STABILIZED, SILVER COATED FILLER-CONTAINING CURABLE

COMPOSITIONS

BACKGROUND

Field

[0001] This invention relates to a conductive curable composition filled with silver coated material, and more particularly, to an organic curable composition comprising micron meter scale fine silver coated material with flaky shape, which have stabilized against premature reaction by the addition of chelating agents, and their application in die attach, and a method for preparing the same.

Brief Description Of Related Technology

[0002] As a method to form an electrical and/or thermal conductive adhesive applied in an electrical circuit board or a printing wire board or metal pad for semiconductor packaging industry, together with an organic or inorganic binder, thermal and/or electrical conductive filler is used as the media to conduct electron or heat. Metals, inorganic oxides, and some high conductive compounds in particle form are the common fillers, by which, the adhesive can be liquid state to meet the various particular applications. Noble metals such as silver are the major choice. However, silver fillers are expensive. It has been desired to develop, as a substitute, an electrically/thermally conductive composition using an inexpensive material, such as copper and/or glass, as the core material and coated with a thin layer of silver on its surface as low cost conductive fillers to replace pure silver filler. The replacement of silver by silver coated low cost fillers to develop conductive materials recently became an area of interest in some areas of the electronic industry, such as conductive die-attach adhesives.

[0003] An English-language abstract of Japanese Patent Document No. JP09296158A discloses a conductive adhesive obtained by mixing and dispersing conductive metal powder and silver-coated glass powder as conductive fillers into a thermosetting or thermoplastic resin, where the silver-coated glass powder desirably comprises 20-80wt.% of the conductive fillers and the preferable characteristics of the conductive metal powder comprise a flaky or spherical particle shape. An English-language abstract of Japanese Patent Document No. JP2005079251A discloses a resin paste for semiconductor comprising a thermosetting resin, a hardening agent, and a filler containing glass beads which are metal-plated at the surface thereof in the average gain size of 1.0 to 50 micrometer and 5 wt. % or more of the materials. In these abstracts of the Japanese patent documents, the silver coated glass is either in a minor amount present in the filler (in JP2005079251A, >5% of the filler, 13% and 18% in example), or not in a flaky shape.

[0004] With an average particle diameter from 1 to 25 μπι, silver coated copper particles have been described as conductive fillers in compositions. For instance, an

English-language abstract of Japanese Patent Document No. JP07138549A disclosed a conductive composition with 75-90% by weight metal (e.g. 1-20% Ag) coated Cu powder with spherical shape, and into epoxy binder. And English-language abstracts of Japanese Patent Document Nos. JP11092739A /JP11092626A also published the application of spherical silver coated copper powder application in conductive composition, which contains the conductive filler combined by silver coated copper and pure silver powder with total amount of 75-97% by weight. The resin here is epoxy and acrylate. English-language abstracts of Japanese Patent Document Nos. JP2004047418A, JP2004063445A and

JP2004063446A disclosed the conductive composition using conductive filler also combined with Ag coated Cu and pure silver powder. And English-language abstract of Japanese Patent Document Nos. JP2004063445A and JP2004063446A disclosed about 3-20% flat-like silver covering copper powder. These fillers seem to be either roughly spherical silver coated copper powder, or the combination of roughly spherical silver coated copper powder with pure silver powder. And only a little flat-like silver coated copper powder (3-20%) could be used. Since the application requirement of such composition is not at the very high end, the filler and their combination has been adequate. However, such spherical powder and combination can not be used as die attach adhesive. For instance, in a low viscosity, high thixotropic index (TI) system, the spherical silver coated copper powder tends to settle to the bottom when storing, resulting in a lower than desired TI.

[0005] International Patent Application No. PCT/CN2008/001269 is directed to curable compositions comprising conductive filler, where the conductive filler comprises silver coated material as a filler in flake form, and particularly its use in die attach compositions. [0006] Notwisthstanding the state of the art, it would be desirable to provide a silver coated material as a filler in flake form in curable compositions, such as die attach compositions, which compositions show improved shelf life stability.

SUMMARY

[0007] A conductive curable composition is provided that uses silver coated material in flake form as a conductive filler, curable epoxy, acrylate, or bismaleimide, for instance as a resin, and a chelating agent to proved improved shelf life stability to the composition at room temperature. A method for preparing the composition is also provided. The composition is capable of showing desired workability as dispensable die attach adhesive with an

appropriate range of rheology and viscosity, being excellent in reliability of conductivity or corrosion resistance, and reducing the amount of high price silver in composition. And of significance the composition as noted shows improved shelf life stability, even at room temperature.

[0008] In one embodiment, the present invention provides a curable composition for die attach comprising conductive filler, where the conductive filler comprises a silver coated material in flake form as a filler, and the composition also includes a chelating agent. In one aspect, the silver coated material in flake form may be in an amount of about 30% or more (up to 100%) by weight of the conductive filler. More specifically, the conductive filler may be in an amount of about 22% to about 92%, such as about 35% to about 90%, desirably about 60% to about 90%, by weight of the composition.

[0009] In one desirable aspect, the silver coated material in flake form used as a filler is a silver coated copper flake filler. The silver coated copper flake filler may be in an amount of about 40% or more by weight of the conductive filler. The conductive filler as so defined may be in an amount of about 50% to about 92% by weight of the composition.

[0010] In some embodiments, the conductive filler including the silver coated material in flake form as a filler may be treated with a fatty acid.

