PATENT DOCUMENT

Publication Number: US-9942986-B1
Application Number: US-201715400677-A
Country: US
Kind Code: B1

Title: System with field-assisted conductive adhesive bonds

Abstract:
Components may have substrates with metal traces that form mating contacts. The components may be bonded together using anisotropic conductive adhesive bonding techniques. During bonding, conductive particles may be concentrated over the contacts by application of magnetic or electric fields or by using a template transfer process. Gaps between the contacts may be at least partially free of conductive particles to help isolate adjacent contacts. Polymer between the substrates may attach the substrates together. The conductive particles may be embedded in the polymer and crushed or melted to short opposing contacts together.

Claims:
What is claimed is: 
     
       1. An apparatus, comprising:
 a first component having a first substrate with first metal contacts; 
 a second component having a second substrate with second metal contacts; 
 a polymer layer that attaches the first and second components together; and 
 conductive particles in the polymer layer, wherein the conductive particles have a first density overlapping the first contacts and have a second density overlapping gaps between the first contacts, and wherein the first density divided by the second density is at least five. 
 
     
     
       2. The apparatus defined in  claim 1  wherein each conductive particle includes a dielectric core and a metal coating. 
     
     
       3. The apparatus defined in  claim 1  wherein each conductive particle is a solid metal particle. 
     
     
       4. The apparatus defined in  claim 1  wherein each of the first contacts includes a magnetic material. 
     
     
       5. The apparatus defined in  claim 3  wherein each of the conductive particles includes a magnetic material. 
     
     
       6. The apparatus defined in  claim 1  wherein each of the first contacts includes a copper layer and a metal coating on the copper layer. 
     
     
       7. The apparatus defined in  claim 6  wherein the each of the first contacts includes a magnetic material and wherein the each of the conductive particles includes a magnetic material. 
     
     
       8. The apparatus defined in  claim 7  wherein each of the conductive particles includes a dielectric core and wherein the magnetic material that is included in the conductive particle is a coating on the dielectric core. 
     
     
       9. The apparatus defined in  claim 1  wherein the first substrate is a flexible polymer substrate and wherein the second substrate comprises a substrate selected from the group consisting of: a touch sensor substrate and a display substrate. 
     
     
       10. The apparatus defined in  claim 9  wherein the first density divided by the second density is at least twenty. 
     
     
       11. The apparatus defined in  claim 1  wherein each of the first metal contacts includes a metal material, wherein each of the conductive particles includes a magnetic material, and wherein the magnetic material in each of the first metal contacts is configured to align the conductive particles with the first metal contacts. 
     
     
       12. An apparatus, comprising:
 a first substrate with first contacts; 
 a second substrate with second contacts; 
 a polymer layer that attaches the first and second substrates together; and 
 conductive particles in the polymer layer that short each of the first contacts to a respective one of the second contacts, wherein the conductive particles have a first density overlapping the first contacts and have a second density overlapping gaps between the first contacts and wherein the first density divided by the second density is at least ten. 
 
     
     
       13. The apparatus defined in  claim 12  wherein each conductive particle comprises a conductive particle selected from the group consisting of: a conductive particle that includes a dielectric core and a metal coating and a solid metal particle without a coating. 
     
     
       14. The apparatus defined in  claim 12  wherein the each conductive particle comprises a core covered with a metal coating. 
     
     
       15. The apparatus defined in  claim 12  wherein the first contacts comprise a magnetic material. 
     
     
       16. The apparatus defined in  claim 12  wherein the first substrate comprises a flexible polymer layer and wherein the second substrate comprises a display substrate. 
     
     
       17. The apparatus defined in  claim 12  wherein the conductive particles each have at least one conductive layer. 
     
     
       18. The apparatus defined in  claim 17  wherein the conductive layer comprises a conductive layer selected from the group consisting of: a magnetic material layer and a dielectric layer. 
     
     
       19. A method for forming an anisotropic conductive adhesive bond between first contacts on a first substrate and respective second contacts on a second substrate, wherein the first contacts include magnetic material, the method comprising:
 dispensing a layer of conductive particles that include magnetic material on the first substrate; 
 concentrating the conductive particles on the first contacts using an electromagnetic field and the magnetic material in the first contacts; and 
 after concentrating the conductive particles, forming a solid polymer layer between the first and second substrates, wherein the solid polymer layer includes the conductive particles, wherein the solid polymer layer attaches the first substrate to the second substrate, and wherein each of the first contacts is shorted to a respective one of the second contacts by a respective portion of the conductive particles. 
 
