PATENT DOCUMENT

Publication Number: US-9335187-B2
Application Number: US-201213679699-A
Country: US
Kind Code: B2

Title: Methods for assembling devices using pressure indicator adhesives

Abstract:
Pressure indicator pressure sensitive adhesive may contain microspheres that burst and release indicator when subjected to pressure and thereby produce a detectable indication of how much pressure has been applied when forming an adhesive joint between opposing structures. Electronic device structures can be assembled using the pressure indicator pressure sensitive adhesive. A camera or other sensor may monitor joint formation. The camera can gather infrared image data, visible light image data, or ultraviolet light image data. Sensor data such as magnetic or ultrasonic sensor data can also be collected on an adhesive joint. Joint inspection can be performed on test structures and production structures and corresponding adjustments made to the joint formation process. Positioners and other equipment that compresses the pressure indicator pressure sensitive adhesive can be adjusted in real time or calibrated using information about the condition of the pressure indicator pressure sensitive adhesive.

Claims:
What is claimed is: 
     
       1. A method of forming adhesive joints, comprising:
 compressing a pressure indicator pressure sensitive adhesive between a first structure and a second structure, wherein compressing the pressure indicator pressure sensitive adhesive comprises controlling computer-controlled positioners; 
 inspecting the pressure indicator pressure sensitive adhesive to evaluate an adhesive joint formed from the pressure indicator pressure sensitive adhesive between the first structure and the second structure, wherein inspecting the pressure indicator pressure sensitive adhesive comprises capturing images of the pressure indicator pressure sensitive adhesive with a camera; and 
 analyzing information from the camera and making pressure application adjustments to the computer-controlled positioners to adjust formation of the adhesive joint based on the analyzed information. 
 
     
     
       2. The method defined in  claim 1  wherein the first structure comprises glass, wherein the second structure comprises metal, and wherein compressing the pressure indicator pressure sensitive adhesive comprises compressing the pressure indicator pressure sensitive adhesive between the glass and the metal. 
     
     
       3. The method defined in  claim 2  wherein the pressure indicator pressure sensitive adhesive includes indicator, wherein the method further comprises applying primer that contains developer to the metal, and wherein the developer interacts with the indicator during compression of the pressure indicator pressure sensitive adhesive. 
     
     
       4. The method defined in  claim 1  further comprising providing the pressure indicator pressure sensitive adhesive between the first and second structures before compressing the pressure indicator pressure sensitive adhesive, wherein providing the pressure indicator pressure sensitive adhesive comprises applying pressure sensitive adhesive containing microspheres to the first structure and applying developer to the second structure. 
     
     
       5. The method defined in  claim 1  further comprising providing the pressure indicator pressure sensitive adhesive between the first and second structures before compressing the pressure indicator pressure sensitive adhesive, wherein providing the pressure indicator pressure sensitive adhesive comprises applying pressure sensitive adhesive material that contains microspheres with indicator to at least the first structure. 
     
     
       6. The method defined in  claim 1  further comprising providing the pressure indicator pressure sensitive adhesive between the first and second structures before compressing the pressure indicator pressure sensitive adhesive, wherein providing the pressure indicator pressure sensitive adhesive between the first and second structures comprises applying adhesive tape that contains developer, pressure sensitive adhesive material, and microspheres containing indicator that is configured to react with the developer. 
     
     
       7. The method defined in  claim 1  wherein the pressure indicator pressure sensitive adhesive comprises first microspheres containing a first type of indicator and second microspheres containing a second type of indicator and wherein compressing the pressure indicator pressure sensitive adhesive comprises compressing the first type of microspheres and the second type of microspheres between the first structure and the second structure. 
     
     
       8. The method defined in  claim 7  wherein inspecting the pressure indicator pressure sensitive adhesive comprises detecting a color formed by mixing the first type of indicator and the second type of indicator. 
     
     
       9. The method defined in  claim 7  wherein inspecting the pressure indicator pressure sensitive adhesive comprises detecting a color associated with a selected one of first type of indicator and the second type of indicator. 
     
     
       10. The method defined in  claim 1  wherein the first structure comprises a layer of glass coated with a layer of visibly opaque and infrared-light-transparent material and wherein inspecting the pressure indicator pressure sensitive adhesive comprises capturing infrared images of the pressure indicator pressure sensitive adhesive through the layer of visibly opaque and infrared-light-transparent material. 
     
     
       11. The method defined in  claim 1  wherein the pressure indicator pressure sensitive adhesive comprises magnetic material and wherein inspecting the pressure indicator pressure sensitive adhesive comprises measuring the magnetic material with a magnetic sensor. 
     
     
       12. The method defined in  claim 1  wherein inspecting the pressure indicator pressure sensitive adhesive comprises disassembling the first and second structures. 
     
     
       13. The method defined in  claim 1  wherein the pressure indicator pressure sensitive adhesive comprises transparent pressure sensitive adhesive material with microspheres containing indicator and wherein inspecting the pressure indicator pressure sensitive adhesive comprises observing the microspheres through the transparent pressure sensitive adhesive material. 
     
     
       14. The method defined in  claim 1  wherein the first structure comprises glass, wherein the second structure comprises metal, and wherein compressing the pressure indicator pressure sensitive adhesive comprises compressing the pressure indicator pressure sensitive adhesive between the glass and the metal. 
     
