Abstract:
An anisotropic electrically conducting interconnect is disclosed in which an adhesive comprising particles having a breakable coating of at least one electrically nonconductive material is compressed between a first contact and a second contact. Compression to two contacts breaks the breakable coating exposing an electrically conducting material which makes contact with the first and second contacts. The electrically conducting material may be a metal conductor or a two-part reactive conductive resin/catalyst system. Also disclosed are processes for making such electrical interconnects and adhesives for use in making electrical interconnect.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a continuation of U.S. Ser. No. 10/842,306, filed May 10, 2004, pending, which is a continuation of U.S. Pat. No. 6,777,071, issued Aug. 17, 2004. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates generally to semiconductors, and more specifically to methods and apparatus for making anisotropic electrical interconnects.  
         [0003]     Anisotropic electrical interconnects are known in the art. U.S. Pat. No. 6,194,492 B1 discloses an anisotropic conductive film which exhibits a conductivity in the thickness direction thereof by pressurizing the film in the thickness direction, the film including: an adhesive; and conductive particles dispersed in the adhesive; wherein the adhesive is a thermosetting or photosetting adhesive containing as a main component at least one kind selected from a group consisting of (a) a polymer obtained by acetalation of a polyvinyl alcohol, (b) a compound containing an allyl group, (c) a monomer containing an acryloxy group or methacryloxy group, and (d) a polymer obtained by polymerization of one or more selected from a group consisting of an acrylic monomer and a methacrylic monomer.  
         [0004]     U.S. Pat. No. 5,932,339 discloses an anisotropically electricity-conductive film obtainable by dispersing in an adhesive agent electrically conductive particles, the adhesive agent being a curable adhesive agent comprising as a major component at least one polymer selected from the group consisting of an ethylene-vinyl acetate copolymer; a copolymer of ethylene, vinyl acetate and an acrylate and/or methacrylate monomer; a copolymer of ethylene, vinyl acetate and maleic acid and/or maleic anhydride; a copolymer of ethylene, an acrylate and/or methacrylate monomer and maleic acid and/or maleic anhydride; and an ionomer resin wherein molecules of an ethylene-methacrylic acid copolymer are linked with each other through a metal ion.  
         [0005]     U.S. Pat. No. 5,865,703 discloses an anisotropic, electrically conductive adhesive film including insulating adhesive, electrically conductive particles dispersed in the electrically insulating adhesive, and transparent, spherical glass particles dispersed in the insulating adhesive.  
         [0006]     U.S. Pat. No. 5,162,087 discloses an anisotropic conductive adhesive composition comprising an insulating adhesive component and particles dispersed in said insulating adhesive component, said anisotropic conductive adhesive composition being characterized in that said insulating adhesive component comprises a copolymer of acrylic ester having an alkyl group of 1-4 carbon atoms and a maleimide derivative, 5 to 60 parts by weight, based on 100 parts by weight of the copolymer, of a thermosetting resin, and 0.05 to 5.0 parts by weight, based on 100 parts by weight of the copolymer, of a coupling agent, and said particles are metallic-layer containing particles comprising a core made of resin, a metallic layer covering said core and a resin layer formed from finely divided resin fixed by the dry blending method on the surface of said metallic layer.  
         [0007]     U.S. Pat. No. 4,740,657 discloses an adhesive composition or film capable of exhibiting anisotropic-electroconductivity comprising electroconductive particles comprising polymeric core materials coated with thin metal layers, and electrically insulating adhesive component.  
         [0008]     U.S. Pat. No. 5,965,064 discloses an anisotropically electroconductive adhesive to be used for establishing electric connection between terminals of, for example, an IC chip and of a circuit pattern, which adhesive comprises an electrically insulating adhesive matrix and electroconductive particles comprise at least two electroconductive particulate products of different average particle sizes and wherein each particle of both the particulate products is coated with an electrically insulating resin insoluble in the insulating adhesive matrix.  
