REWORKABLE THERMOSETTING RESIN COMPOSITIONS

Abstract: This invention relates to thermosetting resin compositions useful for mounting onto a circuit board semiconductor devices, such as chip size or chip scale packages ("CSPs"), ball grid arrays ("BGAs"), and the like, each of which having a semiconductor chip, such as large scale integration ("LSI"), on a carrier substrate. The compositions of this invention are reworkable when subjected to appropriate conditions.

Description: REWORKABLE THERMOSETTING RESIN COMPOSITIONS BACKGROUND OF THE INVENTION Field of the Invention This invention relates to thermosetting resin compositions useful for mounting onto a circuit board semiconductor devices, such as chip size or chip scale packages ("CSPs"), ball grid arrays ("BGAs"), and the like, each of which having a semiconductor chip, such as large scale integration ("LSI"), on a carrier substrate. The compositions of this invention are reworkable when subjected to appropriate conditions. Brief Description of Related Technology In recent years, the popularity of small-sized electronic appliances, such as camera-integrated video tape recorders ("VTRs") and portable telephone sets, has made size reduction of LSI devices desirable. As a result, CSPs and BGAs are being used to reduce the size of packages substantially to that of bare chips. Such CSPs and BGAs improve the characteristics of the electronic device while retaining many of their operating features, thus serving to protect semiconductor bare chips, such as LSIs, and facilitate testing thereof. Ordinarily, the CSP/BGA assembly is connected to electrical conductors on a circuit board by use of a solder connection or the like. However, when the resulting CSP/BGA/circuit board structure is exposed to thermal cycling, the reliability of the solder connection between the circuit board and the CSP/BGA often becomes suspect . Recently, after a CSP/BGA assembly is mounted on a circuit board, the space between the CSP/BGA assembly and the circuit board is often now filled with a sealing resin (often referred to as underfill sealing) in order to relieve stresses caused by thermal cycling, thereby improving heat shock properties and enhancing the reliability of the structure. However, since thermosetting resins are typically used as the underfill sealing material, in the event of a failure after the CSP/BGA assembly is mounted on the circuit board, it is very difficult to replace the CSP/BGA assembly without destroying or scrapping the structure in its entirety. To that end, techniques for mounting a bare chip on a circuit board are accepted as substantially similar to the mounting of a CSP/BGA assembly onto a circuit board. One such technique, disclosed in Japanese Laid-Open Patent Publication No. 102343/93, involves a mounting process where a bare chip is fixed and connected to a circuit board by use of a photocurable adhesive, where, in the event of failure, this bare chip is removed therefrom. However, this technique is limited to those instances where the circuit board includes a transparent substrate (e.g. , glass) which permits exposure to light from the back side, and the resulting structure exhibits poor heat shock properties. Japanese Laid-Open Patent Publication No. 69280/94 discloses a process where a bare chip is fixed and connected to a substrate by use of a resin capable of hardening at a predetermined temperature. In the event of failure, this bare chip is removed from the substrate by softening the resin at a temperature higher than the predetermined temperature. However, no specific resin is disclosed, and there is no disclosure about treating the resin which remains on the substrate. Thus, the disclosed process is at best incomplete. As pointed out in Japanese Laid-Open Patent Publication No. 77264/94, it is conventional to use a solvent to remove residual resin from a circuit board. However, swelling the resin with a solvent is a time consuming process and the corrosive organic acid ordinarily used as the solvent may reduce the reliability of the circuit board. Instead, that disclosure speaks to a method for removing residual resin by irradiation with electromagnetic radiation. Japanese Laid-Open Patent Publication No. 251516/93 also discloses a mounting process using bisphenol A type epoxy resin (CV5183 or CV5183S; manufactured by Matsushita Electric Industrial Co., Ltd.). However, the removal process so disclosed does not consistently permit easy removal of the chip, the curing step is lengthy at elevated temperatures, and the process generally results in poor productivity. Of course, mechanical methods of removing/replacing semiconductor chips from/on a substrate are known, such as by cutting the chip to be removed/replaced. See U.S. Patent No. 5,355,580 (Tsukada) . Thermoplastic underfill resins are known for use in semiconductor chip attachment. See U.S. Patent No. 5,783,867 (Belke, Jr.). However, such thermoplastic resins tend to leak under relatively modest temperature conditions. In contrast, thermosetting resins cure into a matrix which ordinarily have greater thermal stability under end use operating temperatures . U.S. Patent Nos . 