illustrates an adhesive layer applied to a substrate using conventional methods. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description should be read with reference to the drawings, in which identical reference numbers refer to like elements throughout the different figures. The drawings, which are not necessarily to scale, depict selective embodiments and are not intended to limit the scope of the invention. The detailed description illustrates by way of example, not by way of limitation, the principles of the invention. 
     As used herein, spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, for example, the term “below” can encompass both an orientation of above and below, depending on the orientation of the device. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     Light emitting pixel arrays are light emitting devices in which a large number of small light emitting devices, such as, for example LEDs, are arrayed on a single chip. The individual LEDs, or pixels, in a light emitting pixel array may be individually addressable, may be addressable as part of a group or subset of the pixels in the array, or may not be addressable. Thus, light emitting pixel arrays are useful for any application requiring or benefiting from fine-grained intensity, spatial, and temporal control of light distribution. These applications may include, but are not limited to, precise special patterning of emitted light from pixel blocks or individual pixels. Depending on the application, emitted light may be spectrally distinct, adaptive over time, and/or environmentally responsive. The light emitting pixel arrays may provide pre-programmed light distribution in various intensity, spatial, or temporal patterns. The emitted light may be based at least in part on received sensor data and may be used for optical wireless communications. Associated electronics and optics may be distinct at a pixel, pixel block, or device level. 
     Light emitting pixel arrays have a wide range of applications. Light emitting pixel array luminaires can include light fixtures which can be programmed to project different lighting patterns based on selective pixel activation and intensity control. Such luminaires can deliver multiple controllable beam patterns from a single lighting device using no moving parts. Typically, this is done by adjusting the brightness of individual LEDs in a 1D or 2D array. Optics, whether shared or individual, can optionally direct the light onto specific target areas 
     Light emitting pixel arrays may be used to selectively and adaptively illuminate buildings or areas for improved visual display or to reduce lighting costs. In addition, light emitting pixel arrays may be used to project media facades for decorative motion or video effects. In conjunction with tracking sensors and/or cameras, selective illumination of areas around pedestrians may be possible. Spectrally distinct pixels may be used to adjust the color temperature of lighting, as well as support wavelength specific horticultural illumination. 
     Street lighting is an important application that may greatly benefit from use of light emitting pixel arrays. A single type of light emitting array may be used to mimic various street light types, allowing, for example, switching between a Type I linear street light and a Type IV semicircular street light by appropriate activation or deactivation of selected pixels. In addition, street lighting costs may be lowered by adjusting light beam intensity or distribution according to environmental conditions or time of use. For example, light intensity and area of distribution may be reduced when pedestrians are not present. If pixels of the light emitting pixel array are spectrally distinct, the color temperature of the light may be adjusted according to respective daylight, twilight, or night conditions 
     Light emitting arrays are also well suited for supporting applications requiring direct or projected displays. For example, warning, emergency, or informational signs may all be displayed or projected using light emitting arrays. This allows, for example, color changing or flashing exit signs to be projected. If a light emitting array is composed of a large number of pixels, textual or numerical information may be presented. Directional arrows or similar indicators may also be provided. 
     Vehicle headlamps are a light emitting array application that requires large pixel numbers and a high data refresh rate. Automotive headlights that actively illuminate only selected sections of a roadway can be used to reduce problems associated with glare or dazzling of oncoming drivers. Using infrared cameras as sensors, light emitting pixel arrays activate only those pixels needed to illuminate the roadway, while deactivating pixels that may dazzle pedestrians or drivers of oncoming vehicles. In addition, off-road pedestrians, animals, or signs may be selectively illuminated to improve driver environmental awareness. If pixels of the light emitting pixel array are spectrally distinct, the color temperature of the light may be adjusted according to respective daylight, twilight, or night conditions. Some pixels may be used for optical wireless vehicle to vehicle communication. 
     An example of a type of light emitting pixel array is a micro-LED, also referred to as a μLED.  FIGS. 1A and 1B  illustrate an example of a micro-LED.  FIG. 1A  shows a plan view of a micro-LED array  110 , along with an exploded view of a 3×3 portion of LED array  110 . In  FIG. 1A , each square  111  represents a single LED, or pixel. As shown in the 3×3 portion exploded view, LED array  110  may include pixels  111  with a width w 1 , which may be between 30 μm and 500 μm, for example approximately 100 μm or less, e.g. 40 μm. The gaps, or lanes,  113  between the pixels may be separated by a width, w 2 , which may be between 30 μm and 500 μm, for example, approximately 20 μm or less, e.g., 5 μm. The lanes  113  may provide an air gap between pixels or may contain other material, as shown in  FIG. 1B . The distance d 1  from the center of one pixel  111  to the center of an adjacent pixel  111  may be approximately 120 μm or less (e.g., 45 μm). Such a micro-LED array may have hundreds, thousands, or millions of LEDs positioned together on substrates that may have, for example, an area in the range of centimeters, although the size of the area may vary. It will be understood that the widths and distances provided herein are examples only, and that actual widths and/or dimensions may vary. For instance, the width, w 2 , may be in the order of at least a millimeter, to form a sparse micro-LED, but may be larger or smaller. 