         [0009]     U.S. Pat. No. 5,302,456 discloses an anisotropic conductive material including micro-capsules dispersed in a bonding resin. The micro-capsules contain, as a filler material, a conductor and a polymerization initiator, a curing agent or a curing promotor. A wall member encapsulating the filler material is formed of a thermoplastic or thermosetting insulative resin. Therefore, if the micro-capsules in the anisotropic conductive material are broken or destroyed by pressure or both of pressure and heat, electrical connection can be established between electrode pads and electrode terminals of a wiring substrate through the conductors contained in the micro-capsules. Simultaneously, the polymerization initiator, the curing agent or the curing promotor flows out, so that the insulative bonding resin is solidified.  
         [0010]     The above prior art typically achieves the anisotropic effect by controlling filler loading. In other words, to obtain an anisotropic interconnect the adhesive must use few particles. However, these prior art methods still have serious leakage problems if the filler loading is too high or too uneven. The filler loading is hard to control especially if the filler responds to gravity or magnetic fields.  
       BRIEF SUMMARY OF THE INVENTION  
       [0011]     In one preferred embodiment, the invention is an electrical interconnect comprising (a) at least one first electrical contact; (b) at least one second electrical contact; and, (c) an adhesive interposed between and in contact with the first electrical contact and the second electrical contact, the adhesive comprising an electrically non-conductive resin and particles, the particles comprising at least one electrically conductive material and a breakable coating of at least one electrically non-conductive material, wherein the first electrical contact is positioned close enough to the second electrical contact to break the breakable coating of the particles in the interposed adhesive such that the electrically conducting material of the particles is exposed and in contact with both the first electrical contact and the second electrical contact, wherein the exposed electrically conducting material has sharp edges. This embodiment includes semiconductor dies or chips and semiconductor packages comprising such an interconnect.  
         [0012]     In another preferred embodiment, the invention is an electrical interconnect comprising: (a) a first substrate having a surface and at least one first electrical contact projecting from the first substrate surface; (b) a second substrate having a surface and at least one second electrical contact projecting from the second substrate surface and aligned with the first electrical contact, such that the first substrate surface is substantially parallel to the second substrate surface; and, (c) an adhesive interposed between and in contact with the first substrate surface and electrical contact and the second substrate surface and electrical contact, the adhesive comprising an electrically non-conductive resin and particles, the particles comprising a core of at least one electrically conductive material and a breakable coating of at least one electrically non-conductive material, wherein the first electrical contact is positioned close enough to the second electrical contact to break the breakable coating material of the particles in the adhesive interposed between the first electrical contact and the second electrical contact such that the electrically conducting material of the particles is exposed and in contact with both the first electrical contact and the second electrical contact, wherein the exposed electrically conducting material has sharp edges, provided that the coating of the particles interposed between the first substrate surface and the second substrate surface, but not interposed between the first electrical contact and the second electrical contact, is not broken. This embodiment includes semiconductor dies or chips and semiconductor packages comprising such an interconnect.  
         [0013]     In another preferred embodiment, the invention is an electrical interconnect comprising: (a) at least one first electrical contact; (b) at least one second electrical contact; and, (c) an adhesive interposed between and in contact with the first electrical contact and the second electrical contact, the adhesive comprising an electrically non-conductive resin and particles, the particles comprising a core of at least one electrically conductive reactive material and a breakable coating of at least one electrically non-conductive material, the core comprising: (1) at least one first subparticle comprising a reactive resin, having conductive material therein, encapsulated inside a rupturable membrane; and, (2) at least one second subparticle comprising a catalyst encapsulated inside a rupturable membrane, wherein the first electrical contact is positioned close enough to the second electrical contact to break the breakable coating of the particles in the interposed adhesive such that the first subparticle membrane and the second subparticle membrane are ruptured, whereby the reactive resin and the catalyst react to form a conductive adhesive between the first electrical contact and the second electrical contact. This embodiment includes semiconductor dies or chips and semiconductor packages comprising such an interconnect.  