5,512,613 (Afzali-Ardakani) and 5,560,934 (Afzali-Ardakani) , each refer to a reworkable thermoset composition based on a diepoxide component in which the organic linking moiety connecting the two epoxy groups of the diepoxide includes an acid cleavable acyclic acetal group. With such acid cleavable acyclic acetal groups forming the bases of the reworkable composition, a cured thermoset need only be introduced to an acidic environment in order to achieve softening and a loss of much of its adhesiveness. U.S. Patent No. 5,872,158 (Kuczynski) refers to thermosetting compositions capable of curing upon exposure to actinic radiation, which are based on acetal diacrylates, and reaction products of which are reported to be soluble in dilute acid. U.S. Patent No. 5,760,337 (Iyer) refers to thermally reworkable crosslinked resins to fill the gap created between a semiconductor device and a substrate to which it is attached. These resins are produced by reacting a dienophile (with a functionality greater than 1) with a 2.5-dialkyl substituted furan-containing polymer. International Patent Publication No. PCT/US98/00858 refers to a thermosetting resin composition capable of sealing underfilling between a semiconductor device including a semiconductor chip mounted on a carrier substrate and a circuit board to which said semiconductor device is electrically connected. The composition includes about 100 parts by weight of an epoxy resin, about 3 to about 60 parts by weight of a curing agent, and about 1 to about 90 parts by weight of a plasticizer. Here, the area around the cured thermoset is to be heated at a temperature of about 190 to about 260°C for a period of time ranging from about 10 seconds to about 1 minute in order to achieve softening and a loss of much of its adhesiveness. Notwithstanding the state of the art, it would be desirable for an underfilling sealing material to provide good productivity and thermal shock properties, while allowing the substrates with which it is to be used to be readily processed and easily separated from a semiconductor device without application of acidic media or elevated temperature conditions that may compromise the integrity of the semiconductor devices remaining on the substrate or the substrate itself. SUMMARY OF THE INVENTION The thermosetting resin composition, which is used as an underfill sealant between a semiconductor device and a circuit board to which the semiconductor device is electrically connected, includes broadly a curable resin component an epoxy resin component, a portion of which is an epoxy compound having at least one thermally cleavable linkage; an optional inorganic filler component; and a curing agent component including an anhydride component, a nitrogen-containing component, such as an amine compound, an amide compound, and/or an imidazole compound, and combinations thereof. Reaction products of these compositions are capable of softening under exposure to elevated temperature conditions, such as in excess of the tempertures used to cure the composition. Such temperature exposure combined with the epoxy compound having at least one thermally cleavable linkage provides the reworkable aspect of this invention. The remaining components, discussed below, provide the physical properties and characteristics for the compositions and reaction products to render the compositions attractive for commercial use, particularly in the microelectronics industry. The epoxy compounds with at least one thermally cleavable linkage may be chosen from those within the following formula: where each R is independently selected from hydrogen, methyl, ethyl, propyl , isopropyl, butyl, isobutyl, t-butyl, C j^ . 4 alkoxy, halogen, cyano and nitro, and each R 3 is independently selected from hydrogen, methyl, ethyl, propyl, and isopropyl, R x and R 2 are each independently selected from hydrogen, methyl, ethyl, propyl, phenyl , tolyl, and benzyl, provided that both R x and R 2 cannot be hydrogen and m is 0 or 1. Particularly desirable epoxy compounds within formula I are given in the section entitled "Detailed Description of the Invention", which follows hereinafter. The inventive thermosetting resin composition is useful as an underfilling sealing resin, and enables a semiconductor device, such as a CSP/BGA assembly which includes a semiconductor chip mounted on a carrier substrate, to be securely connected to a circuit board by short-time heat curing and with good productivity. Reaction products of the inventive compositions demonstrate excellent heat shock properties (or thermal cycle properties) , and permit the semiconductor device to be easily removed from the circuit board by localized heating in the event of semiconductor device or connection failure. This makes it possible to reuse the circuit board (with the remaining functioning semiconductor devices still electrically attached) and thereby achieve an improvement in the yield of the production process and a reduction in production cost. The compositions of this invention may also be used for microelectronic applications beyond sealing underfill, such as with glob top, die attachment and other applications for thermosetting compositions in which rapid cure time and an extended useful working life are desirable. Other benefits and advantages of the present invention will become more readily apparent after a reading of the "Detailed Description" section