     
       15. The method defined in  claim 1  further comprising providing the pressure indicator pressure sensitive adhesive between the first and second structures before compressing the pressure indicator pressure sensitive adhesive, wherein providing the pressure indicator pressure sensitive adhesive between the first and second structures comprises applying adhesive tape that contains developer, pressure sensitive adhesive material, and microspheres containing indicator that is configured to react with the developer, wherein the microspheres are configured to burst and release the indicator when the pressure indicator pressure sensitive adhesive is compressed between the first and second structures. 
     
     
       16. The method defined in  claim 1  further comprising providing the pressure indicator pressure sensitive adhesive between the first and second structures before compressing the pressure indicator pressure sensitive adhesive, wherein providing the pressure indicator pressure sensitive adhesive comprises applying pressure sensitive adhesive containing microspheres to the first structure and applying developer to the second structure, and wherein compressing the pressure indicator pressure sensitive adhesive comprises bringing the pressure sensitive adhesive containing microspheres into direct contact with the developer. 
     
     
       17. A method of forming adhesive joints, comprising:
 compressing a pressure indicator pressure sensitive adhesive between a first structure and a second structure; and 
 inspecting the pressure indicator pressure sensitive adhesive to evaluate an adhesive joint formed from the pressure indicator pressure sensitive adhesive between the first structure and the second structure, wherein inspecting the pressure indicator pressure sensitive adhesive comprises capturing infrared images with an infrared camera. 
 
     
     
       18. The method defined in  claim 17 , further comprising providing the pressure indicator pressure sensitive adhesive between the first and second structures before compressing the pressure indicator pressure sensitive adhesive, wherein providing the pressure indicator pressure sensitive adhesive between the first and second structures comprises applying adhesive tape that contains microspheres containing indicator that is detectable at infrared wavelengths. 
     
     
       19. A method of forming adhesive joints, comprising:
 compressing a pressure indicator pressure sensitive adhesive between a first structure and a second structure; and 
 inspecting the pressure indicator pressure sensitive adhesive to evaluate an adhesive joint formed from the pressure indicator pressure sensitive adhesive between the first structure and the second structure, wherein inspecting the pressure indicator pressure sensitive adhesive comprises capturing ultrasonic images with an ultrasonic imaging sensor.

