PATENT DOCUMENT

Publication Number: US-9266310-B2
Application Number: US-201113329010-A
Country: US
Kind Code: B2

Title: Methods of joining device structures with adhesive

Abstract:
Structures such as layers of material associated with an electronic device may be assembled using adhesive. The adhesive may be dispensed onto the surface of an electronic device layer in liquid form. The liquid adhesive material may be a liquid pressure sensitive adhesive precursor material. Patterned structures such as touch sensor electrodes, black ink masking layers, and other structures may be formed on the electronic device layer. The use of liquid adhesive material may help the adhesive material flow over the edges of the patterned structures without forming bubbles or voids. Following application of the liquid pressure sensitive adhesive precursor material, the liquid pressure sensitive adhesive precursor material may be cured to form a solid layer of pressure sensitive adhesive. The layer of material on which the solid layer of pressure sensitive adhesive has been formed may then be vacuum laminated to an additional electronic device layer.

Claims:
What is claimed is: 
     
       1. A method for assembling electronic device structures that include a first layer and a second layer, comprising:
 dispensing a liquid pressure sensitive adhesive precursor material onto the first layer; 
 curing the liquid pressure sensitive adhesive precursor material using a curing tool to create a layer of pressure sensitive adhesive on the first layer; 
 following creation of the layer of pressure sensitive adhesive on the first layer, laminating the first and second layers together with the pressure sensitive adhesive so that the layer of pressure sensitive adhesive is interposed between the first and second layers, wherein the first layer comprises a surface on which an array of touch pad electrodes is formed, wherein the array of touch pad electrodes form a patterned set of surface structures on the first layer, wherein each touch pad electrode in the array of touch pad electrodes has respective first and second opposing surfaces, wherein the first surface is in direct contact with the first layer, and wherein the second surface is separated from the first layer by a step height, and wherein dispensing the liquid pressure sensitive adhesive precursor material comprises coating the surface of the first layer and the array of touch pad electrodes on the surface of the first layer with the liquid pressure sensitive adhesive precursor material; and 
 applying a dam structure to portions of the first layer, comprising:
 using an adhesive to attach portions of the dam structure to the portions of the first layer, wherein the dam structure is configured to at least partly laterally confine the liquid pressure sensitive adhesive precursor material. 
 
 
     
     
       2. The method defined in  claim 1  wherein laminating the first and second layers comprises vacuum laminating the first and second layers using pressure sensitive adhesive vacuum lamination equipment. 
     
     
       3. The method defined in  claim 2  wherein the first and second layers comprise rigid layers and wherein laminating the first and second layers together comprises laminating the rigid layers together. 
     
     
       4. The method defined in  claim 2  wherein the first and second layers comprise first and second display layers in a display and wherein laminating the first and second layers together comprises laminating the first and second display layers together. 
     
     
       5. The method defined in  claim 1  wherein the first and second layers comprise touch pad layers and wherein laminating the first and second layers together comprises laminating the touch pad layers together. 
     
     
       6. The method defined in  claim 1  wherein the first and second layers comprise rigid layers including at least one layer of glass, wherein laminating the first and second layers together comprises laminating the rigid layers together, wherein the curing tool comprises an ultraviolet light source, and wherein curing the liquid pressure sensitive adhesive precursor material using the curing tool to create the layer of pressure sensitive adhesive on the first layer comprises applying ultraviolet light to the layer of liquid pressure sensitive adhesive precursor material using the ultraviolet light source. 
     
     
       7. The method defined in  claim 1  wherein the curing tool comprises an ultraviolet light source and wherein curing the liquid pressure sensitive adhesive precursor material using the curing tool to create the layer of pressure sensitive adhesive on the first layer comprises applying ultraviolet light to the layer of liquid pressure sensitive adhesive precursor material using the ultraviolet light source. 
     
     
       8. The method defined in  claim 1  further comprising removing at least some of the dam structure using trimming equipment. 
     
     
       9. The method defined in  claim 8  wherein removing at least some of the dam structure using the trimming equipment comprises removing the dam structure using laser trimming. 
     
     
       10. The method defined in  claim 1  further comprising applying a release liner to the liquid pressure sensitive adhesive precursor material. 
     
     
       11. The method defined in  claim 10  further comprising flattening the release liner with a planar member. 
     
     
       12. The method defined in  claim 11  wherein curing the liquid pressure sensitive adhesive precursor material using the curing tool comprises applying ultraviolet light to the liquid pressure sensitive adhesive precursor material through the planar member and the release liner after the release liner is flattened with the planar member. 
     
