PATENT DOCUMENT

Publication Number: US-9565773-B2
Application Number: US-201414231454-A
Country: US
Kind Code: B2

Title: Methods for assembling electronic devices with adhesive

Abstract:
An electronic device may have housing structures, electrical components, and other electronic device structures. Adhesive may be used to join electronic device structures. Adhesive may be dispensed as liquid adhesive and cured to form adhesive joints. Adhesive joints may be debonded. Chain reactions may be initiated by applying a localized initiator such as a chemical or localized energy to the adhesive. Once initiated, the chain reaction may spread throughout the adhesive to cure the adhesive, to globally change adhesive viscosity, or to weaken the adhesive to facilitate debonding. Local changes to adhesive may also be made such as local increases and decreases to adhesive viscosity. Chain reaction curing may be used to cure adhesive or debond adhesive that is hidden from view within gaps in the electronic device structures. Viscosity changes may be used to control where adhesive flows.

Claims:
What is claimed is: 
     
       1. A method for attaching structures in an electronic device, comprising:
 dispensing adhesive in a gap within the structures; and 
 in a localized area of the adhesive that is uncovered by the structures, initiating a chain reaction in the adhesive that changes all of the adhesive both inside and outside of the gap, wherein initiating the chain reaction comprises applying energy to only the localized area. 
 
     
     
       2. The method defined in  claim 1  wherein applying the energy to only the localized area comprises:
 applying light to only the localized area. 
 
     
     
       3. The method defined in  claim 1  wherein applying the energy to only the localized area comprises:
 applying heat to only the localized area. 
 
     
     
       4. The method defined in  claim 1  wherein applying the energy to only the localized area comprises applying sound to only the localized area. 
     
     
       5. The method defined in  claim 1  wherein initiating the chain reaction comprises initiating an adhesive curing chain reaction that cures all of the adhesive. 
     
     
       6. The method defined in  claim 1  wherein initiating the chain reaction comprises initiating an adhesive-viscosity-increasing chain reaction that increases adhesive viscosity for all of the adhesive. 
     
     
       7. The method defined in  claim 1  wherein initiating the chain reaction comprises initiating an adhesive-viscosity-decreasing chain reaction that decreases adhesive viscosity for all of the adhesive. 
     
     
       8. The method defined in  claim 1  wherein initiating the chain reaction comprises initiating an adhesive-weakening chain reaction to debond the adhesive. 
     
     
       9. A method, comprising:
 dispensing liquid adhesive on an electronic device structure, wherein the electronic device structure includes a localized area with adhesive-viscosity-increasing material; 
 increasing the viscosity of the liquid adhesive with the adhesive-viscosity-increasing material by flowing the dispensed liquid adhesive until the liquid adhesive reaches the adhesive-viscosity-increasing material, wherein reaching the adhesive-viscosity-increasing material causes only portions of the liquid adhesive that are adjacent to the adhesive-viscosity-increasing material to increase in viscosity; and 
 applying localized energy to only the portions of the liquid adhesive that are adjacent to the adhesive-viscosity-increasing material, wherein applying the localized energy initiates a chain reaction in the adhesive that spreads throughout all of the adhesive. 
 
     
     
       10. The method defined in  claim 9  wherein the electronic device structure includes an integrated circuit and a printed circuit board to which the integrated circuit is mounted, and wherein the adhesive-viscosity-increasing material comprises material on the printed circuit board. 
     
     
       11. The method defined in  claim 9  further comprising:
 decreasing the viscosity of the liquid adhesive with adhesive-viscosity-decreasing material. 
 
     
     
       12. The method defined in  claim 11  wherein decreasing the viscosity comprises flowing the dispensed liquid adhesive until the liquid adhesive reaches the adhesive-viscosity-decreasing material.

