PATENT DOCUMENT

Publication Number: US-9815259-B2
Application Number: US-201414334416-A
Country: US
Kind Code: B2

Title: Reworkable adhesive tape for joining device structures

Abstract:
Double-sided reworkable pressure sensitive adhesive tape joins electronic device structures. The reworkable pressure sensitive adhesive tape has a pair of polymer carrier layers that are attached to each other using a thermoplastic adhesive. Opposing outer surfaces of the carrier layers are coated with pressure sensitive adhesive. The thermoplastic material that is used in attaching the carriers to each has a softening temperature that allows the thermoplastic material to be softened without significantly softening the carrier layers. When the thermoplastic material is softened, the structures that have been joined using the tape may be separated from each other. This divides the tape into two tape remnants. After cooling the tape remnants to restore cohesive strength to the pressure sensitive adhesive, the tape remnants can be cleanly peeled away from the structures. Additional reworkable tape may then be used to reattach the structures.

Claims:
What is claimed is: 
     
       1. Reworkable adhesive tape, comprising:
 a first carrier comprising a first flexible polymer layer; 
 a second carrier comprising a second flexible polymer layer; 
 a thermoplastic adhesive that attaches the first carrier to the second carrier, wherein the thermoplastic adhesive has a softening temperature of 50-120° C., and wherein the first and second flexible polymer layers are formed from a polymer that does not soften at temperatures below the softening temperature of the thermoplastic adhesive; 
 a first layer of adhesive on the first carrier; and 
 a second layer of adhesive on the second carrier. 
 
     
     
       2. The reworkable adhesive tape defined in  claim 1  wherein the first and second layers of adhesive are pressure sensitive adhesive layers. 
     
     
       3. The reworkable adhesive tape defined in  claim 2  further comprising first and second release liners coupled to the first and second pressure sensitive adhesive layers. 
     
     
       4. The reworkable adhesive tape defined in  claim 1  wherein the first carrier has a protruding tab. 
     
     
       5. The reworkable adhesive tape defined in  claim 1  wherein the first and second flexible polymer layers are polyester films. 
     
     
       6. The reworkable adhesive tape defined in  claim 1  wherein the thermoplastic adhesive comprises polycarbonate. 
     
     
       7. The reworkable adhesive tape defined in  claim 6  wherein the thermoplastic adhesive is elastomeric. 
     
     
       8. The reworkable adhesive tape defined in  claim 1  wherein the first and second carriers, the thermoplastic adhesive, and the first and second layers of adhesive exhibit a temperature gradient when heated. 
     
     
       9. A method, comprising:
 attaching first and second electronic device structures together using double-sided reworkable pressure sensitive adhesive tape having first and second flexible polymer carrier films each having a thickness of 2-50 microns, having a thermoplastic adhesive that attaches the first and second flexible polymer carrier films together, having a first pressure sensitive adhesive layer on the first flexible polymer carrier film, and having a second pressure sensitive adhesive layer on the second flexible polymer carrier film; 
 heating the reworkable pressure sensitive adhesive tape to soften the thermoplastic adhesive; and 
 separating the first and second electronic device structures by pulling apart the tape while the thermoplastic adhesive is softened so that the reworkable pressure sensitive adhesive tape divides along the thermoplastic adhesive into first and second reworkable pressure sensitive adhesive tape remnants. 
 
     
     
       10. The method defined in  claim 9  wherein attaching the first and second electronic device structures together comprises pressing together the first and second electronic device structures. 
     
     
       11. The method defined in  claim 10  wherein heating the reworkable pressure sensitive adhesive tape comprises applying localized heat to the reworkable pressure sensitive adhesive tape using equipment selected from the group consisting of: infrared heating equipment and inductive heating equipment. 
     
     
       12. The method defined in  claim 11  wherein the first electronic device structure is a display cover layer, wherein the second electronic device structure is an electronic device housing, and wherein heating the reworkable pressure sensitive adhesive tape comprises creating a temperature gradient so that the display cover layer is hotter than the electronic device housing while the thermoplastic adhesive is being softened. 
     
     
       13. The method defined in  claim 9  further comprising:
 cooling at least the first reworkable pressure sensitive adhesive tape remnant to restore cohesive strength to the first pressure sensitive adhesive layer after heating the reworkable pressure sensitive adhesive tape. 
 
     
     
       14. The method defined in  claim 13  further comprising cleanly peeling at least the first reworkable pressure sensitive adhesive tape remnant from the first electronic device structure after cooling the first reworkable pressure sensitive adhesive tape remnant. 
     
     
       15. The method defined in  claim 14  further comprising reattaching the first and second electronic device structures together with additional reworkable pressure sensitive adhesive tape. 
     