     It will be understood that although rectangular pixels arranged in a symmetric matrix are shown in  FIGS. 1A and 1B , pixels of any shape and arrangement may be applied to the embodiments disclosed herein. For example, LED array  110  of  FIG. 1A  may include 10,000 pixels in any applicable arrangement such as a 100×100 matrix, a 200×50 matrix, a symmetric matrix, a non-symmetric matrix, or the like. It will also be understood that multiple sets of pixels, matrixes, and/or boards may be arranged in any applicable format to implement the embodiments disclosed herein. 
     Micro-LEDs can be formed from pcLEDs. One method for forming a micro-LED is to use epitaxial growth to form the multiple individual LEDs  110  on a die in a flip-chip construction as in known in the art.  FIG. 1B  illustrates a side view of a portion of one type of micro-LED device taken through line AA of  FIG. 1A . 
       FIG. 1B  shows the pixels  111  and lanes  113 . Each pixel  111  is formed of an LED die  140 , which is positioned on, for example, a chip  120 , which may provide the electrical signals to the LED die  140 . A phosphor  163  is over and on LED dies  140 . The phosphor  163  may be formed of phosphor particles contained in a matrix, for example, garnet particles contained in silicone. Alternatively, or in addition, the phosphor  163  contains a densely sintered phosphor ceramic, such as Lumiramic™. In one example, the individual LEDs produce a blue light and the phosphor converts the blue light to a white light to produce a micro-LED that is monochrome white at a CCT of about 5700K.  FIG. 1B  shows phosphor  163  as a single plate covering both the LED dies  140  and the gaps  113  between the LED dies  140 . However, phosphor  163  may be singulated, and cover just the individual LED dies  140 , as shown in more detail in examples below. 
     One method of forming a pcLEDs, including micro-LEDs, is to separately form a phosphor converting material into a tile (which also may be referred to as a plate, platelet, wafer, film or other shape), such as, for example, Lumiramic™, as phosphor  163 . The phosphor, which is also referred to as a phosphor tile, is then attached or bonded to the separately formed LED die or plurality of LED dies. 
     The phosphor tile is typically attached or bonded to an LED or substrate using a layer of an adhesive positioned between the LED dies and the phosphor. The dimensions and uniformity of this adhesive layer are critical to the optical and thermal performance of the device, as well as its mechanical robustness. 
     In current manufacturing, there are several different methods used to apply this adhesive layer. One approach is to dispense a small volume of an adhesive solution (typically a liquid containing silicones and solvents) onto the surface of the LED die. A phosphor plate is then placed on top of the die. The droplet of adhesive solution then flows out the edges of the plate, and once dried and cured, forms a thin bond-line between die and phosphor. Another approach is to coat a similar adhesive solution onto a continuous phosphor wafer or film by a method such as spin-coating, spray-coating, or aerosol-jet printing. After coating the phosphor wafer or film, the phosphor is singulated to form plates, which are then attached to the LED die and the adhesive film cured. Each of these methods has its own drawbacks. 
     In the adhesive solution dispense approach, the final gap between the ceramic phosphor and the die is typically determined by a combination of factors, such as: the surface tension and viscosity of the adhesive solution, force and time of the “pick and place” tool, volume of the droplet, position of the droplet relative to the center of the surface of the die, temperature of the die, time elapsed between droplet dispense and attach, and rate of solvent evaporation. Unfortunately, this is a complex process that is difficult to control, and thus results in large variability of the average thickness between devices as well as large variability within each device. Additionally, this is a serial process (each adhesive solution droplet is dispensed sequentially), which decreases throughput. This process also does not scale well to micro-LEDs due the impractically small volumes of adhesive required. In the approach where the phosphor wafer or film is coated with adhesive first and then singulated, surface roughness can lead to adhesive layer non-uniformity. Even if the surface is smooth, if the surface energy of the converter layer of film is too low or too variable, the adhesive solution could partially de-wet coating, leading to an incomplete layer. 
       FIG. 2  shows a converter layer bonding device  200  that can be used to form pcLEDs, and in particular, is useful for forming light emitting pixel arrays, such as micro-LEDs. Converter layer bonding device  200  includes a release liner  210  coated with an adhesive layer  220 . 