Description:
BACKGROUND 
     This relates generally to electronic devices, and, more particularly, to assembling structures in electronic devices using adhesive. 
     Electronic devices include components such housing structures, electrical devices, printed circuits, and other device structures. Some structures may be assembled using screws and other fasteners. In other situations, adhesive is used to attach structures together. 
     It can be challenging to assemble structures in electronic devices using adhesive. Light-cured adhesive can be difficult to cure within recesses that are hidden from view. Liquid adhesive can be too viscous to dispense into narrow gaps or can be insufficiently viscous so that the adhesive wicks into locations where no adhesive is desired. After curing adhesive, it can be difficult to disassemble joined parts without damaging the parts. 
     It would therefore be desirable to be able to provide improved arrangements for using adhesive to join structures in electronic devices. 
     SUMMARY 
     An electronic device may have housing structures, electrical components, and other electronic device structures. Adhesive may be used to join structures such as electronic device structures for an electronic device. 
     Adhesive may be dispensed as uncured liquid adhesive. The liquid adhesive can be cured to form adhesive joints. Adhesive joints may subsequently be debonded to facilitate rework, repair, debugging, and failure analysis. 
     Chain reactions may be initiated by applying a localized initiator such as a chemical or localized energy to the adhesive. Once initiated the chain reaction may spread throughout the adhesive to cure the adhesive, to globally change adhesive viscosity, or to weaken the adhesive to facilitate debonding. 
     Local changes to adhesive may also be made such as local increases and decreases to adhesive viscosity. Locally applied energy may be used to locally adjust adhesive viscosity. Adhesive viscosity can also be locally adjusted using patterned viscosity-increasing material and viscosity-decreasing material. 
     Chain reactions may be used to cure adhesive or to debond adhesive that is hidden from view within gaps in the electronic device structures. Viscosity changes may be used to control where adhesive flows. For example, adhesive viscosity can be increased to prevent adhesive from flowing into areas in which no adhesive is desired. Adhesive viscosity can be decreased to facilitate wicking of adhesive under integrated circuits and other components mounted on a printed circuit to underfill the components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device such as a handheld computing device of the type that may be provided with structures joined with adhesive in accordance with an embodiment. 
         FIG. 2  is a cross-sectional side view of adhesive which is being locally modified to initiate a chain reaction in accordance with an embodiment. 
         FIG. 3  is a cross-sectional side view of the adhesive of  FIG. 2  showing how the local modification to the adhesive creates a resulting localized change in the properties of the adhesive in accordance with an embodiment. 
         FIG. 4  is a cross-sectional side view of the adhesive of  FIG. 3  showing how the localized change in the adhesive can propagate to an adjacent portion of the adhesive in accordance with an embodiment. 
         FIG. 5  is a flow chart of illustrative steps involved in using a chain reaction to modify an adhesive in accordance with an embodiment. 
         FIG. 6  is a diagram showing how a chain reaction can be initiated in a portion of an adhesive that is not shadowed in accordance with an embodiment. 
         FIG. 7  is a diagram showing how the chain reaction that was initiated using the equipment of  FIG. 6  may propagate to an adjacent portion of the adhesive that is in a location that is blocked from view in accordance with an embodiment. 
         FIG. 8  is a diagram showing how the adhesive of  FIG. 6  may be cured following propagation of the chain reaction through the adhesive in accordance with an embodiment. 
         FIG. 9  is a diagram showing equipment and operations that may be used in assembling structures in an electronic device using adhesive in accordance with an embodiment. 
         FIG. 10  is a flow chart of illustrative steps involved in assembling structures using equipment of the type shown in  FIG. 9  in accordance with an embodiment. 
         FIG. 11  is a cross-sectional side view of structures that have been joined using adhesive showing how a chain reaction may be initiated in the adhesive to weaken the adhesive in accordance with an embodiment. 
         FIG. 12  is a flow chart of illustrative steps involved in debonding structures by weakening adhesive using a locally initiated chain reaction in accordance with an embodiment. 
         FIG. 13  is a system diagram showing equipment and operations involved in locally enhancing adhesive viscosity in accordance with an embodiment. 
         FIG. 14  is a flow chart of illustrative steps involved in locally increasing adhesive viscosity in accordance with an embodiment. 
         FIG. 15  is a system diagram showing equipment and operations involved in locally decreasing adhesive viscosity in accordance with an embodiment. 
         FIG. 16  is a flow chart of illustrative steps involved in locally reducing adhesive viscosity in accordance with an embodiment. 
         FIG. 17  is a perspective view of an illustrative structure to which adhesive is being applied in accordance with an embodiment. 
         FIG. 18  is a perspective view of an illustrative structure that is configured to mate with the structure of  FIG. 17  and that has been selectively coated with adhesive-viscosity-increasing material and adhesive-viscosity-decreasing material in accordance with an embodiment. 