     
       16. Apparatus, comprising:
 reworkable pressure sensitive adhesive tape having first and second flexible polymer carrier films each having a thickness of 2-50 microns, a thermoplastic adhesive that attaches the first flexible polymer carrier film to the second flexible polymer carrier film, a first pressure sensitive adhesive layer on the first flexible polymer carrier film, and a second pressure sensitive adhesive layer on the second flexible polymer carrier film, wherein the thermoplastic adhesive has a softening temperature and wherein the first and second polymer carrier films are formed from a polymer that does not soften at temperatures below the softening temperature of the thermoplastic adhesive; 
 a first electronic device structure; and 
 a second electronic device structure that is attached to the first electronic device structure by the reworkable pressure sensitive adhesive tape. 
 
     
     
       17. The apparatus defined in  claim 16  wherein the first electronic device structure comprises a display cover layer. 
     
     
       18. The apparatus defined in  claim 16  wherein the second electronic device structure comprises an electronic device housing. 
     
     
       19. The apparatus defined in  claim 16  wherein at least the first flexible polymer carrier film has a tab that protrudes from between the first and second electronic device structures. 
     
     
       20. The apparatus defined in  claim 16  wherein the softening temperature is 80-100° C.

Description:
This application claims the benefit of provisional patent application No. 61/905,485, filed Nov. 18, 2013, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to adhesive and, more particularly, to reworkable adhesive tape structures for joining structures such as electronic device structures. 
     Devices such as cellular telephones, computers, displays, and other electronic equipment contain structures that are joined using adhesive. Adhesive is often dispensed in the form of double-sided adhesive tape. 
     Faults are sometimes detected when manufacturing an electronic device. For example, a faulty component may be identified or an assembly operation may be performed imperfectly. In some situations, faults may be serious enough that a device must be scrapped. In other situations, it is possible to rework a device and thereby salvage unaffected components. During rework operations, a faulty component can be replaced with a defect-free component. 
     The ability to easily rework a device can often lead to substantial improvements in assembly efficiency. In contrast, a device design that is difficult to rework may result in the need to scrap an undesirably large number of devices. 
     To ensure that device structures are satisfactorily bonded together, adhesive tape is often used that can form strong adhesive bonds. To help disassemble parts that have been attached to each other using adhesive tape, the adhesive tape can be heated. This reduces the cohesive strength of the adhesive in the adhesive tape sufficiently that the parts can be pulled apart. Unfortunately, tape that is pulled apart in this way tends to leave stubborn adhesive residues on the surfaces of the disassembled parts. Before the parts can be reworked, solvents must be used to remove the adhesive residues. The use of solvents to clean the surface of the parts can be time consuming and messy. 
     It would therefore be desirable to be able to provide adhesive tape structures that facilitate rework operations during electronic device assembly. 
     SUMMARY 
     Reworkable pressure sensitive adhesive tape may be used to attach structures together. For example, a display cover layer may be attached to a device housing using reworkable adhesive tape or other electronic device structures may be bonded to each other using reworkable adhesive tape. The tape may be debonded by localized application of heat when it is desired to rework the device structures. 
     The reworkable pressure sensitive adhesive tape may have a pair of flexible polymer carrier layers that are attached to each other using a thermoplastic adhesive. Opposing outer surfaces of the carrier layers may be coated with pressure sensitive adhesive. The pressure sensitive adhesive may be used in attaching structures together such as electronic device structures. 
     The thermoplastic material that is used in joining the flexible polymer carrier layers to each other may have a softening temperature that allows the thermoplastic material to be softened without softening the carrier layers. For example, the thermoplastic material may have a softening temperature of 80-100° C., whereas the carrier layers may be formed from a flexible polymer that does not soften at temperatures below 100° C. 
     When bonding two structures together, the pressure sensitive adhesive on a first of the pair of carriers may be attached to a first of the structures and the pressure sensitive adhesive on a second of the pair of carriers may be attached to a second of the structures. 
     When the thermoplastic material is softened, the bonded structures can be separated from each other. During this process, the tape may be divided into two pieces, one of which remains attached to the first of the structures and the other of which remains attached to the second of the structures. The tape remnants can be removed from the first and second structures to facilitate rework. Cooling the tape remnants restores cohesive strength to the pressure sensitive adhesive on the tape remnants, allowing the tape remnants to be cleanly peeled away from the structures. Additional reworkable tape may then be used to reattach the structures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device such as a laptop computer with structures that are attached using adhesive tape in accordance with an embodiment. 
         FIG. 2  is a perspective view of an illustrative electronic device such as a handheld electronic device with structures that are attached using adhesive tape in accordance with an embodiment. 
