PATENT DOCUMENT

Publication Number: US-10224304-B2
Application Number: US-201715421194-A
Country: US
Kind Code: B2

Title: Conductive adhesive film structures

Abstract:
Conductive adhesive films can include a binding material having a first set of conductive particles therewithin. The binding material can be electrically non-conductive and can flow between and bond external electronic components during a bonding process. The first set of conductive particles can each have cores formed of a first material, such as polymer, and coatings surrounding the cores, the coatings formed of a second material that is electrically conductive, such as nickel. The binding material can also include a second set of smaller conductive particles formed of a third material that is electrically conductive, such as copper, which can have coatings formed of a fourth material that is electrically conductive, such as silver. The first set of conductive particles can each be sphere shaped, and the second set of conductive particles can each be flake shaped. The conductive particles can form electrical paths between the external electronic components.

Claims:
What is claimed is: 
     
       1. A conductive adhesive, comprising:
 a binding material configured to flow between and bond electrical contacts during a bonding process, the binding material being electrically non-conductive; 
 a first conductive particle contained within the binding material, wherein the first conductive particle includes a non-electrically conductive core surrounded by a first electrically conductive material; and 
 a second conductive particle contained within the binding material, wherein the second conductive particle includes an electrically conductive core composed of a second electrically conductive material and the second conductive particle is smaller than the first conductive particle. 
 
     
     
       2. The conductive adhesive of  claim 1 , wherein the first conductive particle is characterized as having a diameter that is at least four times a length of the second conductive particle. 
     
     
       3. The conductive adhesive of  claim 1 , wherein the first conductive particle has a generally spherical shape, and the second conductive particle has a generally flake shape. 
     
     
       4. The conductive adhesive of  claim 1 , wherein the non-electrically conductive core of the first conductive particle is composed of a polymer. 
     
     
       5. The conductive adhesive of  claim 1 , wherein the first electrically conductive material is composed of nickel and the second electrically conductive material is composed of copper. 
     
     
       6. The conductive adhesive of  claim 1 , wherein the electrically conductive core of the second conductive particle is surrounded by a coating. 
     
     
       7. The conductive adhesive of  claim 6 , wherein the coating has a thickness of about 1 micrometer to about 2 micrometers. 
     
     
       8. The conductive adhesive of  claim 6 , wherein the electrically conductive core of the second conductive particle is composed of copper and the coating is composed of one or both of silver and nickel. 
     
     
       9. The conductive adhesive of  claim 1 , wherein the first conductive particle has a diameter between about 5 micrometers and about 30 micrometers. 
     
     
       10. The conductive adhesive of  claim 1 , wherein the second conductive particle has a length that is at least ten times greater than a thickness of the second conductive particle. 
     
     
       11. An electronic device, comprising:
 a first electronic component having a first electrical contact; 
 a second electronic component having a second electrical contact; and 
 a conductive adhesive electrically coupling the first electronic component to the second electronic component, the conductive adhesive including a first conductive particle and a second conductive particle, wherein the first conductive particle includes a non-electrically conductive core surrounded by a first electrically conductive material, and wherein the second conductive particle includes an electrically conductive core composed of a second electrically conductive material and the second conductive particle is smaller than the first conductive particle. 
 
     
     
       12. The electronic device of  claim 11 , wherein the first electrical contact is composed of aluminum and the second electrical contact is composed of copper. 
     
     
       13. The electronic device of  claim 11 , wherein the first conductive particle is characterized as having a diameter that is at least four times a length of the second conductive particle. 
     
     
       14. The electronic device of  claim 11 , wherein the non-electrically conductive core of the first conductive particle is composed of a polymer. 
     
     
       15. The electronic device of  claim 11 , wherein the first conductive particle has a generally spherical shape, and the second conductive particle has a generally flake shape. 
     
     
       16. The electronic device of  claim 11 , wherein one or both of the first electrical contact and the second electrical contact have a bonding pad characterized by a bonding area ranging between about 0.5 mm 2  to about 2 mm 2 . 
     
     
       17. The electronic device of  claim 11 , wherein the electrically conductive core of the second conductive particle is surrounded by a coating. 
     
     
       18. The electronic device of  claim 17 , wherein the electrically conductive core of the second conductive particle is composed of copper and the coating is composed of one or both of silver and nickel. 
     
     
       19. A method of coupling electronic components, the method comprising:
 placing a conductive adhesive between a first electrical contact of a first electronic component and a second electrical contact of a second electronic component, wherein the conductive adhesive includes a first conductive particle and second conductive particle contained within a binding material, wherein the first conductive particle includes a non-electrically conductive core surrounded by a first electrically conductive material, and wherein the second conductive particle includes an electrically conductive core composed of a second electrically conductive material and the second conductive particle is smaller than the first conductive particle; and 
 compressing the conductive adhesive between the first electrical contact and the second electrical contact, thereby forming an electrical path between the first electrical contact and the second electrical contact. 
 
     
     
       20. The method of  claim 19 , wherein the second conductive particle is positioned between the first conductive particle and one of the first second electrical contact and the second electrical contact during the compressing.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application No. 62/398,265, filed Sep. 22, 2016, and entitled “CONDUCTIVE ADHESIVE FILM STRUCTURES,” which is incorporated herein by reference in its entirety and for all purposes. 
    