         FIG. 19  is a cross-sectional side view of the structures of  FIGS. 17 and 18  following assembly and attachment using adhesive in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Adhesive may be used or joining structures such as structures formed from plastic, metal, glass, ceramic, carbon-fiber composite material and other composites, and other materials. The adhesive may be cured using heat, light (e.g., ultraviolet light or visible light), chemicals (e.g., moisture), and other suitable curing agents. Adhesive debonding operations may be performed by weakening cured adhesive using a chemical such as a solvent, heat, light, or other adhesive weakening agents. Local changes may be made to adhesive viscosity, thereby controlling the flow of adhesive when joining structures together. Chain reactions can be used to cure adhesive, to weaken adhesive, to change adhesive viscosity, or to otherwise modify adhesive properties. Chain reactions can be initiated locally in a limited portion of an adhesive layer and, once initiated, can propagate throughout the entire adhesive layer. 
     Structures in an electronic device or other structures may use adhesive-based assembly and disassembly operations such as these.  FIG. 1  is a perspective view of an illustrative electronic device of the type that may be include structures that are attached to each other using adhesive. An electronic device such as electronic device  10  of  FIG. 1  may be a computing device such as 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. In the illustrative configuration of  FIG. 1 , device  10  is a portable device such as a cellular telephone, media player, tablet computer, or other portable computing device. Other configurations may be used for device  10  if desired. The example of  FIG. 1  is merely illustrative. 
     Device  10  may have one or more displays such as display  14  mounted in housing structures such as housing  12 . Housing  12  of device  10 , which is sometimes referred to as a case, may be 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 display pixel structures such as organic light-emitting diode display pixels, electrophoretic display pixels plasma display pixels, etc. 
     Electronic device  10  may include control circuitry. The control circuitry of device  10  may include storage and processing circuitry for controlling the operation of device  10 . Control circuitry in device  10  may, for example, include storage such is hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Control circuitry in device  10  may include processing circuitry based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio codec chips, application specific integrated circuits, etc. 
     Input-output devices in device  10  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output devices for device  10  may also include input-output components with which a user can control the operation of device  10 . A user may, for example, supply commands through input-output devices in device  10  and may receive status information and other output from device  10  using the output resources of input-output devices in device  10 . 
     Input-output devices for device  10  may include sensors and status indicators such as an ambient light sensor, a proximity sensor, a temperature sensor, a pressure sensor, a magnetic sensor, an accelerometer, a touch sensor, a fingerprint sensor, and light-emitting diodes and other components for gathering information about the environment in which device  10  is operating and providing information to a user of device  10  about the status of device  10 . Device  10  may include audio components such as speakers and tone generators for presenting sound to a user of device  10  and microphones for gathering user audio input. The input-output devices of device  10  may include one or more displays. Displays may be used to present images for a user such as text, video, and still images. Sensors in device  10  may include a touch sensor array that is formed as one of the layers in display  14 . During operation, user input may be gathered using buttons and other input-output components such as touch pad sensors, buttons, joysticks, click wheels, scrolling wheels, touch sensors such as a touch sensor array in a touch screen display or a touch pad, key pads, keyboards, vibrators, cameras, and other input-output components. The input-output devices of device  10  may include wired and wireless communications circuitry (e.g., circuitry to support digital data communications, a radio-frequency transceiver and antennas for supporting wireless communications, etc.). 
     Adhesive may be used in attaching together the structures of device  10  such as the structures of the control circuitry and input-output circuitry of device  10 , the structures associated with housing  12 , and other device components. Portions of electrical components can be attached to each other and electronic components can be mounted to housing structures or other structures using adhesive. As an example, layers in a display may be assembled using adhesive, internal and external housing structures, mounting brackets, printed circuits, integrated circuits, control circuitry components, input-output components, and other structural and electrical components associated with device  10  may be attached to each other and to other structures in device  10  using adhesive. Adhesive may also be used to encapsulate components. For example, adhesive may be used to encapsulate integrated circuits or other electrical components that are mounted on a printed circuit board. 