Description:
BACKGROUND 
     This relates generally to adhesives and, more particularly, to pressure sensitive adhesives. 
     Electronic devices often include components that are assembled using adhesives. Adhesives tend to be more compact than screws and other fasteners. Adhesives such as pressure sensitive adhesives, which are a class of adhesive that can be activated by application of pressure, are easier to rework than welds. The use of pressure sensitive adhesives may also help minimize assembly complexity and materials costs. Cellular telephones and other modern electronic devices often contain numerous joints formed from pressure sensitive adhesives. 
     Although pressure sensitive adhesives offer advantages over other techniques for forming joints in electronic devices, care must be taken to ensure uniform activation in a pressure sensitive adhesive layer. If pressure is unevenly applied during assembly, a pressure sensitive adhesive joint may have weak portions that are prone to failure. 
     To ensure that pressure sensitive adhesive joints are being formed properly, manufacturers can perform spot tests using special test units. In a typical scenario, parts in a test device are assembled using layers of pressure indicator film (sometimes referred to as pressure paper). The layers of pressure indicator film exhibit color changes that are proportional to applied pressure. If the layers of pressure indicator film indicate that pressure is being applied with inadequate uniformity, remedial changes can be made to the manufacturing process. 
     It is not always possible, however, to accurately predict how pressure sensitive adhesive joints will be formed from test results obtained using pressure indicator film. There is often a poor correlation between pressure indicator film tests and the actual pressure sensitive adhesive joints that are formed in production units, because pressure indicator film tests do not measure the actual pressures experienced by the adhesive. 
     It would therefore be desirable to provide improved ways for forming and evaluating pressure sensitive adhesive joints. 
     SUMMARY 
     Pressure indicator pressure sensitive adhesive may be provided for forming adhesive joints. The pressure indicator pressure sensitive adhesive may have microspheres that contains indicator. The microspheres are configured to burst upon application of pressure to the adhesive. Developer can be incorporated into the adhesive that reacts with the indicator when the indicator is released from the microspheres. The indicator produces a detectable indication of how much pressure has been applied when forming an adhesive joint between opposing structures. For example, the indicator may produce a visible stain at the adhesive joint when the adhesive joint is formed using more than a given amount of pressure. 
     Electronic device structures can be assembled using the pressure indicator pressure sensitive adhesive. A camera or other sensor may monitor joint formation. The camera can gather infrared image data, visible light image data, or ultraviolet light image data. Sensor data such as magnetic or ultrasonic sensor data can also be collected on a joint. 
     Control circuitry and manual visual inspection can be performed on test structures and production structures. Corresponding adjustments to the adhesive joint formation process can then be made. Positioners and other equipment that compresses the pressure indicator pressure sensitive adhesive can be adjusted in real time or can be calibrated using information about the condition of the pressure indicator pressure sensitive adhesive. 
     Pressure indicator pressure sensitive adhesive may contain one type of microsphere such as a microsphere that produces a stain of a particular color upon bursting or may contain multiple types of microspheres each of which is configured to release a stain of a different color when a different respective pressure has been exceeded. 
     Further features, their nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device such as a handheld electronic device with structures that have been assembled using pressure sensitive adhesive in accordance with an embodiment. 
         FIG. 2  is a cross-sectional side view of an electronic device of the type shown in  FIG. 1  showing how pressure sensitive adhesive may be used to join structures such as a display cover layer and electronic device housing in accordance with an embodiment. 
         FIG. 3  is a cross-sectional side view of a pair of device structures being joined using a pressure sensitive adhesive layer containing indicator and an associated developer layer in accordance with an embodiment. 
         FIG. 4  is a cross-sectional side view of the structures of  FIG. 3  following joining with pressure indicator adhesive formed from the pressure sensitive adhesive material, indicator, and developer in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of device structures joined using pressure indicator adhesive in a configuration in which pressure was unevenly applied to the pressure indicator adhesive during joint formation in accordance with an embodiment. 
         FIG. 6  is a cross-sectional side view of a pressure indicator adhesive configuration based on a layer of pressure sensitive adhesive with pressure indicator microspheres in accordance with an embodiment. 
         FIG. 7  is a cross-sectional side view of a pressure indicator adhesive arrangement based on two layers of pressure sensitive adhesive with embedded pressure indicator microspheres in accordance with an embodiment. 
         FIG. 8  is a side view of a system being used to produce pressure indicator pressure sensitive adhesive in the form of flexible adhesive tape for use in joining electronic device structures in accordance with an embodiment. 
         FIG. 9  is a cross-sectional side view of a pressure indicator pressure sensitive adhesive tape formed from a single polymer backing layer in accordance with an embodiment. 
         FIG. 10  is a cross-sectional side view of a pressure indicator pressure sensitive adhesive tape formed from a pair of polymer backing layers in accordance with an embodiment. 
         FIG. 11  is side view of a system for gathering and using information from a pressure indicator adhesive in real time during formation of an adhesive joint in accordance with an embodiment. 
         FIG. 12  is a cross-sectional side view of structures being joined by a layer of adhesive having different types of pressure indicator microspheres that are configured to burst at different pressures in accordance with an embodiment. 
         FIG. 13  is a graph showing how the three different sets of pressure indicator microspheres of  FIG. 12  are configured to release indicator material at three different respective pressures in accordance with an embodiment. 
         FIG. 14  is a cross-sectional side view of a layer of adhesive having pressure indicator microspheres that are configured to release indicators such as dyes of different colors at different respective pressure thresholds in accordance with an embodiment. 
         FIG. 15  is a graph showing how a pair of indicator microspheres of the type shown in  FIG. 14  can be configured to release indicators that mix to produce a color that differs from the colors of the released indicators in accordance with an embodiment. 