         FIG. 3  is a perspective view of an illustrative electronic device such as a tablet computer with structures that are attached using adhesive tape in accordance with an embodiment. 
         FIG. 4  is a perspective view of an illustrative electronic device such as a display for a computer or television with structures that are attached using adhesive tape in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of illustrative electronic device structures that are attached using adhesive tape in accordance with an embodiment. 
         FIG. 6  is a cross-sectional side view of illustrative double-sided thermally debondable adhesive tape in accordance with an embodiment. 
         FIG. 7  is a cross-sectional side view of electronic device structures being attached to each other using reworkable adhesive tape such as the tape of  FIG. 6  in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view of the illustrative structures of  FIG. 7  after separating the structures from each other by performing thermal debonding operations on the reworkable adhesive tape in accordance with an embodiment. 
         FIG. 9  is a cross-sectional side view of one of the illustrative structures of  FIG. 8  in which an adhesive tape remnant that remained on the surface of the structure following thermal debonding operations is being peeled from the surface to facilitate rework in accordance with an embodiment. 
         FIG. 10  is a diagram of illustrative equipment for dispensing thermoplastic between flexible polymer carrier layers for use in forming an adhesive tape in accordance with an embodiment. 
         FIG. 11  is a diagram of illustrative equipment for coating opposing upper and lower surfaces of a tape structure of the type shown in  FIG. 10  to form adhesive tape in accordance with an embodiment. 
         FIG. 12  is a diagram of illustrative heat-based debonding equipment for selectively raising the temperature of different parts of an electronic device assembly to thermally debond adhesive tape in accordance with an embodiment. 
         FIG. 13  is a perspective view of an illustrative electronic device having portions that are being selectively heated using an inductive heating apparatus for thermally debonding adhesive tape in accordance with an embodiment. 
         FIG. 14  is a cross-sectional side view of structures in an electronic device that have been attached to each other using adhesive tape during a thermal debonding process showing how thermal gradients may arise across the adhesive tape in accordance with an embodiment. 
         FIG. 15  is a diagram showing how electronic device structures may be attached to each other using adhesive tape and showing how the structures may be reworked in accordance with an embodiment. 
         FIG. 16  is a flow chart of illustrative steps involved in attaching electronic structures together using adhesive tape and in reworking the attached electronic device structures by removing the adhesive tape and applying new adhesive tape in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Structures such as electronic device structures may be attached to each other using welds, solder, screws and other fasteners, and adhesive. Adhesive may be advantageous for forming compact and inexpensive bonds. For example, adhesive may be used in attaching electronic device structures to each other in situations in which device bulk is to be minimized and in which it is desired to avoid the cost and complexity of alternative fastening mechanisms. 
     It is often desirable to attach structures with adhesive tape. Adhesive tape includes a flexible layer, sometimes referred to as a carrier or substrate. Pressure sensitive adhesive can be used to coat a single carrier surface or double-sided tape can be formed by coating opposing carrier surfaces with pressure sensitive adhesive. In many applications, pressure sensitive adhesive tapes are preferred to other adhesives due to ease of application. For example, pressure sensitive adhesive tapes such as double-sided tapes can be used to attach electronic device structures together in situations in which liquid or sprayed adhesives might be difficult to control. 
     Component and assembly defects are sometimes detected during manufacturing, necessitating rework. For example, testing may reveal that two device structures are not aligned as accurately as desired. It may therefore be desirable to correct the misalignment. As another example, a manufacturer may desire to replace a component that has been incorporated within a partly or fully assembled device with a fresh component. Devices may sometimes be reworked in the field after being sold to an end user. For example, devices may be repaired by service personnel. 
     Rework operations such as these may involve debonding adhesive tape joints. Rework operations can be facilitated by incorporating a thermoplastic layer into the middle of an adhesive tape stack-up. When it is desired to rework an adhesive tape joint, heat may be applied to the joint. The heat softens the thermoplastic layer sufficiently to debond the joint, thereby permitting structures that were attached to each other by the adhesive tape to be separated from each other. Following cooling, remnants of the adhesive tape may be peeled off of the structures. Cooling of the adhesive tape to room temperature after debonding operations helps to restore the cohesive strength of the pressure sensitive adhesive, which allows the tape to be peeled off cleanly, without leaving behind patches of pressure sensitive adhesive. The use of solvents can therefore be reduced or even eliminated. 
     Illustrative electronic devices of the types that may be provided with structures that are joined using adhesive tape are shown in  FIGS. 1, 2, 3, and 4 . 