     
     
       20. The method defined in  claim 19  wherein concentrating the conductive particles comprises generating a magnetic field with a magnet. 
     
     
       21. The method defined in  claim 19  wherein concentrating the conductive particles comprises applying a voltage to the first contacts with a signal source and wherein the voltage causes the first contacts to generate an electric field that attracts the conductive particles to the first contacts.

Description:
This application claims the benefit of provisional patent application No. 62/399,168, filed Sep. 23, 2016, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to electronic devices and, more particularly, to electronic devices with metal electrodes that are joined using anisotropic conductive adhesive. 
     Electronic devices often include components with metal electrodes. It may be desirable to form electrical connections between mating sets of metal electrodes on a pair of components. Typical anisotropic conductive adhesive bonding involves forming electrical connections between top and bottom mating electrodes while avoiding direct particle bridging between laterally adjacent electrodes. If care is not taken, however, adjacent electrodes may be shorted together when forming conductive adhesive bonds or contact resistance may be higher than desired. 
     SUMMARY 
     Components such as printed circuits, displays, touch sensors, integrated circuits, and other components may have interconnects that are bonded together using anisotropic conductive adhesive. The components may have substrates such as flexible polymer substrates, rigid substrates of polymer or glass, or other substrates. The substrates may have metal electrodes (e.g., interconnects formed from metal traces on the substrates may have contacts). 
     During anisotropic conductive adhesive bonding, a pair of components may be bonded together. Conductive particles may be assembled (concentrated) over the contacts in the components by application of magnetic or electric fields during bonding or by using a template transfer process. The conductive particles may be embedded in a polymer and crushed between opposing contacts to short the opposing contacts together. If desired, the conductive particles may be melted when shorting contacts together (e.g., when using conductive particles formed from low temperature solder that melts upon application of heat). 
     The polymer may attach the substrates of the components together. Because the conductive particles are concentrated over the contacts during bond formation, gaps between contacts will be partly or entirely free of conductive particles, thereby enhancing isolation between adjacent contacts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of illustrative components with contacts joined with anisotropic conductive adhesive in accordance with an embodiment. 
         FIG. 2  is a top view of an illustrative sets of contacts and gaps between contacts following initial coverage with conductive particles in accordance with an embodiment. 
         FIG. 3  is top view of the sets of contacts of  FIG. 2  following application of electromagnetic fields to the conductive particles to concentrate the particles over the contacts in accordance with an embodiment. 
         FIG. 4  is a cross-sectional side view of portions of two components that have been bonded together using anisotropic conductive adhesive in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of an illustrative contact on a substrate in a component in accordance with an embodiment. 
         FIG. 6  is a cross-sectional side view of an illustrative conductive particle in accordance with an embodiment. 
         FIGS. 7, 8, and 9  are cross-sectional side views of components being bonded together using illustrative field-assisted anisotropic conductive adhesive bonding techniques in which conductive particles are carried by a polymer material during bonding in accordance with an embodiment. 
         FIGS. 10, 11, and 12  are cross-sectional side views of components being bonded together using illustrative field-assisted anisotropic conductive adhesive bonding techniques in which conductive particles are dispensed in a solvent that is evaporated before using polymer material to finish bonding operations in accordance with an embodiment. 
         FIGS. 13, 14, and 15  are cross-sectional side views of components being bonded together using an illustrative template transfer technique in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An illustrative system having components that can be electrically coupled together is shown in  FIG. 1 . As shown in  FIG. 1 , system  10  may include a first component such as component  12  and a second component such as component  14 . System  10  may include input-output circuit, control circuitry, and other components for forming an electronic device such as a cellular telephone, computer, embedded system, watch, or other electronic equipment. Components  12  and  14  may be flexible printed circuits, rigid printed circuits, glass substrates (e.g., a thin-film transistor layer in a liquid crystal display), may be touch sensor substrates (e.g., touch sensor substrates formed from a flexible polymer sheet), may be organic light-emitting diode display substrates or other display substrates (e.g., flexible display substrates formed from layers of polyimide or sheets of other flexible polymers), may include packaged and/or unpackaged integrated circuits (e.g., integrated circuit dies and/or packaged integrated circuits, system-in-package devices containing multiple integrated circuits, and/or other circuit components), and/or may include other suitable electrical components. 