         FIG. 16  is a cross-sectional side view of sensor equipment being used to monitor joint formation using pressure indicator pressure sensitive adhesive in accordance with an embodiment. 
         FIG. 17  is a flow chart of illustrative steps involved in using pressure indicator adhesive in forming adhesive bonds between device structures in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Adhesive may be used in attaching parts together such as structures formed from metal, plastic, ceramic, glass, carbon-fiber composites and other fiber-based composites, or other materials. An illustrative electronic device of the type that can be assembled using adhesive is shown in  FIG. 1 . 
     Electronic device  10  of  FIG. 1  is a handheld device such as a cellular telephone, music player, gaming device, navigation unit, or other compact device. In this type of configuration for device  10 , housing  12  has opposing front and rear surfaces. Display  14  is mounted on a front face of housing  12 . Display  14  may have an exterior layer that includes openings for components such as button  16  and speaker port  18 . 
     The configuration of  FIG. 1  in which device  10  is a small portable device is merely illustrative. In general, electronic device  10  may be a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, or other wearable or miniature device, a television, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, equipment that implements the functionality of two or more of these devices, or other electronic equipment. 
     Housing  12  of device  10 , which is sometimes referred to as a case, is formed of materials such as plastic, glass, ceramics, carbon-fiber composites and other fiber-based composites, metal (e.g., machined aluminum, stainless steel, or other metals), other materials, or a combination of these materials. Device  10  may be formed using a unibody construction in which most or all of housing  12  is formed from a single structural element (e.g., a piece of machined metal or a piece of molded plastic) or may be formed from multiple housing structures (e.g., outer housing structures that have been mounted to internal frame elements or other internal housing structures). 
     Display  14  may be a touch sensitive display that includes a touch sensor or may be insensitive to touch. Touch sensors for display  14  may be formed from an array of capacitive touch sensor electrodes, a resistive touch array, touch sensor structures based on acoustic touch, optical touch, or force-based touch technologies, or other suitable touch sensor components. 
     Display  14  for device  10  includes display pixels formed from liquid crystal display (LCD) components or other suitable image pixel structures such as image pixel structures based on organic light-emitting diodes, electrophoretic display structures, electrowetting displays, or other display technologies. 
     A display cover layer may cover the surface of display  14  or a display layer such as a color filter layer or other portion of a display may be used as the outermost (or nearly outermost) layer in display  14 . The outermost display layer may be formed from a transparent glass sheet, a clear plastic layer, or other transparent member. 
       FIG. 2  is a cross-sectional side view of device  10  of  FIG. 1  taken along line  19  and viewed in direction  21 . As shown in  FIG. 2 , display  14  is mounted in housing  12 . Display  14  has a display cover layer such as display cover layer  20  and a display module such as display module  22 . Display cover layer  20  is a clear transparent member such as a layer of clear glass or a layer of transparent plastic. Display module  22  contains liquid crystal display structures, electrowetting display structures, electrophoretic display structures, organic light-emitting diode display structures, or other display structures. Display module  22  creates images for viewer  30  in central active area AA of display  14 . Active area AA may have a rectangular shape when viewed by viewer  30  in direction  32 . 
     Inactive area IA of display  14  of  FIG. 2  surrounds active area AA. Display module  22  does not extend into inactive area IA, so images are not displayed in inactive area IA. In rectangular devices such as device  10  of  FIG. 1 , inactive area IA forms a rectangular ring. The underside of display cover layer  20  in inactive area IA is covered with a layer of opaque masking material such as ink  34 . Ink  34  may be black or white, or may have other suitable colors. The presence of ink  34  may block internal device components from view by viewer  30 . 
     Housing  12  may form an interior cavity in which electronic components and other structures are mounted. Structures  26  in the internal cavity may include electrical components such as sensors, cameras, buttons, integrated circuits, audio components, light-emitting components, and other device components. Electrical components and other components may be interconnected using one or more electrical paths such as paths formed in substrates such as substrate  24 . Substrates such as substrate  24  may be formed from plastic, printed circuit material (e.g., rigid printed circuit board material such as fiberglass-filled epoxy or flexible printed circuit substrate materials such as sheets of polyimide or other flexible layers of polymer), ceramic, or other dielectric. 
     In addition to structures such as structures  26  that are mounted to substrate  24 , device  10  may contain internal structures that are mounted to housing  12  such as structure  36  and may contain structures that are mounted to each other (with or without being attached to housing  12 ) such as structures  38  and  40 . 
     Structures  26 ,  36 ,  38 , and  40  may, in general, include electrical components, housing structures (e.g. internal housing structures such as brackets, rails, plates, or other support structures), display components, printed circuits, substrates for antennas and other devices, members formed from glass, metal, ceramic, polymers, or other structures in device  10 . 
     As shown in  FIG. 2 , structures such as structures  20 ,  12 ,  36 ,  38 ,  40 ,  26 , and  24  may be attached to one another using adhesive such as pressure sensitive adhesive  28 . Adhesive  28  preferably has pressure indicator functions to ensure that assembly operations are performed satisfactorily. Pressure sensitive adhesive with pressure indicator capabilities is sometimes referred to herein as pressure indicator pressure sensitive adhesive or pressure indicator adhesive. Pressure indication functionality may be implemented using structures that indicate how much pressure is applied to the adhesive using light-based indicator structures such as visual indicator structures, magnetic indicator structures, or indicator structures that reflect how much pressure is applied to the adhesive using other techniques. Pressure indicator adhesive may be monitored during joint formation and/or after joint formation to assess joint quality. 