     Electronic device  10  of  FIG. 1  has the shape of a laptop computer and has upper housing  12 A and lower housing  12 B with components such as keyboard  16  and touchpad  18 . Device  10  has hinge structures  20  (sometimes referred to as a clutch barrel) to allow upper housing  12 A to rotate in directions  22  about rotational axis  24  relative to lower housing  12 B. Display  14  is mounted in housing  12 A. Upper housing  12 A, which may sometimes be referred to as a display housing or lid, is placed in a closed position by rotating upper housing  12 A towards lower housing  12 B about rotational axis  24 . 
       FIG. 2  shows an illustrative configuration for electronic device  10  based on 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  26  and speaker port  28 . 
     In the example of  FIG. 3 , electronic device  10  is a tablet computer. In electronic device  10  of  FIG. 3 , housing  12  has opposing planar front and rear surfaces. Display  14  is mounted on the front surface of housing  12 . As shown in  FIG. 3 , display  14  has an opening to accommodate button  26 . 
       FIG. 4  shows an illustrative configuration for electronic device  10  in which device  10  is a computer display, a computer that has an integrated computer display, or a television. Display  14  is mounted on a front face of housing  12 . With this type of arrangement, housing  12  for device  10  may be mounted on a wall or may have an optional structure such as support stand  30  to support device  10  on a flat surface such as a table top or desk. 
     Display  14  may be a liquid crystal display, an organic light-emitting diode display, a plasma display, an electrophoretic display, an electrowetting display, a display using other types of display technology, or a display that includes display structures formed using more than one of these display technologies. If desired, a touch sensor may be incorporated into display  14 . 
     Adhesives may be used in attaching together structures within equipment such as electronic devices  10  of  FIGS. 1, 2, 3, and 4  and other electronic devices. Adhesives such as pressure sensitive adhesives may be dispensed using flexible carrier substrates. For example, reworkable pressure sensitive adhesive tape (sometimes referred to as pressure sensitive tape) may be used to couple together plastic structures, metal structures, glass structures, ceramic structures, display structures, housing structures, internal device structures, electrical components in the interior of an electronic device, other structures, or combinations of these structures. Examples of pressure sensitive adhesives include acrylic pressure sensitive adhesives and silicone pressure sensitive adhesives. Other types of pressure sensitive adhesive may be used in forming a reworkable pressure sensitive adhesive tape if desired. 
     Adhesive tape may be provided with flexible carriers such as one or more flexible polymer layers. Examples of polymers that may be used as tape carriers include polyester film (i.e., polyethylene terephthalate) and polyimide. Other polymer layers that may be used as pressure sensitive adhesive tape carriers may be used if desired. Tape may be dispensed in the form of elongated strips, in ring shapes (e.g., die cut circular or rectangular rings with open centers), L-shaped and C-shaped patterns, circles, squares, other solid shapes, or other suitable shapes. 
     If desired, non-stick release liners may be coupled to the exposed surfaces of pressure sensitive adhesive tapes. Release liners may facilitate tape handling during manufacturing. The release liner(s) on an adhesive tape structure may be removed just prior to use of the adhesive tape structure in attaching structures in an electronic device together. 
       FIG. 5  is a cross-sectional side view of a portion of an illustrative electronic device in which pressure sensitive adhesive tape is being used to attach device structures to each other. As shown in  FIG. 5 , device  10  may include display cover layer  32  and housing  12 . Display cover layer  32  may be a layer of clear glass, a transparent plastic layer, or other display structure for display  14 . Housing  12  may be a machined metal housing (e.g., an aluminum housing or stainless steel housing), a plastic housing (e.g., a molded plastic housing and/or a plastic housing with housing surfaces formed by machining, etc.), a ceramic housing, a glass housing, or other suitable housing for device  10 . If desired, display cover layer  32  may be provided with an opaque masking layer such as opaque masking layer  34 . Opaque masking layer  34  may be formed in peripheral inactive area IA of display  14 . Opaque masking layer  34  may be, for example, a coating of ink such as black ink or white ink or other opaque material. 
     Reworkable (debondable) pressure sensitive adhesive tape  36  may be interposed between display cover layer  32  and housing  12  and may be used in attaching display cover layer  32  or other display structures to housing  12 . Pressure sensitive adhesive tape  36  may include a thermoplastic layer that is heated when it is desired to debond tape  36  and thereby separate bonded structures from each other such as display cover layer  32  and housing  12 . 
     Reworkable pressure sensitive adhesive tape  36  may have multiple layers of material.  FIG. 6  is a cross-sectional side view of an illustrative segment of pressure sensitive adhesive tape  36 . As shown in  FIG. 6 , opposing first and second sides of tape  36  (i.e., the outer surfaces of tape  36 ) may be coated with pressure sensitive adhesive such as pressure sensitive adhesive layer  38  and opposing pressure sensitive adhesive layer  46 , thereby forming a double-sided tape. Tape  36  may contain first and second carrier (substrate) layers formed from flexible materials such as flexible sheets of polymer. Tape  36  may, for example, have first flexible polymer carrier  40  and second flexible polymer carrier  44 . Pressure sensitive adhesive layer  38  may be deposited as a coating on flexible polymer carrier  40 . Pressure sensitive adhesive layer  46  may be deposited on flexible polymer carrier  44 . 