         [0014]     In yet another preferred embodiment, the invention is an electrical interconnect comprising: (a) a first substrate having a surface and at least one first electrical contact projecting from the first substrate surface; (b) a second substrate having a surface and at least one second electrical contact projecting from the second substrate surface and aligned with the first electrical contact, such that the first substrate surface is substantially parallel to the second substrate surface; and, (c) an adhesive interposed between and in contact with the first electrical contact and the second electrical contact, the adhesive comprising an electrically non-conductive resin and particles, the particles comprising a core of at least one electrically conductive reactive material and a breakable coating of at least one electrically non-conductive material, the core comprising: (1) at least one first subparticle comprising a reactive resin, having conductive material therein, encapsulated inside a rupturable membrane; and, (2) at least one second subparticle comprising a catalyst encapsulated inside a rupturable membrane, wherein the first electrical contact is positioned close enough to the second electrical contact to break the breakable coating of the particles in the interposed adhesive such that the first subparticle membrane and the second subparticle membrane are ruptured, whereby the reactive resin and the catalyst react to form a conductive adhesive between the first electrical contact and the second electrical contact provided that the coating of the particles interposed between the first substrate surface and the second substrate surface, but not interposed between the first electrical contact and the second electrical contact, is not broken. This embodiment includes semiconductor dies or chips and semiconductor packages comprising such an interconnect.  
         [0015]     In yet another preferred embodiment, the invention is an electrical interconnect comprising: (a) at least one first electrical contact; (b) at least one second electrical contact; and, (c) an adhesive interposed between and in contact with the first electrical contact and the second electrical contact, the adhesive comprising: (1) an electrically non-conductive resin; (2) multiple first particles, each first particle comprising a core comprising at least one reactive resin, having an electrically conductive material therein, and a breakable coating of at least one electrically non-conductive material; and (3) multiple second particles, each second particle comprising a core comprising a catalyst and a breakable coating of at least one electrically non-conductive material, wherein the first electrical contact is positioned close enough to the second electrical contact to break the breakable coatings of the first particles and the second particles in the interposed adhesive, whereby the reactive resin and the catalyst react to form a conductive adhesive between the first electrical contact and the second electrical contact. This embodiment includes semiconductor dies or chips and semiconductor packages comprising such an interconnect.  
         [0016]     In another preferred embodiment, the invention is an electrical interconnect comprising: (a) a first substrate having a surface and at least one first electrical contact projecting from the first substrate surface; (b) a second substrate having a surface and at least one second electrical contact projecting from the second substrate surface and aligned with the first electrical contact, such that the first substrate surface is substantially parallel to the second substrate surface; and, (c) an adhesive interposed between and in contact with the first electrical contact and the second electrical contact, the adhesive comprising: (1) an electrically non-conductive resin; (2) multiple first particles, each first particle comprising a core comprising at least one reactive resin, having an electrically conductive material therein, and a breakable coating of at least one electrically non-conductive material; and (3) multiple second particles, each second particle comprising a core comprising a catalyst and a breakable coating of at least one electrically non-conductive material, wherein the first electrical contact is positioned close enough to the second electrical contact to break the breakable coatings of the first particles and the second particles in the interposed adhesive, whereby the reactive resin and the catalyst react to form a conductive adhesive between the first electrical contact and the second electrical contact, contact provided that the coating of the particles interposed between the first substrate surface and the second substrate surface, but not interposed between the first electrical contact and the second electrical contact, is not broken. This embodiment includes semiconductor dies or chips and semiconductor packages comprising such an interconnect.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     Preferred embodiments of the invention are described below with reference to the following accompanying drawings, which are for illustrative purposes only. Throughout the following views, reference numerals will be used in the drawings, and the same reference numerals will be used throughout the several views and in the description to indicate same or like parts.  
         [0018]      FIG. 1  is a schematic view of one embodiment of the apparatus of the invention prior to the formation of the interconnect.  
         [0019]      FIG. 2  is a cross-sectional view of a particle of  FIG. 1 .  
         [0020]      FIG. 3  is a schematic view of the apparatus of  FIG. 1  at a processing step subsequent to forming the interconnect.  
         [0021]      FIG. 4  is a schematic view of one embodiment of the apparatus of the invention prior to the formation of the interconnect.  