     
       13. The method defined in  claim 12  further comprising removing the release liner before laminating the first and second layers. 
     
     
       14. The method defined in  claim 1  wherein dispensing the liquid pressure sensitive adhesive precursor material onto the first layer comprises applying the liquid pressure sensitive adhesive precursor material using equipment selected from the group consisting of: a valve, spraying equipment, and screen printing equipment. 
     
     
       15. The method defined in  claim 1  further comprising flattening the pressure sensitive adhesive before laminating the first and second layers together with the pressure sensitive adhesive. 
     
     
       16. The method defined in  claim 15  wherein flattening the pressure sensitive adhesive comprises applying heat to the dispensed liquid pressure sensitive adhesive precursor material. 
     
     
       17. The method defined in  claim 1  wherein dispensing the liquid pressure sensitive adhesive precursor material onto the first layer and curing the liquid pressure sensitive adhesive precursor material using the curing tool to create the layer of pressure sensitive adhesive on the first layer comprises:
 dispensing multiple sublayers of liquid pressure sensitive adhesive precursor material; and 
 curing each of the sublayers of liquid pressure sensitive adhesive precursor material to form the layer of pressure sensitive adhesive on the first layer. 
 
     
     
       18. A method of assembling first and second electronic device layers, wherein at least the first electronic device layer has surface structures, wherein the surface structures each have first and second opposing surfaces connected by third and fourth opposing surfaces, and wherein the third surface of each surface structure is in direct contact with the first electronic device layer, the method comprising:
 applying a liquid pressure sensitive adhesive precursor material onto the first electronic device layer over the surface structures such that the liquid pressure sensitive adhesive precursor material directly contacts the first, second, and fourth surfaces of each surface structure; 
 forming a patterned layer of ink on the first electronic device layer, wherein applying the liquid pressure sensitive adhesive precursor material comprises coating the first electronic device layer and the patterned layer of ink on the first electronic device layer with the liquid pressure sensitive adhesive precursor material; 
 curing the liquid pressure sensitive adhesive precursor material to form a solid layer of pressure sensitive adhesive; 
 laminating the first and second electronic device layers together with the solid layer of pressure sensitive adhesive; and 
 applying a dam structure to portions of the first electronic device layer, comprising:
 using an adhesive to attach portions of the dam structure to the portions of the first electronic device layer, wherein the dam structure is configured to at least partly laterally confine the liquid pressure sensitive adhesive precursor material. 
 
 
     
     
       19. The method defined in  claim 18  wherein the first electronic device layer comprises a layer of glass and wherein curing the liquid pressure sensitive adhesive precursor material comprises applying ultraviolet light to the liquid pressure sensitive adhesive precursor material. 
     
     
       20. The method defined in  claim 19  further comprising:
 applying a release liner to the solid layer of pressure sensitive adhesive on the layer of glass. 
 
     
     
       21. The method defined in  claim 9  wherein removing the dam structure using laser trimming further comprises removing the liquid pressure sensitive adhesive precursor material that has spread laterally outward over portions of the dam structure using laser trimming. 
     
     
       22. The method described in  claim 18  wherein the surface structures are separated by gaps, and wherein the surface structures comprise touch sensor electrodes.