     Flexible polymer carriers  40  and  44  may be attached to each other using a layer of thermoplastic adhesive such as thermoplastic layer  42 . Thermoplastic adhesive layer  42  may be formed from a material such as polyurethane (i.e., thermoplastic polyurethane), polyester, ethylene-vinyl acetate, polyamide, polycarbonate, silicone, ethylene-acrylate, styrene block copolymers, etc. 
     The total thickness T of tape  36  may be 50-400 microns, 100-200 microns, 150-200 microns, more than 50 microns, less than 400 microns, less than 200 microns, more than 100 microns, or other suitable thickness. The thickness of pressure sensitive adhesive layer  38  may be about 10 microns (e.g., 2-50 microns). Pressure sensitive adhesive layer  46  may be about 10 microns (e.g., 2-50 microns). Flexible polymer carrier layers  40  and  44  may each be about 10-20 microns (e.g., 2-50 microns). Thermoplastic layer  42  may have a thickness of about 20 microns (e.g., 2-200 microns, 2-50 microns, or other suitable thickness). 
     The material that is used for thermoplastic layer  42  may be rigid or elastomeric. If desired, the thickness and elasticity of layer  42  may be selected so that tape  36  forms a cushion in the event of an unexpected impact event such as when device  10  is unexpectedly dropped onto a hard surface. 
     Thermoplastic layer  42  preferably has a softening temperature that allows tape  36  to be separated into two pieces by applying heat without over-heating surrounding device structures or other portions of tape  36 . Thermoplastic layer  42  may, for example, have a softening temperature of 80-100° C., 50-120° C., less than 100° C., or less than 90° C. (as examples). When tape  36  is raised to a temperature that is sufficient to soften thermoplastic layer  42  and thereby allow tape  36  to be pulled apart, the remaining portions of tape  36  remain intact (e.g., carriers  40  and  44  will not soften significantly while thermoplastic layer  42  is being heated sufficiently to soften). If, for example, layer  42  has a softening temperature of 100° C., carriers  40  and  44  may be formed form a material that does not exhibit a softening temperature below 100° C. 
     With a configuration of the type shown in  FIG. 6 , tape  36  facilitates rework (e.g., rework such as repair during manufacturing or in the field that involves disassembling structures that have been bonded together using adhesive by debonding the adhesive). Illustrative operations involved in performing rework operations with tape  36  are shown in  FIGS. 7, 8, and 9 . 
     As shown in the example of  FIG. 7 , tape  36  may be used to attach together a pair of electronic device structures such as structures  48  and  50 . Structures  48  and  50  may be structures such as a display cover glass, a housing formed from metal, glass, ceramic, plastic, carbon fiber or other fiber-based composite, or a combination of such housing materials, a metal member, a glass member, a plastic member, other structures in device  10  formed from materials such as metal, glass, ceramic, plastic, carbon fiber or other fiber-based composite, or a combination of such materials, electronic components, internal device structures, internal frame structures, housing midplate members, etc. 
     Initially, structures  48  and  50  may be attached together by pressing structures  48  and  50  towards each other in directions  52  and  54 , respectively. Pressure sensitive adhesive tape  36  may be interposed between structures  48  and  50  so that pressure sensitive adhesive tape  36  is compressed between structures  48  and  50  when structures  48  and  50  are pressed towards each other. Structures  48  and  50  may be pressed together manually and/or using computer-controlled assembly equipment. Sufficient pressure may be used to press structures  48  and  50  together to form pressure sensitive adhesive bonds between pressure sensitive adhesive layer  38  and the adjacent surface of structure  48  and between pressure sensitive adhesive layer  46  and the adjacent surface of structure  50 . 
     To facilitate removal of tape remnants from structures  48  and  50  following thermal debonding, carrier layers  40  and  44  may be provided with one or more protrusions such as tabs  40 T and  44 T. Tabs  40 T and  44 T may protrude out from between structures  48  and  50  and may be configured to be manually grasped and/or engaged using computer-controlled equipment during tape remnant removal operations. 
     When it is desired to rework the assembly of  FIG. 7  (e.g., to permit repair or replacement of structures  48  and/or  50  and/or other structures within device  10  such as structures that would otherwise be obstructed due to the attachment of structures  48  and/or  50 ), heat may be applied to tape  36 . The applied heat is used to raise the temperature of thermoplastic layer  42  above its softening temperature without raising the temperature of carrier layers  40  and  44  sufficiently to soften carrier layers  40  and  44  significantly (i.e., layers  40  and  44  do not exhibit a softening temperature equal to or below the softening temperature o thermoplastic layer  42 ). As shown in  FIG. 8 , once thermoplastic layer  42  has been sufficiently softened, structures  48  and  50  may be pulled apart in directions  56  and  58 , respectively. This divides tape  36  into two portions such as first portion  36 - 1  and second portion  36 - 2 . Portions  36 - 1  and  36 - 2  may sometimes be referred to as tape remnants. 
     As shown in  FIG. 8 , tape portion  36 - 1  includes pressure sensitive adhesive layer  38 , flexible polymer carrier  40 , and first portion  42 - 1  of thermoplastic layer  42 . Tape portion  36 - 2  includes pressure sensitive adhesive layer  46 , flexible polymer carrier layer  44 , and second portion  42 - 2  of thermoplastic layer  42 . Portions  42 - 1  and  42 - 2  may form divided thermoplastic layers on opposing surfaces of layers  40  and  44 , respectively. Thermoplastic  42  may be sufficiently soft and liquid that thermoplastic  42  does not offer substantial resistance when pulling apart structures  48  and  50 , thereby reducing the possibility of damage during disassembly. Debonding the joint formed by tape  36  in this way helps ensure that structures  48  and  50  will not be subjected to excessive forces when being separated from each other. 