    
     FIELD 
     The described embodiments relate generally to adhesive materials. More particularly, the described embodiments relate to conductive adhesive film structures that bond and provide electrical connections for electronic device components. 
     BACKGROUND 
     It is often desirable to couple electronic device components in a manner that also provides electrical contacts. This can sometimes involve the use of an adhesive that facilitates electrical contacts. An anisotropic conductive film (“ACF”) is one example of a conductive adhesive film having electrically conductive particles dispersed within a binder material. ACFs are commonly used, for example, in the manufacture of liquid crystal displays to bond and create electrical connections between display components and integrated circuit (“IC”) components. In some applications, an ACF is placed between electrodes of a display component and electrodes of another electronic or IC component. The components are then pressed together such that both a mechanical bonding and electrical connections are made. The resulting structure is anisotropic with unidirectional electrical connections between the display component and the IC component (e.g., z direction) but no electrical connections between adjacent electrodes of the display component or IC component (e.g., x or y directions). 
     Various ACF and other conductive adhesive film applications can include providing a foil shield for electronic components, such as touch screen sensors or other items where signal shielding is preferable. In some applications, it is also desirable for there to be flexibility in and around the foil shield region. Due to this desire for flexibility, as well as the bonding nature of ACFs and other similar films, this has traditionally required that the foil shield have multiple stacked layers. This results in relatively high costs and a significant thickness to the foil shield. 
     While existing conductive adhesive films have worked well in the past, there can be room for improvement. Accordingly, there is a need for improved conductive adhesive film structures that bond and provide electrical connections for electronic device components. 
     SUMMARY 
     Representative embodiments set forth herein include various structures, methods, and features for the disclosed conductive adhesive film structures. In particular, the embodiments disclosed set forth systems and methods for providing conductive adhesive film structures with robust functionality while being thinner and cheaper than existing conductive adhesive films. 
     According to various embodiments, the disclosed systems and methods can provide improved conductive adhesive films suitable for bonding electronic components. An exemplary conductive adhesive includes a binding material configured to flow between and bond electrical contacts during a bonding process. The binding material is electrically non-conductive. The conductive adhesive also includes a first conductive particle contained within the binding material. The first conductive particle includes a non-electrically conductive core surrounded by a first electrically conductive material. The conductive adhesive further includes a second conductive particle contained within the binding material. The second conductive particle is composed of a second electrically conductive material and is smaller than the first conductive particle. 
     According to some embodiments, an electronic device is described. The electronic device includes a first electronic component having a first electrical contact and a second electronic component having a second electrical contact. The electronic device also includes a conductive adhesive electrically coupling the first electronic component to the second electronic component. The conductive adhesive includes a first conductive particle and a second conductive particle. The first conductive particle includes a non-electrically conductive core surrounded by a first electrically conductive material. The second conductive particle is composed of a second electrically conductive material and is smaller than the first conductive particle. 
     According to further embodiments, a method of coupling electronic components is described. The method involves placing a conductive adhesive between a first electrical contact of a first electronic component and a second electrical contact of a second electronic component. The conductive adhesive includes a first conductive particle and second conductive particle contained within a binding material. The first conductive particle includes a non-electrically conductive core surrounded by a first electrically conductive material. The second conductive particle is composed of a second electrically conductive material and is smaller than the first conductive particle. The methods also involves compressing the conductive adhesive between the first electrical contact and the second electrical contact, thereby forming an electrical path between the first electrical contact and the second electrical contact. 
     This Summary is provided merely for purposes of summarizing some example embodiments so as to provide a basic understanding of some aspects of the subject matter described herein. Accordingly, it will be appreciated that the above-described features are merely examples and should not be construed to narrow the scope or spirit of the subject matter described herein in any way. Other features, aspects, and advantages of the subject matter described will become apparent from the following Detailed Description, Figures, and Claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The included drawings are for illustrative purposes and serve only to provide examples of possible structures and methods for the disclosed conductive adhesive film structures. These drawings in no way limit any changes in form and detail that may be made to the embodiments by one skilled in the art without departing from the spirit and scope of the embodiments. The embodiments will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements. 
         FIG. 1A  illustrates in side cross-sectional view an exemplary ACF structure prior to flowing according to various embodiments of the present disclosure. 
         FIG. 1B  illustrates in side cross-sectional view an exemplary ACF structure after flowing according to various embodiments of the present disclosure. 
         FIG. 2A  illustrates in side cross-sectional view an exemplary conductive adhesive film application using a polyimide and copper foil shield according to various embodiments of the present disclosure. 
         FIG. 2B  illustrates in side cross-sectional view an exemplary conductive adhesive film application using an aluminum foil shield according to various embodiments of the present disclosure. 
         FIG. 3A  illustrates in side cross-sectional view an exemplary conductive adhesive film structure for use with an aluminum foil shield according to various embodiments of the present disclosure. 
         FIG. 3B  illustrates in side cross-sectional view an exemplary conductive adhesive film structure having coated particles for use with an aluminum foil shield according to various embodiments of the present disclosure. 
         FIGS. 4A and 4B  illustrate in side cross-sectional views an exemplary conductive adhesive film structure having a first set of coated sphere-shaped particles and a second set of flake-shaped particles for use with an aluminum foil shield according to various embodiments of the present disclosure. 