Description:
BACKGROUND 
     This relates generally to electronic devices, and more particularly, to joining electronic device structures using adhesive. 
     Adhesives are widely used to assemble components for electronic devices such as computers, cellular telephones, media players, and other electronic equipment. For example, sheets of pressure sensitive adhesive are often used to join planar structures. Planar structures may, for example, be laminated together with pressure sensitive adhesive using lamination equipment. Pressure sensitive adhesive layers are, however, only able to accommodate a limited amount of surface topology. When pressure sensitive adhesive layers are used to join structures with substantial step heights or other abrupt features, there is a risk that bubbles or voids may develop. The risk of bubble formation may be reduced by using softer pressure sensitive adhesive materials, but this tends to weaken bond strength and other desirable properties. 
     Liquid adhesives can be used to overcome step height discontinuities, because liquid adhesives can flow over abrupt features. However, the process of joining electronic device structures using liquid adhesives is often disfavored because of the challenges associated with using liquid adhesives in a production environment. 
     It would therefore be desirable to be able to provide improved ways to join structures such as electronic device structures using adhesive. 
     SUMMARY 
     Structures such as layers of material associated with an electronic device or other structures may be assembled using adhesive. The layers of material may include layers of glass or polymer associated with a display, layers of glass or polymer associated with a touch pad, or layers of material or other device structures associated with an electronic device. 
     The adhesive may be dispensed onto the surface of an electronic device layer in liquid form. The liquid adhesive material may be a liquid pressure sensitive adhesive precursor material. Patterned structures such as touch sensor electrodes, black ink masking layers, and other structures may be previously formed on the electronic device layer. These structures may have edges that are characterized by a step height. The use of liquid adhesive material may help the adhesive material flow over the edges of the patterned structures without forming bubbles or voids due to the presence of the step height. 
     Following application of the liquid pressure sensitive adhesive precursor material, the liquid pressure sensitive adhesive precursor material may be cured to form a solid layer of pressure sensitive adhesive. The layer of material on which the solid layer of pressure sensitive adhesive has been formed may then be laminated to an additional electronic device layer using a pressure sensitive adhesive lamination tool. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device such as a portable computer having structures that may be joined using adhesive in accordance with an embodiment of the present invention. 
         FIG. 2  is a perspective view of an illustrative electronic device such as a cellular telephone or other handheld electronic device of the type that may have device structures that may be joined using adhesive in accordance with an embodiment of the present invention. 
         FIG. 3  is a side view of illustrative device structures such as display structures that may be joined using adhesive in accordance with an embodiment of the present invention. 
         FIG. 4  is a side view of the illustrative device structures of  FIG. 3  following assembly using adhesive in accordance with an embodiment of the present invention. 
         FIG. 5  is a side view of illustrative device structures such as structures associated with a touch pad in an electronic device that may be joined using adhesive in accordance with an embodiment of the present invention. 
         FIG. 6  is a side view of the illustrative device structures of  FIG. 5  following assembly using adhesive in accordance with an embodiment of the present invention. 
         FIG. 7  is a diagram showing equipment and assembly operations that may be used in assembling device structures using adhesive in accordance with an embodiment of the present invention. 
         FIG. 8  is a diagram showing how a planarization tool may optionally be used to help planarize a layer of adhesive during the assembly operations of  FIG. 7  in accordance with an embodiment of the present invention. 
         FIG. 9  is a diagram showing equipment and assembly operations that may be used in applying an adhesive dam structure and that may be used in applying adhesive during device structure assembly operations in accordance with an embodiment of the present invention. 
         FIG. 10  is a diagram of additional equipment and assembly operations that may be used during device structure assembly operations following the operations of  FIG. 9  in accordance with an embodiment of the present invention. 
         FIG. 11  is a diagram of illustrative equipment and assembly operations that may be used to assembly device structures in accordance with another embodiment of the present invention. 
         FIG. 12  is a diagram showing operations that may be involved in dispensing adhesive adjacent to a dam structure and performing dam structure trimming operations in accordance with an embodiment of the present invention. 