     It can be time consuming to globally heat adhesive to cure the adhesive. Global heating is also sometimes not desirable because excessive heat may damage sensitive components. Light-based adhesive curing can reduce the need to apply heat during curing. Light-based curing schemes involve application of ultraviolet light or visible light to cure adhesive. In light-based schemes, it can be challenging to apply light to adhesive that is blocked from view by opaque structures. For example, it can be challenging to apply ultraviolet light to liquid adhesive that is in a recess between opposing opaque structures. 
     If desired, adhesives can be provided with additives that promote chain reactions. The chain reactions can be used to cure liquid adhesive, to increase or decrease the viscosity of liquid adhesive, to weaken cured adhesive to facilitate debonding operations, or to otherwise modify the properties of adhesive. The additives may include one or more chemical additives, microspheres or other particles, hollow microspheres that have been filled with one or more chemical additives, fibers, or other materials. 
     Chain reactions in the adhesive may be globally or locally initiated. For example, an adhesive-changing chain reaction may be locally initiated by applying an initiator to a localized portion of the adhesive. Illustrative chain reaction initiators include chemical initiators and energy-based initiators. Examples of chemical initiators include moisture (i.e., water), other liquids, gaseous agents (e.g., oxygen), and other chemicals (i.e., catalysts) in liquid, gaseous, and/or solid form. Examples of energy-based initiators include heat, visible light, ultraviolet light, infrared light, energy in the form of radio-frequency signals, electrons or other energized particles, other forms of radiation, alternating current (AC) and direct current (DC) electrical current, and sound waves (e.g., ultrasonic energy, a shock from an impact, audible sound waves, or other sonic energy). Other types of initiators may be used if desired. These examples of adhesive-changing chain reaction initiators are merely illustrative. 
       FIGS. 2, 3, and 4  illustrate how a locally initiated chain reaction may propagate through an adhesive. As shown in  FIG. 2 , adhesive  20  may include additive  22 . In the example of  FIG. 2 , additive  22  includes a mechanical agent such as hollow microspheres  24  filled with a chemical agent such as agent  26 . Additive  22 , which may sometimes be referred to as a chain-reaction propagation agent or agent, may be used to promote propagation of a chain reaction that has been locally initiated throughout the entirety of adhesive  20 . 
     As shown in  FIG. 2 , local chain reaction initiator  28  may be applied to localized region  30  of adhesive  20 . The application of initiator  28  causes additive  22  to change its state in region  30 . As an example, microspheres  24  may dissolve, be ruptured, or may otherwise be changed so that chemical agent  26  is released into adhesive  20  and can react with adhesive  20 . As part of this reaction, adhesive  20  may change its state, as shown by region  30  in  FIG. 3 . For example, if adhesive  20  is initially in an uncured state, region  30  of  FIG. 3  may be cured adhesive. As another example, if adhesive  20  is initially viscous, region  30  of  FIG. 3  may be characterized by reduced viscosity. In scenarios in which adhesive  20  initially has a relatively low viscosity, changed region  30  of  FIG. 3  may be characterized by an increased viscosity. In some scenarios, it is desirable to weaken cured adhesive to help debond an adhesive joint. In this type of situation, adhesive  20  is initially in a cured state. The exposure of adhesive  20  in region  30  to chemical agent  26  (e.g., a solvent) may serve to weaken the adhesive in region  30  of  FIG. 3  relative to the remaining adhesive. 
     The curing of adhesive  20  or other change to the state of adhesive  20  in region  30  of  FIG. 3  may be the result of exposure of adhesive  20  to agent  26  of additive  22 . Agent  26  may, for example, include a curing-promoting component such as moisture or other chemical that promotes adhesive curing (i.e., polymer cross-linking), may be a chemical that increases adhesive viscosity, may be a chemical that reduces adhesive viscosity, or may be a chemical that weakens adhesive (e.g., a solvent that softens and/or dissolves cured adhesive). The change in the state of adhesive  20  in region  30  of  FIG. 3  may, if desired, be the result of the production of heat, light, or other byproduct of the reaction between agent  26  and adhesive  20 . 
     The change in state of adhesive in region  30  may serve to propagate a chain reaction that spreads throughout the remainder of adhesive  20 . As an example, the reaction of agent  26  of additive  22  with adhesive  20  may produce heat in region  30 . The heat that is produced in region  30  may be conducted to adjacent portions of adhesive  20  (e.g., by thermal conduction through adhesive  20 ). Once the adjacent portion of adhesive  20  has been heated such as adjacent portion  30 ′ of  FIG. 4 , the heat that is present in that adjacent region will cause additive  22  in region  30 ′ to change its state (e.g., the heat will case cause agent  26  to be released front microspheres  24 ). The released agent  26  will then react with adhesive in region  30  to change the state of adhesive  20  in region  30 ′, just as when initiator  28  was applied to region  30  of  FIG. 2 . In the example of  FIGS. 2, 3, and 4 , heat may be used to cause microspheres  24  to dissolve, be ruptured, or exhibit other changes in region  30 ′ so that chemical agent  26  is released into adhesive  20  and can react with adhesive  20  to change the state of adhesive  20  in region  30 ′. Other types of change to additive  22  and adhesive  20  can be initiated using initiator  28  if desired. 