         [0022]      FIG. 5  is a cross-sectional view of a particle of  FIG. 4 .  
         [0023]      FIG. 6  is a schematic view of the apparatus of  FIG. 4  at a processing step subsequent to forming the interconnect.  
         [0024]      FIG. 7  is a schematic cross-section view of one embodiment of the apparatus of the invention prior to the formation of the interconnect.  
         [0025]      FIG. 8  is a schematic cross-section view of the apparatus of  FIG. 7  at a processing step subsequent to forming the interconnect. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]     In the following detailed description, references made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that electrical changes may be made without departing from the spirit and scope of the present invention.  
         [0027]     The terms “wafer” or “substrate” used in the following description include any semiconductor-based structure having a silicon surface. Wafer and substrate are to be understood as including silicon-on-insulator (SOI) or silicon-on-sapphire (SOS) technology, doped and undoped semiconductors, epitaxial layers of silicon supported by a base semiconductor foundation, and other semiconductor structures. Furthermore, when references made to a wafer or substrate in the following description, previous process steps may have been used to form regions or junctions in the base semiconductor structure or foundation. Preferred substrates are semiconductor structures such as semiconductor dies, semiconductor chips and semiconductor packages.  
         [0028]      FIG. 1  shows a step of a preferred process for making one embodiment of the inventive electric interconnect. A first substrate  1  having a first electrical contact  3  is positioned opposite a second substrate  5  having a second electrical contact  7 . The first substrate  1  and the second substrate  5  are positioned relative to each other such that the first electrical contact  3  is aligned with the second electrical contact  7 . An adhesive  9  is interposed between the first electrical contact  3  and the second electrical contact  7 . The adhesive  9  comprises particles  11 .  
         [0029]     The adhesive  9  may be any insulating adhesive resin usable in the art. Such adhesives resins are described in U.S. Pat. No. 5,336,443, incorporated herein by reference, and include ethylene-vinyl acetate copolymeric resins unmodified or modified with carboxyl groups, copolymers of ethylene with methyl, ethyl or isobutyl acrylate, polyamide resins, polyester resins, poly(methyl methacrylate) resins, poly(vinyl ether) resins, poly(vinyl butyral) resins, polyurethane resins, styrene-butadiene-styrene block copolymers unmodified or modified with carboxyl groups, styrene-isoprene-styrene copolymeric resins, styrene-ethylene-butylene-styrene copolymers unmodified or modified with maleic acid, polybutadiene rubbers, polychloroprene rubbers unmodified or modified with carboxyl groups, styrene-butadiene copolymeric rubbers, isoprene-isobutylene copolymers, nitrile rubbers modified with carboxyl groups, epoxy resins, silicone resins and the like. These polymeric materials can be used either singly or as a combination of two kinds or more according to need.  
         [0030]     It is optional that the above named adhesive polymeric material is admixed with a tackifier such as rosins and derivatives thereof, terpene resins, terpene-phenol copolymeric resins, petroleum resins, coumarone-indene resins, styrene-based resins, isoprene-based resins, phenolic resins, alkylphenol resins and the like either singly or as a combination of two kinds or more.  
         [0031]     Further, the adhesive resin can optionally be admixed with various kinds of known additives including reaction aids, catalysts, or cross-linking agents such as phenolic resins, polyol compounds, isocyanate compounds, melamine resins, urea resins, urotropine compounds, amine compounds, acid anhydrides, organic peroxides, metal oxides, metal salts of an organic acid, e.g., chromium trifluoroacetate, alkoxides of a metal, e.g., titanium, zirconium and aluminum, and organometallic compounds, e.g., dibutyltin oxide, as well as photopolymerization initiators, e.g., 2,2-diethoxy acetophenone and benzil, sensitizer, e.g., amine compounds, phosphorus compounds and chlorine compounds, and so on. The adhesive  9  is preferably in the form of a film or a paste.  
         [0032]     Preferably, the adhesive resin does not expand when cured, more preferably, the adhesive resin shrinks during cure.  
         [0033]     The adhesive  9  may be positioned to interpose the two substrates before the first substrate  1  and the second substrate  5  are aligned in relation to each other. For example, the adhesive  9  may be deposited over the surface of one of the substrates followed by positioning the other substrate.  