[0011] In one aspect, the silver coated material flakes may have an average diameter desirably from about 0.001 μηι to about 100 μηι, more desirably from about 1 μπι to about 50 μπι, such as from about 2 μιη to about 25 μπι. In one aspect, the desirable aspect ratio (diameter/thickness) of the silver coated material flake is from about 200 to about 2, more desirably from about 150 to about 2.5, such as from about 100 to about 3. In one aspect, the plated silver coating layer by weight is desirably in the range of from about 1% to about 70%, more desirably from about 1% to about 50%, still more desirably from about 3% to about 40%, such as from about 5% to about 30%. The silver coated material in flake form as a filler may be a silver coated copper flake. The silver coated copper flakes may comprise a silver coating content from about 1% to about 50% by weight.

[0012] In a further aspect, the composition may also comprise a resin and optionally a hardener or curing agent. The resin may be a monomer, oligomer, or polymer organic resin which can be cured or polymerized by chemical or by physical methods, or any combination thereof. The resin may be in an amount of about 1% to about 60%, such as about 10% to about 60%, desirably about 10% to about 40%, by weight of the composition. The hardener or curing agent may be in an amount of about 0.01% to about 20% by weight of the composition.

[0013] In one aspect, the present invention provides a curable composition, comprising a conductive filler in an amount of from about 22% to about 92% by weight of the composition, with a silver coated material flake filler being about 30% or more (up to 100%») by weight of the conductive filler; a resin in an amount of from about 1% to about 60% by weight of the composition; and a hardener in an amount of from about 0.01% to about 20% by weight of the composition.

[0014] And as noted above, the composition includes a chelating agent. The chelating agent may be selected from ionic or nonionic materials, though nonionic materials are particularly desirable. Of the nonionic materials, many are possible choices. For instance, polyamines, carboxylic acids, phosphoric acids, sulfuric acids, disulfides, thiols,

benzotriazole and derivatives thereof, triazoles and derivatives thereof, imidazoles, phenolics, oximes and acetoacetonates (such as poly(ethylene glycol) diacetoacetate) may be used.

Examples of these materials include acetylacetone, benzoylacetone, ethyl acetoacetate, acetoacetamide, acetoacetanilide, 2-acetylcyclohexanone, malonic acid, dimethyl malonate, 2-hydroxybenzophenone, ethylenediamine, pentamethyldiethylenetriamine,

ethylenediaminetetraacetic acid, ethylenediaminetetraacetic acid tetrasodium salt, oxalic acid, salicylic acid, maleic acid, adipic acid, etidronic acid, ort/jo-catechol, salicylaldehyde, 2,2'-bipyridyl, 1,10-phenanthroline, 2,2'-bipyridine-4,4'-dicarboxylic acid,

dimethylglyoxime, biguanidine and Schiff's base obtained by condensation of

pyridine-2,6-dialdehyde and aniline, lH-benzotriazole-1 -methanol, 2-[3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl]ethyl methacrylate, Tinuvin P Phenol,

2- (2H-benzotriazol-2-yl)-4-methyl, 2,2'-dithiobis(benzothiazole), 4,4'-dithiodibutyric acid;

3- carboxypropyl disulfide. Some inorganic ion exchanger may also be used as a chelating agent. For example, aluminosilicate, hydrous metal oxide, acidic salts of multivalent metal, hetropolic acid, and hydrotalcite-like compounds. The inorganic ion exchanger should be present in an amount of about 0.01% to about 5%, such as about 0.05% to about 2%, by weight of the composition.

[0015] Polymer-bound chelating agents may also be suitable for use herein. For instance, PhosphonicS™ is a trade name under which a series of polymer bound catalysts - including an ethyl thiophenyl sulfonic acid silica SPhSA and an ethyl/butyl

phosphonic acid silica POH1— are available commercially from PhosphonicS Ltd., UK. See Wilson, J.; Sullivan A., Speciality Chemicals Magazine, 2006, June edition, 28. In addition, DOWEX™ M4195 available commercially from Dow Chemical Company, is based upon a special chelating amine ligand which is partially quaternized by sulfuric acid as received. When in this conjugate sulfuric acid salt form, the resin is fully swollen and hydrated, and ready for scavenging metals from acidic media. More specifically,

DOWEX™ M4195 has a styrene-DVB, Macroporous matrix with bis-picolylamine functional groups. The chelating agent should be present in an amount of about 0.01% to about 5%, such as about 0.05% to about 2%, by weight of the composition.

[0017] In use, the chelating agent may be added included as an additive to the resin system. Alternatively, the chelating agent may be plated onto at least a portion of the surface of the silver coated filler in flake form. Still alternatively, the chelating agent may be used in a pre-treatment wash of the silver coated filler in flake form. The so-pre-treated filler may be include in the composition.

[0018] Irrespective of the manner by which the chelating agent is introduced the amount of chelating agent should be in an amount of about 0.01% to 1%, by weight of the composition.

[0019] In a still further aspect, the curable composition according to the invention may further includes other functional ingredient(s). The functional ingredients include without limitation non-conductive fillers, solvents, radical initiator, catalysts, oligomers, antibleed agents, adhesion promoters, antioxidants, conductivity promoters, or the like, or any combination thereof. [0020] The curable composition according to the invention shows a desirable viscosity range (by Brookfield rheometer at 25°C, 5rpm) from about 3,000 cP to about 80,000 cP, more desirably from about 5,000 cP to about 50,000 cP, most desirably from about 5,000 cP to about 35,000 cP. The value called as thixotropic index (T.I., the ratio of viscosity at 0.5 rpm/viscosity at 5rpm, 25°C) range can be from about 1.3 to about 8, more desirably from about 1.5 to about 7, most desirably from about 2 to about 6.

[0021] In one embodiment, the present invention provides a method for preparing a curable composition for die attach according to the invention, comprising applying a conductive filler part into a resin part, wherein the conductive filler part comprises a silver coated material flake filler in an amount of from about 30% to 100% by weight of the conductive filler. In one aspect, the loading of the conductive filler part may be from about 22% to about 92% by weight of the curable composition. In a further aspect, the resin part also comprises a hardener. The silver coated material filler in flake form may be a silver coated copper flake.