     Release liner  210  may be any material, generally in the form of a flexible sheet, capable of holding adhesive layer  220  and capable of releasing adhesive layer  220  in operation (as shown below in  FIGS. 4A-4D ). Thus, the release liner  210  may be optimized (e.g., for roughness, slippage, and surface energy) so that the adhesive layer  220  coats the release liner  210  evenly, and so that the release liner  210  can release cleanly from the adhesive layer  220  after adhesive layer  220  is transferred to a substrate. Release liner  210  may be a sheet of flexible material, such as polyethylene terephthalate (“PET”), such as, for example, PANAC Corporation SP-PET-50-01 BU. Release liner  210  may be coated with a transfer coating (not shown) positioned between the release liner  210  and the adhesive layer  220  that enhances the release of the adhesive layer  220 . Such a transfer coating may be, for example, a siliconized release coating, examples of which include PANAC Corporation&#39;s PDMS release coating on PET liners and as further described in Dow White Paper “ Release Force Understanding—Recent Findings”  by R. Ekeland, J. Tonge, and G. Gordon, 2018, The Dow Chemical Company, incorporated herein by reference in its entirety. In particular, when the release liner  210  is removed (as shown in the examples below), to ensure a clean transfer of the adhesive layer  220  to the substrate, the peel strength between the adhesive layer  220  and release liner  210  may be below 30 N/m, for example, between 1-5 N/m. 
     Adhesive layer  220  is the adhesive that is transferred to a substrate and that forms a bond layer (as shown below in  FIGS. 4A-4D ). The material used to form the adhesive layer  220  may be chosen to have the following properties. The first is that the material can be coated evenly onto the release liner  210  to form the converter layer bonding device  200 . The second is that the material forms an adhesive layer  220  that is dry, not tacky, and relatively hard, i.e., it does not flow, at a first, lower temperature, e.g., room temperatures. That is, at a first temperature, such as room temperatures, e.g., 15-25° C., the adhesive layer  220 , while adhering to the release liner  210  on which it was formed, is not adhesive enough to attach to a substrate, such as a phosphor tile or LED die. For example, the adhesive layer  220  at a first temperature, such as room temperature, may follow the Dahlquist Criterium of G*(at 1 Hz)&gt;100 KPa (0.1 MPa), for example G*&gt;300 KPa (0.3 MPa). Third, the material forming the adhesive layer  220  becomes tacky and reflows at elevated temperatures. That is, when heat is applied to the adhesive layer  220 , it becomes adhesive, and is then capable of attaching to a substrate. For example, an elevated temperature is chosen such that the G* (at 1 Hz) of adhesive layer  220  becomes between G*=1 KPa and G*=100 KPa, with tan delta typically between 0.5 and 3.0, for example, at between 50° C. and 150° C., e.g., 100° C. Fourth, the material used to form the adhesive layer  220  is capable of forming a bond layer that provides a strong bond between a phosphor and a target substrate. The bond layer may be transparent, or may have additional optical characteristics, such as scattering, R1 gradient, and emissivity, as disclosed in more detail below. 
     In particular, the adhesive layer  220  may not be adhesive enough to attach to a substrate at a first, lower temperature, but becomes adhesive enough at elevated temperature to attach to a substrate, such as a phosphor or LED die, and, after cooling, has a stronger attachment to the substrate than to the release liner  210 , such that the release liner may be easily removed. 
     The thickness T of the adhesive layer  220  is chosen to match the desired target thickness of the bond layer in the final device, and may be in a range of 0.3 μm to 30 μm, for example, less than 10 μm, in the range of between 0.3 μm and 2 μm. The adhesive layer  220  is also formed so that the thickness T is uniform across the layer, for example, T will have a deviation (variation) of less than 20%, for example, less than 10%, across, the adhesive layer  220 . The material used to form the adhesive layer  220  may be, for example, a siloxane adhesive. 
       FIGS. 3A-3D  show a flow chart and illustration of a method of making a converter layer bonding device  200 . At S 310 , the release liner  210  to be used may be coated with a siliconized coating to enhance the release properties as described above. At S 320  an adhesive mixture  302  may be prepared by mixing the adhesive material with a solvent, for example, a resin and solvent, such as a methylphenylsiloxane resin and cyclohexanone solvent, and for example a silicone resin (such as Dow Corning® LF-1112) and a propylene glycol methyl ether acetate solvent. Mass ratios of adhesive material to solvent may be between 10:1 and 1:1. The concentrations of adhesive material and solvent may be chosen to achieve the desired viscosity of the adhesive mixture  302 . The viscosity of the adhesive mixture  302  may be chosen to optimize wetting of the release liner  210 , while still achieving the desired thickness T of the adhesive layer  220  in the converter layer bonding device  200 . For example, the viscosity of the adhesive mixture  302  may range between 70 and 3,000 mPa&#39;s (or cP). 
     As shown in  FIG. 3B , at S 330  the adhesive mixture  302  is coated onto the release liner  210 . Any method that can suitably coat the release liner  210  with a uniform layer of the adhesive mixture  302  at the desired thickness may be used, such as, for example, spin-coating, gravure coating, etc.  FIG. 3B  illustrates, as an example, a spin-coating process for coating release liner  210  with the adhesive mixture  302 . In  FIG. 3B , the release liner  210  is positioned on a spin-coating support  307  and the adhesive mixture  302  is deposited from nozzle  305  as is known by persons having ordinary skill in the art. 