         FIGS. 4C and 4D  illustrate in side cross-sectional views an exemplary conductive adhesive film structure having a first set of coated sphere-shaped particles and a second set of coated flake-shaped particles for use with an aluminum foil shield according to various embodiments of the present disclosure. 
         FIG. 5  illustrates a flowchart of an exemplary method for coupling electronic components according to various embodiments of the present disclosure. 
         FIG. 6  illustrates in block diagram format an exemplary computing device that can contain the disclosed conductive adhesive film structures according to various embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Various conductive adhesive film applications can include providing a flexible foil shield for electronic components, such as touch screen sensors or other items where flexibility and signal shielding are desirable. Due to this desire for flexibility, as well as the bonding nature of ACFs and other similar bonding films, this has traditionally required that the foil shield have multiple stacked layers. This results in a significant thickness to the foil shield, as well as a relatively high cost. While existing conductive adhesive films have worked well in the past, there can be room for improvement. Accordingly, there is a need for improved conductive adhesive film structures that facilitate the bonding of electronic device components. 
     According to various embodiments, the disclosed systems and methods can provide improved conductive adhesive films suitable for bonding electronic components. These conductive adhesive films can be anisotropic in nature, and can include at least a binding material and one or more sets of conductive particles contained therein. The binding material can be electrically non-conductive and can flow during a bonding process to bond other external electronic components. Some or all of the conductive particles can have a core formed of a first material and a coating formed of a second material that is electrically conductive, the coating surrounding the core. Anisotropic electrical paths between the external electronic components that include the conductive particles can be formed when the binding material flows. 
     In various embodiments, the core can be a flexible polymer, while the coating can be a metal, such as nickel. The binding material can also include a second set of smaller conductive particles that help to form the electrical paths. Each of the second set of conductive particles can be formed of a third material that is electrically conductive, such as copper, and each can have a coating that is formed of a fourth material that is electrically conductive, such as silver. The first set of conductive particles can each be sphere shaped, and the second set of conductive particles can be flake shaped, having a length that is at least ten times greater than its thickness. An exemplary application can include a foil aluminum shield having the foregoing conductive adhesive film on one or both sides thereof. 
     The foregoing approaches provide various methods, components, and features for the disclosed conductive adhesive film structures. A more detailed discussion of these methods, components, and features thereof is set forth below and described in conjunction with  FIGS. 1-6 , which illustrate detailed diagrams of devices and components that can be used to implement these methods, components, and features. 
     Turning first to  FIG. 1A , an exemplary ACF structure prior to flowing is shown in side cross-sectional view. In pre-flow arrangement  100 , an electrically conductive film  102  is positioned between a first substrate  104  and a second substrate  106 . In the case of a display assembly, for example, first substrate  104  can correspond to an IC substrate and second substrate  106  can correspond to a display substrate as part of a display assembly. In some embodiments, the IC substrate can be a flexible circuit substrate. First substrate  104  includes first bonding pads (which can be referred to as first contacts or first electrical contacts)  108  that are electrically coupled to an electrical circuit of first substrate  104 . Likewise, second substrate  106  includes second bonding pads  110  (which can be referred to as second contacts or second electrical contacts) that are electrically coupled to an electrical circuit of second substrate  106 . Bonding pads  108  and  110  can be referred to as contact pads or contacts. Electrically conductive film  102  includes conductive particles  112  that are dispersed within binding material  114 , which can be composed of any suitable material including suitable resin or polymer material. Binding material  114  can be primarily liquid form when applied between substrates  104  and  106 , and can transition to a solid form using a curing process. In some embodiments, conductive particles  112  are isotropically (i.e., evenly) distributed within binding material  114 . Conductive particles  112  generally have an average diameter on the scale of a few micrometers, with electrically conductive film  102  having a thickness on the scale of tens of micrometers. In one embodiment, conductive particles  112  have an average diameter of about 3 to 4 micrometers. 
     Continuing with  FIG. 1B , an exemplary ACF structure after flowing is similarly shown in side cross-sectional view. In post-flow arrangement  101 , the first substrate  104  is bonded to the second substrate  106  by compressing first substrate  104  and second substrate  106  together under high pressure and temperature conditions. For example, a bonding machine set at temperatures of about 100 to about 200 degrees Celsius can be used. The high temperature and pressure conditions cause the viscosity of electrically conductive film  102  to decrease and become liquefied. As such, binding material  114  spreads within the voids between first substrate  104  and second substrate  106 . In addition, conductive particles  112  move with the flow of binding material  114  and become redistributed within the compressed space between first substrate  104  and second substrate  106 . In this way, some of conductive particles  112 , such as conductive particle  112   a , get trapped between first bonding pads  108  and second bonding pads  110 . In particular, particle  112   a  gets trapped between spatially matched first bond pad  108  and second bond pad  110 . After some time (e.g., a few seconds), binding material  114  cools downs and becomes solid again. The resultant ACF structure includes conductive particles  112  positioned between first bonding pads  108  and second bonding pads  110 , which thereby provides electrical conduction between the electrical circuits of first substrate  104  and the electrical circuits of second substrate  106 . In an ideal ACF structure, conductive particles  112  provide electrical paths between first bonding pads  108  and second bonding pads  110 , but not between adjacent bonding pads (e.g., between adjacent first bonding pads  108  or between adjacent second bonding pads  110 ). This preferential vertical or z-direction conduction is what gives ACF structure  100  its ideally anisotropic electrical conduction characteristic. 