[0022] In one embodiment, the present invention provides the use of a conductive filler part comprising silver coated material filler in flake form in a curable composition, wherein the loading of the conductive filler part is from about 22% to about 92% by weight of the curable composition, and the silver coated material flake filler is in an amount of from about 30% to 100% by weight of the conductive filler.

[0023] In one embodiment, the present invention provides a method for producing an article with a component bonded to a substrate, the method comprising applying a curable compositions for die attach comprising a silver coated material flake filler onto at least a part of the substrate surface, and bonding the component to the coated substrate surface. In one aspect, the method may further comprise a step of thermally curing the composition at a temperature above room temperature, the step being performed after contacting the substrate with the adhesive. In another aspect, the component bonded to a substrate may be a semiconductor component. In another embodiment, the invention provides an article produced by the method, the article comprising a substrate, a component on the substrate and the composition in accordance with the present invention by which the component bonded to the substrate. The component may be a semiconductor component.

BRIEF DESCRIPTION OF THE FIGURES

[0024] Figure 1 depicts a schematic view of a silver coated copper flake. [0025] Figure 2 depicts a schematic view of a semiconductor package using die attach adhesive.

[0026] Figure 3 depicts a schematic view of a way to dispense die attach adhesive on substrate or die.

[0027] Figure 4 depicts a shape comparison of spherical filler and flaky filler. The shape difference can result in various rheology performance in die attach adhesive.

DETAILED DESCRIPTION

[0028] Unless defined otherwise herein, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although any methods and materials similar or equivalent to those described herein may find use in the practice of the present invention, the desirable methods and materials are described herein. Accordingly, the terms defined immediately below are more fully described by reference to the Specification as a whole. Also, as used herein, the singular "a", "an" and "the" includes the plural reference unless the context clearly indicates otherwise. Numeric ranges are inclusive of the numbers defining the range.

Definitions

[0029] As used herein, the term "flake", "flaky" or "flaky shape" refers to a flat thin piece or layer, which has a 3 ^rd -dimension size much smaller than the other two dimensions, and may be in regular or irregular shape. The "flake" has micrometer scale fine silver as coating material and a core material such as copper. In the context of the present invention, the flake shape conductive filler has the advantages of capable of achieving right rheological property for dispensing (higher TI), and obtaining better conductivity, without settling, compared to the roughly spherical powder.

[0030] As used herein, the term "conductive filler" may comprises one or more silver coated material flake filler with or without any other conductive filler such as silver, copper, alloy, or the like, or any combination thereof. The shape of the conductive filler is not limited.

[0031] As used herein, the term "resin" refers to a curable monomer, oligomer, or polymer resin. [0032] As used herein, the term "RH" or "resin part" refers to a part essentially consisting of resin and hardener, which may further comprise other functional ingredients if necessary according to intended applications, such as non-conductive fillers, solvents, radical initiator, catalysts, oligomers, anti-bleed agents, adhesion promoters, antioxidants, conductivity promoters, or the like, or any combination thereof. That is to say, the term "RH" may refer to a part comprising all the components other than the conductive filler/fillers in the curable composition.

[0033] As used herein, the terms "hardener" and "curing agent" may be used

interchangeably.

[0034] A conductive curable composition used in semiconductor packaging, comprising silver coated material having a flake shape as a conductive filler, curable epoxy, or acrylate, or bismaleimide monomer and/or oligomer or their combination as organic resin, and optionally a hardener, and the method for preparing the same. The composition is capable of showing desired workability as dispensable die attach adhesive with a right rang of rheology, viscosity and physical stability in storing, being excellent in reliability of conductivity or corrosion resistance, and reducing the amount of high price silver in composition. Furthermore, with flake shape, the conductive filler can achieve better conductivity with same loading as in spherical powder form, and do not have the settling issue, which easily occurred in the case of those in spherical powder form.

[0035] In one embodiment, the present invention provides a curable composition for die attach comprising conductive filler, where the conductive filler comprises a silver coated material in flake form as a filler. The silver coated material may be copper.

[0036] In some embodiments, the silver coated material flake filler may be in an amount of about 30% or more (up to 100%) by weight of the conductive filler. In a further aspect, the loading of the conductive filler is desirably from about 22% to about 92%, more desirably from about 25% to about 90%, such as from about 30% to about 86% by weight of the composition.

[0037] In one aspect, the silver coated material flakes have an average diameter desirably from about 0.001 μπι to about 100 μπι, more desirably from about 1 μπι to about 50 μπι, such as from about 2 μπι to about 25 μπα. In another aspect, the desirable aspect ratio

(diameter/thickness) of the silver coated material flake is from about 200 to about 2, more desirably from about 150 to about 2.5, such as from about 100 to about 3. In still another aspect, the plated silver coating layer by weight is desirably in the range of from about 1% to about 70%, more desirably from about 1% to about 50%, still more desirably from about 3% to about 40%, such as from about 5% to about 30%. The silver coated copper flakes may comprise a silver coating content from about 1% to about 50% by weight.

[0038] In a further aspect, the composition may also comprise a resin and optionally a hardener or curing agent. The resin may be a monomer, oligomer or polymer organic resin which can be cured or polymerized by chemical or by physical methods, or any combination thereof. The loading of the resin by weight may be desirably from about 1 % to about 60%, more desirably from about 1% to about 40%, such as from about 1% to about 30%. The hardener or curing agent may be in an amount of from about 0.01% to about 20% by weight of the composition.

[0039] In one aspect, the silver coated material flake filler is to provide a curable composition for die attach,_comprising a silver coated material flake filler and one or more other conductive filler other than the silver coated material filler, a resin, and a hardener.