         [0034]      FIG. 2  shows a cross-sectional view of one embodiment of particle  11 . Typically, the particles  11  are generally rounded in shape, preferably spherical. Particles  11  typically have an average diameter of between about 0.5 μ to about 100 μ. The particle  11  has a core  13  of an electrically conductive material, or a material that can react to form an electrically conductive material, surrounded by a breakable coating  15  of an electrically non-conducting material. Optionally, the core may be pre-broken to form fracture lines  17 . The pre-broken core can be formed by thermally or chemically stressing the core. A pre-broken core may also be formed as an agglomeration of fragments.  
         [0035]     In one preferred embodiment, the core  13  comprises any metal that will form sharp edges when fractured. The metal is preferably nickel, copper, silver or molybdenum. The metal can also be a metal that oxidizes in the presence of oxygen because the metal is in a controlled environment in the interconnect. The metal is preferably pre-cracked in order to facilitate the formation of sharp edges and surfaces on the metal when the particle is broken by compression. The sharp edges and surfaces ensure contact between the contact surfaces.  
         [0036]     The breakable electrically non-conductive coating can be any appropriate material that can hold the conductive material together until the particles are broken by compression between the contacts. Examples of suitable electrically non-conductive materials include polymer resins and ceramics. A suitable ceramic is alumina oxide.  
         [0037]      FIG. 3  shows the process after the interconnect has been formed. The first substrate  1  and the second substrate  5  have been repositioned closer to each other to compress the adhesive  9 . In particular, the two substrates have been repositioned such that the electrically conducting particles  11  are compressed and broken between the first contact  3  and the second contact  7 . The broken particles  19  preferably have sharp edges  21  to enhance the electrical connection between the broken particles  19  and the contacts. The broken particles  19  typically have an average largest dimension of about 0.1 μ to about 20 μ. The particles  11  in adhesive  9  which are not located between the contacts are not subjected to enough compression to break the coating on those particles. As such, an electrical connection is formed between the first contact  3  and the second contact  7  but the adhesive  9  and particles  11  not located between the two contacts remain non-electroconductive.  
         [0038]      FIG. 4  shows a step of this process for making another preferred embodiment the inventive electric interconnect. A first substrate  101  having a first electrical contact  103  is positioned opposite a second substrate  105  having a second electrical contact  107 . The first substrate  101  and the second substrate  105  are positioned relative to each other such that the first electrical contact  103  is aligned with the second electrical contact  107 . An adhesive  109  is interposed between the first electrical contact  103  and the second electrical contact  107 . The adhesive  109  comprises particles  111 .  
         [0039]     The adhesive  109  may be any insulating adhesive resin usable in the art as described above. The adhesive  109  is preferably in the form of a film or a paste.  
         [0040]     The adhesive  109  may be positioned to interpose the two substrates before the first substrate  101  and the second substrate  105  are aligned in relation to each other. For example, the adhesive  109  may be deposited over the surface of one of the substrates followed by positioning the other substrate.  
         [0041]      FIG. 5  shows a cross-sectional view of the particle  111 . Typically, the particles  111  are generally rounded in shape, preferably spherical. The particle  111  has a core  113  of a material that can react to form an electrically conductive material, surrounded by a breakable coating  115  of an electrically non-conducting material. Particle  111  typically has an average diameter of about 0.5 μ to up to about 250 μ.  
         [0042]     Core  113  comprises a multiplicity of first subparticles  117  and second subparticles  123 .  
         [0043]     First subparticles  117  comprise a rupturable membrane  119  and a reactive resin  121  which is electrically conductive. Rupturable membrane  119  may be made of any suitable organic material, for example, polymer resins insoluble in reactive resin  121 . Reactive resin  121  can comprise any resin usable for adhesive  109 , preferably an epoxy resin. Reactive resin  121  is rendered electrically conductive through filling with chunks of electrically conductive materials such as silver, nickel, copper, molybdenum. Second subparticle  123  comprises a rupturable membrane  125  and a catalyst  127  enclosed therein. Rupturable membrane  125  may be any suitable organic material that is insoluble in catalyst  127 , preferably a polymer resin. Catalyst  127  is selected to react with reactive resin  121  to form a cured adhesive.  