     Component  12  may include metal traces  16  on substrate  18 . Component  14  may include metal traces  20  on substrate  22 . Traces  16  and  20  may have portions that form contacts (sometimes referred to as bond pads, contact pads, metal trace pads, metal traces, metal electrodes, etc.). These contacts may be electrically connected using polymer and conductive particles. The polymer may physically attach component  12  to component  14 . The conductive particles may be embedded within the polymer and may be crushed between opposing contacts on substrates  18  and  22  to electrically short the opposing contacts to each other. For example, the conductive particles may short a first contact on the lower surface of substrate  18  to a mating second contact on the upper surface of substrate  22 . 
     Any conductive particles in the gaps between adjacent contacts will not be crushed against the contacts and will tend to be physically and electrically isolated from each other by intervening polymer. To allow the density of contacts in a bonding region to be increased, the number of conductive particles that are located in the gaps between adjacent contacts can be reduced by applying electromagnetic fields to the contacts during bond formation. The applied electromagnetic fields may be, for example, static or alternating-current (AC) fields such as magnetic fields or electric fields. The conductive particles may be charged (e.g., with isotropic and/or anisotropic static electrical charge) and/or may be magnetic (e.g., due to inclusion of nickel or other magnetic material in the particles), so that the application of the fields causes the particles to concentrate over the contacts. Polymer material may be applied before and/or after the particles have been concentrated over the contacts to help attach substrates  18  and  22  together in the bond region and to help electrically isolate residual particles in the gaps between contacts. 
     Consider, as an example, a scenario in which component  14  has contacts  20  formed on an upper surface of substrate  22 . As shown in  FIG. 2 , conductive particles  30  may initially be deposited uniformly over the surface of substrate  22 . As a result, contacts  20  and gaps  28 , which are formed from the exposed portions of substrate  22  between contacts  20 , may be covered with similar or identical concentrations of particles  30 . For example, if the density (number of particles/cm 2 ) of particles  30  over contacts  20  is DC and the density of particles  30  over gap  28  is DG, the ratio of DC to DG may be 1, may be between 0.9 and 1.1, etc. 
     The application of fields (magnetic and/or electric) to component  14  in the vicinity of contacts  20  may help concentrate conductive particles  30  over contacts  20 . This may reduce or eliminate the possibility that laterally adjacent contacts  20  (e.g., other contacts on the surface of substrate  22  of  FIG. 3 ) will inadvertently be shorted to each other through a chain of particles  30 . The enhanced concentration of conductive particles  30  over contacts  20  may also help minimize bond resistance. In the example of  FIG. 3 , gaps  28  are free of conductive particles  30  following application of the fields (i.e., the ratio of DC to DG is infinite). In general, the ratio of DC to DG may have any suitable enhanced value following application of the fields (e.g., DC/DG may be greater than 1, may be at least 2, may be at least 3, may be at least 4, may be at least 5, may be 4-10, may be at least 10, may be at least 20, may be at least 35, may be at least 50, etc.). Higher values of ratio DC/DG may increase the number of particles  30  per contact pad during bonding, thereby minimizing bond resistance, and may decrease the presence of particles in gaps  28  to enhance isolation between adjacent contacts  20 . This allows pad size and/or gap size to be reduced, so that the density of connections that may be formed when coupling contacts  20  of component  14  to contacts  16  of component  12  may be increased. 
     A cross-sectional side view of components  12  and  14  taken along line  24  of  FIG. 1  and viewed in direction  26  is shown in  FIG. 4 . As shown in  FIG. 4 , contacts  20  on upper surface  36  of substrate  22  in component  14  may mate with corresponding opposing contacts  16  on opposing lower surface  34  of substrate  18  in component  12 . Polymer  32 , which may sometimes be referred to as an adhesive layer or polymer layer, may be formed from a thermoset polymer (e.g., epoxy, acrylic, etc.) or may be formed from a thermoplastic polymer. Polymer layer  32  may physically attach substrates  18  and  22  together. Metal or other conductive material in particles  30  may contact metal in contacts  16  and  20  so that each contact  16  is electrically coupled to a corresponding contact  20 . This creates vertical conductive paths (paths running parallel to vertical dimension Z) between components  12  and  14 . Lateral isolation (along dimension X) is provided by removing most or all of conductive particles  30  from gaps  28 . 