         FIG. 13  is a diagram showing how a layer of adhesive may be deposited by performing multiple liquid adhesive dispensing and curing operations to form the layer of adhesive from multiple sublayers of adhesive in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may be provided with structures that are assembled using adhesive. Illustrative electronic devices of the type that may be provided with structures that are assembled using adhesive are shown in  FIGS. 1 and 2 . Electronic device  10  of  FIG. 1  may be, for example, a portable computer. Electronic device  10  of  FIG. 2  may be, for example, a handheld electronic device such as a cellular telephone or media player. In general, electronic device  10  may be any suitable equipment such as a personal computer, a tablet computer, a cellular telephone, a media player, a gaming device, a navigation device, or other electronic equipment. Structures may also be assembled using adhesive that are not part of an electronic device. The assembly of electronic device structures is sometimes described herein as an example. 
     As shown in  FIG. 1 , device  10  may have a housing such as housing  12  and a display such as display  14 . Housing  12  may be formed from glass, plastic, metal, carbon-fiber composites and other fiber-based composites, other materials, or combinations of these materials. Display  14  may be a plasma display, an organic light-emitting diode display, a liquid crystal display, or other suitable display. The surface of display  14  may be covered with a cover layer of glass, plastic, or other transparent material. 
     Housing  12  may have a hinge that joins upper and lower housing portions. The upper and lower housing portions may rotate relative to each other about hinge axis  20 . The upper housing portion may be used to house display  14 . Input-output components such as touch pad  16  and keyboard  18  may be mounted in the lower portion of housing  12 . 
       FIG. 2  is a perspective view of another illustrative configuration that may be used for device  10 . In the example of  FIG. 2 , device  10  has been provided with display  14  in housing  12 . Display  14  may be covered with a display cover layer such as a layer of cover glass or a plastic cover layer. Openings may be formed in the cover layer or other portion of display  14  such as speaker port opening  22  and menu button opening  24 . Additional openings in display  14  and housing  12  may be used to accommodate input-output connectors such as audio connectors and data connectors and other input-output components. 
     The illustrative electronic equipment of  FIGS. 1 and 2  and other electronic devices may have components that can be assembled using adhesive. In some scenarios, the structures that are assembled together may be planar structures such as planar layers of glass, plastic, metal, printed circuit board structures (e.g., rigid printed circuit boards such as fiberglass-filled epoxy boards such as FR4 boards, flexible printed circuits such as sheets of polyimide or other polymer layers with patterned metal traces (“flex circuits”), “rigid flex” printed circuits that include regions of rigid printed circuit board material with flex circuit tails), housing structures, planar structures associated with a display, planar structures associated with an input-output device such as a touch pad or touch screen (e.g., a printed circuit with touch pad electrodes, a covering glass layer for a touch pad, other touch pad substrates and cover layers, etc.), planar structures associated with a planar housing, or other planar structures. In other situations, some or all of the structures being assembled with the adhesive may be non-planar structures (e.g., non-planar housing structures, etc.). Examples in which the structures being assembled are planar structures such as display layers and touch pad layers are sometimes described herein as an example. This is, however, merely illustrative. Any suitable structures may be assembled using adhesive if desired. 
       FIG. 3  is a side view of illustrative structures of the type that may be assembled using adhesive. In the example of  FIG. 3 , upper layer  26  is being attached to lower layer  32 . Layers  26  and  32  may be, for example, layers in a display such as display  14 . One or both of layers  26  and  32  may be rigid by virtue of being formed from a rigid material or being attached to rigid structures. For example, layers  26  and  32  may be formed from rigid layers of glass, rigid layers of plastic, flexible layers of plastic attached to rigid structures such as glass structures. Layers  26  and  32  may also be formed from flexible sheets of material. Examples of display layers that may be assembled using adhesive include a cover layer, a polarizer layer, an anti-scratch layer, an anti-smudge layer, an antireflection layer, a touch panel layer, a color filter layer, a thin-film transistor layer, and backlight structure layers. As an example, layer  26  may be a display cover layer and layer  32  may be an upper polarizer or other layer associated with a liquid crystal display. Other display components (e.g., flexible and/or rigid display layers) may be attached using adhesive if desired. The assembly of display structures such as a cover layer and polarizer layer is merely illustrative. 
     As shown in  FIG. 3 , upper layer  26  (e.g., a display cover layer or other planar layer) may have surface structures such as structures  30  that have an associated thickness T. Structures  30  may, for example, be opaque masking layer structures that surround a peripheral portion of display  14  (e.g., a layer of black ink that has been formed on the underside of layer  26  in the form of a rectangular ring-shaped border for display  14 ). The thickness T of layer  30  may be, for example, about 10-40 microns (as an example). 