together with the figures . BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 depicts a cross-sectional view showing an example of the mounting structure in which the thermosetting resin composition of the present invention is used. FIG. 2 depicts a flow diagram of a procedure useful to rework a cured thermosetting resin composition in accordance with the present invention, so as to remove a semiconductor device from a circuit board to which it had been attached. DETAILED DESCRIPTION OF THE INVENTION As noted above, the thermosetting resin compositions which are useful as underfill sealants between a semiconductor device and a circuit board to which the semiconductor device is electrically connected, includes broadly (a) an epoxy resin component, a portion of which is an epoxy compound having at least one thermally cleavable linkage; (b) an optional inorganic filler component; and (c) a curing agent component including an anhydride component, a nitrogen-containing component, such as an amine compound, an amide compound, and/or an imidazole compound, and/or combinations thereof. Reaction products of these compositions are capable of softening under exposure to elevated temperature conditions, such as in excess of the temperature chosen to cure the composition. Loss of adhesion to the substrate occurs at temperatures greater than that which was used to cure the composition. For instance, at least about 50% of adhesion to the substrate is typically lost at temperatures in excess of about 200°C. Typically, the composition includes about 10 to about 60 weight percent of the epoxy resin component by weight of the total composition, of which about 25 to about 75 weight percent thereof is comprised of an epoxy compound having at least one thermally cleavable linkage; about 0 to about 60 weight percent of the inorganic filler component; and 0.01 to about 60 weight percent of the curing agent component, of which about 0 to about 60 weight percent thereof is comprised of an anhydride compound, 0 to about 5 weight percent thereof is comprised of an amide compound, such as a cyano-functionalized amide, like dicyandamide, and 0 to about 2 weight percent thereof is comprised of an imidazole compound. Of course, depending on the particular set of properties desirable for a composition destined for a specific purpose these values may vary somewhat. Such variation may be achieved without undue experimentation by those persons skilled in the art, and accordingly are contemplated within the scope of the present invention. The epoxy resin component of the present invention may include any common epoxy resin, such as a multifunctional epoxy resin. Ordinarily, the multifunctional epoxy resin should be included in an amount within the range of about 15 weight percent to about 75 weight percent of the total of the epoxy resin component . In the case of bisphenol-F-type epoxy resin, desirably the amount thereof should be in the range of from about 35 to about 65 weight percent, such as about 40 to about 50 weight percent of the total of the epoxy resin component. Examples of the multifunctional epoxy resin include bisphenol-A-type epoxy resin, bisphenol-F-type epoxy resin (such as RE-404-S from Nippon Kayaku, Japan) , phenol novolac-type epoxy resin, and cresol novolac-type epoxy from resin (such as "ARALDITE" ECN 1871 from Ciba Specialty Chemicals, Hawthorne, New York) . Other suitable epoxy resins include polyepoxy compounds based on aromatic amines and epichlorohydrin, such as N,N,N' ,N' -tetraglycidyl-4 , 4 ' -diaminodiphenyl methane; N- diglycidyl-4-aminophenyl glycidyl ether; and N,N,N',N'- tetraglycidyl-1, 3-propylene bis-4-aminobenzoate . Among the epoxy resins suitable for use herein also include polyglycidyl derivatives of phenolic compounds, such as those available commercially under the tradename "EPON", such as "EPON" 828, "EPON" 1001, "EPON" 1009, and "EPON" 1031 from Shell Chemical Co.; "DER" 331, "DER" 332, "DER" 334, and "DER" 542 from Dow Chemical Co.; and BREN-S from Nippon Kayaku. Other suitable epoxy resins include polyepoxides prepared from polyols and the like and polyglycidyl derivatives of phenol-formaldehyde novolacs, the latter of which are available commercially under the tradename "DEN", such as "DEN" 431, "DEN" 438, and "DEN" 439 from Dow Chemical. Cresol analogs are also available commercially under the tradename "ARALDITE", such as "ARALDITE" ECN 1235, "ARALDITE" ECN 1273, and "ARALDITE" ECN 1299 from Ciba Specialty Chemicals Corporation. SU-8 is a bisphenol-A-type epoxy novolac available from Interez, Inc. Polyglycidyl adducts of amines, aminoalcohols and polycarboxylic acids are also useful in this invention, commercially available resins of which include "GLYAMINE" 135, "GLYAMINE" 125, and "GLYAMINE" 115 from F.I.C. Corporation; "ARALDITE" MY-720, "ARALDITE" 0500, and "ARALDITE" 0510 from Ciba Specialty Chemicals and PGA-X and PGA-C from the Sherwin-Williams Co. And of course combinations of the different epoxy resins are also desirable for use herein. The epoxy compounds with at least one thermally cleavable linkage may be chosen from those within the following formula: where each R is independently selected from hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert butyl, Ci- 4 alkoxy, halogen, cyano