     After structures  48  and  50  have been separated, tape remnants  36 - 1  and  36 - 2  may be cooled. For example, tape remnants  36 - 1  and  36 - 2  may be cooled to room temperature or a temperature below room temperature. To cool separated tape structures such as remnants  36 - 1  and  36 - 2  to a reduced temperature, remnants  36 - 1  and  36 - 2  may be placed in a cooled chamber, may be cooled with application of a gas or liquid, may be placed on a cooled plate, or may otherwise by lowered in temperature. 
     Lowering the temperature of tape remnants  36 - 1  and  36 - 2  after structures  48  and  50  have been separated restores the cohesive strength of pressure sensitive adhesive layers  38  and  46  (e.g., the cohesive strength of the pressure sensitive adhesive may be returned to its original level prior to thermal debonding operations). This helps the material of layers  38  and  46  hold together as tape remnants  36 - 1  and  36 - 2  are being removed from structures  48  and  50 . Tape remnants  36 - 1  and  36 - 2  may be removed from structures  48  and  50  by peeling tape remnants  36 - 1  and  36 - 2  away from the surfaces of structures  48  and  50  using tabs  40 T and  44 T, respectively. During peeling operation, the cohesive strength of the pressure sensitive adhesive helps cleanly remove pressure sensitive adhesive material from the structures to which the pressure sensitive adhesive was attached, thereby helping to minimize or eliminate the need to use solvents to clean the surfaces from which the tape is being peeled. An illustrative example is shown in  FIG. 9  in which tape remnant  36 - 2  is being peeled off of structure  50  by pulling tab  44 T of flexible polymer carrier in direction  60  away from surface  62  of structure  50 . 
     Once the surfaces of structures  48  and  50  have been cleaned of pressure sensitive adhesive and other materials associated with tape remnants  36 - 1  and  36 - 2  and after structures  48  and/or  50  and/or other structures in device  10  have been repaired (e.g., replaced with new structures, etc.), a new piece of reworkable pressure sensitive adhesive tape  36  may be used to attach structures  48  and  50  together. 
     Reworkable pressure sensitive adhesive tape  36  may be formed using roll-based processing equipment of the type shown in  FIGS. 10 and 11 . 
       FIG. 10  is a cross-sectional side view of equipment that may be used in forming thermoplastic layer  42  between flexible polymer carriers  40  and  44 . Roller  64  may dispense a flexible sheet of polymer such as layer  40  by rotating in direction  68  about roller axis  66 . Roller  70  may dispense a flexible sheet of polymer such as layer  44  by rotating in direction  74  about roller axis  72 . Heated dispensing head  76  may dispense molten thermoplastic adhesive that pools into pool  78  on the surface of layer  46 . As layers  42  and  44  are fed in direction  84 , melted thermoplastic  78  thins to form layer  80 . Layer  80  may be, for example, a solid homogeneous layer that is substantially free from voids (bubbles). As shown in  FIG. 10 , layer  80  is received between layers  40  and  44  as carriers  40  and  44  are moved in direction  84 . Upon cooling below the softening temperature of the thermoplastic adhesive, layer  80  forms a solid flexible thermoplastic layer  42  that attaches layers  40  and  44  to each other. 
     The coating equipment of  FIG. 11  may be used to deposit pressure sensitive adhesive onto the surfaces of layers  40  and  44 . As shown in  FIG. 11 , as layers  40 ,  42 , and  44  of tape  36  are passed through coating tool  82  in direction  84 , coating tool  82  deposits pressure sensitive adhesive layer  38  onto carrier  40 . As layers  38 ,  40 ,  42 , and  44  pass through coating tool  88  in direction  86 , coating tool  88  deposits pressure sensitive adhesive layer  46  onto carrier  44 . Coating equipment such as tools  82  and  88  may process tape layers that have been previously wound onto a roll at the output of the equipment of  FIG. 10  (as an example). 
       FIG. 12  is a diagram of infrared heating equipment of the type that may be used to heat tape  36  during debonding operations. In the example of  FIG. 12 , structure  48  is attached to structure  50  using a ring of adhesive tape  36  that runs along the periphery of structures  48  and  50 . As shown in  FIG. 12 , infrared heating equipment  102  includes infrared light source  90  and mask  98 . Mask  98  may be formed using heat blocking materials such as metal. Mask  98  may have openings such as openings  94 . Infrared light source  90  produces infrared light (heat)  92 . Infrared light rays such as rays  100  are blocked by the presence of mask  98  and do not reach structures  48  and  50 . Because rays  100  are blocked, the central portions of structures  48  and  50  are not unnecessarily heated and exposed to elevated temperatures. Other rays of infrared light  92  such as rays  96  pass through one or more openings  94  in mask  98  and heat tape  36  and adjacent portions of structures  48  and  50 . The mask opening shape associated with the openings in mask  98  define the pattern of infrared light  96  reaching tape  36 . The patterned infrared light forms a localized heat source that selectively heats only associated portions of structures  48  and  50  that are adjacent to tape  36 . 