     To join upper layer  26  to lower layer  32 , upper layer  26  may be moved towards layer  32 , as illustrated by arrow  28 . 
     As shown in  FIG. 4 , adhesive layer  36  may be interposed between upper layer  26  and lower layer  32 . Adhesive layer  36  may be used to join upper layer  26  and lower layer  32 . Adhesive layer  36  is preferably formed by dispensing adhesive material as a liquid on layer  26 , so that the adhesive covers the step generated at the edges of features  30 . The liquid may be cured to form a solid pressure sensitive adhesive layer. The upper and lower layers may then be joined using lamination equipment to produce an assembly of the type shown in  FIG. 4 . 
     With this type of arrangement, upper layer  26  is joined to lower layer  32  using a layer of solid pressure sensitive adhesive in a pressure sensitive adhesive (PSA) lamination scheme, which is less complex than using lamination schemes involving liquid adhesive. At the same time, because adhesive  36  is initially dispensed in the form of a liquid material, adhesive  36  is able to satisfactorily flow over steps in features  30  (e.g., edge heights of thickness T), thereby avoiding the drawbacks of using a layer of conventional pressure sensitive adhesive such as the need to using thick soft layers to avoid bubbles and voids. 
     In the example of  FIGS. 5 and 6 , upper layer  26  may be a glass layer or other planar structure and lower layer  32  may be a substrate layer (as examples). Upper layer  26  and lower layer  32  may, for example, be an upper and lower layer in a touch pad such as touch pad  16  of  FIG. 1 . Touch pads may include capacitive electrodes that exhibit abrupt changes in height at their edges, as illustrated by features  30  on layer  32  of  FIG. 5 . The height of each pad  30  may, for example, be about 30 microns, about 20-40 microns, or about 10-40 microns (as examples). Layer  26  may also include features  30  (e.g., planar or non-planar structures exhibiting a thickness of about 10-40 microns, etc.). The non-planar features  30  on layer  32  may be coated with liquid adhesive. The liquid adhesive may be cured to form a solid layer of pressure sensitive adhesive on layer  32 . Layers  26  and  32  may then be laminated together using lamination equipment or other suitable equipment. 
     The resulting laminated structure that is formed by attaching layers  26  and  32  in this way is shown in  FIG. 6 . As shown in  FIG. 6 , solid pressure sensitive adhesive layer  36  may be interposed between layers  26  and  32  and, because layer  36  was initially deposited in the form of a liquid, layer  36  may satisfactorily cover the edges of features  30  without forming bubbles or voids. 
     In general, layers  26  and  32  may be associated with any structures in electronic device  10  such as planar display structures, planar touch pad structures, planar housing structures, or other planar structures, non-planar device structures, etc. 
       FIG. 7  is a diagram that shows equipment and assembly operations that may be associated with assembling structures such as layers  26  and  32  using adhesive  36 . 
     Initially, layer  32  may be covered with non-planar structures such structures  30 . The edges of structures  30  may be characterized by a step in height (vertical dimension change) of about 10-40 microns, of 50 microns or less, 100 microns or less, 10-100 microns, 10 microns or more, or other suitable thickness. It may be difficult or impossible to satisfactorily cover features of this type using a sheet of conventional pressure sensitive adhesive, because conventional techniques may require the use of an excessively thick and/or soft pressure sensitive adhesive layer. 
     As shown in  FIG. 7 , this challenge associated with the use of conventional pressure sensitive adhesive attachment techniques can be addressed by forming a conformal layer of pressure sensitive adhesive using a multistep process. Initially, a layer of liquid adhesive (e.g., a liquid monomer pressure sensitive adhesive precursor) may be applied to the surface of layer  32  using liquid adhesive application tool  38 . Because adhesive  36  is liquid when applied by tool  38 , adhesive  36  may coat features  30  on layer  32  without risk of forming bubbles or voids at the edges of features  30 . Following application of the liquid precursor layer, the liquid adhesive layer may be cured using curing tool  40  to produce a solid (cured) pressure sensitive adhesive layer. The pressure sensitive adhesive layer that is produced by tool  40  may be attached to upper layer  26  using pressure sensitive adhesive lamination tool  44 , thereby producing assembled structures  46  of  FIG. 7 . Lamination tool  44  may be hard-to-hard lamination equipment, hard-to-soft lamination equipment, soft-to-soft lamination equipment, or other lamination equipment. Lamination tool  44  may, if desired, apply a vacuum to the layers of material that are being laminated together (i.e., tool  44  may be hard-to-hard vacuum lamination equipment, hard-to-soft vacuum lamination equipment, soft-to-soft vacuum lamination equipment). Lamination tool  44  may also be implemented without vacuum capabilities and/or include autoclave equipment (e.g., equipment that performs lamination operations by applying an elevated pressure of about 2-100 atmospheres and an elevated temperature of about 50-100° C.) 