and nitro, and each R 3 is independently selected from hydrogen, methyl, ethyl, propyl, and isopropyl, Ri and R 2 are each independently selected from hydrogen, methyl, ethyl, propyl, phenyl, tolyl and benzyl, provided that both Rx and R 2 cannot be hydrogen and m is 0 or 1. Particularly desirable epoxy compounds within formula I include: The presence in the epoxy resin component of the epoxy compound (s) with at least one thermally cleavable linkage allows for repair, replacement, recovery and/or recycling of operative electronic components from assemblies that have become at least in part inoperative. These epoxy compounds can be prepared from cycloaliphatic diene esters having the following formula where R, Ri, R 2 , R 3 and m are as given above, which themselves are the condensation product of an alcohol within formula A below: where R, Ri, R 2 , R 3 and m are as given above, with an acid chloride within formula B below: B where R and R 3 are as given above. The condensation reaction is ordinarily performed in an anhydrous polar solvent at a temperature ranging from 0 to 20°C for a time period ranging from 6 to 18 hours. To epoxidize the diene ester, a peracid (such as peracetic acid, perbenzoic acid, meta-chloroperbenzoic acid, and the like) may be used, with the reaction carried out until epoxidization of diene ester occurs, typically within a period of time of from 2 to 18 hours. As an inorganic filler component, many materials are potentially useful. For instance, the inorganic filler component may often include reinforcing silicas, such as fused silicas, and may be untreated or treated so as to alter the chemical nature of their surface. Virtually any reinforcing fused silica may be used. Particularly desirable ones have a low ion concentration and are relatively small in particle size (e.g. , in the range of about 2-10 microns, such as on the order of about 2 microns) , such as the silica commercially available from Admatechs, Japan under the trade designation SO-E5. Other desirable materials for use as the inorganic filler component include those constructed of or containing aluminum oxide, silicon nitride, aluminum nitride, silica- coated aluminum nitride, boron nitride and combinations thereof . The curing agent component should include materials capable of catalyzing the polymerization of the epoxy resin component of the inventive compositions. Desirable curing agents for use with the present invention include an anhydride component, a nitrogen-containing component, such as an amine compound, an amide compound, and an imidazole compound, and combinations thereof. Appropriate anhydride compounds for use herein include mono- and poly-anhydrides, such as hexahydrophthalic anhydride ("HHPA") and methyl hexahydrophthalic anhydride ("MHHPA") (commercially available from Lindau Chemicals, Inc., Columbia, South Carolina, used individually or as a combination, which combination is available under the trade designation "LINDRIDE" 62C) and 5- (2 , 5-dioxotetrahydrol) -3- methyl-3 -cyclohexene-1, 2-dicarboxylic anhydride (commercially available from ChrisKev Co., Leewood, Kansas under the trade designation B-4400) . Of course, combinations of these anhydryde compounds are also desirable for use in the compositions of the present invention. Examples of the amine compounds include aliphatic polyamines, such as diethylenetriamine, triethylenetetramine and diethylaminopropylamine; aromatic polyamines, such as m- xylenediamine and diaminodiphenylamine; and alicyclic polyamines, such as isophoronediamine and menthenediamine . Of course, combinations of these amine compounds are also desirable for use in the compositions of the present invention. Examples of amide compounds include cyano- functionalized amides, such as dicyandiamide . The imidazole compounds may be chosen from imidazole, isoimidazole, and substituted imidazoles -- such as alkyl-substituted imidazoles (e.g. , 2-methyl imidazole, 2-ethyl-4-methylimidazole, 2 , 4-dimethylimidazole, butylimidazole, 2-heptadecenyl-4-methylimidazole, 2- methylimidazole, 2-undecenylimidazole, l-vinyl-2- methylimidazole, 2-n-heptadecylimidazole, 2- undecylimidazole, 2-heptadecylimidazole, 2-ethyl 4- methylimidazole, l-benzyl-2-methylimidazole, l-propyl-2- methylimidazole, 1-cyanoethyl-2-methylimidazole, 1- cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2- undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 1- guanaminoethyl-2-methylimidazole and addition products of an imidazole and trimellitic acid, 2-n-heptadecyl-4- methylimidazole and the like, generally where each alkyl substituent contains up to about 17 carbon atoms and desirably up to about 6 carbon atoms) , and aryl-substituted imidazoles [e.g. , phenylimidazole, benzylimidazole, 2- methyl-4, 5-diphenylimidazole, 2 , 3 , 5-triphenylimidazole, 2- styrylimidazole, 1- (dodecyl benzyl) -2-methylimidazole, 2- (2- hydroxyl-4-t-butylphenyl) -4 , 5-diphenylimidazole, 2- (2- methoxyphenyl) -4, 5-diphenylimidazole, 2- (3-hydroxyphenyl) - 4, 5-diphenylimidazole, 2- (p-dimethylaminophenyl) -4,5- diphenylimidazole, 2- (2-hydroxyphenyl) -4,5- diphenylimidazole, di (4, 5-diphenyl-2-imidazole) -benzene-1, 4 , 2-napnthyl-4 , 5-diphenylimidazole, l-benzyl-2- methylimidazole, 2-p-methoxystyrylimidazole, and the like, generally