       FIG. 2A  illustrates in side cross-sectional view an exemplary conductive adhesive film application using a polyimide and copper foil shield according to various embodiments of the present disclosure. Arrangement  200  includes a sensor  204  or other suitable substrate or electronic component, which can have one or more bonding pads  208  or other suitable electrical contacts. A foil shield  220  can be placed atop sensor  204 , which can be accomplished by way of a layer of conductive adhesive film  202  at one surface of the foil shield  220 . Another layer of conductive adhesive film  202  can also be located above the foil shield  220 , which other layer can be used to bond one or more other electronic components to another surface of the foil shield that is opposite the surface where the sensor  204  is located. Foil shield  220  can be a flexible printed circuit, and/or can provide EMF shielding and/or other benefits to the sensor  204  or other electronic component that it shields. Foil shield  220  can include multiple flexible layers, such as a non-conductive layer  222 , a conductive layer  224 , and a coverlay  226  that provides access to one or more electrical contacts  228 . In some arrangements, the non-conductive layer  222  can be a flexible polyimide substrate, the conductive layer  224  can be copper, the coverlay  226  can be a thin polyimide, and the electrical contact(s)  228  can be electroless nickel immersion gold (“ENIG”), for example. The electrical contact(s)  228  can provide a ground path for the sensor  204  via the bonding pad(s)  208  in some arrangements. 
     In various arrangements, the foil shield  220  can be coupled with the two layers of conductive adhesive film  202  on the top and bottom thereof to form a roll-to-roll material suitable for mass manufacturing operations. The thickness of the foil shield  220  itself can be about 34 to 37 micrometers. In various applications, the foil shield  220  and conductive adhesive film  202  stack can be located at both a top and bottom surface of the sensor  204  or other electronic component, such that the sensor  204  is sandwiched between two separate stacks having a foil shield  220 . Because separate foil shields  220  can be located both above and below the planar sensor  204  layer then, the total thickness for both foil shields can then be about 70 micrometers or more in some arrangements. 
     In the portion shown as contacting sensor  208 , the conductive adhesive film  202  can have a binding material  214  containing conductive particles  212  therein, similar to that which is provided above for electrically conductive film  102  having a binding material  114  containing conductive particles  112  therein. Similar to the foregoing arrangement, binding material  214  can be an organic resin configured to flow during a high temperature and pressure bonding process, and conductive particles  212  can be isotropically distributed within the binding material  214  and configured to facilitate the creation of electrical paths between the bonding pads  208  and electrical contacts  228 . 
       FIG. 2B  illustrates in side cross-sectional view an exemplary conductive adhesive film application using an aluminum foil shield according to various embodiments of the present disclosure. Arrangement  201  similarly includes a sensor  204  or other suitable substrate or electronic component, which can have one or more bonding pads  208  or other suitable electrical contacts. A foil shield  230  can similarly be placed atop sensor  204 , which can similarly be accomplished by way of a layer of conductive adhesive film  240  at one surface of the foil shield  230 . Again, another layer of conductive adhesive film  240  can also be located above the foil shield  230 , which other layer can be used to bond one or more other electronic components to another surface of the foil shield that is opposite the surface where the sensor  204  is located. Foil shield  230  can similarly be flexible, and can provide EMF shielding and/or other benefits to the sensor  204  or other electronic component that it shields. Unlike foregoing arrangement  200 , however, the foil shield  230  of arrangement  201  can simply comprise a layer of aluminum foil. In some arrangements, foil shield  230  may also include a thin layer of aluminum oxide as well. The aluminum foil shield  230  can provide a ground path for the sensor  204  via the bonding pad(s)  208  in some arrangements. 
     In various arrangements, the foil shield  230  can be coupled with the two layers of conductive adhesive film  240  on the top and bottom thereof to form a roll-to-roll material suitable for mass manufacturing operations. The thickness of the foil shield  230  can be about 20 to 25 micrometers in some arrangements, which provides a significant reduction in thickness to the previous foil shield. In various applications, the foil shield  230  and conductive adhesive film  240  stack can similarly be located at both a top and bottom surface of the sensor  204  or other electronic component, such that the sensor  204  is sandwiched between two separate stacks having a foil shield  230 . In arrangements where separate foil shields  230  are located both above and below the sensor  204  layer then, this results in a total foil shield thickness of about 40 to 50 micrometers. Accordingly, use of an aluminum foil shield results in a total stack thickness that is about 20 to 30 micrometers less than the total stack thickness of a traditional polyimide and copper foil shield. Furthermore, the cost of aluminum foil shield  230  is significantly less than the cost of foil shield  220  above. 
     In the portion shown as contacting sensor  208 , the conductive adhesive film  240  can be an anisotropic conductive film or an isotropic conductive film. Also, the conductive adhesive film  240  can have a binding material  244  containing conductive particles  242  therein. Binding material  244  can be a polymer, such as an organic resin configured to flow during a high temperature and pressure bonding process. Conductive particles  242  can be isotropically distributed within the binding material  244  and configured to facilitate the creation of electrical paths between the bonding pads  208  and the aluminum foil shield  230 . Unlike the foregoing arrangements, the conductive particles  242  can have substantially different properties, and may be different from each other in some ways, as set forth in greater detail below. 
     The embodiments described herein provide alternative conductive adhesive film structures that are suitable for use with flexible foil shields formed from aluminum rather than polyimide and copper. In some embodiments, the alternative conductive adhesive film structures include a first set of conductive particles that may be coated, described below with reference to  FIGS. 3A-3B . In some embodiments, the alternative conductive adhesive film structures include first and second sets of conductive particles that may be coated and having varying properties, described below with reference to  FIGS. 4A-4D . An exemplary method for coupling electronic components using such an alternative conductive adhesive film structure is provided at  FIG. 6 , and an exemplary device having such a film structure is provided at  FIG. 7 . 