     The process that has been started in regions  30  and  30 ′ can continue in a chain reaction, with each newly changed area producing additional heat that, in turn changes the state of a new adjacent area, until the state of all of adhesive  20  has changed (i.e., until all of adhesive  20  has been cured, until the viscosity of all of adhesive  20  has increased, until the viscosity of all of adhesive  20  has decreased, or until the strength of all of adhesive  20  has been weakened). If desired, a chain reaction that changes the state of adhesive  20  can be propagated throughout adhesive  20  by producing other reaction byproducts that can affect adjacent portions of adhesive  20  besides heat (e.g., chemical byproducts, light, etc.). The production of heat when additive  20  (agent  26 ) locally reacts with adhesive  20  is merely illustrative. 
     Illustrative steps involved in modifying the properties of adhesive  20  using a locally initiated chain reaction are shown in  FIG. 5 . At step  32 , initiator  28  is applied to a portion of adhesive  20  (see, e.g., localized region  30  of adhesive  20  in  FIG. 2 ). Adhesive  20  is in an initial state (cured, uncured, liquid, solid, low viscosity, high viscosity, etc.). 
     The application of initiator  28  to region  30  of adhesive  20  causes a local change in region  30  of adhesive  20  (e.g., previously uncured adhesive is cured, adhesive viscosity is increased, adhesive viscosity is decreased, adhesive strength is weakened, adhesive temperature is raised, the amount of chemical byproduct or other reaction byproduct is increased, etc.). 
     Due to thermal conduction, light transmission, chemical diffusion, or other mechanism(s), the local change that is made at step  34  propagates to an adjacent portion of adhesive  20  and causes a local change in that adjacent region, as described in connection with  FIG. 4 . 
     As indicated by line  38 , so long as some adhesive  20  remains in its unchanged state, the chain reaction may continue. Once all of adhesive  20  has changed its state, the chain reaction is complete (step  40 ). Optional additional operations may then be performed on adhesive  20  (e.g., global operations such as heating adhesive  20  globally to further change its state to facilitate curing, viscosity change, debonding, etc.). 
     A chain reaction scheme may be used to process adhesive  20  in scenarios in which traditional global processing schemes are difficult or impossible. Consider, as an example, a scenario of the type shown in  FIG. 6  in which adhesive  20  is present between device structures  42  and  44 . Chain reaction initiation equipment  50  locally applies initiator  28  to adhesive  20 . Chain reaction initiation equipment  50  may be a laser, light-emitting diode, lamp or other light source for producing light, may be a chemical dispensing nozzle or other equipment for dispensing chemicals, may be a heat source for producing heat, or may be other equipment for initiating a chain reaction of the type described in connection with  FIG. 5 . 
     Adhesive  20  in region  46  is uncovered (i.e., not shadowed by structures  42  and  44 ) and can therefore be exposed to initiator  28  (e.g., light, heat, a chemical such as water vapor, liquid water, gaseous reactant, liquid reactant, etc.). However, adhesive  20  in region  48  is embedded in a recess between structures  42  and  44  and is therefore shadowed and prevented from being exposed to initiator  28 . For example, structures  42  and  44  may be opaque and may prevent a light-based initiator such as ultraviolet light from reaching adhesive  20  in region  48 . As another example, it may not be possible to expose adhesive  20  in region  48  to a desired chemical or heat. 
     Although adhesive  20  in region  48  is blocked from exposure to initiator  28 , initiator  28  may be locally applied to adhesive  20  in region  46 . The application of initiator  28  may cause portion  30  of adhesive  20  to change, as shown in  FIG. 6 . 
     Due to the chain-reaction properties of adhesive  20 , the change that is caused in region  30  of  FIG. 6  propagates to region  30 ′ of  FIG. 7  and, in turn to all of the rest of adhesive  20 , including the adhesive in blocked region  48 , as shown in  FIG. 8 . 
     This type of chain reaction process may be used to cure adhesive in region  48 , may be used to raise or lower the viscosity of adhesive in region  48 , or may be used to weaken adhesive  20  in region  48 . If desired, components may be embedded within the gap filled by adhesive  20  (see, e.g., components  47  of  FIGS. 6, 7, and 8 , which may include electrical components mounted on a printed circuit board, connector pins, and other device structures). 
     An illustrative system and operations involved in performing chain reaction operations on adhesive  20  are shown in  FIG. 9 . In the example of  FIG. 9 , adhesive  20  is dispensed in liquid form and is cured to attach components in electronic device  10  together. 
     Initially, components such as electronic device components or other structures such as structures  42  and  44  may be assembled using assembly equipment  52  of  FIG. 9 . Assembly equipment  52  may include computer-controlled positioners, manually controlled fixtures and positioners, and other equipment for positioning structures  42  and  44  relative to each other. 