     Another heat source that may be used to selectively apply heat to desired portions of structures  48  and  50  so that tape  36  is heated effectively for debonding operations while minimizing excess heating of structures  48  and  50  that do not overlap tape  36  is shown in  FIG. 13 . In the example of  FIG. 13 , structures  48  and  50  are rectangular structures that are coupled using a ring of pressure sensitive adhesive tape  36 . Inducting heating equipment such as inductive coil  104  applies localized heat to tape  36  by inductively heating adjacent portions of conductive structures  48  and/or  50 . For example, in a configuration in which structure  50  is a metal housing structure in device  10  such as housing  12 , coil  104  will create heat in the portions of housing  12  under coil  104 . The inductive heating of the structures adjacent to tape  36  such as metal housing  12  raises the temperature of tape  36  when a drive signal is applied to coil  104 . Coil  104  may have a shape such as the rectangular shape of  FIG. 13  to debond a rectangular ring of adhesive tape  36  or may have other suitable shapes for locally heating selected portions of structures  48  and  50  and tape  36 . 
     During application of heat, temperature gradients may be formed through structures  48  and  50  and tape  36 . These temperature gradients can be characterized based on known factors such as the materials used to form structures  48  and  50 , the shapes of structures  48  and  50 , and the amount of time for which the heat is applied. If desired, temperature measurements may be made to determine the temperature to which each portion of the heated structures will rise to when localized heat is applied for a given amount of time. 
     The characterized temperature gradient behavior of the structures that are being heated can then be exploited during debonding operations to ensure that structures in device  10  are not heated excessively as thermoplastic  42  is being softened in tape  36 . Consider, as an example, the heating scenario of  FIG. 14 . In the example of  FIG. 14 , structures  48  and  50  have been attached using adhesive tape  36 . When it is desired to debond tape  36 , heat  106  (e.g., infrared light) is applied to structures  48  and  50  and tape  36  in direction  108  by infrared light source  90 . Structure  48  is closest to heat source  90 , so structure  48  is elevated to a temperature of 140° C. (in this example). Structure  48  may be, for example, a display cover glass layer or other device structure in device  10 . Layer  34  may be an opaque masking layer such as a layer of opaque ink (as an example). Because layer  34  is farther from source  90  than structure  48 , layer  34  is heated to a lower temperature such as 130° C. The layers of tape  36  are heated to temperatures that drop as a function of distance from light source  90 . For example, pressure sensitive adhesive layer  38  may be heated to a temperature of 120° C., carrier layer  40  may be heated to a temperature of 110° C., thermoplastic layer  42  may be heated to a temperature of 100° C., carrier  44  may be heated to a temperature of 90° C., and pressure sensitive adhesive  46  may be heated to a temperature of 80° C. Underlying structure  50  may be heated to a temperature of 70° C. 
     The temperature gradient in  FIG. 14  may help ensure that thermoplastic layer  42  is heated above its softening temperature while other structures are maintained at safe temperatures. For example, layer  42  may be softened to debond tape  36  by raising layer  42  to 100° C. Structure  50  may be an anodized aluminum housing structure (as an example) that has an anodized coating that is not damaged when maintained at a temperature below 80° C. (as in the  FIG. 14  example). Structure  48  may be a glass layer that can withstand elevated temperatures (e.g., temperatures of 180° C. or higher). Because structure  48  is heated to 140° C. in the  FIG. 14  example, structure  48  will not be damaged. Layer  34  may be an ink layer that is able to withstand damage if heated to less than 140° C. (e.g., to 130° C. in the  FIG. 14  example). Flexible polymer layers  40  and  44  and pressure sensitive adhesive layers  38  and  46  may withstand damage when heated to less than 130° C. (as in the  FIG. 14  example). If there were no temperature gradient in this example, heating layer  42  to 100° C. would result in heating structure  50  to 100° C., which could damage structure  50 . 
       FIG. 15  shows illustrative equipment and operations of the type that may be involved in reworking an adhesive bond formed using tape  36 . 
     As shown in  FIG. 15 , pressure may be applied to structures  48  and  50  while reworkable pressure sensitive adhesive tape  36  is interposed between structures  48  and  50 , thereby bonding structures  48  and  50  together with tape  36 . 
     Heating tool  110  may produce heat for selectively heating desired portions of device structures  48  and  50  and tape  36 . Heating tool  110  may be a hot plate, a heated chamber, an infrared heat source, an inductive heater, a laser, a lamp, a hot bar, or other heating equipment for locally heating structures  48  and  50  and tape  36 . Once thermoplastic adhesive layer  42  in tape  36  has been heated above the softening point of thermoplastic layer  42 , parts  48  and  50  may be separated from each other. During the softening of thermoplastic layer  42 , pressure sensitive adhesive layers may be heated and my temporarily lose some of their cohesive strength. 
     Following debonding operations and cooling of pressure sensitive adhesive in tape remnants  36 - 1  and  36 - 2 , adhesive removal tool  112  (e.g., a computer-controlled tape peeling machine and/or manually operated equipment) may be used to peel off tape remnants  36 - 1  and  36 - 2  from structures  48  and  50 . The cohesive strength of pressure sensitive adhesive  38  and  46  is restored by cooling the tape, so the tape can be cleanly peeled away from structures  48  and  50  without using solvent. 