       FIG. 3A  illustrates in side cross-sectional view an exemplary conductive adhesive film structure for use with an aluminum foil shield according to various embodiments of the present disclosure. Post-flow arrangement  301  depicts a close-up view of what one alternative conductive adhesive film structure looks like after flowing with respect to a suitable bonding pad  308  as one external electronic component and an aluminum layer  330  as another external electronic component. It will be readily appreciated that the bonding pad  308  can be included on a surface of a larger sensor or other suitable electronic component (not shown), and that the aluminum layer  330  can be part of a larger aluminum foil shield suitable for providing shielding for the larger sensor or other electronic component. Similar to the foregoing example, aluminum layer  330  can be a foil layer that is about 20 to 25 micrometers thick in some arrangements. Bonding pad  308  can be a copper, copper alloy, or ENIG pad, for example, among other possible types of electrical connectors. In addition, an aluminum oxide layer  331  or other suitable passivation or protective layer may also be formed at the surface of the aluminum layer  330 . 
     As shown, a conductive adhesive layer  340  has flowed during a bonding process to couple and provide electrical connectivity between the bonding pad  308  and aluminum layer  330 . Conductive adhesive layer  340  can be an anisotropic conductive film or an isotropic conductive film. Conductive adhesive layer  340  can include a binding material  344  and a plurality of conductive particles  342  that provide electrical paths from the bonding pad  308  to the aluminum layer  330 . These electrical paths created from the bonding pad  308  to the aluminum layer  330  can be ground paths, for example. The binding material  344  can be a polymer, such as an organic resin configured to flow during a high temperature and pressure bonding process. In various embodiments, binding material  344  can comprise an acrylic, epoxy, elastomer, other resin, coupling agent (e.g., silane or siloxane), or any suitable mixture thereof. The binding material  344  may also include a corrosion inhibitor in some arrangements, so as to limit the amount of corrosion to the aluminum layer. 
     In various embodiments, the conductive particles  342  can be solid nickel particles, which are hard enough to dent through aluminum oxide layer  331  to provide the electrical paths. Due to the relative inelasticity of nickel and mismatches in the thermal expansion properties of the various components, however, there can be some drawbacks with the use of arrangement  301  over time, particularly with respect to cycled use and low resiliency over time. In particular, nickel can be sufficiently hard, but is relatively inelastic and not resilient. Accordingly, further examples using multiple materials for the conductive particles are also provided. 
       FIG. 3B  illustrates in side cross-sectional view an exemplary conductive adhesive film structure having coated particles for use with an aluminum foil shield according to various embodiments of the present disclosure. Post-flow arrangement  303  similarly depicts a close-up view of what another alternative conductive adhesive film structure looks like after flowing with respect to a suitable bonding pad  308  as one external electronic component and an aluminum layer  330  as another external electronic component. Again, it will be readily appreciated that the bonding pad  308  can be included on a surface of a larger sensor or other suitable electronic component (not shown), and that the aluminum layer  330  can be part of a larger aluminum foil shield suitable for providing shielding for the larger sensor or other electronic component. Similar to the foregoing example, aluminum layer  330  can be a foil layer that is about 20 to 25 micrometers thick in some arrangements. Bonding pad  308  can be a copper, copper alloy, or ENIG pad, for example, among other possible types of electrical connectors. In addition, an aluminum oxide layer  331  or other suitable passivation or protective layer may also be formed at the surface of the aluminum layer  330 . 
     As shown, a conductive adhesive layer  341  has flowed during a bonding process to couple and provide electrical connectivity between the bonding pad  308  and aluminum layer  330 . Conductive adhesive layer  341  can be an anisotropic conductive film or an isotropic conductive film. Conductive adhesive layer  341  includes a binding material  344 , as detailed above, and a plurality of coated conductive particles  343  that provide electrical paths from the bonding pad  308  to the aluminum layer  330 . These electrical paths created from the bonding pad  308  to the aluminum layer  330  can be ground paths, for example. In various embodiments, the coated conductive particles  343  can form about 10% of the volume of conductive adhesive layer  341 , and/or these coated conductive particles  343  can be spherical or substantially spherical in shape. In various embodiments, the coated conductive particles  343  can be mono-dispersed throughout the binding material  344 , with each of the particles having a size that is within about 10% of a standard size for the set of particles. This standard size for the coated conductive particles  343  can be a diameter of between about 5 to 30 micrometers. In some arrangements, this diameter can be about 25 micrometers. 
     Each coated conductive particle  343  can have a core  345  of one material and a coating  346  (also referred to as a shell) of another different material, with the coating preferably being electrically conductive. For example, coated conductive particles  343  can have cores  345  that are a flexible polymer and coatings  346  that are an electrically conductive material, such as a metal. In various embodiments, the coating  346  can have a thickness of about 1 to 2 micrometers. Preferably, the combination of materials is hard enough to dent through aluminum oxide layer  331  to provide the electrical paths, while still having sufficient elasticity and resiliency still to provide reliable electrical paths over time, many use cycles, and/or many thermal cycles. 
     Various combinations of materials for coated conductive particles  343  have been found to provide varying results. For example, where the cores  345  are a flexible polymer and the coatings  346  are gold, the resulting coated conductive particles  343  tend to be too soft to dent through the aluminum oxide layer  331  to reach the aluminum layer reliably. As another example, where the cores  345  are a flexible polymer and the coatings  346  are nickel, there can be adequate denting through the aluminum oxide layer  331  due to the nickel coatings, as well as sufficient elasticity or retraction in the particles due to the flexible polymer cores. In some embodiments, coatings  346  are composed of nickel and another metal, such as gold. As another example, where the cores  345  are copper and the coatings  346  are silver, there can be a good amount of denting through the aluminum oxide layer  331 , but a lesser amount of elasticity or retraction in the particles due to the metal cores. In general then, good results can be obtained using coated conductive particles  343  having flexible cores  345  and hard and electrically conductive coatings  346 . In some embodiments, the cores  345  can be a flexible polymer that is also electrically conductive, such as a polymer saturated with a metallic powder, for example. This can provide added conductivity across a given coated conductive particle  343 . 