     As shown in  FIG. 3C , at S 340  the adhesive mixture  302  coated onto release liner  210  is dried to remove solvent. Depending on the adhesive used, at S 350  the adhesive mixture may be additionally cured to stabilize the material and improve uniformity of the subsequent transfer from the converter layer bonding device  200 . The resulting converter layer bonding device  200  is shown in  FIG. 3D . This process results in an adhesive layer  220  that may be thin (may be under 4 μm), uniform, defect-free, and can be made in a large area, such as such as from 0.1 m to 3 m wide, and even tens of meters to thousands of meters in length, such as in a roll. Note that roll-to-roll methods such as gravure coating technology may be used for large area coating. 
       FIGS. 4A-4E  show a flow chart and illustration of an example of the method of using the converter layer bonding device  200 . A vacuum lamination process may be used to transfer the adhesive layer  220  onto a substrate  415 . 
     As shown in  FIG. 4B , at S 410 , a converter layer bonding device  200  may be aligned over a substrate  415 . As shown in  FIG. 4B , the adhesive layer  220  of the converter layer bonding device  200  is facing a surface  417  of the substrate  415  to which the adhesive layer  220  is to be applied. 
     As shown in  FIG. 4C , at S 420 , a vacuum may be applied to the converter layer bonding device  200  and substrate  415 , and at S 430 , the converter layer bonding device may be brought into contact with the substrate at elevated temperatures. The temperature used depends on the particular adhesive material that forms the adhesive layer. In general, the temperature is high enough to make the adhesive layer  220  flow and become tacky, i.e., adhesive, enough to stick to the substrate  415 . The elevated temperature may be chosen such that the G* (at 1 Hz) is between G*=1 KPa, and G*=100 KPa, with tan delta typically between 0.5 and 3.0. At the same time, the temperature should be low enough to prevent excessive flow, so that the adhesive layer  220  maintains its shape and coverage of the substrate  415 . The substrate  415  with the converter layer bonding device  200  attached may then be cooled, for example, back to room temperature 
     As shown in  FIG. 4D , at S 440 , once the adhesive liner  220  has cooled, the release liner  210  may be removed, leaving a continuous layer of the adhesive behind on the substrate  415 . As the adhesive layer  220 , after heat treatment, is more strongly attached to the substrate than the release liner  210 , the release liner  210  may be removed, for instance, mechanically by peeling off the adhesive layer  220  that is attached to substrate  415 . As noted above, the ensure clean transfer, the release liner may be designed to have a peel strength between the adhesive layer  220  and release liner  210  of below 30 N/m, for example 1-5 N/m. The adhesive layer  220  remains on the substrate  415  after removal of release liner  210 . 
     As shown in  FIG. 4E , at S 450 , the sample  430  to be bonded to substrate  415  may be brought into contact with the transferred adhesive layer  220 . Heat may be applied to cure the adhesive layer and form a bond layer  420  between the substrate  415  and sample  430 . The bonded substrate  415  and sample  430  may then be cooled. 
     The thickness of the resulting bond layer  420  may be very thin, and be between 0.3 μm and 30 μm, for example, between 0.3 μm and 2 μm. The bond layer  420  has a uniform thickness over the surface of the substrate to which it is applied, and the variation in thickness across the bond layer may be less than 20%, and for example, may be less than 10%. For example, for a bond layer  420  that has a thickness of 1 μm, the variation in thickness across the bond layer between substrate  415  and sample  430  would be less than +/−0.2 μm at a 20% variation, and +/−0.1 μm at a 10% variation. Additionally, if the substrate  415  has a relatively large area on which numerous minute LED dies are form, such as, for example, as is used for making a light emitting pixel array, such as a micro-LED, the adhesive layer  220  and subsequent bond layer  420  provides a thin and uniform bond layer over the entire area of the device and form the numerous minute light emitters. Thus, for a micro-LED having thousands to millions of individually addressable LEDs over and area with, for example, 5-50 μm per side (25-2,500 μm 2 ) or for somewhat larger arrays, for example, 50-500 μm per side (2,500-25,000 μm 2 ), the bond layer  420  is uniform, which improves the performance of the device. Further advantages of the bond layer  420  formed from the converter layer bonding device  200  as disclosed herein are described in more detail below. 
     The bond layer  420  may be transparent. The bond layer  420  may also include dispersed particles and/or dyes which could provide additional optical, physiochemical or mechanical characteristics, such as higher refractive index, enhanced light scattering, light absorption or emission at different wavelengths. To form a bond layer  420  having dispersed particles and/or dyes, the particles and/or dyes may be included in the adhesive mixture  302  (at S 320 ) used to form the adhesive layer  220  on the converter layer bonding device  200 . 
       FIGS. 5A-5E  illustrate an example application of the converter layer bonding device in which the adhesive layer is transferred onto a phosphor, followed by die attach. A converter layer bonding device  200  may be prepared as described above with respect to  FIGS. 2A-2D . 