where each aryl substituent contains up to about 10 carbon atoms and desirably up to about 8 carbon atoms] . Examples of commercial imidazole compounds are available from Air Products, Allentown, Pennsylvania under the trade designation "CUREZOL" 1B2MZ and from Synthron, Inc., Morganton, North Carolina under the trade designation "ACTIRON" NXJ-60. Of course, combinations of these imidazole compounds are also desirable for use in the compositions of the present invention. The curing agent component may be used in an amount of from about 5 to about 40 parts by weight, per 100 parts of the epoxy resin, such as from about 5 to about 40 parts by weight, per 100 parts of the epoxy resin. In addition, the composition may also include a flowability agent, such as a silane and/or titanate. Appropriate silanes for use herein include octyl trimethoxy silane (commercially available from OSI Specialties Co., Danbury, Connecticut under the trade designation A-137) , and methacryloxy propyl trimethoxy silane (commercially available from OSI under the trade designation A-174) . Appropriate titanates for use herein include titanium IV tetrakis [2, 2-bis [ (2-propenyloxy) methyl] -1- butanolato-0] [bis (ditridecylphosphito-0) , dihydrogen] 2 (commercially available from Kenrich Petrochemical Inc., Bayonne, New Jersey under the trade designation KR-55) . When used, the flowability agent may be used in an amount of 0 to about 2 parts by weight, per 100 parts of the epoxy resin. In addition, adhesion promoters, such as the silanes, glycidyl trimethoxysilane (commercially available from OSI under the trade designation A-187) or gamma-amino propyl triethoxysilane (commercially available from OSI under the trade designation A-1100) , may be used. Cyanate esters may also be used in the inventive compositions. The cyanate esters useful as a component in the inventive compositions may be chosen from dicyanatobenzenes, tricyanatobenzenes, dicyanatonaphthalenes, tricyanatonaphthalenes, dicyanato- biphenyl, bis (cyanatophenyl) methanes and alkyl derivatives thereof, bis (dihalocyanatophenyl) propanes, bis (cyanatophenyl) ethers, bis (cyanatophenyl) sulfides, bis (cyanatophenyl) propanes, tris (cyanatophenyl) phosphites, tris (cyanatophenyl) phosphates, bis (halocyanatophenyl) methanes, cyanated novolac, bis [cyanatophenyl (methylethylidene) ] benzene, cyanated bisphenol-terminated thermoplastic oligomers / and combinations thereof. More specifically, aryl compounds having at least one cyanate ester group on each molecule and may be generally represented by the formula Ar(OCN) m , where Ar is an aromatic radical and m is an integer from 2 to 5. The aromatic radical Ar should contain at least 6 carbon atoms, and may be derived, for example, from aromatic hydrocarbons, such as benzene, biphenyl, naphthalene, anthracene, pyrene or the like. The aromatic radical Ar may also be derived from a polynuclear aromatic hydrocarbon in which at least two aromatic rings are attached to each other through a bridging group. Also included are aromatic radicals derived from novolac-type phenolic resins -- i.e., cyanate esters of these phenolic resins. The aromatic radical Ar may also contain further ring-attached, non-reactive substituents . Examples of such cyanate esters include, for instance, 1, 3-dicyanatobenzene; 1, 4-dicyanatobenzene; 1,3,5- tricyanatobenzene; 1,3-, 1,4-, 1,6-, 1,8-, 2,6- or 2,7- dicyanatonaphthalene; 1, 3 , 6-tricyanatonaphthalene; 4,4'- dicyanato-biphenyl; bis (4-cyanatophenyl) methane and 3 , 3 ' , 5, 5 ' -tetramethyl bis (4-cyanatophenyl) methane; 2,2- bis (3, 5-dichloro-4-cyanatophenyl)propane; 2,2-bis(3,5- dibromo-4-dicyanatophenyl) propane; bis (4- cyanatophenyl) ether; bis (4-cyanatophenyl) sulfide; 2,2-bis(4- cyanatophenyl) propane; tris (4-cyanatophenyl) -phosphite; tris (4-cyanatophenyl) phosphate; bis (3-chloro-4- cyanatophenyl) methane; cyanated novolac; 1,3-bis [4- cyanatophenyl-1- (methylethylidene) ] benzene and cyanated bisphenol-terminated polycarbonate or other thermoplastic oligomer . Other cyanate esters include cyanates disclosed in U.S. Patent Nos. 4,477,629 and 4,528,366, the disclosure of each of which is hereby expressly incorporated herein by reference; the cyanate esters disclosed in U.K. Pat. No. 1,305,702, and the cyanate esters disclosed in International Patent Publication WO 85/02184, the disclosure of each of which is hereby expressly incorporated herein by reference. Of course, combinations of these cyanate esters within the imidazole component of the compositions of the present invention are also desirably employed herein. A particularly desirable cyanate ester for use herein is available commercially from Ciba Specialty Chemicals, Tarrytown, New York under the tradename "AROCY" L10 [1, 1-di (4-cyanatophenylethane) ] . When used, the cyanate esters may be used in an amount of about 1 to about 20 weight percent based on the total amount of the epoxy resin component . Conventional additives may also be used in the compositions of the present invention to achieve certain desired physical properties of the composition, the cured reaction product, or both. For instance, it may be desirable in certain instances (particularly where a large volume of inorganic filler component is used) to include a reactive co-monomer component for the epoxy resin component, such as a reactive diluent. Appropriate reactive diluents for use herein may include monofunctional or certain multifunctional epoxy resins . The reactive diluent should have a viscosity which is lower than that of the epoxy resin component . Ordinarily, the reactive diluent should have a viscosity less than about 250 cps . In the event such a monofunctional epoxy resin is included as a reactive diluent, such resin should be employed in an amount of up to about 50 parts based on the total of the epoxy resin component. - - The monofunctional epoxy resin should have an epoxy group with an alkyl group of about 6 to about 28 carbon atoms, examples of which include C 6 _ 28 alkyl glycidyl ethers, C 6 . 