     When assembled, a gap such as gap  54  may be produced between portions of structures  42  and  44 . This gap can be filled by dispensing adhesive  20  into gap  54  in liquid form. Adhesive dispensing equipment  56  may include a needle dispenser, a spray dispenser, an adhesive dispensing nozzle, ink-jet printing equipment, or other equipment for dispensing liquid adhesive  20 . Adhesive  20  may have as relatively low viscosity (i.e., adhesive  20  may be a thin uncured adhesive liquid) to promote wicking into gap  54 . 
     After filling gap  54  with uncured liquid adhesive, chain reaction initiation equipment  50  may initiate a chain reaction in an exposed portion of adhesive  20 . The localized exposure of adhesive  20  to initiator  28  may cause adhesive  20  to locally cure. The localized exposure of adhesive  20  may also trigger to chain reaction that cures the rest of adhesive  20 , including the portions of adhesive  20  in gap  54 , thereby attaching structure  42  to structure  44  (and, if desired, encasing any components in gap  54  in adhesive  20 ). 
     Illustrative steps involved in using equipment of the type shown in  FIG. 9  to cure adhesive  20  using a chain reaction are shown in  FIG. 10 . At step  57 , equipment such as assembly equipment  56  may be used to place structures that are to be bonded together such as device components  42  and  44  of  FIG. 9  into desired positions. 
     Adhesive dispensing equipment  56  can apply uncured liquid adhesive to components  42  and  44  at step  58 . Adhesive can be applied after components  42  and  44  have been assembled using equipment  52  or may be applied to component  42  and/or component  44  before components  42  and  44  have been assembled. Arrangements in which more than two components are attached with adhesive may also be used (see, e.g., embedded components  47  of  FIGS. 6, 7, and 8 ). 
     After components  42  and  44  have been assembled and after liquid adhesive  20  is in place, chain reaction initiation equipment  50  may be used to apply initiator  28  to an exposed area of uncured liquid adhesive  20  (step  60 ). This initiates chain reaction curing of all of adhesive  20  and thereby forms an adhesive bond that attaches components  42  and  44  together. 
     In some situations, it may be desirable to use a chain reaction to facilitate debonding of a previously formed adhesive bond between electronic device components. This type of scenario is illustrated in  FIG. 11 . As shown in the example of  FIG. 11 , structures  42 ,  44 - 1 , and  44 - 2  may be attached together with cured adhesive  20 . Structure  44 - 2  may be a printed circuit (e.g., a rigid printed circuit board formed from a rigid printed circuit board material such as fiberglass-filled epoxy or a flexible printed circuit formed from a sheet of polyimide or other flexible polymer layer). Structure  44 - 1  may be an integrated circuit or other electronic component that is soldered to printed circuit  44 - 2 . Structure  42  may be to shield can lid that forms part of an electromagnetic shield for integrated circuit  44 - 1 . Other structures may be debonded if desired. These structures are merely illustrative. 
     During initial assembly operations, integrated circuit  44 - 1  was soldered to printed circuit  44 - 2  and shield can lid  42  was used to cover integrated circuit  44 - 1 . Cured adhesive  20  was used to encapsulate integrated circuit  44 - 1  and attach lid  42  to integrated circuit  44 - 1  and printed circuit  44 - 2 . Due to the presence of shadowing lid  42 , it is not possible (in this example) to expose adhesive  20  under lid  42  to light or chemicals. Accordingly, chain reaction initiation equipment  50  is used to apply initiator  28  to an exposed (unshadowed) portion of cured adhesive  20 . The exposure of adhesive  20  to initiator  28  locally weakens adhesive  20  and via chain reaction, weakens all of adhesive  20 , including the portions of adhesive  20  under shield lid  42 . Once all of adhesive  20  has been weakened, lid  42  may be removed. The ability to debond adhesive joints in this way may be used to facilitate rework and repair and to allow components of device  10  to be examined during failure analysis and prototyping. 
       FIG. 12  is a flow chart of illustrative steps involved in debonding adhesive joints by initiating an adhesive-weakening chain reaction by exposing a portion of cured adhesive  20  to a debonding chain-reaction initiator. 
     At step  62 , components such as components  42 ,  44 - 1 , and  44 - 2  may be assembled. For example, assembly equipment  52  may be used to solder integrated circuit  44 - 1  to printed circuit  44 - 2 , may be used to solder a shield fence for an electromagnetic interference shield to printed circuit  44 - 2 , may be used to attach shield lid  42  to the shield fence or other structures, etc. 
     At step  64 , liquid adhesive may be applied to the assembled structures (e.g., liquid adhesive  20  may be used to encapsulate integrated circuit  44 - 1  and fill the gaps between structures  44 - 1 ,  44 - 2 , and  42 , as shown in  FIG. 11 ). The uncured liquid adhesive may be cured using a global curing process or other curing process. As an example, adhesive  20  may be cured using a chain reaction started by an initiator or by heat mg structures  42 ,  44 - 1 , and  44 - 2  in an oven or otherwise exposing structures  42 ,  44 - 1 , and  44 - 2  to elevated temperatures. 
     At step  68 , when it is desired to debond the adhesive joint that has been formed, chain reaction initialization equipment  50  may be used to apply initiator  28  to an exposed portion of the cured adhesive  20 . The debonding chain reaction that is initiated in this way propagates throughout cured adhesive  20 , weakening all of adhesive  20  and thereby facilitating subsequent debonding and disassembly operations (step  68 ). 