     In  FIG. 5A , a phosphor film or wafer  535 , such as, for example, a Lumiramic™ tile, may be mounted onto a carrier tape  530 . The phosphor wafer  535  may be 02-plasma treated to improve adhesion of subsequently-transferred adhesion layer  220 . Vacuum lamination may then be used to transfer the adhesive layer  220  onto the phosphor wafer  535  as follows. As shown in  FIG. 5A , the converter layer bonding device  200  may be aligned over the phosphor  535  with the adhesive layer  220  facing the phosphor  535 . As shown in  FIG. 5B , vacuum may be applied, then the converter layer bonding device  200  brought into contact with phosphor  535  at elevated temperature (for example, between 50° C. and 150° C., e.g., 100° C.) so that the adhesive layer  220  may be in contact with the surface of the phosphor  535  to be bonded. As shown in  FIG. 5C , once the converter layer bonding device is cooled, the release liner  210  may be removed, leaving adhesive layer  220  behind on phosphor  535 . In  FIG. 5D , LED die  540  may be attached to the adhesive layer  220 , using, for example, a pick-and-place tool as is known by persons having ordinary skill in the art. The LED die  540  are positioned onto the adhesive layer  220  with the light emitting side of the LED die facing and in contact with the adhesive layer  220 . The adhesive layer  220  may then be cured at an elevate temperature (for example, between 50° C. and 150° C., e.g., 100° C.) to form bond layer  520  that is transparent. As shown in  FIG. 5D , the phosphor  535  may then be singulated by forming slots  550  through the bond layer  520  and phosphor  535  between each LED die  540  if desired. 
     This method illustrated in  FIGS. 5A-5E  may be used to form light emitting pixel arrays, such as micro-LEDs. The representative LED die  540  and bonded phosphor portions  537  may be a portion of a large array of LED die. As shown in  FIG. 5E , the light emitting device shown in  FIG. 5D  may be electrically connected to a signal source, such as with a substrate  590 , that provides each LED die  540  with a signal, such that each LED die  540  is individually addressable. The carrier tape  530  may be removed by methods known to persons having ordinary skill in art, resulting in a micro-LED having a thin and uniform bond layer  420  attaching the phosphor to the numerous LED die. In another example, each LED die  540  represents a die with multiple pixels and phosphor  535  a phosphor tile to form multiple light emitting pixel arrays, and advantageously each will have a bond layer  520  with a consistent, uniform thickness. 
     The resulting LED devices each have a phosphor portion  537  bonded to an LED die  540 . The converter layer bonding device  200  and method can form a bond layer  520  between each LED die  540  and phosphor portion  537  that is very thin, between 0.3 μm and 30 μm, for example, between 1 μm and 2 μm, as described above, and have a very uniform thickness, as described above. Additionally, the bond layer  520  substantially maintains the shape of the of the adhesive layer  220 , and thus does not flow out of or over the edges of the LED die  540  and phosphor  537 . Additionally, when singulated, the bond layer  520  can be cleanly diced, which also leaves the edge of the bond layer flush with the edge of the phosphor  535  and/or the LED die  540 . 
       FIGS. 6A-6D  illustrate an example application of the converter layer bonding device in which the adhesive layer is transferred onto a phosphor, followed by phosphor array patterning and LED die attach. A converter layer bonding device  200  may be prepared as described above with respect to  FIGS. 2A-2D . 
       FIG. 6A  shows adhesive layer  220  transferred onto phosphor  535  on carrier tape  530  by a vacuum lamination method as described above with respect to  FIGS. 5A-5C . As shown in  FIG. 6B , after removal of the release liner  210 , the phosphor  535  and adhesive layer  220  may be patterned, for example, into n×m arrays of phosphor tiles  640 .  FIG. 6C  is a plan view of the n×m arrays of phosphor tiles  640  of  FIG. 6B . Patterning of the phosphor  535  and adhesive layer  220  may accomplished by any applicable manner of dicing, segmenting, dividing, apportioning, slicing or compartmentalizing as is known in the art, such as, for example, sawing, etching, applying a mask to dice, using one or more lasers, and/or chemical treatments. Patterning may include forming slits  615  through the phosphor  535  and adhesive layer  220 , but not the carrier tape  530 , to form individual phosphor elements  645  of the n×m arrays of phosphor tiles  640 . Patterning may also include slicing through the carrier tape  530  to form openings  625 , which separate n×m arrays  640  if multiple arrays are to be formed. As shown in  FIG. 6D , the n×m arrays  640  may be placed onto to LED die  660  such that the adhesive layer  220  is in contact with the light emitting face  662  of the LED die  660 . LED die  660  may be on substrate  670  for this purpose. A pick-and-place tool may be used to place the n×m arrays of phosphor tiles  640  on the LED dies  660 , as in known in the relevant art. The n×m arrays  640  on the LED dies  660  may then be heated to an elevated temperature (for example, between 50° C. and 150° C., e.g., 100° C.) to heat and fully cure the adhesive layer  220  and form bond layer  620  that is transparent. 
     The method shown in  FIGS. 6A-6E  may be used to form micro-LEDs. LED die  660  in  FIGS. 6D and 6E  may include numerous minute LEDs that form the micro-LED, and each n×m phosphor array  640  may be aligned over each of the minute LEDs  661  in LED die  660 . That is, the dimension and count of the minute LED die pixels  661  in LED die  660  match up with those of the n×m arrays  640 . Thus, multiple micro-LEDs may be formed using this method, and advantageously, each will have a bond layer with a consistent, uniform thickness. 