       FIG. 3  is a cross-sectional side view of structures in device  10  during adhesive joint formation. Structures  50  and  52  may be any suitable structures associated with device  10  such as structures  20 ,  12 ,  36 ,  38 ,  40 ,  26 , and  24  of  FIG. 2  (as examples). In the example of  FIG. 3 , a pressure indicator adhesive joint is being formed using layers  28 A and  28 B. The configuration of  FIG. 3  uses a two-part system in which layer  28 A serves as an indicator film and layer  28 B serves as a developer film. When the two films are combined under pressure to form pressure indicator pressure sensitive adhesive joint  28 , a visible indicator or other measurable characteristic is produced that is responsive to the amount of pressure used to form the adhesive joint. 
     With one illustrative configuration for the two-part system of  FIG. 3 , layer  28 B is a developer that reacts with an indicator material in microspheres  58  or other structures in layer  28 A to form a visible stain or other detectable characteristic indicating that a given pressure has been applied to the adhesive. As shown by illustrative microsphere  58 ′, each microsphere  58  of  FIG. 3  contains indicator material  62  (e.g., a dye that reacts with developer or other material that can produce a visible stain or measureable characteristic when microspheres  58  burst). Material  62  is contained within a coating such as spherical shell  64  of microsphere  58 ′. 
     Shells such as shell  64  may be formed from a material such as polymer that bursts when subjected to more than a threshold amount of pressure. When microspheres  58  burst in this way, indicator material  62  is exposed to developer layer  28 B and forms a visible indicator such as a colored area that indicates that adhesive joint  28  has been exposed to more than the threshold amount of pressure. Due to manufacturing variations, there is generally a range of pressures over which microspheres  58  of a given type will burst. To allow precise measurement of applied pressure, microspheres  58  may, if desired, be configured to burst over a relatively narrow range of pressures. 
     When forming certain joints such as joints between metal structures, it may be desirable to pretreat exposed metal surfaces. Pretreating may be performed by coating exposed metal with a polymer-based metal primer that prepares the exposed metal for satisfactory bonding to pressure sensitive adhesive. To minimize the number of coating layers to be applied to the metal structure, layer  28 B may be formed using a combination of developer and primer (i.e., the developer can be mixed into the primer, so that both the developer and primer materials are applied as part of the same coating). If desired, primer and developer layers can also be applied separately when metal surfaces are being bonded. 
     To bond structures  50  and  52  together, structures  50  may be moved in direction  54  and/or structures  52  may be moved in direction  56 . A computer-controlled press or manually controlled press or other equipment may be used in pressing structures  50  and  52  together. The process of moving structures  50  and  52  together applies pressure to layers  28 A and  28 B. Layers  28 A and  28 B therefore combine to form pressure indicator pressure sensitive adhesive layer  28  of  FIG. 4 . 
     When sufficient pressure is applied to pressure indicator pressure sensitive adhesive  28 , a satisfactory pressure sensitive adhesive joint will be formed between structures  50  and  52  and the indicator in adhesive  28  will be activated (e.g., microspheres  58  will break to release indicator  62 , as shown in  FIG. 4 ). 
     In some situations, pressure sensitive adhesive joints may be poorly formed. For example, if parts of pressing equipment are misaligned, joints may experience more pressure in some areas than in others. As a result, adequate pressure may only be applied to adhesive  28  in part of the joint. By using pressure indicating adhesive, the locations in a joint that are experiencing inadequate pressure can be identified and appropriate action taken. For example, a press may be calibrated or other adjustments made to the manufacturing process. 
       FIG. 5  is a side view of structures  50  and  52  during the process of forming a joint with pressure indicating adhesive  28 . In the  FIG. 5  example, a relatively large amount of force  64  (e.g., an amount of force that exceeds the activation threshold of adhesive  28  and the pressure indicator in adhesive  28 ) is being exerted on portion  70  of adhesive  28 , so indicator  62  in portion  70  is activated. A relatively small amount of force  66  is being exerted on portion  72  of adhesive  28 , so portion  72  is not activated. Upon inspection, the inadequacy of the bond formed in portion  72  can be detected and corrective actions taken (e.g., by applying more pressure in region  72 ). 
     Potential problems with forming joints from pressure sensitive adhesive can be revealed by forming joints with pressure indicating adhesive in special test structures or in actual production devices such as device  10  of  FIG. 1 . As an example, a test version of device  10  can be formed that does not include black ink  34 , thereby facilitating visual inspection of pressure indicating adhesive  28  through display cover layer  20  in inactive area IA. Test units may also be formed that omit expensive (but irrelevant) components while retaining structures associated with joint formation so that these structures may be tested by forming test joints of pressure indicator pressure sensitive adhesive. In production units that include opaque layer  34 , pressure indicating adhesive  28  can be inspected by removing display cover layer  20  (e.g., by applying heat to soften adhesive  28  sufficiently to allow display cover layer  20  to be removed from housing  12 ). 
     Adhesive  28  (e.g., pressure sensitive adhesive material  60 ) may be formed from an opaque or transparent material. Opaque adhesive may be helpful in blocking light leakage in devices with displays and other light sources and may enhance device aesthetics. Transparent adhesives may facilitate inspection of activated indicator in adhesive  28 . For example, in a situation in which one or both of structures  50  and  52  is transparent, the use of transparent material in adhesive  28  may facilitate visual inspection of the adhesive joint formed from adhesive  28  through the transparent structures and the transparent adhesive material. 
     If desired, pressure indicating adhesive  28  can be formed using microspheres  58  embedded in a single layer of pressure sensitive adhesive material, as shown in  FIG. 6 . When structures  50  and  52  are moved towards each other to apply pressure to adhesive  28  of  FIG. 6 , microspheres  58  (sometimes referred to as indicator capsules) will burst and release indicator  62  (i.e., indicator  62  will stain the surfaces of structures such as structure  52  and/or structure  50 ). Developer may be incorporated into adhesive  28  to facilitate activation of the indicator material. 