     It may sometimes be desired to increase the viscosity of adhesive  20  to prevent adhesive  20  from wicking into recesses between components where no adhesive is wanted. Using a catalyst such as moisture or other chemical and/or locally applied light, heat or other energy, adhesive  20  can be changed (locally, or globally via chain reaction) from a relatively low viscosity state to a relatively high viscosity state. This type at approach is shown in  FIG. 13 . 
     As shown in  FIG. 13 , electronic device structure  72  may have a gap or other recess such as gap  74 . There is a potential for liquid adhesive to wick into gap  74 . In the example of  FIG. 13 , it is desired to keep gap  74  free from adhesive. Accordingly, viscosity-increasing material  76  and/or localized energy in the vicinity of structures  76  may be supplied to increase the viscosity of adhesive  20  once adhesive  20  has spread outward sufficiently to reach material  76  and/or the localized energy in the vicinity of structures  76 . 
     In the  FIG. 13  example, it is desired to encapsulate component  70  on structure  72  with adhesive. Structure  72  may be a printed circuit or other substrate. Component  70  may be an integrated circuit or other electronic device component. 
     Initially, adhesive dispensing equipment  56  may dispense uncured liquid adhesive onto the center of component  70 . The adhesive initially occupies area  20 - 1 . As more adhesive is dispensed from equipment  56 , the adhesive flows outwards to region  20 - 2 . The liquid adhesive that is dispensed has a relatively low viscosity, which facilitates the spreading of adhesive  20 . Finally, a sufficient amount of liquid adhesive has been dispensed onto component  70  that the adhesive has flowed outward enough to overlap viscosity-increasing material  76  and/or the viscosity-increasing, light heat, or other energy that is applied in the vicinity of structures  76  (see, e.g., adhesive area  20 - 3  of  FIG. 13 ). At this point, the viscosity of the liquid adhesive increases. The viscosity increase may be local (i.e., in the vicinity of material  76 , in the vicinity of the locally applied energy, etc.) or the viscosity increase may be global (i.e., by including a viscosity-increasing additive in adhesive  20  that supports a viscosity-increasing chain reaction through adhesive  20  that is initiated by material  76  or the applied energy in the vicinity of material  76 ). 
     The viscosity increase that is imparted to adhesive  20  ensures that the outward flow of adhesive  20  is constrained, thereby preventing adhesive  20  from flowing into gap  74 . Adhesive  20  may then be cured using adhesive curing equipment  78  (e.g., by application of global and/or local energy or by application of moisture or other adhesive-curing-promotion chemical). 
     Illustrative steps involved in using increases to the viscosity of adhesive  20  during the formation of adhesive joints between electronic device components are shown in  FIG. 14 . 
     As shown in  FIG. 14 , electronic device components can be assembled at step  80 . For example, assembly equipment  52  may be used to solder components together, may be used to weld components together, may be used to attach components with fasteners, adhesive, or other attachment techniques. It may be desired to encapsulate some of the assembled structures using adhesive. 
     At step  82 , adhesive dispensing equipment  56  ( FIG. 13 ) may dispense liquid adhesive onto the structures that are to been encapsulated (see, e.g., structure  70  of  FIG. 13 ). Adhesive viscosity-increasing material  76  may be deposited on the structures that are being encapsulated using material deposition equipment such as ink-jet printing equipment, pad printing equipment, nozzle-based equipment, a needle-dispenser, physical vapor deposition equipment, chemical vapor deposition equipment, or other equipment for deposing and patterning material (e.g., in a ring or other pattern surrounding structure  70 ). In addition to providing viscosity-increasing material  76  or as an alternative to using material  76 , localized energy such as light, heat, or other energy may be supplied to the location occupied by material  76  (e.g., in a ring on the surface of structure  72  that surrounds component  70  or other suitable pattern). 
     At step  84 , a localized viscosity-increasing agent such as material  76  and/or locally supplied energy from a light source, heat source, or other energy source is used to locally increase the viscosity of adhesive  20  to prevent adhesive  20  from flowing beyond desired boundaries (and, if desired, globally increases the viscosity of adhesive  20  through a chain reaction). By controlling the flow of adhesive  20  prior to curing, adhesive  20  can be prevented from intruding into sensitive areas where no adhesive is desired (see, e.g., recess  74  of  FIG. 13 ). 
     At step  86 , adhesive  20  can be cured (e.g., using an oxen or other structure that applies curing energy to adhesive  20  such as adhesive curing equipment  78  of  FIG. 13 ). 
     In situations in which it is desired to underfill an integrated circuit or other component or in other situations, it may be desirable to decrease the viscosity of adhesive  20 . Using a catalyst such as moisture or other chemical agent and/or an energy-based agent such is locally applied light, heat, or other energy, adhesive  20  can be changed (locally, or globally via chain reaction) from a relatively high viscosity state to a relatively low viscosity state. This type of approach is illustrated in  FIG. 15 . 