     Liquid adhesive application tool  38  may include equipment for dispensing liquid adhesive onto the surface of layer  32 . Tool  38  may, for example, use a robotically or manually controlled liquid adhesive dispensing valve such as a slit valve or other valve to dispense liquid adhesive on the surface of layer  32 . Liquid adhesive may also be dispensed on the surface of layer  32  using spraying, screen printing, pad printing, or other liquid adhesive application techniques. The liquid adhesive may be heated to reduce its viscosity. Liquid adhesive heating operations may be performed on the liquid adhesive before applying the adhesive to layer  32 , during the process of dispensing liquid adhesive onto layer  32 , or after applying the liquid adhesive to the surface of layer  32 . As an example, liquid adhesive that has been applied to layer  32  may be planarized by placing layer  32  on a heated surface and/or by exposing the surface of layer  32  and the liquid adhesive on layer  32  to an infrared lamp or other heat source to raise the temperature of the liquid adhesive to about 60-70° C. or other elevated temperature. The primary purpose of heating the adhesive is to reduce viscosity and “flow” the adhesive to form a planar surface. If desired, liquid adhesive that has a sufficiently low viscosity to form a planar surface without heating may be deposited. 
     After a liquid adhesive layer has been formed on layer  32  to coat layer  32  while avoiding bubbles and voids at the edges of non=planar features  30  of layer  32 , tool  40  may be used to cure the liquid adhesive to form a solid layer of pressure sensitive adhesive. The curing process may be performed by applying heat, ultraviolet (UV) light, or other curing stimulus to the liquid adhesive using curing tool  40 . Curing tool  40  may, for example, be a UV light source such as a UV lamp that converts the monomer precursor material of the liquid adhesive into a solid (non-liquid) pressure sensitive adhesive polymer (e.g., by promoting cross linking of the monomers in the liquid adhesive layer). 
     The resulting layer of pressure sensitive adhesive on the surface of layer  32  (prior to attachment of additional layer  26 ) may be characterized by satisfactory planarity and coverage over the steps in height produced by the edges of surface features  30 , while simultaneously being sufficiently solid (non-liquid) following curing with tool  40  to avoid the handling difficulties associated with liquid adhesive lamination operations. 
     Because curing tool  40  produces a solid (non-liquid) pressure sensitive adhesive layer on the surface of layer  32 , lamination tool  44  may be a pressure sensitive adhesive lamination tool of the type that is configured to laminate opposing layers of material using a solid interposed layer of pressure sensitive adhesive (i.e., to laminate layers  26  and  32  to produce laminated structures  46 ). Structures (assembly)  46  may be associated with structures in display  14  such as a display cover layer and underlying display layers, may be associated with layers in a touch pad such as touch pad  16  of  FIG. 1 , or may be associated with other device structures such as other planar device structures (as examples). 
       FIG. 8  shows how optional adhesive planarization operations may be performed during an assembly process of the type shown in  FIG. 7 . Following curing of liquid adhesive layer  36  to form pressure sensitive adhesive layer  36  of  FIG. 8 , the surface of layer  36  (i.e., surface  50  of  FIG. 8 ) may be rough. To smooth surface  50 , layer  50  may be planarized using flattening (planarization) tool  48 . Flattening tool  48  may include layer flattening equipment such as a hot knife, a heat lamp to promote adhesive reflow operations (e.g., to reflow and thereby planarize adhesive layer  36  following curing), a press that presses a planar tool member against a release liner and thereby flattens layer  36 , or other planarization equipment. Following planarization with flattening tool  48 , irregular surface  50  of adhesive layer  36  may be characterized by a planar surface such as smooth planarized surface  52  of  FIG. 8 . If desired, planarization operations with equipment such as equipment  48  (and/or equipment  38  of  FIG. 7 ) may also be performed prior to adhesive curing, as described in connection with  FIG. 7 . 
     If desired, a removable patterned structure such as a patterned polymer sheet that forms a dam structure may be used to help control the flow of liquid adhesive  36  before curing. This type of approach for joining layers  26  and  32  is shown in  FIGS. 9 and 10 . 
     As shown in  FIG. 9 , prior to dispensing liquid adhesive, layer  32  may be fabricated. Layer  32  may, for example, include non-planar surface structures such as surface features  30  and, if desired, optional additional structures such as housing frame structures  54 . 
     Dam attachment tool  56  (e.g., equipment for automatically and/or manually applying a patterned layer of polymer using a removable adhesive) may be used to apply a layer of material such as dam structures  58 . Structures  58  may be held in place on layer  32  (e.g., on surface features  30  or elsewhere on layer  32 ) using a reworkable adhesive on the lower surface of structures  58  (i.e., an adhesive that forms a temporary bond that has sufficient strength to hold dam structures  58  in place during assembly operations while being sufficiently weak to allow structures  58  (or at least portions of structures  58 ) to be removed by peeling later in the assembly process if desired. Other types of attachment mechanisms may be used for dam structures  58  if desired (e.g., more permanent adhesive, etc.). 