[0040] In a still further aspect, for application purpose, the curable composition according to the invention may further includes other functional ingredient(s). The functional ingredients include without limitation non-conductive fillers, solvents, radical initiator, catalysts, oligomers, anti-bleed agents, adhesion promoters, antioxidants, conductivity promoters, or the like, or any combination thereof.

[0041] The curable composition according to the invention shows a desirable viscosity range (by Brookfield rheometer at 25°C, 5rpm) from about 3,000 cP to about 80,000 cP, more desirably from about 5,000 cP to about 50,000 cP, most desirably from about 5,000 cP to about 35,000 cP. The value called as thixotropic index (T.I., the ratio of viscosity at 0.5 rpm/viscosity at 5rpm, 25°C) range can be from about 1.3 to about 8, more desirably from about 1.5 to about 7, most desirably from about 2 to about 6.

[0042] In one embodiment, the present invention provides a method for preparing a curable composition for die attach according to the invention, comprising applying a conductive filler part into a resin part, wherein the conductive filler part comprises a silver coated material flake filler in an amount of from about 30% up to 100% by weight of the conductive filler. In one aspect, the loading of the conductive filler part may be from about 22% to about 92% by weight of the curable composition. In a further aspect, the resin part also comprises a hardener. [0043] In one embodiment, the present invention provides the use of a conductive filler part comprising silver coated material flake filler in a curable composition, wherein the loading of the conductive filler part is from about 22% to about 92% by weight of the curable composition, and the silver coated material flake filler is in an amount of from about 30% to 100% by weight of the conductive filler.

[0044] In one embodiment, the present invention provides a method for producing an article with a component bonded to a substrate, the method comprising applying a curable compositions for die attach comprising a silver coated material flake filler onto at least a part of the substrate surface, and bonding the component to the coated substrate surface. As used herein, the term "substrate" may mean a substrate for a semiconductor die or the semiconductor die itself, such as those would occur when two or more dies are arranged in a stacked geometry. The silver coated material flake filler may be a silver coated copper flake In one aspect, the method may further comprise a step of thermally curing the composition at a temperature above room temperature, the step being performed after contacting the substrate with the adhesive. In another aspect, the component bonded to a substrate may be a semiconductor component. In another embodiment, the invention provides an article produced by the method, the article comprising a substrate, a component on the substrate and the composition in accordance with the present invention by which the component bonded to the substrate. The component may be a semiconductor component.

Resin

[0045] In some embodiments, the resin may be a curable monomer, oligomer, or polymer organic resin. The monomer and/or oligomer may be epoxy monomer and/or oligomer. Exemplary epoxy monomer and/or oligomer contemplated for use in the practice of the present invention include, but not limited to liquid epoxy, liquid epoxy combination, and solid epoxy in solution. For example, the epoxy monomer and/or oligomer may selected from substituted (e.g., amine or hydroxyl substituted) or unsubstituted epoxy, such as,

1 ,2-epoxypropane, 1,3-epoxypropane, butylene oxide, n-hexyl propylene epoxide or the like. Examples of commercially available epoxy monomer(oligomer) may be Araldite DY 027 (Chemica Inc., Los Angeles, CA), Cardula N-10 (Vantico Inc., Brewster, NY), Epiclon EXA-830CRP (from DIC Corporation, Japan), or the combination thereof. [0046] In other embodiments, the monomer and/or oligomer may be (meth)acrylate monomer and/or oligomer. The (meth)acrylate monomer and/or oligomer contemplated for use in the practice of the present invention include, but not limited to liquid (meth)acrylate, liquid (meth)acrylates combination and solid (meth)acrylate monomer(oligomer) in solution. For example, the (meth)acrylate monomer and/or oligomer may be selected from methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, ethyl hexyl (meth)acrylate, isobutyl acrylate or the like. Examples of commercially available

(meth)acrylate monomer(oligomer) may be SR248, SR355, or their combination

(commercially available from Sartomer Inc. (Shanghai), 500 Fu Te 2nd East Road, Wai Gao Qiao Free Trade Zone, Shanghai, 200131).

[0047] In some embodiments, the monomer and/or oligomer may be cyanate ester monomer and/or oligomer. The cyanate ester may comprise various suitable cyanate ester known in the art, including isocyanates. Suitable cyanates include, for example, ethylene diisocyanate; 1 ,4-tetramethylene diisocyanate; 1,4 and/or 1 ,6-hexamethylene diisocyanate; 1,12-dodecane diisocyanate; cyclobutane-l,3-diisocyanate; cyclohexane-1,3- and 1 ,4-diisocyanate and mixtures of these isomers; l-isocyanato-3,3,5- trimethyl-5-isocyanatomethyl cyclohexane; 2,4- and 2,6-hexahydrotolylene diisocyanate and mixtures of these isomers; hexahydro-1.,3- and/or 1 ,4-phenylene diisocyanate; perhydro-2,4'- and/or 4,4'-diphenyl methane diisocyanate; 1,3- and 1 ,4-phenylene diisocyanate; 2,4- and 2,6-toluene diisocyanate and mixtures of these isomers; diphenyl methane-2,4'- and/or 4,4'-diisocyanate; naphthylene-l,5-diisocyanate; 1,3- and 1,4-xylylene diisocyanate, 4,4'-methylene-bis(cyclohexyl isocyanate), 4,4'-isopropyl- bis(cyclohexyl isocyanate), 1 ,4-cyclohexyl diisocyanate and

3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (IPDI); 2,4- and 2,6-toluene diisocyanate; diphenylmethane diisocyanate; hexamethylene diisocyanate;

dicyclohexylmethane diisocyanate; isophorone diisocyanate; l-methyoxy-2,4-phenylene diisocyanate; l-chlorophenyl-2,4-diisocyanate; p-(l-isocyanatoethyl)-phenyl isocyanate; m-(3-isocyanatobutyl)-phenyl isocyanate and 4-(2-isocyanate-cyclohexyl-methyl)-phenyl isocyanate, isophorone diisocyanate, toluene diisocyanate and mixtures thereof.