       FIGS. 4A and 4B  illustrate in side cross-sectional views an exemplary conductive adhesive film structure having a first set of coated sphere-shaped particles and a second set of flake-shaped particles for use with an aluminum foil shield according to various embodiments of the present disclosure. Post-flow arrangement  401  is similar to foregoing examples in that it also depicts a close-up view of what yet another alternative conductive adhesive film structure looks like after flowing with respect to a suitable bonding pad  408  as one external electronic component and an aluminum layer  430  as another external electronic component. Again, it will be readily appreciated that the bonding pad  408  can be included on a surface of a larger sensor or other suitable electronic component (not shown), and that the aluminum layer  430  can be part of a larger aluminum foil shield suitable for providing shielding for the larger sensor or other electronic component. Similar to the foregoing examples, aluminum layer  430  can be a foil layer that is about 20 to 25 micrometers thick in some arrangements. Bonding pad  408  can be a copper, copper alloy, or ENIG pad, for example, among other possible types of electrical connectors. In addition, an aluminum oxide layer  431  or other suitable passivation or protective layer may also be formed at the surface of the aluminum layer  430 . 
     As shown, a conductive adhesive layer  440  has flowed during a bonding process to couple and provide electrical connectivity between the bonding pad  408  and aluminum layer  430 . Conductive adhesive layer  440  can be an anisotropic conductive film or an isotropic conductive film. Conductive adhesive layer  440  includes a binding material  444 , a first set of coated conductive particles  443 , and a second set of conductive particles  450 . Binding material  444  can be identical or substantially similar to binding material  344  above. Both sets of conductive particles  443  and  450  help to provide electrical paths from the bonding pad  408  to the aluminum layer  430 . These electrical paths created from the bonding pad  408  to the aluminum layer  430  can again be ground paths, for example. The first set of coated conductive particles  443  can be spherical or substantially spherical in shape in various embodiments. 
     Each coated conductive particle  443  can again have a core  445  of one material and a coating  446  of another different material, with the coating preferably being electrically conductive. Preferably, the combination of materials is hard enough to dent through aluminum oxide layer  431  to provide the electrical paths to the aluminum layer  430 , as shown. In some embodiments, the cores  445  can be a flexible polymer while the coatings  446  can be nickel. In some variations, the first set of coated conductive particles  443  can be further coated with a thin layer of gold (not shown), which additional coating can function to provide even greater electrical conductivity. Again, coated conductive particles  443  can form about 10% of the volume of conductive adhesive layer  440 , can be spherical or substantially spherical in shape, can be mono-dispersed throughout the binding material  444 , and each of the particles having a size that is within about 10% of a standard size for the set of particles, with the standard size diameter being between about 5 to 30 micrometers. In some arrangements, this diameter can be about 25 micrometers. The coatings  446  can have a thickness of about 1 to 2 micrometers. 
     In various embodiments, the second set of conductive particles  450  can include solid particles that are smaller than the particles in the first set of coated conductive particles  443 . The second set of conductive particles  450  can be composed of any suitable conductive material. In some particular embodiments, the second set of conductive particles  450  are formed of solid copper. The conductive particles  450  of second set can be substantially smaller than the conductive particles  443  of the first set. For example, the conductive particles  443  of the first set can be at least four times larger than the conductive particles  450  of the second set. In particular embodiments, the diameters of the conductive particles  443  of the first set are at least four times greater than the lengths of the conductive particles  450  of the second. In this manner, the second set of conductive particles  450  can serve to fill gaps in the flowed binding material  444  to create parts of and/or enhance the existing electrical paths created by the first set of coated conductive particles  443  between the bonding pad  408  and the aluminum layer  430 . For example, in some, many, or all locations, a given coated conductive particle  443  may not contact both the aluminum layer  430  and the underlying bonding pad  408 . In such locations, one or more of the second set of conductive particles  450 , which again may be smaller in size, can bridge the gap between the coated conductive particle and the bonding pad  408  to create a complete electrical path. For example, a given electrical path through the binding material  444  may include a single coated conductive particle  443  and multiple conductive particles  450 . Again, such an electrical path can be a ground path. In some embodiments, all of the electrical paths to the aluminum layer  430  can be ground paths. 
     Some or all of the second set of conductive particles  450  can be flake shaped in some embodiments. That is, some or all of these conductive particles can define a length and a thickness where the length is substantially greater than the thickness. In some cases, the second set of conductive particles  450  have lengths that are about ten times greater than their widths, or greater. This is sometimes referred to as an aspect ratio (length-to-width) of about 10 to 1 (10:1) or greater. For example, the length can be about 5 micrometers, while the width is about 0.5 micrometers for many or all of the second set of conductive particles  450 . Due to this flake shape, and the smaller nature of the second set of conductive particles  450 , these secondary particles are better configured to fill gaps and bridge contacts where the sphere shaped and primary first set of conductive particles  443  may not complete a given electrical contact or connection. For example, where compression or reflowing of the binding material  444  and overall conductive adhesive layer  440  is restricted, the use of the second set of conductive particles  450  helps to complete electrical paths where the first set of conductive particles  443  provides most or a substantial portion of the electrical paths. In this manner, there can be some electrical paths formed where no single particle contacts both of the bonding pad  408  and the aluminum layer  430 . Due to the small nature of the second set of conductive particles  450 , however, it is unlikely for these particles alone to establish any given electrical path, particularly where their density within the binding material is appropriately controlled. This can serve to prevent or limit the amount of electrical path shorts between contacts of the same electronic component, for example. 