28 fatty acid glycidyl esters and C 6 . 28 alkylphenol glycidyl ethers. Commercially available monofunctional epoxy resin reactive diluents include those from Pacific Epoxy Polymers, Richmond, Michigan, under the trade designations PEP-6770 (glycidyl ester of neodecandoic acid) , PEP-6740 (phenyl glycidyl ether) and PEP-6741 (butyl glycidyl ether) . Commercially available multifunctional epoxy resin reactive diluents include those from Pacific Epoxy Polymers, under the trade designations PEP-6752 (trimethylolpropane triglycidyl ether) and PEP-6760 (diglycidyl aniline) . The compositions of the present invention may further contain other additives, such as defoaming agents, leveling agents, dyes, and pigments. Moreover, photopolymerization initiators may also be incorporated therein, provided that such initiators do not adversely affect the properties of the composition or reaction products formed therefrom. The thermosetting resin compositions of the present invention may be of the one-pack type, in which all the ingredients are mixed together, or of the two-pack type in which the curable component (s) , is (are) included in one part and the curing agent is stored separately in a second part, and mixed together only prior to use. During application, the thermosetting resin compositions according to the present invention penetrate and flow readily into the space between the semiconductor chip and the circuit board, or at least show a reduction in viscosity under heated or use conditions thus penetrating and flowing easily. Generally, it is desirable to prepare thermosetting resin compositions of this invention by selecting the types and proportions of various components to reach a viscosity at a temperature of 25°C in the range of 500 to 70,000 cps, such as 800 to 3,000 cps, depending on the amount present (if any) of an inorganic filler component, so as to improve its ability to penetrate into the space (e.g. , of 10 to 200 μm) between the circuit board and the semiconductor device. At this viscosity, the gel times of the compositions will also be tailored to a specified period of time (such as 15 seconds, or 1 or 2 minutes) at a temperature of about 150°C. In such case, the inventive compositions should show no or substantially no increase of viscosity after a period of time of about six hours. With such a gel time, the compositions penetrate into the space (e.g. , of 10 to 200 μm) between the circuit board and the semiconductor device relatively rapidly, and allow for a greater number of assemblies to be filled without observing a viscosity increase in the composition thereby rendering it less effective for application. Reference to FIG. 1 shows a mounted structure (i.e. , a FC package) in which a thermosetting resin composition of the present invention has been applied and cured. The FC package 4 is formed by connecting a semiconductor chip (a bare chip) 2 to a carrier substrate 1 (e.g. , a circuit board) and sealing the space therebetween suitably with a thermosetting resin composition 3. More specifically, for example, in the assembly of FC semiconductor devices using SBB technology, the semiconductor chip 2 may be passed over a substrate bearing a conductive adhesive paste (such as a metal-filled epoxy) to form a layer thereof on the semiconductor chip 2. The layer is ordinarily formed by a printing mechanism. The conductive adhesive paste may be applied on either the carrier substrate or the semiconductor chip. One way to do this is with the stencil claimed and described in International Patent Publication No. PCT/FR95/00898. Alternatively, this connection may also be made by an anisotropically conductive adhesive. See International Patent Publication No. PCT/US97/13677. Thereafter, the semiconductor chip 2 is positioned over the carrier substrate 1 in such a manner so that the semiconductor chip 2 is in alignment with the electrodes 5 and 6 on the carrier substrate 1, now coated with a patterned layer of conductive adhesive paste or solder, 7 and 8. The conductive adhesive paste may be cured by a variety of ways, though ordinarily a heat cure mechanism is employed. In order to improve reliability, the space between the semiconductor chip 2 and the carrier substrate 1 is sealed with a thermosetting resin composition 3. The cured product of the thermosetting resin composition should completely fill that space. The semiconductor ship ordinarily may be coated with a polyimide-, benzocyclobutane- or silicone nitride- based material to passivate environmental corrosion. Carrier