[0048] The monomer and/or oligomer may also be silane monomer and/or oligomer. The silanes may include non-functional silanes and functionalized silanes including

amino-functional, epoxy-functional, acrylate-functional and other functional silanes, which are known in the art. Exemplary functionalized silanes include

n r-glycidoxypropyl-trimethoxysilane, y -glycidoxypropyltriethoxysilane,

r-glycidoxypropyl-methyldiethoxysilane, glycidoxypropyltrimethoxysilane,

glycidoxypropyltriethoxysilane, glycidoxypropylmethyldimethoxysilane,

glycidoxypropylmethyldiethoxysilane, 5,6-epoxyhexyltriethoxysilane,

epoxycyclohexylethyltrimethoxysilane, and the like. Other exemplary functionalized silanes include trimethoxysilylpropyldiethylene-triamine, N-methylaminopropyltrimethoxysilane, aminoethylaminopropylmethyldimethoxysilane, aminoethylaminopropyltrimethoxysilane, aminopropylmethyldimethoxysilane, aminopropyltrimethoxysilane,

aminoethylaminoethylaminopropyl-trimethoxysilane,

N-methylamino-propyltrimethoxysilane, methylamino-propyltrimethoxysilane,

aminopropylmethyl-diethoxysilane, aminopropyltriethoxysilane, 4-aminobutyltriethoxysilane, oligomeric aminoalkylsilane, m-aminophenyltrimethoxysilane,

phenylaminopropyltrimethoxysilane, aminoethylaminopropyltriethoxysilane,

aminoethylaminoisobutylmethyldimethoxysilane, and the like. Additional exemplary functional silanes include (3-acryloxypropyl)-trimethoxysilane,

gamma-methacryloxypropyltrimethoxysilane, gamma-mercapto-propyltriethoxysilane, and olefinic silanes, such as vinyltrialkoxysilane, vinyltriacetoxysilane, alkylvinyldialkoxysilane, allyltrialkoxysilane, hexenyltrialkoxysilane and the like.

[0049] The monomer(oligomer)s can also be monofunctional monomer(oIigomer)s, such as alkoxylated tetrahydrofurfuryl acrylate, 2(2-ethoxyethoxy) ethyl acrylate, stearyl acrylate, lauryl acrylate, issoctyl acrylate, tridecyl acrylate, caprolactone acrylate, lauryl methacrylate, isobonyl methacrylate; and difunctional monomer(oligomer)s, such as difunctional cyclohexane dimethanol diacrylate, tetraethylene glycol diacrylate, or multiple functional monomer(oligomer)s, such as trimethylolpropane triacrylate, propoxylated glyceryl triacrylate, di-trimethylolpropane tetraacrylate, pentacarylate ester, and so on. (e.g., commercially available from Sartomer Inc. (Shanghai), 500 Fu Te 2nd East Road, Wai Gao Qiao Free Trade Zone, Shanghai, 200131).

[0050] The monomer and/or oligomer may also be monomer or oligomer having at least one maleimide, nadimide or itaconimide functional group. For instance, The maleimides, nadimides, and itaconimides in the solid state include those compounds having the following structures I, II and III, respectively

(I) (II) (III) where:

m = l-15,

p = 0-15,

each R ² is independently selected from hydrogen or lower alkyl, and

J is a monovalent or a polyvalent moiety comprising organic or organosiloxane radicals, and combinations of two or more thereof.

[0051] More specific representations of the maleimides, itaconimides and nadimides in the solid state include those corresponding to structures I, II, or HI, where

m = 1-6,

P = 0,

R ² is independently selected from hydrogen or lower alkyl, and J is a monovalent or polyvalent radical selected from hydrocarbyl, substituted hydrocarbyl, heteroatom-containing hydrocarbyl, substituted heteroatom-containing hydrocarbyl, hydrocarbylene, substituted hydrocarbylene, heteroatom-containing

hydrocarbylene, substituted heteroatom-containing hydrocarbylene, polysiloxane, polysiloxane-polyurethane block copolymer, and combinations of two or more thereof, optionally containing one or more linkers selected from a covalent bond, -0-,

-S-, -NR-, -O-C(O)-, -0-C(0)-0-, -0-C(0)-NR-,

-NR-C(O)-, -NR-C(0)-0-, -NR-C(0)-NR-, -S-C(O)-, -S-C(0)-0-, -S-C(0)-NR-,

-S(O)-, -S(0) ₂ -, -0-S(0) ₂ -, -0-S(0) ₂ -0-, -0-S(0) ₂ -NR-, -O-S(O)-, -0-S(0)-0-,

-0-S(0)-NR-, -O-NR-C(O)-, -0-NR-C(0)-0-, -0-NR-C(0)-NR-, -NR-O-C(O)-,

-NR-0-C(0)-0-, -NR-0-C(0)-NR-, -O-NR-C(S)-, -0-NR-C(S)-0-, -0-NR-C(S)-NR-, -NR- O-C(S)-, -NR-0-C(S)-0-, -NR-0-C(S)-NR-, -O-C(S)-, -0-C(S)-0-, -0-C(S)-NR-,

-NR-C(S)-, -NR-C(S)-0-, -NR-C(S)-NR-, -S-S(0) ₂ -, -S-S(0) ₂ -0-, -S-S(0) ₂ -NR-, -NR-O-S(O)-, -NR-0-S(0)-0-, -NR-0-S(0)-NR-, -NR-0-S(0) ₂ -, -NR-0-S(0) ₂ -0-, -NR-O-S (0) ₂ -NR-, -O-NR-S(O)-, -0-NR-S(0)-0-, -0-NR-S(0)-NR-, -0-NR-S(0) ₂ -0-, -0-NR-S(0) ₂ -NR-, -0-NR-S(0) ₂ -, -0-P(0)R ₂ -, -S-P(0)R ₂ -, -NR-P(0)R ₂ -, where each R is independently hydrogen, alkyl or substituted alkyl, and combinations of any two or more thereof.