       FIG. 4B  shows how second set of conductive particles  450 , due to their smaller size and/or flake shape, can become positioned between the first set of conductive particles  443  and aluminum layer  430  and bonding pad  408  during the bonding process (i.e., based on the flow of binding material  444 ). This positioning of the second set of conductive particles  450  can occur when the bonding surface areas of bonding pad  408  and/or aluminum layer  430  are relatively large. For example, in some applications the bonding area of bonding pad  408  is between about 0.5 mm 2  to about 2 mm 2 . In some applications the bonding area of bonding pad  408  is between about 6.5 mm 2  to about 2.5 cm 2 . In particular, when bonding pad  408  and aluminum layer  430  have relatively large bonding surface areas, they may bow during the compression process due, thereby creating spaces between bonding pad  408  and aluminum layer  430  in middle regions the bonding pad  408 . Without the first set of conductive particles  443 , binding material  444  can flow in these larger spaces, which creates an insulation gap and blocking electrical coupling. The smaller second set of conductive particles  450  can become positioned in these constrained spaces between aluminum layer  430  and bonding pad  408 , thereby bridging the conductive path between aluminum layer  430  and bonding pad  408 .  FIGS. 4A and 4B  show how second set of conductive particles  450  can position themselves during the bonding process in a way that adapts to the local topography to create conductive paths between aluminum layer  430  and bonding pad  408 . Thus, the combination of the larger first set of conductive particles  443  and the smaller second set of conductive particles  450  (which can be referred to as a hierarchical scheme) provide an electrically conductive adhesive that adapts to and self-adjusts based on the geometry of surrounding structures. 
       FIGS. 4C and 4D  illustrate in side cross-sectional views an exemplary conductive adhesive film structure having a first set of coated sphere-shaped particles and a second set of coated flake-shaped particles for use with an aluminum foil shield according to various embodiments of the present disclosure. Post-flow arrangement  403  is similar to the foregoing examples, particularly arrangement  401  above. In particular, all items can be similar or identical to those of arrangement  401 , with the exception of the second set of conductive particles  453 . Unlike the foregoing arrangement  401 , however, arrangement  403  can include a conductive adhesive layer  441  that can have a second set of conductive particles  453  that are coated with a different material. For example, the second set of conductive particles  453  can have cores  455  of one material and coatings  456  of another material. As one non-limiting example, the second set of conductive particles  453  can have copper cores  455  and silver coatings  456 . Again, these secondary conductive particles can be flake shaped, and can be smaller than the sphere shaped primary or first set of conductive particles  443 . 
       FIG. 4D  shows how second set of conductive particles  453 , become positioned between the first set of conductive particles  443  and aluminum layer  430  and bonding pad  408  during the compression process due to their smaller size and/or flake shape. As described above with reference to  FIG. 4B , second set of conductive particles  453  can bridge a conductive path between aluminum layer  430  and bonding pad  408  that would otherwise be filled with insulating binder material  444  in cases where the bonding surface areas of bonding pad  408  and/or aluminum layer  430  are relatively large. 
     Turning next to  FIG. 5 , a flowchart of an exemplary method for coupling electronic components is provided. Method  500  can be carried out by one or more processors or other controllers that may be associated with an automated manufacturing system, for example. Method  500  starts at a first process step  502 , where a conductive adhesive film can be formed. Such a conductive adhesive film can be that of any of the foregoing examples, such as, for example, conductive adhesive layers  240 ,  340 ,  341 ,  440 , or  441 . The conductive adhesive film can comprise a binding material having various conductive particles contained therein. In some arrangements, the conductive particles can include a first set of conductive particles having a core formed of a first material and a coating surrounding the core and formed of a second material that is electrically conductive. In some embodiments, the conductive particles can further include a second set of conductive particles formed of a third material that is also electrically conductive. The second set of conductive particles may also have coatings formed of a fourth material, which may also be electrically conductive. Again, any of the foregoing arrangements can have the conductive adhesive film formed at process step  502 . 
     At a following process step  504 , the conductive adhesive film can be placed between electronic components. This can include, for example, a first electronic component having a first set of electrical contacts and a second electronic component having a second set of electrical contacts. In some embodiments, the first electronic component can be a sensor, while the second electronic component can be a foil shield. The first and second electronic components can be various display and other IC components as well. At the next process step  506 , the conductive adhesive film can be compressed between the first electronic component and the second electronic component. This can be part of a bonding process, and may include a temperature increase as well. The compressing can form electrical paths between the electronic components. For example, electrical paths can be formed between the first set of electrical contacts and the second set of electrical contacts using a first set of conductive particles and a second set of conductive particles. In various embodiments, this can include a first set of sphere shaped conductive particles and a second set of smaller flake shaped conductive particles. In some embodiments, at least some of the electrical paths can have no conductive particles that contact both of the electrically coupled contacts from the first and second electronic components. 
     For the foregoing flowchart, it will be readily appreciated that not every step provided is always necessary, and that further steps not set forth herein may also be included. For example, added steps that involve details regarding the formation of the conductive adhesive film may be added. Also, steps that provide more detail with respect to the amount of compression force, the temperature rise, and the amount of time for a full bonding process may be added. Other steps not included may also involve testing steps for the bonded components. Further, the exact order of steps may be altered as desired, and some steps may be performed simultaneously. For example, steps  502  and  504  may be performed simultaneously in some embodiments. 