     In the illustrative configuration of  FIG. 7 , pressure indicating adhesive  28  has been implemented using upper and lower layers of adhesive material  60  with embedded microspheres  58  containing indicator  62 . When structures  50  and  52  are brought together by moving structures  50  in direction  54  and/or by moving structures  52  in direction  56 , adhesive  28  will form an adhesive joint between structures  50  and  52 . Microspheres  58  that are subjected to more than a predetermined threshold amount of pressure will release indicator  62  to facilitate evaluation of the pressure experienced by adhesive  28 . Developer may be incorporated into adhesive  28  to facilitate activation of the released indicator. 
       FIG. 8  is a system diagram showing equipment of the type that may be used in forming pressure indicator adhesive  28 . Adhesive  28  may be formed on one or more carrier layers (sometimes referred to as backing layers). The carrier layers may be formed from sheets of polymer such as polyethylene terephthalate. In the illustrative configuration of  FIG. 8 , carrier  80  (e.g., a sheet of polymer) is wrapped around drum  74 . During the process of forming a tape of pressure indicator adhesive  28 , drum  74  rotates in direction  78  about rotational axis  76 . This dispenses carrier  80  in direction  88 . Carrier  80  moves past material dispensing tools  82 ,  84 , and  86 . Tools  82 ,  84 , and  86  may be, for example, spraying equipment. 
     In the example of  FIG. 8 , material dispensing tool  82  dispenses developer, material dispensing tool  84  dispenses indicator structures such as microspheres  58  filled with indicator, and material dispensing equipment  86  dispenses pressure sensitive adhesive  60  on the opposing upper and lower surfaces of carrier  80 . 
       FIG. 9  is a cross-sectional side view of a layer of pressure indicator adhesive tape  28  formed using the equipment of  FIG. 8 . Carrier layer  80  is formed from a layer of polymer. Developer  90  and indicator structures such as microspheres  58  form a mixture on the upper surface of carrier  80 . Pressure sensitive adhesive  60  may include upper layer  60 A and lower layer  60 B. Developer  90  and microspheres  58  are shown as forming a distinct layer of material in pressure indicator adhesive tape  28  of  FIG. 9 , but may form clumps of material and/or material that becomes partly or completely dispersed within pressure sensitive adhesive layer  60 A. 
     If desired, pressure indicator adhesive  28  may be formed using multiple carriers. This type of configuration is shown in the illustrative example of  FIG. 10 . In the  FIG. 10  configuration, pressure indicator adhesive tape  28  has upper carrier  80 A and lower carrier  80 B. Carriers  80 A and  80 B may be formed from flexible polymer films. A layer of developer  90  and indicator microspheres  58  may be interposed between carrier layers  80 A and  80 B. Pressure sensitive adhesive material  60  may also be interposed between carrier layers  80 A and  80 B if desired. Upper pressure sensitive adhesive layer  60 A and lower pressure sensitive adhesive layer  60 B may be formed on the upper and lower surface of carriers  80 A and  80 B, respectively. 
       FIG. 11  is a system diagram of equipment  92  that is being used to form an adhesive bond between structures  50  and  52  using pressure indicator adhesive  28 . Equipment  92  (sometimes referred to as a press) includes a press member such as member  106  that is used to exert force in direction  54  on structure  50 . If desired, press structures such as press member  106  may be included in equipment  92  to move structure  52  in direction  56 . When structures  50  and/or  52  are moved by equipment  92 , adhesive  28  is compressed between structures  50  and  52  to form an adhesive bond. 
     Computer-controlled positioners such as positioners  96  and  98  may be used in controlling the movement of press structures  106 . A light source such as light source  100  can be used to provide illumination  102 . Illumination  102  may include infrared light, visible light, and/or ultraviolet light. One or more cameras such as camera  104  capture digital images of the structures being bonded using adhesive  28 . Camera  104  may be located in a position that allows camera  104  to image adhesive  28  through one or more of structures  50  and  52 . For example, as shown in  FIG. 11 , camera  104  may be configured to view adhesive  28  through a transparent structure that forms press member  106  (or through an opening in press member  106 ), through structure  50 , through optional layer  108  on structure  50 , and through the material in adhesive  28  itself. Camera  104  may also be located in a position such as the position occupied by camera  104 ′ in  FIG. 11  to allow direct viewing of an exposed edge portion of adhesive  28 . 
     The way in which camera  104  is used to monitor the state of adhesive  28  depends on the type of light that is being produced by light source  100  and the light transmission characteristics of the structures that lie between source  100  and adhesive  28  and between adhesive  28  and camera  104 . Consider, as an example, a scenario in which light source  100  produces visible light  102 . Press member  106  in this scenario can have an opening that allows visible light  102  to reach structure  50  or may be formed from a visibly transparent material. Structure  50  can be visibly transparent. Layer  108  (e.g., a layer of opaque masking material such as material  34  of  FIG. 2 ) may be omitted to allow visible light  102  to reach adhesive  28  (e.g., structures  50  and  52  from which layer  108  is omitted may be test structures that are used only for test purposes and not for manufacturing finished products). Adhesive  28  may be opaque or may be formed from a material that is transparent in the visible spectrum to facilitate visible inspection. In this type of configuration, visible light that illuminates adhesive  28  is picked up by camera  104 , which is operating in the visible spectrum. The visible light images that are captured in this type of scenario can be used to evaluate the bond formed by adhesive  28  between structures  50  and  52 . 
     If desired, light source  100  may produce infrared light. Layer  108  may be transparent to infrared light. For example, layer  108  may be a layer of infrared ink that is opaque at visible light wavelengths to serve as opaque masking layer  34  of  FIG. 2  but that is transparent in the infrared portion of the light spectrum to allow visual inspection by camera  104  (e.g., a camera that is sensitive to infrared light). To prevent the undesired blocking of infrared light  102  in this type of inspection scenario, structure  106  may be formed from a material that is transparent to infrared light or may have an opening that allows light  102  to pass. Structures  50  (and, if desired, adhesive  28 ) may also be transparent to infrared light. 
     Ultraviolet light may also be used in inspecting adhesive  28 . To perform ultraviolet light inspection, light source  100  produces ultraviolet light  102 , camera  104  is an ultraviolet light sensitive camera, adhesive  28  preferably fluoresces under ultraviolet light illumination, and the intervening structures such as structures  50  (and, if present, optional layer  108 ) are formed from materials that are transparent to ultraviolet light. 