[0052] When one or more of the above described monovalent or polyvalent groups contain one or more of the above described linkers to form the "J" appendage of a maleimide, nadimide or itaconimide group, as readily recognized by those of skill in the art, a wide variety of linkers can be produced, such as, for example, oxyalkyl, thioalkyl, aminoalkyl, carboxylalkyl, oxyalkenyl, thioalkenyl, aminoalkenyl, carboxyalkenyl, oxyalkynyl, thioalkynyl, aminoalkynyl, carboxyalkynyl, oxycycloalkyl, thiocycloalkyl, aminocycloalkyl, carboxycycloalkyl, oxycloalkenyl, thiocycloalkenyl, aminocycloalkenyl,

carboxycycloalkenyl, heterocyclic, oxyheterocyclic, thioheterocyclic, aminoheterocyclic, carboxyheterocyclic, oxyaryl, thioaryl, aminoaryl, carboxyaryl, heteroaryl, oxyheteroaryl, thioheteroaryl, aminoheteroaryl, carboxyheteroaryl, oxyalkylaryl, thioalkylaryl,

aminoalkylaryl, carboxyalkylaryl, oxyarylalkyl, thioarylalkyl, aminoarylalkyl,

carboxyarylalkyl, oxyarylalkenyl, thioarylalkenyl, aminoarylalkenyl, carboxyarylalkenyl, oxyalkenylaryl, thioalkenylaryl, aminoalkenylaryl, carboxyalkenylaryl, oxyarylalkynyl, thioarylalkynyl, aminoarylalkynyl, carboxyarylalkynyl, oxyalkynylaryl, thioalkynylaryl, aminoalkynylaryl or carboxyalkynylaryl, oxyalkylene, thioalkylene, aminoalkylene, carboxyalkylene, oxyalkenylene, thioalkenylene, aminoalkenylene, carboxyalkenylene, oxyalkynylene, thioalkynylene, aminoalkynylene, carboxyalkynylene, oxycycloalkylene, thiocycloalkylene, aminocycloalkylene, carboxycycloalkylene, oxycycloalkenylene, thiocycloalkenylene, aminocycloalkenylene, carboxycycloalkenylene, oxyarylene, thioarylene, aminoarylene, carboxyarylene, oxyalkylarylene, thioalkylarylene,

aminoalkylarylene, carboxyalkylarylene, oxyarylalkylene, thioarylalkylene,

aminoarylalkylene, carboxyarylalkylene, oxyarylalkenylene, thioarylalkenylene,

aminoarylalkenylene, carboxyarylalkenylene, oxyalkenylarylene, thioalkenylarylene, aminoalkenylarylene, carboxyalkenylarylene, oxyarylalkynylene, thioarylalkynylene, aminoarylalkynylene, carboxy arylalkynylene, oxyalkynylarylene, thioalkynylarylene, aminoalkynylarylene, carboxyalkynylarylene, heteroarylene, oxyheteroarylene,

thioheteroarylene, aminoheteroarylene, carboxyheteroarylene, heteroatom-containing di- or polyvalent cyclic moiety, oxyheteroatom-containing di- or polyvalent cyclic moiety, thioheteroatom-containing di- or polyvalent cyclic moiety, aminoheteroatom-containing di- or polyvalent cyclic moiety, carboxyheteroatom-containing di- or polyvalent cyclic moiety, disulfide, sulfonamide, and the like.

[0053] In another embodiment, maleimides, nadimides, and itaconimides contemplated for use in the practice of the present invention have the structures I, II, or III, where m = 1-6, p = 0-6, and J is selected from saturated straight chain alkyl or branched chain alkyl, optionally containing optionally substituted aryl moieties as substituents on the alkyl chain or as part of the backbone of the alkyl chain, and where the alkyl chains have up to about 20 carbon atoms; a siloxane having the structure: -(C(R ³ ) ₂ ) _d -[Si(R ⁴ ) ₂ -0] _f Si(R ⁴ ) ₂ -(C(R ³ ) ₂ ) _e -,

-(C(R ³ ) ₂ ) _d -C(R ³ )-C(0)0-(C(R ³ ) ₂ ) _d -[Si(R ⁴ ) ₂ -0]rSi(R ⁴ ) ₂ -(C(R ³ ) ₂ )e-0(0)C-(C(R ³ ) ₂ )e-,

or -(C(R ³ ) ₂ ) _d -C(R ³ )-0(0)C-(C(R ³ ) ₂ ) _d -[Si(R ⁴ ) ₂ -0]rSi(R ⁴ ) ₂ -(C(R ³ ) ₂ )e-C(0)0-(C(R ³ ) ₂ )e-, where:

each R ³ is independently hydrogen, alkyl or substituted alkyl,

each R ⁴ is independently hydrogen, lower alkyl or aryl,

d = 1-10,

e = 1-10, and

f = 1-50;

a polyalkylene oxide having the structure:

[(CR ₂ ) _r -0-MCR ₂ ) _s - where:

each R is independently hydrogen, alkyl or substituted alkyl,

r = 1-10,

s = 1-10, and

f is as defined above;

aromatic groups having the structure:

O O

Ar-C-O-Z-O-C-Ar- where:

each Ar is a monosubstituted, disubstituted or trisubstituted aromatic or heteroaromatic ring having in the range of 3 up to 10 carbon atoms, and