       FIGS. 7A-7D  show transferring the adhesive layer onto LED die on tile, which LED die may have significant surface topography. A converter layer bonding device  200  may be prepared as described above with respect to  FIGS. 2A-2D . 
     As shown in  FIG. 7A , LED die  715  may be attached to a substrate, such as a tile. This may create a significant (potentially in the range of &gt;100 μm) height variations in the top of the LED die  715 . Before transferring the adhesive layer  220 , the LED die surface may be O2-plasma treated to improve adhesion of subsequently-transferred adhesive layer  220 . Vacuum lamination, as described above with respect to  FIGS. 4A-4E  may then be used to transfer the adhesive layer  220  onto the die surface, as shown in  FIG. 7B . 
     Once the converter layer bonding device is cooled, release liner  210  may be removed as shown in  FIG. 7C . Removal of the release liner  210  leaves a uniform adhesive layer  220  only on the surfaces  772  of the LED die  715 . Portions  722  of the adhesive layer  220  that are between LED die  715  are not adhered to the LED die  715  and thus are not transferred and remain on the release liner  210 . As shown in  FIG. 7D , phosphor platelets  725  may then be placed on the adhesive layer  220  on the LED die  715  at elevated temperatures (for example, between 50° C. and 150° C., e.g., 100° C.) to fully cure adhesive layer  220  and form bond layer  720  that is transparent. A pick-and-place tool may be used to place the phosphor platelets  725 . 
       FIGS. 8A and 8B  show a cross-sectional view and plan view, respectively, of a converter layer bonding device having a patterned adhesive layer that can be used, for example, to improve oxygen permeability, which reduces browning and thus improves transparency and device performance (as described, for example, in Cree® XLamp® LEDs Chemical Compatibility, CLD-AP63 REV 6A, August, 2018, Cree, Inc., incorporated herein by reference in its entirety). A converter layer bonding device  200  may be prepared as described above with respect to  FIGS. 2A-2D . Cutting the channels  805  may be accomplished by methods including, for example, dicing, laser ablation or laser cutting, and stamping, as is known by persons having ordinary skill in the art, and is possible because the adhesive layer  220  is relatively solid at a first, lower temperature, such as room temperature. Channels  805  of a given kerf are cut into adhesive layer  220 , but release liner  210  is left intact. The channels  805  may be open on at least one of the edges of the adhesive layer  220 , so as to allow ambient gasses, such as air or pure oxygen, to pass into the adhesive layer  220 . The size and spacing of the channels depend on the application. The channels may only be large enough to allow gas to pass into the layer, and may be spaced close enough together so that the gas entering the channels can diffuse significantly into the bond layer, but not so many channels or so close together to weaken the bonding. For example, channels with a width of 20 μm may be diced into the layer with a pitch of 200 μm. The resulting patterned converter layer bonding device  800  may be used in a similar manner to the converter layer bonding device  200  as disclosed herein. 
       FIGS. 9A-9D  illustrate use of a patterned converter layer bonding device  800 . In  FIGS. 9A-9D , a phosphor film or wafer  935  may be mounted onto a carrier tape  930 . The phosphor wafer  935  may be O 2 -plasma treated to improve adhesion of subsequently-transferred adhesion layer  220  having channels  805 . Vacuum lamination is then used to transfer the adhesive layer  220  having channels  805  onto the phosphor  935  as disclosed above with respect to  FIGS. 5A-5D . As shown in  FIG. 9A , after aligning the converter layer bonding device  800  with the phosphor wafer  935 , vacuum may be applied, then the converter layer bonding device  800  may be brought into contact with phosphor  935  at elevated temperature (for example, between 50° C. and 150° C., e.g. 100° C.) so that the adhesive layer  220  with channels  805  may be in contact with the surface of the phosphor  935  to be bonded. As shown in  FIG. 9B , once the patterned converter layer bonding device  800  is cooled, the release liner  210  may be removed, leaving adhesive layer  220  having channels  805  adhered on phosphor  935 . As shown in  FIG. 9C , LED die  915  may be attached to the adhesive layer  220  having channels  805 , using, for example, a pick-and-place tool as is known in the relevant art. The LED die  915  are positioned onto the adhesive layer  220  with the light emitting side of the LED die  915  facing and in contact with the adhesive layer  220 , and also positioned over the channels  805 . The adhesive layer  220  having channels  805  may then be cured at an elevate temperature (for example, between 50° C. and 150° C., e.g., 100° C.) to form transparent bond layer  920  having channels  805 . As shown in  FIG. 9D , the phosphor  935  may then be singulated by forming slots  975  through the bond layer  920  and phosphor  935  between each LED die  915  if desired. 