     Following attachment of dam structures  58  of  FIG. 9 , liquid adhesive  36  (e.g., a liquid monomer pressure sensitive adhesive precursor material) may be applied to layer  32  using liquid adhesive application tool  60  (e.g., a tool that includes equipment such as liquid adhesive application equipment  38   FIG. 7 ). The liquid adhesive material may coat surface  32  and features  30  on surface  32  with minimal risk of introducing bubbles or voids. The shape and location of patterned dam structure  58  may be selected so as to at least partly laterally confine the liquid pressure sensitive adhesive precursor material that is applied using tool  60 . 
     Following formation of the layer of liquid adhesive, equipment  62  may be used to cure and level the liquid adhesive to form cured solid pressure sensitive adhesive layer  36  with planar surface  64 . Equipment  62  may include curing equipment such as UV curing equipment  40  of  FIG. 7  or other equipment that can cross link the monomers of the liquid adhesive layer to form solid polymeric pressure sensitive adhesive layer  36  with planar surface  64 . Equipment  62  may also include leveling equipment such flattening tool  48  of  FIG. 8 ) to help planarize adhesive layer  36  (e.g., following curing or, if desired, prior to curing). 
     During the curing and leveling process, some of adhesive layer  36  may spread laterally outward over portions of the surface of dam structure  58 . If desired, this type of laterally spread adhesive and excess portions of dam structure  58  may be removed by trimming dam structure  58 . As shown in  FIG. 9 , for example, dam trimming tool  66  may be used to form cut  68  in structure  58  to allow structure  58 E to be removed from layer  32  (e.g., by peeling portion  58 E away from layer  32  to leave behind trimmed structure  58 ). Dam trimming tool  66  may include a laser to perform laser trimming operations, a knife or other scoring tool to perform cutting operations, or other equipment for trimming dam structure  58 . 
     After edge portion  58 E of dam structure  58  of  FIG. 9  has been removed from layer  32 , equipment of the type shown in  FIG. 10  may be used to complete assembly operations. Equipment such as releasable liner application tool  70  may, if desired, be used to apply releasable liner layer  72  to the surface of solid pressure sensitive adhesive layer  36 . Liner  72  may be formed from a flexible sheet of polymer and may be covered with a non-stick coating to facilitate release of liner  72  from adhesive layer  36 . Tool  70  may include a manually and/or automatically controlled roller, a planar structure that presses liner  72  downwards against the surface of adhesive  36 , or other liner attachment equipment. 
     Following application of liner  72 , layer  32  may be transported to a desired location for finalizing assembly layers  26  and  32 . The presence of liner  72  may help protect the surface of pressure sensitive adhesive layer  36  during transport. 
     Before attaching layer  26  to layer  32 , liner  72  may be removed from pressure sensitive adhesive layer  36 . Pressure sensitive adhesive lamination tool  74  (e.g., a tool such as tool  44  of  FIG. 7 ) may then be used to perform lamination operations, thereby laminating layer  26  to layer  32 . As shown at the bottom of  FIG. 10 , the resulting assembled structure includes upper layer  26 , lower layer  32 , and an interposed layer of pressure sensitive adhesive (layer  36 ). 
     Another illustrative approach for assembling layers  26  and  32  is shown in  FIG. 11 . 
     As shown in  FIG. 11 , dam attachment tool  56  may be used to attach dam structures  58  to layer  32  before application of adhesive  36 . 
     Following attachment of dam structures  58 , liquid adhesive application tool  60  may be used to apply liquid monomer pressure sensitive adhesive precursor material to the surface of layer  32 . Because the precursor material is liquid, the precursor material will flow over structures  30  and will create a satisfactory conformal coating layer on the surface of layer  32 . 
     Prior to curing, linear application tool  70  may be used to attach release liner  72  to layer  32  on top of liquid adhesive  36 . Release liner  72  may be formed from a flexible sheet of polymer with a coating to prevent liner  72  from permanently sticking to adhesive  36 . Liner  72  of  FIG. 11  is preferably sufficiently transparent to ultraviolet light to allow ultraviolet light to pass through liner  72  to underlying adhesive  36  during curing operations. 
     To promote planarity in the surface of pressure sensitive adhesive layer  36 , equipment  88  may press a planar member downwards onto the top of layer  72  and adhesive  36  during curing operations. Equipment  88  may be flattening (planarization) equipment such as manual or computer-controlled equipment that uses positioners  84  and clear plate  86  to press downwards on layer  72 . Plate  86  may be formed from a layer of material such as fused silica, a layer of transparent ceramic, plastic, or glass, or other clear planar structure. When pressed downwards against the surface of adhesive layer  36 , the surface of adhesive layer  36  may be planarized. While being flattened by plate  86  in this way, adhesive curing equipment such as ultraviolet light source  80  may be used to illuminate liquid adhesive layer  36  with ultraviolet light  82 . Light  82  may pass through transparent plate  86  and release liner  72 . The application of light  82  or other suitable curing stimulus (e.g., heat) may promote cross linking of the monomers in the liquid adhesive layer to form a solid polymer pressure sensitive adhesive layer such as layer  36  at the bottom of  FIG. 11 . 