     Camera  104  can be configured to examine a portion of the bond formed from adhesive  28  or the can be configured to capture images of the entire bond being formed from adhesive  28 . Control circuitry  94  such as a computer or other computing equipment, microprocessors, microcontrollers, memory, and other storage and processing circuitry receives image data from camera  104  and processes this data to determine how to control equipment such as positioners  96  and light source  100 . If, for example, the right-hand portion of the bond being formed by adhesive  28  is being provided with inadequate pressure, equipment  92  may be calibrated by adjusting positioner  98  to supply additional pressure to the right-hand side of the bond. Adjustments may be made in real time while capturing images of the bond that is being formed (i.e., feedback may be provided dynamically during joint formation) or calibrating adjustments may be made after a given bond has been attempted so that subsequent bonds may be formed more satisfactorily. In a typical calibration scenario, one or more calibration units (e.g., test units) may be used calibrating equipment  92  (e.g., once per day). Following calibration, equipment  92  may be used to produce numerous production devices. 
     Microspheres  58  may be configured to burst in a narrow pressure range, there allowing indicator  62  to be activated only when a desired pressure threshold has been exceeded (i.e., pressure indicator adhesive  28  may be configured to exhibit a nearly binary behavior in which no indicator is visible below the activation threshold and in which the indicator is substantially all activated when adhesive  28  is exposed to pressures above the activation threshold). The amount of pressure to which adhesive  28  is exposed may also be revealed by incorporating microspheres  58  with different pressure release thresholds and different corresponding indicators  62  into adhesive  28 . 
     Consider, as an example, the scenario of  FIG. 12  in which adhesive  28  has been provided with three different types of microspheres  58 : red indicator microspheres R, blue indicator microspheres B, and green indicator microspheres G. Adhesive  28  includes pressure sensitive adhesive  60  and optional developer  90 . When pressure is applied to bring structures  50  and  52  together, the microspheres in adhesive  28  burst and release indicator, which may react with developer  90  (if used). 
     As shown in  FIG. 13 , the color of the indicator that is released depends on the amount of pressure that is applied to adhesive  28 . Red microspheres R are configured to burst at a relatively low value of applied pressure to adhesive  28  as indicated by curve  106  of  FIG. 13 , whereas green microspheres G are configured to burst at a relatively high value of applied pressure to adhesive  28  as indicated by curve  110  of  FIG. 13 . Blue microspheres B burst at a pressure above the activation pressure for red microspheres R and below the activation pressure for green microspheres G, as indicated by curve  108  of  FIG. 13 . Using manual visual inspection and/or using camera  104  in equipment  92 , the pressure to which adhesive  28  is exposed can be determined by evaluating the colors present in adhesive  28 . 
     In the illustrative configuration of  FIG. 14 , pressure indicator adhesive  28  has been provided with yellow and blue microspheres. As shown by curve  112  in the graph of in the graph of  FIG. 15 , yellow microspheres Y may be configured to burst at an activation pressure that is lower than blue microspheres B are configured to burst. Yellow microspheres Y and blue microspheres B in this example have been configured to exhibit an overlapping range GR of burst pressures. In range GR, most of yellow microspheres Y and some of blue microspheres B will burst, giving rise to green color in adhesive  28 . By visual inspection of adhesive  28  and/or using camera  104  of equipment  92 , the pressure level to which adhesive  28  has been exposed during bond formation can be ascertained from the color of the activated adhesive (i.e., yellow, green, or blue). 
     If desired, microspheres  58  may be provided with indicator  62  that exhibits magnetic properties or other properties that are detectable using sensors in addition to camera sensor  104  of equipment  92 . The magnetic properties or other properties may change when microspheres  58  burst (e.g., ferromagnetic indicator material may be exposed to a developer that renders the indicator non-magnetic upon release of the ferromagnetic indicator material from microspheres  58 , etc.) As shown in  FIG. 16 , equipment  92  may include sensor  104 ″ for monitoring the status of indicator  62  in adhesive  28 . Sensor  104 ″ may be a magnetic sensor for measuring the magnetism of adhesive  28 , an ultrasonic sensor for capturing ultrasonic images of adhesive  28 , or other sensor. Positioners and control circuitry may be coupled to sensor  104 ″ as described in connection with equipment  92  of  FIG. 11 , so that equipment  92  can make adjustments to the manufacturing process being used to form adhesive bond  28 . 
     Illustrative steps involved in using pressure indicator pressure sensitive adhesive in manufacturing device  10  and structures for use in device  10  are shown in  FIG. 17 . 
     At step  150 , pressure indicator adhesive  28  may be formed using equipment of the type shown in  FIG. 8  or other suitable equipment. One or more polymer carrier layers may be used in forming the pressure indicator adhesive. Pressure sensitive adhesive material may be added to the carrier layers using spraying techniques or other adhesive material application techniques. To provide adhesive  28  with pressure indicator capabilities, indicator structures such as microspheres that contain indicator may be incorporated into adhesive  28 . The microspheres may contain indicator that contain dyes or other substances that release color when the microspheres burst and/or may contain indicators that produce colors upon being released from burst microspheres and reacting with developer. Developer  90  may be incorporated into adhesive  28  and/or may be incorporated into other materials such as primer. 
     At step  152 , components to be joined such as structures  50  and  52  (e.g., structures such as structures  20 ,  12 ,  36 ,  38 ,  40 ,  26 , and  24  of  FIG. 2  or other structures to be joined by adhesive) may be assembled using adhesive  28 . Adhesive  28  (e.g., pressure indicator adhesive tape) may be implemented using a one-part system (applied to one or both surfaces to be joined) or may be implemented using a two-part system (e.g., a system in which indicator material is applied to one of the surfaces to be joined and in which developer is applied to an opposing surface to be joined). Indicator can be implemented using a material that is detectable at infrared wavelengths, that is visible in the visible wavelength portion of the light spectrum, that fluoresces when exposed to ultraviolet light, that is magnetically detectable, that exhibits detectable qualities under ultrasonic imaging, or that is otherwise measurable by human visual inspection, camera  104  or a magnetic sensor, ultrasonic imaging sensor, or other sensors (e.g., sensor  104 ″). 