     Interconnects (electrodes) in components  12  and  14  such as contacts  16  and  20  may be formed from a single metal layer, two metal layers, three metal layers, more than three metal layers, alloy layers, elemental metal layers, layers of conductive materials such as carbon nanotubes, layers of other conductive materials, and/or or combinations of these layers. 
     With one illustrative configuration, which is shown in  FIG. 5 , metal interconnect structures in components  12  and  14  contain multiple layers of metal that are patterned to form contacts, signal lines, and/other interconnect structures. As shown in  FIG. 5 , contact  38  may be formed on substrate  40 . Contact  38  may be one of contacts  16  and/or one of contacts  20 . Substrate  40  may be substrate  22  or substrate  18 . Contact  38  may include a high-conductivity layer such as core layer  42 . Layer  42  may be formed from a metal such as copper (as an example). Coating layer  44  may be formed on layer  42 . Coating layer  44  may enhance corrosion resistance and may be formed from a material such as nickel. The thickness of layer  42  may be less than 4 microns, less than 5 microns, more than 0.4 microns, 0.1-10 microns, or other suitable thickness. The thickness of coating layer  44  may be less than 4 microns, less than 5 microns, more than 0.4 microns, 0.1-10 microns, or other suitable thickness. Outer coating layer  46  may be formed on layer  44  to enhance corrosion resistance and to reduce contact resistance. With one illustrative configuration, outer coating layer  46  may be a layer of gold. The thickness of coating layer  46  may be less than 1 micron, 0.1-2 microns, more than 0.2 microns, less than 1.5 microns, or other suitable thickness. 
     A cross-sectional side view of an illustrative conductive particle is shown in  FIG. 6 . In the example of  FIG. 6 , conductive particle  30  includes core  48 , inner coating layer  50 , and outer coating layer  60 . If desired, conductive particle  30  may include only core  48 . Core  48  may be, for example, a particle of conductive material such as metal (e.g., an elemental metal, solder or other metal alloys, etc.). In some configurations, core  48  may be formed from a dielectric such as a polymer that allows particle  30  to be crushed when squeezed between opposing contacts. In this type of arrangement, coating layer  50  may be formed from a conductive material such as metal (e.g., nickel, etc.). Optional layer  60  may be formed from a dielectric such as a polymer and may be used to help prevent particles  30  from being unintentionally shorted to each other within gaps  28 . 
     In general, any suitable configuration may be used for conductive particles  30 . The foregoing examples are merely illustrative. Particles  30  may have cores and coatings of any suitable material (metal, dielectric, etc.) and any suitable dimensions. For example, core  48  may have a diameter of 3-10 microns, more than 2 microns, less than 15 microns, 3-7 microns, 5 microns, or other suitable diameter. Coating layer  50  and coating layer  60  may each have a thickness of 0.5 microns, 0.2 to 0.8 microns, more than 0.1 microns, more than 0.3 microns, less than 1 micron, or other suitable thickness. 
     When the contacts being bonded (e.g., contacts  20 ) and particles  30  contain magnetic materials such as nickel (e.g., materials that are paramagnetic, superparamagnetic, or ferromagnetic), contacts  20  can concentrate magnetic flux from a source of magnetic field, thereby allowing contacts  20  to attract particles  30 . This enhances the density of particles  30  over the contacts. If desired, particles  30  may be statically charged (e.g., with isotropic or anisotropic charging schemes) to allow particles  30  to be attracted to contacts  20  that have been biased to from a static electric field. In other configurations, contacts  20  may be biased with an alternating-current signal and may produce a corresponding alternating-current electric field. This electric field may induce a dipole moment in particles  30  that allows particles  30  to be attracted to contacts  20 . If desired, fields may also be applied to contacts  16  to attract particles  30 . The application of fields to contacts  20  is merely illustrative. 
       FIGS. 7, 8, and 9  show how particle-concentrating magnetic and/or electric fields may be applied during bonding to concentrate particles  30  on contacts  20 . In the example of  FIGS. 7, 8 , and  9 , particles  30  are embedded in polymer  32 . 
     Initially, polymer  32  may be in an uncured liquid state. This allows particles  30  and polymer  32  to be dispensed onto substrate  22  by spraying, printing, dipping, dripping, needle dispensing or other techniques, as shown in  FIG. 7 . In this state, particles  30  may be suspended within polymer  32  and may be uniformly distributed over the surface of substrate  22 . 
     After applying polymer  32  and suspended particles  30  on substrate  22 , particle-concentrating fields may be applied. As shown in  FIG. 8 , for example, magnetic field source  70  may apply magnetic field  72 . Source  70  may be a permanent magnet or electromagnet that generates magnetic field  72 . 