     Assembly of layers  26  and  32  may then be completed using lamination tool  74 , as shown in  FIG. 10 . 
     The assembled structures that include layers  26  and  32  (and any additional structures that are attached to these layers) may be assembled into finished electronic devices  10  such as devices  10  of  FIGS. 1 and 2 . Because thin pressure sensitive adhesive layers  36  and layers  36  that are not excessively soft may be used in attaching layers  26  and  32  together, devices  10  may be more compact and/or may contain stronger adhesive bonds than devices formed using conventional pressure sensitive adhesive lamination techniques. 
     If desired, trimming operations such as laser trimming operations may involve forming a cut in adhesive  36  that allows substantially all of dam structure  58  to be removed during trimming. This type of trimming operation is shown in  FIG. 12 . 
     Initially, dam structure  58  may be formed on layer (e.g., using dam attachment tool  56  of  FIG. 11 ). Following attachment of dam structure  58 , a dispensing tool such as liquid adhesive application tool  60  may be used to apply liquid monomer pressure sensitive adhesive precursor material to the surface of layer  32 . Because the precursor material is liquid, the precursor material will flow over structures  30  and will create a satisfactory conformal coating layer on the surface of layer  32 . Dam structure  58  may help contain the liquid adhesive material around the edges of layer  32 . 
     Layer  36  may then be planarized and cured. For example, planarization operations may be performed using a pressurized liner of the type described in connection with  FIG. 11 . Curing may be performed using a UV lamp (e.g., lamp  80  of  FIG. 11 ). 
     As part of the planarization process (e.g., when pressing downwards on liner  72  of  FIG. 11 , some of adhesive  36  may be forced laterally outward over the edge of dam structure  58 , forming portion  36 T of  FIG. 12 . 
     As shown in  FIG. 12 , a laser beam such as beam  100  may be applied using laser trimming equipment. The laser beam may be applied along the innermost edge of dam structure  58  to remove portion  102  of adhesive layer  36  (and possibly portions of the inner edge of dam structure  58 ). By cutting through adhesive layer  36 , portion  36 T of adhesive layer  36  and dam structure  58  may be trimmed away from the rest of layer  36 . Following removal of the trimmed away portion of dam structure  58  and adhesive portion  36 T, a trimmed version of layer  36  may remain on layer  32 . Because dam structure  58  has been removed from layer  32 , dam structure  58  will not interfere with subsequent lamination operations. 
     If desired, layer  36  may be planarized by depositing layer  36  in multiple thinner sublayers rather than a single layer. The use of multiple sublayers may help each sublayer flow to conform to underlying surface topology, resulting in a smooth flat surface for the resulting composite layer formed from the multiple sublayers. 
     The use of multilayer adhesive dispensing techniques to flatten layer  36  is illustrated in  FIG. 13 . In the example of  FIG. 13 , a first dispensing and curing cycle has been used to deposit adhesive layer  36 A. Following formation of sublayer  36 A, one or more additional liquid adhesive dispensing and curing operations may be used to form additional sublayers such as sublayer  36 B. There may be, for example, two or more sublayer deposition cycles, three or more sublayer deposition cycles, four or more sublayer deposition cycles, etc. Sublayers may be dispensed using liquid adhesive application tools such as screen printing equipment, valves, etc. Curing may be performed using UV lamps or other equipment. Multilayer planarization operations of the type illustrated in  FIG. 13  may be performed using equipment  38  and  40  of  FIG. 7 , may be used to perform flattening as described in connection with tool  48  of  FIG. 8 , may be used to implement the leveling and curing operations of tool  62  of  FIG. 9 , or may otherwise be used in flattening adhesive layer  36 . 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.

Metadata:
Filing Date: 20111216
Publication Date: 20160223
Grant Date: 20160223
Priority Date: 20111216
Inventors: KROGDAHL JAMES R.
CUSEO JAMES M.
Assignee: APPLE INC
CPC Classifications: [{"code": "B32B2305/34", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y10T156/1002", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B37/1284", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B37/003", "inventive": true, "first": true, "tree": "[]"}, {"code": "B32B2457/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B37/003", "inventive": true, "first": true, "tree": "[]"}, {"code": "B32B37/1284", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y10T156/1002", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B2305/34", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B2457/00", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 48608911