     As part of the joining process of step  152 , adhesive  28  is interposed between opposing structures to be joined such as structures  50  and  52  and is subjected to pressure. A press that is operated using computer-controlled positioners may apply pressure to structures  50  and  52  to compress adhesive  28  between opposing surface of structures  50  and  52  and thereby pressure activate the pressure sensitive adhesive material that is contained within adhesive  28 . While applying pressure in this way, the indicator functions of adhesive  28  are activated. 
     The amount of activation of the pressure indicator in adhesive  28  and therefore the amount of indicator that becomes visible or otherwise exhibits a detectable indicator characteristic depends on the amount of pressure that is applied to each portion of adhesive  28 . If, for example, a portion of the joint that is being formed is exposed to sufficient pressure to burst microspheres  58  in adhesive  28 , those microspheres will release indicator and will exhibit a visible stain or other detectable activation characteristic. At the same time, if a portion of the joint that is being compressed between structures  50  and  52  is exposed to insufficient pressure to activate the pressure sensitive adhesive material and indicator material in adhesive  28 , microspheres  58  will fail to burst and the expected visible stain or other detectable activation characteristic of the pressure indicator adhesive will not be present. 
     Camera  104  and other sensors  104 ″ can monitor the activation of adhesive  28  during joint formation and/or the adhesive joint may be inspected following joint formation. Joints may be formed in production units and/or in test units. Test structures can be constructed using the same structures that are used in production structures or can be constructed using comparable structures that have been modified to facilitate inspection. As an example, if it is difficult to visually inspect a joint between display cover layer  20  and housing  12  under inactive area IA due to the presence of opaque masking layer  28  in production units, opaque masking layer  28  can be omitted in test units to provide equipment  92  with feedback on the adhesive joint formation process. Test units can also be disassembled to facilitate inspection (step  154 ). For example, test units can be disassembled by heating adhesive  28  sufficiently to allow the joint formed from adhesive  28  to be pulled apart and inspected. 
     When real-time inspection with equipment  92  reveals that the adhesive joint formed from adhesive  28  is not being formed perfectly, dynamic adjustments can be made to equipment  92 . For example, if camera  104  detects that one side of a joint is being subjected to sufficient pressure but that another side of the joint is being subjected to insufficient pressure, control circuitry  94  can direct the computer controlled positioner  98  that is being used to form the low-pressure side of the joint to apply an increased amount of pressure. In this way, the joint formation process can be continuously monitored and controlled to ensure that satisfactory adhesive joints are formed. 
     The monitoring process of step  152  (and, if desired, the post-disassembly operations of step  154 ) may use infrared images taken through infrared ink or other infrared-transparent (but visibly opaque) masking layers such as layer  34  of  FIG. 2 , using visible light, using ultraviolet light, using microspheres  58  that contain dye or other indicator that is visible upon microsphere rupturing without using developer, using microspheres  58  that contain indicator that becomes visible when microspheres  58  burst to release the indicator and thereby cause the indicator to react with developer, using microspheres that have one type (e.g., a single color) of indicator, using microspheres that contain multiple colors of indicator that are released at different respective pressures and that can color-mix upon activation, using microspheres that contain multiple colors of indicator that are configured to activate at respective discrete ranges of activation pressures (e.g., mutually exclusive ranges of activation pressures), using magnetic indicator materials, or using other suitable pressure indicator arrangements. 
     At step  156 , the results from the disassembly and inspection operations of step  154  may be used to calibrate equipment  92 . For example, if inspection of a test unit reveals that insufficient pressure is being applied on one side of a joint, equipment  92  can be adjusted so that subsequent joints that are formed on production units will be properly formed using satisfactory pressure on that side of the joint. Equipment  92  may also be calibrated using information from camera  104  or other sensors (i.e., equipment  92  can adjust how much pressure is applied using positioners  98  to ensure even pressure application). In general, pressure application adjustments made by control circuitry  94  may be made during the process of acquiring data at step  152  with camera  104  (or other sensors) and while pressure is being applied to a given joint at step  152  or may be made following application of pressure to a joint, analysis of the joint that was formed, and subsequent calibrating adjustment of the pressure application process during step  156 . 
     Production units formed during the operations of step  156  may exhibit uniform and satisfactory adhesive joint formation due to real time pressure application adjustments and/or calibration of fabrication equipment  92 . 
     The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20121116
Publication Date: 20160510
Grant Date: 20160510
Priority Date: 20121116
Inventors: MCCLURE STEPHEN R.
WRIGHT DEREK W.
PETERSON CARL R.
BABIARZ KRISTINA A.
Assignee: APPLE INC
CPC Classifications: [{"code": "C09J5/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "C09J2400/163", "inventive": false, "first": false, "tree": "[]"}, {"code": "C08K9/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J5/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "C09J7/0207", "inventive": true, "first": false, "tree": "[]"}, {"code": "C09J2205/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J2400/143", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01D11/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "C09J11/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "C09J2301/412", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J11/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "C09J7/38", "inventive": true, "first": false, "tree": "[]"}, {"code": "C09J2400/143", "inventive": false, "first": false, "tree": "[]"}, {"code": "C08K9/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J5/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "C09J11/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "C09J2400/143", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J7/38", "inventive": true, "first": false, "tree": "[]"}, {"code": "C09J2301/412", "inventive": false, "first": false, "tree": "[]"}, {"code": "C08K9/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01D11/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "C09J2400/163", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J2400/163", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 50726793