Z is: saturated straight chain alkylene or branched chain alkylene, optionally containing saturated cyclic moieties as substituents on the alkylene chain or as part of the backbone of the alkylene chain, or

polyalkylene oxides having the structure:

-[(CR ₂ ) _r -0-] _q -(CR ₂ )s- where:

each R is independently hydrogen, alkyl or substituted alkyl, r and s are each defined as above, and

q falls in the range of 1 up to 50;

- or tri-substituted aromatic moieties having the structure:

where:

each R is independently hydrogen, alkyl or substituted alkyl,

t falls in the range of 2 up to 10,

u falls in the range of 2 up to 10, and

Ar is as defined above;

aromatic groups having the structure:

O O II II

Ar [ - o (C)o _, — (CR ₂ ) _t ] _k Ar— [(Οο _, ι~0- (CR ₂ ) _t ] _k

where:

each R is independently hydrogen, alkyl or substituted alkyl,

t = 2-10,

k = 1, 2 or 3, g = 1 up to about 50,

each Ar is as defined above,

E is -O- or -NR ⁵ -, where R ⁵ is hydrogen or lower alkyl; and

W is straight or branched chain alkyl, alkylene, oxyalkylene, alkenyl, alkenylene, oxyalkenylene, ester, or polyester, a siloxane having the

structure -(C(R ³ ) ₂ ) _d -[Si(R ⁴ ) ₂ -0] _r Si(R ⁴ ) ₂ -(C(R ³ ) ₂ )e-,

-(C(R ³ ) ₂ ) _d -C(R ³ )-C(0)0-(C(R ³ )^

or -(C(R ³ ) ₂ ) _d -C(R ³ )-0(0)C-(C^

each R ³ is independently hydrogen, alkyl or substituted alkyl,

each R ⁴ is independently hydrogen, lower alkyl or aryl,

d = 1-10,

e = 1-10, and

f= 1-50; or

a polyalkylene oxide having the structure:

-[(CR ₂ ) _r -0-]r(CR ₂ ) _s - where:

each R is independently hydrogen, alkyl or substituted alkyl,

r = 1-10,

s = 1-10, and

f is as defined above;

optionally containing substituents selected from hydroxy, alkoxy, carboxy, nitrile, cycloalkyl or cycloalkenyl;

a urethane group having the structure:

R ⁷ -U-C(0)-NR ⁶ -R ⁸ -NR ⁶ -C(0)-(0-R ⁸ -0-C(0)-NR ⁶ -R ⁸ -NR ⁶ -C(0)) _v -U-R ⁸ - where:

each R ⁶ is independently hydrogen or lower alkyl,

each R ⁷ is independently an alkyl, aryl, or arylalkyl group having 1 to 18 carbon atoms,

each R ⁸ is an alkyl or alkyloxy chain having up to about 100 atoms in the chain, optionally substituted with Ar,

U is -0-, -S-, -N(R)-, or -P(L),, ₂ -,

where R as defined above, and where each L is independently =0, =S, -OR or -R; and v = 0-50;

polycyclic alkenyl; or

mixtures of any two or more thereof.

[0054] The monomer and/or oligomer may also be monomer or oligomer having at least one benzoxazine functional group. For instance, the benzoxazine may be embraced by the following structure:

where o is 1-4, X is selected from a direct bond (when o is 2), alkyl (when o is 1), alkylene (when o is 2-4), carbonyl (when o is 2), thiol (when o is 1), thioether (when o is 2), sulfoxide (when o is 2), and sulfone (when o is 2), Rj is selected from hydrogen, alkyl, alkenyl and aryl, and R is selected from hydrogen, halogen, alkyl and alkenyl. Or the benzoxazine may be embraced by the following structure:

where p is 2, Y is selected from biphenyl (when p is 2), diphenyl methane (when p is 2), diphenyl isopropane (when p is 2), diphenyl sulfide (when p is 2), diphenyl sulfoxide(when p is 2), diphenyl sulfone (when p is 2), and diphenyl ketone (when p is 2), and R4 is selected from hydrogen, halogen, alkyl and alkenyl.

[0055] The monomer and/or oligomer may also be monomer or oligomer having at least one oxazoline functional group. Curing Agents/Hardeners

[0056] The curing agent used in the practice of the present invention may include, for example, Lewis acid, Lewis base, imidazole, anhydride, or the combination thereof.

Typically, the curing agent is present in the range of from 0.01% to about 20 % by weight of the curable composition.

Radical Initiators

[0057] The radical initiator used in the practice of the present invention may include, but not limited to peroxide, persulphate, azo compound and their combination. The desirable radical initiator may include peroxide, such as methyl ethyl ketone peroxides, tertiary- amyl peroxy-2-ethylhexyl carbonate, tertiary-butyl peroxyacetate, and dicumyl peroxide, with dicumyl peroxide being particularly desirable. Typically, the radical initiator is present in the range of about 0.01% - 20% by weight of the curing composition, desirably from 0.05% to about 5% by weight.

Anti-bleed Agents

[0058] In one embodiment of the present invention, the curable composition of the invention may comprising an anti-bleed agent. For example, the anti-bleed agent may be a functional fluoride anti-bleed agent, which has the formula R-X, where X is(are) reactive functional group(s), R is a fluoro group containing organic chain, with carbon number from about 1 to about 100 or more, desirably, from about 1 to about 20, and desirably X contains a substituted or unsubstituted epoxy, a substituted or unsubstituted amino, a substituted or unsubstituted maleimide group, a substituted or unsubstituted silane group, a substituted or unsubstituted oxane group, or a substituted or unsubstituted cyanate ester group, or the like, or the combination thereof. In one aspect, R may have a formula CF ₃ (CF ₂ ) _n , wherein n is an integer from 1 to about 100 or more; desirably, from about 1 to about 20; more desirably, from about 1 to about 16; most desirably, from about 1 to about 9. Other appropriate anti-bleed agents known in the art may be contemplated in the present invention, for example, alcohols, amides, amines, carboxylic acid, and esters containing two to about twelve carbon atoms (see e.g. U.S. Patent No. 4,483,898, which is hereby expressly incorporated herein by reference). Catalysts