     As shown in  FIG. 15 , assembly equipment  52  may be used to assemble electronic device components such as structures  90 ,  92 , and  88 . As assembled, there may be gaps within these components such as illustrative gap  94  between the underside of component  92  and the upper surface of component  88 . It may be desirable to ensure that liquid adhesive is viscous enough to cover component  90  (e.g., to encapsulate component  90 ) while also ensuring that the liquid adhesive is thin enough to wick into gap  92  under component  92 . Accordingly, localized energy  98  and/or viscosity-decreasing material in the vicinity of energy  98  may be supplied to decrease the viscosity of adhesive  20  once adhesive  20  has spread outward sufficiently to reach energy  98  (and/or viscosity-decreasing material at the same location as energy  98 ). 
     In the  FIG. 15  example, it is desired to encapsulate component  90  on structure  88  with adhesive and it is desired to underfill component  92  by providing adhesive in gap  94 . Structure  88  may be a printed circuit or other substrate. Component  90  may be an electrical or structural component. Component  92  may be an integrated circuit that is soldered to printed circuit  88  or may be another electronic device component. 
     Adhesive dispensing equipment  56  may dispense uncured liquid adhesive onto the center of component  90 . The adhesive flows outwards until some of the adhesive is exposed to energy  98  from localized energy source  96  (e.g., a laser, light-emitting diode, lamp, or other light source, a heat source, etc.) or localized viscosity-reducing material (e.g., moisture or other chemical, etc.). The localized viscosity reducing agent (energy and/or viscosity-reducing material) reduces the viscosity of adhesive  20  so that the reduced-viscosity adhesive may flow into recess  94 . Curing equipment (e.g., an oven) may then be used to heat adhesive  20  to an elevated temperature to cure adhesive  20 . If desired, a localized source such as source  96  may be used to apply localized energy to adhesive  20  to increase adhesive viscosity, as described in connection with  FIG. 13 . 
     Illustrative steps involved in using local viscosity-decreasing material and/or energy to selectively reduce the viscosity of adhesive  20  are shown in  FIG. 16 . As shown in  FIG. 16 , components such as components  88 ,  92 , and  90  may be assembled at step  100  (e.g., using assembly equipment  52 ). 
     At step  102 , adhesive dispensing equipment  56  may dispense uncured liquid adhesive on the components. 
     Localized source  96  may provide localized energy  98  and/or locally patterned viscosity-decreasing material may be provided at desired locations on the assembled components. At step  104 , as the flowing adhesive that was deposited at step  102  reaches the viscosity-reducing agent such as locally applied energy from source  96  and/or the viscosity-decreasing material, the properties of the adhesive are modified (e.g., locally) to decrease the viscosity of the adhesive. This allows the adhesive to flow into gaps such as gap  94  of  FIG. 15 . Some of the adhesive such as the adhesive that remains over component  90  of  FIG. 15  may retain an unreduced viscosity so that the adhesive that does not have reduced viscosity can be used to encapsulate the component. 
     At step  106 , the adhesive that has been dispensed and that has flowed to desired regions of the assembled components can be cured. For example, an oven or other heat source may be used to apply heat that elevates the temperature of adhesive  20  to cure adhesive  20 . 
     If desired, both viscosity-increasing and viscosity-decreasing materials can be deposited on the same electronic device structures during assembly. 
     As shown in  FIG. 17 , adhesive dispensing equipment  114  may apply liquid adhesive  120  to an electronic device component such as a shield can lid or other structure (component  116 ). Equipment  114  may include an adhesive dispensing head such as nozzle  112  and a positioner such as computer-controlled positioner  110  for controlling the position of nozzle  112  as adhesive  120  is dispensed. 
     Component  116  may have a shape that mates with a box-like component (e.g., part of a shield structure such as a shield can body) such as component  118  of  FIG. 18 . Before lid  116  is attached to body  118 , equipment  120  may dispense adhesive-viscosity-decreasing material  126  and adhesive-viscosity-increasing material  128  on body  118 . Equipment  120  may dispense materials  126  and  128  by using computer-controlled positioner  122  to control the position of dispensing head (nozzle)  124 . 
     When lid  116  is attached to body  118 , material  126  locally decreases the viscosity of adhesive  120  to promote wicking of adhesive  120  along the interface formed between inner sidewall  130  of body  118  and the corresponding surface of lid  116 . Material  128  increases the viscosity of adhesive  120  to prevent the wicking liquid adhesive from flowing too far into the interior of body  118 . A cross-sectional side view of lid  116  in an assembled position on top of body  118  is shown in  FIG. 19 . 
     If desired, a technique of the type described in connection with  FIGS. 17, 18, and 19  in which both local viscosity enhancement and local viscosity reduction techniques are used may be used in combination with localized techniques for curing and or debonding and/or may be used in combination with techniques for initiating chain reactions (e.g., for curing, debonding, viscosity enhancement, and/or viscosity reduction). The configuration of  FIGS. 17, 18, and 19  is merely illustrative. 
     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: 20140331
Publication Date: 20170207
Grant Date: 20170207
Priority Date: 20140331
Inventors: BAKER JOHN J.
Assignee: APPLE INC
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Family ID: 54192465