substrates may be constructed from ceramic substrates of A1 2 0 3 , SiN 3 and mullite (Al 2 0 3 -Si0 2 ) ; substrates or tapes of heat-resistant resins, such as polyimides; glass-reinforced epoxy; ABS and phenolic substrates which are also used commonly as circuit boards; and the like. Any electrical connection of the semiconductor chip to the carrier substrate may be used, such as connection by a high- melting solder or electrically (or anisotropically) conductive adhesive and the like. In order to facilitate connections, particularly in SBB technology, the electrodes may be formed as wire bond bumps . After the semiconductor chip is electrically connected to the carrier substrate, the resulting structure is ordinarily subjected to a continuity test or the like. After passing such test, the semiconductor chip may be fixed thereto with a thermosetting resin composition, as described below. In this way, in the event of a failure, the semiconductor chip may be removed before it is fixed to the carrier substrate with the thermosetting resin composition. Using a suitable application means, such as a dispenser, a thermosetting resin composition in accordance with this invention is applied to the periphery of the electronically-connected semiconductor chip. The composition penetrates by capillary action into the space between the carrier substrate and the semiconductor chip. The thermosetting resin composition is then thermally cured by the application of heat. During the early stage of this heating, the thermosetting resin composition shows a significant reduction in viscosity and hence an increase in fluidity, so that it more easily penetrates into the space between the carrier substrate and the semiconductor chip. Moreover, by preheating the carrier substrate, the thermosetting resin composition is allowed to penetrate fully into the entire space between the carrier substrate and the semiconductor chip. Thermosetting resin compositions of the present invention may ordinarily be cured by heating to a temperature in the range of about 120 to about 180°C for a period of time of about 0.5 to 30 minutes. However, generally after application of the composition, an initial cure time of about 1 minute sets up the composition, and complete cure is observed after about 5 to about 15 minutes at 165°C. Thus, the composition of the present invention can be used at relatively moderate temperatures and short- time curing conditions, and hence achieve very good productivity. The amount of thermosetting resin composition applied should be suitably adjusted so as to fill almost completely the space between the carrier substrate and the semiconductor chip, which amount of course may vary depending on application. Cured reaction products of the thermosetting resin compositions of the present invention demonstrate excellent adhesive force, heat resistance and electric properties, and acceptable mechanical properties, such as flex-cracking resistance, chemical resistance, moisture resistance and the like, for the applications for which they are used herein. In the mounting process by using the thermosetting resin composition of the present invention, after the semiconductor device is mounted on the circuit board as described above, the resulting structure is tested with respect to characteristics of the semiconductor device, connection between the semiconductor device and the circuit board, other electrical characteristics, and the state of sealing. In the event a failure is found, repair can be made in the following manner and as shown in the flow diagram depicted in FIG. 2. The area around the semiconductor device which has failed is heated at a temperature of about 190 to about 260 °C for a period of time ranging from about 10 seconds to about 1 minute. (See FIG. 2, step 1.) Desirably, the temperature should be maintained in the range of about 210 to about 220°C and the period of time should be within the 30 seconds to 1 minute range. Although no particular limitation is placed on the way in which heating occurs, localized heating is particularly desirable, such as the application of hot air to the failure site by a heating gun. As soon as the solder is melted and the resin is softened by partial decomposition to cause a reduction in bond strength, the semiconductor device may be pulled apart and removed from the substrate, such as with tweezers or pliers . After the semiconductor device 4 is removed, a residue of the cured reaction product of the thermosetting resin composition and a residue of the solder are left on the circuit board 5. The residue of the cured product of the thermosetting resin composition can be removed, for example, by scraping it off after the residue has been softened by heating it to a predetermined temperature. The residue of the solder can be removed, for example, by use of a solder-absorbing braided wire. (See FIG. 2, step 2.) Finally, a new semiconductor chip may be mounted again onto the circuit board (which has been cleaned as described above) in the manner as described above. (See FIG. 2, step 3.) Following mounting, a thermosetting resin composition in accordance with this invention may be dispensed in the area between the semiconductor device and the circuit board. (See FIG. 2, step 4.) Repair of the failure