     Adhesive application tool  114  (e.g., computer-controlled equipment and/or manually controlled equipment) may be used to apply a fresh layer of adhesive tape  36 ′ to join structures  48  and  50  after replacing or repairing structures  48  and/or  50  or other associated device structures. The operations of  FIG. 15  may be performed during manufacturing or in the field (e.g., at a service center). 
       FIG. 16  shows illustrative steps involved in using tape  36  to assemble and rework structures for electronic devices. 
     At step  116 , electronic device structures such as structures  48  and  50  may be bonded using reworkable pressure sensitive adhesive tape  36 . For example, pressure may be applied to structures  48  and  50  at room temperature so that a layer of tape  36  is compressed between the opposing surfaces of structures  48  and  50 . 
     During testing or use of device  10  in the field, it may be determined that part of device  10  should be repaired. To facilitate rework, debonding operations may be performed on the joint formed from tape  36 . In particular, heating equipment may selectively apply heat to tape  36  during the operations of step  118 . Heat may be applied using an infrared heat source, an inductive heater, a laser, a hot bar or hot plate or other equipment that heats objects through direct contact, or other heating equipment. Heat may be applied in localized area and/or may be applied in a way that gives rise to a thermal gradient through structures  48  and  50  and tape  36 . This allows sufficient heat to be applied to thermoplastic adhesive layer  42  of tape  36  without damaging structures  48  and  50  or other structures in device  10 . 
     During the operations of step  118 , thermoplastic adhesive layer  42  is preferably heated above its softening temperature, so that layer  42  is liquefied and/or otherwise is weakened sufficiently to allow structures  48  and  50  to be separated at step  120  without disrupting the pressure sensitive adhesive layers and carrier layers in tape  36 . The disassembly operations of step  120  involve pulling apart structures  48  and  50  along the weakened interface created by softened thermoplastic  42 . 
     At step  122 , structures  48  and  50  and the remnants of tape  36  that remain stuck to structures  48  and  50  may be cooled to room temperature or a lowered temperature. This helps ensure that the cohesive strength of the pressure sensitive adhesive in the tape remnants will be restored to its original level or higher. 
     At step  124 , tabs or other structures protruding from the carriers in the tape remnants may be pulled to peel the tape remnants cleanly off of structures  48  and  50 . 
     Once structures  48  and  50  have been separated and tape  36  has been removed, repairs may be made by replacing faulty parts with replacement parts that are defect-free or may be made by correcting problems with a faulty part or by correcting problems with the way in which a part has been incorporated into device  10 . 
     Following these rework operations, structures  48  and  50  may be reattached to each other using fresh tape  36  (step  126 ). 
     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: 20140717
Publication Date: 20171114
Grant Date: 20171114
Priority Date: 20131118
Inventors: KROGDAHL JAMES R.
Assignee: APPLE INC
CPC Classifications: [{"code": "B32B2250/02", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B27/08", "inventive": true, "first": true, "tree": "[]"}, {"code": "Y10T428/2848", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J2201/162", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J2201/606", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y10T428/24942", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B2405/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B7/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B2255/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J2201/128", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B2255/26", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B2250/24", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J2400/226", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J7/0296", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B2250/40", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J2301/302", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J2301/124", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J2301/302", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J2301/162", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J2301/162", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J2301/124", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J7/22", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y10T428/2848", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J2400/226", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B2255/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B2250/40", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J7/22", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y10T428/24942", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y10T428/24942", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y10T428/2848", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B2255/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J2400/226", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B27/08", "inventive": true, "first": true, "tree": "[]"}, {"code": "B32B2405/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B2250/24", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B2255/26", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B7/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B2405/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B27/08", "inventive": true, "first": true, "tree": "[]"}, {"code": "B32B2250/02", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B2255/26", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B7/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B2250/24", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 53173098