     If desired, signal paths such as path  68  may short contacts  20  to electric field source  66  (e.g., a direct-current signal generator or an alternating-current signal generator) and may couple source  66  to counter electrode  68 ′. Source  66  may supply a static or alternating-current voltage to contacts  20  that causes contacts  20  to generate a static electric field or an alternating-current electric field (see, e.g., electric field E of  FIG. 8 ). 
     The fields that are applied using field-producing sources such as sources  70  and  66  of  FIG. 8  may attract particles  30  onto contacts  20 . For example, magnetic field flux may be concentrated over contacts  20  due to the presence of nickel or other magnetic material in contacts  20 . This concentrated magnetic field may attract magnetic material in particles  30 , thereby causing particles  30  to become concentrated over contacts  20 . 
     If desired, particles  30  may have a static electric charge that allows particles  30  to be drawn towards a static electric field supplied by contacts  20  when contacts  20  receive a static voltage from source  66 . For example, if a negative voltage is applied to terminal  69  and contacts  20  while a positive voltage is applied to terminal  71  and counter electrode  68 ′, electric field E will cause positively charged particles  30  to migrate to contacts  20 . 
     In other configurations, particles  30  may exhibit a polar (dipole) characteristics when exposed to alternating-current fields. This property may induce dielectrophoresis, (the migration of uncharged particles toward a position of maximum field strength in an alternating-current electric field). The application of alternating-current fields to induce dielectrophoresis may be used to cause particles  30  to be attracted to contacts  20 . 
     After concentrating particles  30  in the areas of substrate  22  that overlap contacts  20 , the liquid polymer material of polymer  32  may be sandwiched between component  12  and component  14  and cured by application of heat and/or ultraviolet light. As shown in  FIG. 9 , for example, component  12  may be aligned with component  14  so that each contact  16  in component  12  mates with a corresponding contact  20  in component  14 . Once aligned in this way, tool structures  74  and  76  may press inwardly in directions  78  to crush conductive particles  30  between opposing upper and lower contacts. Tool structure  74  and/or tool structure  76  may be heated. The heat from structures  74  and  76  and optional ultraviolet light that is applied to layer  32  may cure the liquid polymer material of polymer layer  32 , causing polymer layer  32  to cure, solidify, and attach substrate  18  of component  12  to substrate  22  of component  14 . 
       FIGS. 10, 11, and 12  show how particle-concentrating magnetic and/or electric fields may be applied during bonding to concentrate particles  30  on contacts  20  in a configuration in which particles  30  are dispensed in a liquid solvent. 
     As shown in  FIG. 10 , liquid solvent  80  may contain suspended conductive particles  30 . To concentrate particles  30  on contacts  20 , magnetic field source  70  may apply magnetic field  72  and/or signal generator  66  and paths such as path  68  may be used to apply voltages to contacts  20  that cause contacts  20  to produce static and/or alternating-current electric fields. This causes suspended particles  30  to concentrate on contacts  20 . After concentrating particle  30  on contacts  20 , heat  83  may be applied to solvent  80  by optional heat source  82  (e.g., a lamp, etc.) to evaporate solvent  80  and/or solvent  80  may be evaporated at room temperature. This leaves concentrated particles  30  on contacts  20  and leaves the gaps between contacts  20  free of particles  20  as shown in  FIG. 11 . 
     After forming a concentrated layer of particles  30  on contacts  20 , polymer  32  may be placed between component  12  and component  14  and components  12  and  14  may be aligned to align contacts  16  with contacts  20 , as shown in  FIG. 12 . Polymer  32  may be applied as a liquid or in solid form. Tool structures  74  and  76  may apply heat to polymer  32 . Solid polymer may be melted by the heat and then cooled to solidify the molten polymer to form a bond. Uncured liquid polymer may be cured and solidified by the heat and by optional ultraviolet light. During bonding, tool structures  74  and  76  may be moved in directions  78  to press components  12  and  14  together. Once conductive particles  30  have been crushed between contacts  16  and aligned contacts  20  and after polymer  32  has been cured and solidified, tool structures  74  and  76  may be released. 
       FIGS. 13, 14, and 15  illustrate operations and equipment of the type that may be used to form conductive bonds with a particle template transfer arrangement. 