       FIG. 6  illustrates in block diagram format an exemplary computing device that can contain the disclosed conductive adhesive film structures, according to some embodiments. In particular, the detailed view illustrates various components that can be included in an electronic device having anisotropic conductive films used to bond components therein, such as that which is described above with respect to  FIGS. 1-5 . As shown in  FIG. 6 , the computing device  600  can include a processor  602  that represents a microprocessor or controller for controlling the overall operation of computing device  600 . The computing device  600  can also include a user input device  608  that allows a user of the computing device  600  to interact with the computing device  600 . For example, the user input device  608  can take a variety of forms, such as a button, keypad, dial, touch screen, audio input interface, visual/image capture input interface, input in the form of other sensor data, etc. Still further, the computing device  600  can include a display  610  (screen display) that can be controlled by the processor  602  to display information to the user (for example, a movie or other AV or media content). A data bus  616  can facilitate data transfer between at least a storage device  640 , the processor  602 , and a controller  613 . The controller  613  can be used to interface with and control different equipment through and equipment control bus  614 . The computing device  600  can also include a network/bus interface  611  that couples to a data link  612 . In the case of a wireless connection, the network/bus interface  611  can include a wireless transceiver. 
     The computing device  600  can also include a storage device  640 , which can comprise a single disk or a plurality of disks (e.g., hard drives), and includes a storage management module that manages one or more partitions within the storage device  640 . In some embodiments, storage device  640  can include flash memory, semiconductor (solid state) memory or the like. The computing device  600  can also include a Random Access Memory (RAM)  620  and a Read-Only Memory (ROM)  622 . The ROM  622  can store programs, utilities or processes to be executed in a non-volatile manner. The RAM  620  can provide volatile data storage, and stores instructions related to the operation of the computing device  600 . 
     The various aspects, embodiments, implementations or features of the described embodiments can be used separately or in any combination. Various aspects of the described embodiments can be implemented by software, hardware or a combination of hardware and software. The described embodiments can also be embodied as computer readable code on a computer readable medium. The computer readable medium is any data storage device that can store data which can thereafter be read by a computer system. Examples of the computer readable medium include read-only memory, random-access memory, CD-ROMs, DVDs, magnetic tape, hard disk drives, solid state drives, and optical data storage devices. The computer readable medium can also be distributed over network-coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. 
     The foregoing description, for purposes of explanation, uses specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of specific embodiments are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the described embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20170131
Publication Date: 20190305
Grant Date: 20190305
Priority Date: 20160922
Inventors: LIN, WEI
GUPTA, NATHAN K.
CHEN, PO-JUI
Assignee: APPLE INC
CPC Classifications: [{"code": "C08K9/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "C08K7/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "C08K2003/0806", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29347", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2924/01028", "inventive": false, "first": false, "tree": "[]"}, {"code": "C08K2003/0862", "inventive": false, "first": false, "tree": "[]"}, {"code": "C08K2003/0862", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L24/32", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L24/83", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2224/2929", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J9/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L24/29", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2924/01047", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29455", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L24/29", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L2224/83201", "inventive": false, "first": false, "tree": "[]"}, {"code": "C08K9/02", "inventive": false, "first": false, "tree": "[]"}, {"code": "C08K7/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L24/83", "inventive": true, "first": false, "tree": "[]"}, {"code": "C09J11/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "C09J11/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2224/29499", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/32227", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2924/07811", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/83851", "inventive": false, "first": false, "tree": "[]"}, {"code": "C08K2201/001", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29439", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2924/01029", "inventive": false, "first": false, "tree": "[]"}, {"code": "C08K2003/0806", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/32225", "inventive": false, "first": false, "tree": "[]"}, {"code": "C08K2201/003", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2924/01047", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2924/01028", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L24/32", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2224/29439", "inventive": false, "first": false, "tree": "[]"}, {"code": "C08K9/02", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L24/83", "inventive": true, "first": false, "tree": "[]"}, {"code": "C09J9/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "C08K7/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29499", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/32227", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/2929", "inventive": false, "first": false, "tree": "[]"}, {"code": "C08K2003/0806", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29347", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/83201", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2924/07811", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J11/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2924/01029", "inventive": false, "first": false, "tree": "[]"}, {"code": "C08K2003/0862", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29455", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L24/29", "inventive": true, "first": true, "tree": "[]"}, {"code": "C08K9/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "C08K2201/001", "inventive": false, "first": false, "tree": "[]"}, {"code": "C08K2201/003", "inventive": false, "first": false, "tree": "[]"}, {"code": "C09J9/02", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L2224/83399", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29455", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29444", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29439", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29124", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29291", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29186", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/2939", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29355", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29347", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/05647", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/05644", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/05155", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/29147", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/2929", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 61620656