[0059] The catalysts used in the practice of the present invention may include, for example, amine catalysts and/or acid catalysts such as lewis acid, lewis base, imidazole, phenol, or the like or the combination thereof. Exemplary amine catalyst may include, but not limited to, primary amine, secondary amine and the combination. The desirable amine catalyst is primary amine, for example, N,N'-(4-methyl-l,3-phenylene)-bis-l- pyrrolidine-carboxamide. Exemplary acid catalyst may include, but not limited to carboxylic acid, acid anhydride and their combination. For example, the acid catalyst may be glutaric acid. Typically, the catalyst is present in the range of from 0.001% to about 20 % by weight of the whole bulk resin, desirably from 0.05% to about 10 % by weight.

Other Components

[0060] If desired, the curable composition may further comprise other components, for example, conductive fillers other than the silver coated material in flake form,

non-conductive fillers, solvents, oligomers, adhesion promoters, antioxidants, conductivity promoters and the like. These ingredients can be appropriately selected from those known ingredients by those skilled in the art depending on the purpose of the application of the curable composition according to the present invention.

EXAMPLES

[0061] For all the examples illustrated below, mixing was performed by hand for a period of time of 5 minutes, with an additional period of 5 minutes if the formulation did not appear to be visually homogenous. For viscosity measurements, about 0.5 ml was used with a Brookfield cone/plate viscometer with spindle type CP-51 to measure viscosity at 0.5 rpm and 5 rpm rotation rate respectively. Electrical conductivity is expressed as volume resistivity (VR) and was measured on a glass slide on which a 5 cm by 5 mm track was applied with a thickness in the range from 15 - 200 microns; typical thickness is 30-50 microns. After cure of the material the resistance was measured and the volume resistance was calculated from the equation:

VR=R*W*T/L

where R is track resistance in Q cm measured along the length L; W is width of track in centimeters; T is thickness of track in centimeters; L is length of track in centimeters. Example El:

[0062] Here, 21 or 20.5 weight parts of the die attach formulation SDA1245-28 RH, where SDA 1245-28 RH includes based on resin content an acrylate component (composed of a combination of dicyclopenenyloxyethyl methacrylate and acrylated polybutadiene) 72%, bismaleimide 16%, oligomer 5%, additives (such as fumed silica, conductivity promoters, peroxides and antioxidants) 7% was mixed with the silver coated copper flake filler batch A (SAB-121(9H616), available from DOWA Inc.). El-2 also included 0.5 weight parts of the ion exchange powder, known as IXE-700F (hydrotalcite-like compound) from Toagosei Co. Ltd in Japan.

Table 1

[0063] The viscosity of the two compositions in Table 1 was recorded with a Brookfield viscometer HBDV-III ultra C using rotating speed of 0.5 and 5 rpm. The thixotropic index was also measured with the Brookfield viscometer. The composition were also cast into thin films and cured in an oven at a temperature of 175°C for a period of time of 60 minutes. The volume resistivity was recorded by four-point probe and is shown in Table 2.

Table 2

Example E2:

[0064] Here, 21 or 20.95 weight parts of the die attach formulation SDA 1245-28 RH was mixed with the silver coated copper flake filler batch B (SAB-121(9L640), available from DOWA Inc.). For E2-2, 0.05 weight parts of chelating agent, known as

2,2'-dithiobis(benzothiazole), was also added.

Table 3

[0065] The viscosity of the two compositions in Table 3 was recorded with a Brookfield viscometer HBDV-III ultra C using rotating speed of 0.5 and 5 rpm. The thixotropic index was also measured with the Brookfield viscometer. The composition were also cast into thin films and cured in an oven at a temperature of 175°C for a period of time of 60 minutes. The volume resistivity was recorded by four-point probe. These results are shown in Table 4.

Table 4

Example E3:

[0066] Here, 21 weight parts of the die attach formulation SDA 1245-28 RH was mixed with a silver coated copper flake filler. For E3- 1 batch A was chosen; for E3-2 batch C was chosen, where batch C has a chelator

Table 5

[0067J The viscosity of the two compositions was recorded with a Brookfield viscometer HBDV-III ultra C using rotating speed of 0.5 and 5 rpm. The thixotropic index was also measured with the Brookfield viscometer. The composition were also cast into thin films and cured in an oven at a temperature of 175°C for a period of time of 60 minutes. The volume resistivity was recorded by four-point probe. These results are shown in Table 6.

Table 6

[0068] Silver coated copper flake 600C purchased from Ferro Inc. has a particle

terms of diameter of about 15-20 um. [0069] Figure 2 shows where the die attach adhesive is used. In semiconductor packages, die attach means to attach functionalized semiconductor die onto metal or printed circuit board (PCB) substrates by means of film, paste, solder and so on. Among them, die attach adhesive is the major.

[0070] Dispensing adhesive by syringe needle onto substrate or die (Figure 3) is a typical method on die attach. To dispense well, the liquid adhesive has to show the proper range of viscosity and rheology.

[0071] Particle shape can make an important role to get the desired viscosity and rheology range (Figure 4). In theory, spherical particle has not obvious effect to adjust viscosity and rheology.

[0072] Particularly for silver coated copper flakes, with the limitation on aspect ratio in making such products, and the surface treatment, the viscosity and rheology adjustment are tricky.

[0073] From these examples we can see that the chelating agent proved to be effective in improving work life stability in silver coated copper flake filler-containing conductive die attach paste, while leaving other properties such as viscosity, thixotropic index and volume resistance without significant change.