     As shown in  FIG. 13 , surface  84  of particle transfer member  82  may be coated with a layer of conductive particles  30 . Member  82  may be a polymer layer (e.g., a layer of polytetrafluoroethylene or other suitable polymer) or may be formed from other materials. Surface  84  may be sticky due to the properties of member  82  (material type, texture, etc.) and/or surface  84  may attract particles  30  through electrostatic attraction, van der Waals attraction, surface tension effects, or other effects. If desired, a thin liquid layer or other layer of material may be applied to surface  84  to increase or decrease the stickiness of surface  84 . Particles  30  may be temporarily attached to surface  84  by blowing particles  30  onto surface  84 , by pressing surface  84  against a reservoir of particles  30 , and/or by otherwise placing particles  30  into contact with surface  84 . If desired, particles  30  may be attached to an elastomeric layer or other stretchable substrate which can be stretched laterally to adjust the density of particles  30  that are present. The elastomeric layer may then be pressed against surface Particles  30  may resist sticking to each other so that only a single layer of particles  30  becomes attached to surface  84  (as an example). 
     After attaching particles  30  to surface  84  of member  82 , member  82  may be moved in direction  80  so that particles  30  press against the surfaces of contacts  20 . If desired, optional fields (e.g., magnetic fields) may be applied by contacts  20  (e.g., using source  70  to generate magnetic field  72  that is concentrated by contacts  20 ). Contacts  20  may also be provided with textures, liquid coating layers or other coatings, or other surface treatments that help contacts  20  attract particles  30 . 
     The attraction of particles  30  to the surfaces of contacts  20  after particles  30  are pressed against contacts  20  is preferably greater than the attraction of particles  30  to surface  84  of member  82 , so that particles  30  that touch the surfaces of contacts  20  will adhere to the surfaces of contacts  20  and will separate from surface  84  of member  82  as member  82  is retracted in direction  86  as shown in  FIG. 14 . This process places particles  30  on the surfaces of contacts  20  while leaving the gaps between contacts  20  free of particles  30 . 
     In general, particles  30  may be applied to contacts  20  using magnetic fields or without applying magnetic fields. In scenarios in which particles  30  are transferred to contacts  20  without applying a magnetic field, an appropriate amount of pressure should be applied to transfer particles  30  from surface  84  to contacts  20 . Once the applied pressure (pressing member  82  with particles  30  toward contacts  20 ) is strong enough, particles  30  may be satisfactorily transferred from surface  84  to contacts  20 . Care should be taken, however, to ensure that the applied pressure is not too strong, which might cause particles  30  to be transferred to gaps  28 . Because of this consideration, pressure-based transfer techniques preferably involve accurate pressure control (short working range). In contrast, arrangements involving the application of magnetic fields may allow for a longer working range because such arrangements do not generally involve the generation of high pressure while pressing particles  30  against the surfaces of contacts  20 . Transfer techniques involving pressure-based particle transfer may sometimes be referred to as “hard contact” transfer techniques, whereas transfer techniques involving the use of magnetic fields may sometimes be referred to as “soft contact” transfer techniques. 
     After coating contacts  20  with particles  30 , liquid or solid polymer  32  may be placed between components  12  and  14 . As shown in  FIG. 15 , components  12  and  14  may be aligned so that contacts  16  align with contacts  20 . Tool structures  74  and  76  may then be moved in directions  78  while applying heat and optional ultraviolet light to polymer  32 . This melts and/or cures uncured liquid polymer  32 . Conductive particles  30  are embedded within polymer  32  and are therefore crushed between opposing contacts on substrates  18  and  22  to electrically short the opposing contacts to each other. After cooling, tool structures  74  and  76  may be removed. Polymer  32  may attach components  12  and  14  together while the presence of conductive particles  30  shorts contacts  16  to corresponding contacts  20 . 
     As the examples of  FIGS. 7-15  demonstrate, anisotropic conductive adhesive formed from polymer and conductive particles may be used in forming conductive bonds between mating metal contacts. During bond formation, the density of conductive particles overlapping contacts in a component can be enhanced relative to the density of the conductive particles in gaps between the contacts using field-directed assembly techniques (e.g., by applying static and/or alternating-current magnetic fields and/or electric fields to the conductive particles) or by using a transfer member process. Fields may be applied to particles using the contacts while an external source such as a permanent magnet is used to produce a magnetic field and/or a voltage generator is used to generate static and/or alternating current voltages for the contacts that cause the contacts to generate respective static and/or alternating-current electric fields. 
     The foregoing is merely illustrative and various modifications can be made to the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20170106
Publication Date: 20180410
Grant Date: 20180410
Priority Date: 20160923
Inventors: HAN KOOHEE
CHEN HUI
SUNG KUO-HUA
LIU CYRUS Y.
Tan To C.
Assignee: APPLE INC
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Family ID: 61685986