         [0044]     The breakable electrically non-conductive coating  115  can be any appropriate material that can hold the conductive material together until the particles are broken by compression between the contacts. Examples of suitable electrically non-conductive materials include polymer resins and ceramics. A suitable ceramic is alumina oxide.  
         [0045]      FIG. 6  shows the process after the interconnect has been formed. The first substrate  101  and the second substrate  105  have been repositioned closer to each other to compress the adhesive  109 . In particular, the two substrates have been repositioned such that the particles  111  are compressed and broken between the first contact  103  and the second contact  107 .  
         [0046]     When particles  111  are compressed and broken, membranes  119  of first subparticles  117  and  125  of second subparticle  123  are ruptured permitting reactive resin  121  and catalyst  127  to intermingle and react. As a result, a cured adhesive bond  129  is formed between first contact  103  and second contact  107  wherein the adhesive is electrically conductive.  
         [0047]      FIG. 7  shows a cross-sectional view of a process for making one embodiment of the inventive electric interconnect. A first substrate  201  having a first electrical contact  203  is positioned opposite a second substrate  205  having a second electrical contact  207 . The first substrate  201  and the second substrate  205  are positioned relative to each other such that the first electrical contact  203  is aligned with the second electrical contact  207 . An adhesive  209  is interposed between the first electrical contact  203  and the second electrical contact  207 . The adhesive  209  comprises first particles  211  and second particles  217 .  
         [0048]     The adhesive  209  may be any insulating adhesive resin usable in the art as described above. The adhesive  209  is preferably in the form of a film or a paste.  
         [0049]     The adhesive  209  may be positioned to interpose the two substrates before the first substrate  201  and the second substrate  205  are aligned in relation to each other. For example, the adhesive  209  may be deposited over the surface of one of the substrates followed by positioning the other substrate.  
         [0050]     First particle  211  comprises a conductive resin  215  contained within a breakable coating  213  of an electrically nonconducting material. Conductive resin  215  comprises one-half of a two-part adhesive, preferably an epoxy resin, filled with electrically conducting material. The electrically conducting material is preferably silver but may also be nickel, copper or molybdenum. The breakable electrically non-conductive coating  215  can be any appropriate material that can hold the conductive material together until the particles are broken by compression between the contacts. Examples of suitable electrically non-conductive materials include polymer resins and ceramics. A suitable ceramic is alumina oxide.  
         [0051]     Second particle  217  comprises a catalyst  221  encased within a breakable coating  219  made from an electrically nonconducting material. The catalyst  221  is selected to react with the conductive resin  215  as the other component of the two-part adhesive, preferably an epoxy resin. The breakable electrically non-conductive coating  219  can be any appropriate material that can hold the conductive material together until the particles are broken by compression between the contacts. Examples of suitable electrically non-conductive materials include polymer resins and ceramics. A suitable ceramic is alumina oxide.  
         [0052]      FIG. 8  shows the process after the interconnect has been formed. The first substrate  201  and the second substrate  205  have been repositioned closer to each other to compress the adhesive  209 . In particular, the two substrates have been repositioned such that the particles  211  and the second particles  217  are compressed and broken between the first contact  203  and the second contact  207 . The conductive resin  215  from broken first particles  211  intermingles with and reacts with the catalyst  221  from broken second particles  217 . The reaction of conductive resin  215  with catalyst  221  results in a cured adhesive  223 . First particles  211  and second particles  217  which are not located between first contact  203  and second contact  207  are not broken in the compression step.  
         [0053]     The electrical interconnect of the current invention is usable for any interconnection between two semiconductor parts each having a contact. In particular, the inventive interconnect is usable on semiconductor dies, chips or package. The inventive adhesive could replace solder paste in forming interconnects with die, chips and packages. The inventive adhesive can also be used as a surface mount material.  
         [0054]     In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.