     The resulting transparent bond layer  920  between LED die  915  and phosphor  935  has open channels  805  of a certain aspect ratio, for example, having a 20 μm width and a depth (or height) that is the thickness T of the bond layer  920  or less than the thickness T of the bond layer, and, for example, may be 2 μm. Other examples of bond layers with channels, additives used to modify the optical characteristics, and use of a second material to back-fill the channels may be found in U.S. patent application Ser. No. 16/584,642 titled “Fabrication For Precise Line-Bond Control and Gas Diffusion Between LED Components”, incorporated herein by reference in its entirety. These channels  805  may decrease the path length for oxygen to diffuse into the bond layer  920 , reducing the browning that can occur to high refractive index/high phenyl-content siloxanes. Although  FIGS. 8A and 8B  illustrate a pattern with multiple straight channels  805 , other patterns may be used. Also, the patterned converter layer bonding device  800  may be used in place of the converter layer bonding device  200  without patterns in any of the applications disclosed herein. 
       FIGS. 10A-10E  illustrate an application of stacked adhesive layers by a multiple lamination process onto a phosphor wafer for improved oxygen permeability. In  FIG. 10A , a first converter layer bonding device  1080  is prepared with a first adhesive layer  1020  on first release liner  1010  (as described with respect to  FIGS. 3A-3D ). First adhesive layer  1020  may, for example, be patterned to include channels  1005  as described above with respect to  FIGS. 8A-8B . As shown in  FIG. 10B , the first adhesive layer  1020  with channels  1005  may be transferred to phosphor  1035  in a manner as described above with respect to  FIGS. 9A-9B . As shown in  FIG. 10C , a second converter layer bonding device  1081 , having second adhesive layer  1021  on second release liner  1011  may then be positioned onto and transferred to first adhesive layer  1020 . Second converter layer bonding device  1081  may be prepared as described above with respect to  FIGS. 3A-3D . Second adhesive layer  1021  may have different physicochemical characteristics than first adhesive layer  1020 , such as, for example, higher oxygen permeability. As shown in  FIG. 10C , the second adhesive layer  1021  of second bonding device  1081  is positioned so as to be in contact with the first adhesive layer  1020 . The vacuum lamination process is then repeated, and the second converter layer bonding device  1081  is heated to an elevated temperature at which the second adhesive layer  1021  becomes adhesive, to adhere second adhesive layer  1021  to first adhesive layer  1020 . The second converter layer bonding device is then cooled and the second release liner  1011  is removed, leaving the second adhesive layer  1021  adhered to the first adhesive layer  1020 , which is adhered to phosphor  1035 . This process may be repeated to add additional adhesive layers. The resulting stack of at least two adhesive layers  1020  and  1021 , may have different optical and/or physical properties and/or morphologies. 
     As shown in  FIG. 10E , LED die  1015  may be attached to the second adhesive layer  1021  with the light emitting side of the LED die  1015  facing and in contact with the side of the second adhesive layer  1021  opposite the phosphor  1035 . The LED die  1015  may be positioned on the second adhesive layer  1021  at an elevated temperature (e.g. 100° C.). A pick-and-place tool may be used for this purpose, as is known to persons having ordinary skill in the art. The multilayer adhesive stack of first adhesive layer  1020  and second adhesive layer  1021  is then fully cured to form multilayer bond layer  1032  having a first bond layer  1030  formed from the first adhesive layer  1020  and a second bond layer  1031  formed from second adhesive layer  1021 . The multilayer bond layer  1032  and phosphor  1035  may be singulated. The resulting portion of the multilayer bond layer  1032  may have differentiated properties in each of the different layers.  FIGS. 10A-10E  illustrate an example where one layer has channels  1005  of a certain aspect ratio and the other layer does not have channels. The channels or/and the increased permeability of the stack towards oxygen will result in increased oxygen concentration in the bond layer, reducing the adhesive browning intrinsic to high refractive index/high phenyl-content siloxanes. Other embodiments of a multilayer bond layer may be made with layers that do not have channels but have other different physical properties, or that both have channels but the channels differ, for instance in direction of pattern or width of cut, or both layers may be the same. The different layer may have different physical characteristics, such as higher oxygen permeability, refractive index, or other optical characteristics, including, but not limited to scattering light, optical absorption and emission. 
       FIGS. 11A-11E  illustrate another method of forming a multilayer bond layer, in this case by forming a converter layer bonding device that includes a multilayer adhesive layer. 
     Similar to the method disclosed above with respect to  FIGS. 3A-3D , the release liner  1110  to be used may be coated with a siliconized coating to enhance the release properties as described above (not shown). A first adhesive mixture  1102  may be prepared by mixing a first adhesive material with a solvent. As shown in  FIG. 11A , the first adhesive mixture  1102  is then coated onto the release liner  1110 . Any method that can suitably coat the release liner  1110  with a uniform layer of the first adhesive mixture  1102  at the desired thickness may be used, such as, for example, spin-coating, gravure printing, etc.  FIG. 11A  illustrates, as an example, a spin-coating process for coating release liner  1110  with the first adhesive mixture  1102 . In  FIG. 11A , the release liner  1110  is positioned on a spin-coating support  1105  and the first adhesive mixture  1102  is deposited from nozzle  1107  as is known by persons having ordinary skill in the art. 
     As shown in  FIG. 11B , the first adhesive mixture  1102  coated onto release liner  1110  is dried to remove solvent. Depending on the adhesive used, the first adhesive mixture  1102  may be additionally cured to stabilize the material and improve uniformity of the subsequent transfer from the converter layer bonding device. 
     As shown in  FIG. 11C , the release liner  1110  and first adhesive layer  1120  formed from the dried first adhesive mixture  1102  may then be coated with a second adhesive mixture  1103 . Any suitable method may be used to coat second adhesive mixture  1103  onto the first adhesive layer  1120 .  FIG. 11C  illustrates a spin-coating method as disclosed above. 
     As shown in  FIG. 11D , the second adhesive mixture  1103  may then be dried to remove solvent. The resulting converter layer bonding device  1100  is shown in  FIG. 11E  with second adhesive layer  1121  adhered on top of and in contact with first adhesive layer  1120 , which is on release liner  1110 . Both adhesive layers  1120  and  1121  may be thin (may be under 4 μm), uniform, defect-free, and can be made in a large area. The first adhesive layer  1120  and second adhesive layer  1121  may be different. The second adhesive layer  1121  may be patterned as described above with respect to  FIGS. 8A-8B . The first adhesive layer  1120  may have different physical characteristics, such as higher oxygen permeability, refractive index, or other optical characteristics, including, but not limited to scattering light, optical absorption and emission, than the first adhesive layer  1121 . The converter layer bonding device  1100  may be used in any applications in which a converter layer bonding device  1100  with a single adhesive layer is used, and may be used to transfer adhesive layers  1120  and  1121  to a substrate (e.g., a phosphor or LED die) in a same manner as disclosed above with respect to  FIGS. 4A-4D  for single adhesive layer  220 . 
     The bond layer that is formed using the converter layer bonding device and methods disclosed herein, and the pcLED devices, including micro-LEDs, formed using the converter layer bonding device and method, have several advantages, in particular, as compared to the adhesive dispensing process conventionally used in the art. Because the adhesive layer is transferred onto the substrate, such as the phosphor or LED die, as a dry film, there will be no excess adhesive extruded out when phosphor and die are brought into contact, and therefore no “wings” or “fillets” along the edges of the devices. The dry adhesive layer does not spread out when transferred, but maintains its shape. The adhesive layer stays where it is positioned. Additionally, during the curing process, the temperature is controlled so that the resulting bond layer also does not flow and spread, but maintains its shape. Additionally, there will be no significant bond-line variation, as the thickness of the bond layer is determined before application by the thickness of the adhesive layer. Additionally, in the example disclosed above with respect to  FIG. 8A-8E , the patterning of the adhesive layer can be performed to allow air channels in the pcLED device. 
     The bond layer formed using the converter layer bonding device and method disclosed herein also has advantages over other coating methods, such as spin-coating and spray-coating for applying adhesive.  FIG. 12A  shows a schematic of an expanded view of a substrate  1315  and the surface of the substrate  1317 , which is rough and not flat. Phosphor tiles and LED dies may have such surface roughness. Adhesive layer  220  transferred onto the substrate  1315  using the converter layer bonding device and method disclosed here, conforms to the native surface roughness of the substrate  1315 , while maintaining a uniform layer thickness T.  FIG. 12B  shows, for comparison, a surface coated with a conventional solution-state method for application of adhesive, for example, spin coating or spray coating. As seen in  FIG. 13B , an adhesive solution  1301  flows to fill in the surface structures, and may leave portions of the surface exposed. Also, of note, is that the adhesive coating of  FIG. 12A  may result in small air voids between the adhesive layer and a sample surface to be bonded. 
     The devices and methods disclosed herein have several additional benefits over the methods typically used. First, the device and method can be used in a batch process, and can coat large areas in a single transfer. Thus, light emitting pixel arrays, such as micro-LEDs, that are formed from pcLEDs can be made efficiently and uniformly. Secondly, the device and method allow for precise control of the bond layer thickness, down to very thin (˜1 μm) layers. Most importantly, the adhesive film transfer coating methods disclose herein are applicable to a wide variety of substrates, as it is less sensitive to surface roughness and surface energy than solution-state coating processes. As described with respect to  FIGS. 12A and 12B  above, even a substrate with significant surface topography, such as a tile with attached die, can be coated. Additionally, because transfer is a dry process, solvent compatibility with the target substrate is not an issue. Additionally, the adhesive layer can be patterned on the release liner before it is transferred to a substrate, as described with respect to  FIGS. 8A-8B , this pattern facilitates gas transport and can prevent browning in high refractive index silicone adhesives, as well as improve optical performance in micro-LED applications. 
     This disclosure is illustrative and not limiting. Further modifications will be apparent to one skilled in the art in light of this disclosure and are intended to fall within the scope of the appended claims.