site is thus completed. Where a failure site is found in the circuit board, the semiconductor device can be reused by removing the residue of the cured reaction product of the thermosetting resin composition and the residue of the - - solder left on the bottom of the semiconductor device in the same manner as described above . The present invention will be more readily appreciated with reference to the examples which follow. EXAMPLES In these examples, compositions in accordance with the present invention were prepared and evaluated for performance . Thermosetting Resin Composition A thermosetting resin composition in accordance with this invention was prepared by mixing together in accordance with this invention for a period of time of about 10 minutes at room temperature in an open vessel the following components in the order noted: 1. an epoxy resin component including 24.95 grams of bisphenol-F-type epoxy resin (commercially available from Nippon Kayaku under the trade designation RE-404-S) , and 24.95 grams of the epoxy compound having at least one thermally cleavable linkage represented by formula III; and 2. a curing agent component including 0.2 grams of an imidazole component (commercially available from Air Products under the trade designation "CUREZOL" 1B2MZ) , and 50 grams of an anhydride component comprised of 42.42 grams of a mixture in an 50:50 ratio of "HHPA" and "MHHPA" anhydrides (commercially available from Lindau under the trade designation "LINDRIDE" 62C) , and 7.48 grams of a cycloaliphatic dianhydride (commercially available from ChrisKev under the trade designation B-4400) . Seven other formulations (Sample Nos. 2-8) were prepared having the following components in the amounts noted below in Table 1. Table 1 While the compositions were used upon formation (see below) , they may be stored for a period of time of up to about 3 to about 6 months at a temperature of about -40°C without experiencing viscosity increase. After formation, the composition was transferred to a 10 ml syringe made of non-reactive plastic. Mounting Process Using cream solder (PS10R-350A-F92C; manufactured by Harima Chemicals, Inc.), a CSP having a package of 20mm square, an electrode diameter of 0.5mm, an electrode pitch of 1.0mm, and a carrier substrate made of alumina was mounted on a 1.6mm thick glass-reinforced epoxy board having a circuit formed thereon. - - Underfilling Process The compositions of this invention may be dispensed through a 12G needle connected to the syringe into the junction between the carrier substrate and semiconductor device an assembly previously formed as above. After such dispensing, the assembly was transferred to an oven while the temperature was maintained at about 165°C. The composition cured initially after about 1 minute, and thereafter cured completely after about 15 minutes at that temperature. Physical Properties The compositions have a variety of properties in both the uncured and cured state which are measurable and useful parameters for the end user in choosing a particular formulation for a desired need. For instance, in the uncured state, the flow rate is of interest; in reaching the cured state, the adhesion and reworkability are of interest . The flow time allows the end user to determine the rapidity with which the adhesive may be applied during a fabrication process, such as a circuit assembly operation. It may be measured by passing the composition through a 25 μm gap between glass slides aligned perpendicular to one another, using metal shims as spacers. The time required for the composition to flow between the slides is then measured at a length of about one inch, at 0.25 inch intervals. Values in seconds for the flow times of the compositions set forth above are presented as an average of three measurements below in Table 2. The cure schedule refers to the time required for the onset of cure to occur at a certain temperatrue, in a specified period of time. This may be seen in more detail with regard to certain of the samples prepared in accordance with the present invention below in Table 2. Table 2 In the cured state, a variety of properties are useful depending on the end use for which the composition is destined. For instance, the adhesion provides information on the strength of the bond formed by the cured composition. The glass transition temperature ("Tg"), which is measured by differential scanning calerimetry ("DSC") or by thermal mechanical analysis ("TMA"), provides information on the hardness and strength of the cured reaction product (or, network) , and its behavior with respect to changes in temperature -- that is, a higher Tg should afford a material that is better able to withstand elevated temperatures. And of course reliability is important for the cured composition. Reliability testing is described below. Thermal Cycling Test Several samples (nos. 1-2 and 4-5) prepared as described above were exposed to thermal cycling tests, such as liquid-liquid thermal shock tests ("L-L") or air-air heat cycling tests ("A-A"). In the L-L tests, the samples were exposed to temperatures between -55 and 125°C, with a 5 minute dwell time at each extreme. In the A-A tests, the temperature range was the same as for the L-L test, but the dwell time was increased to 20 minutes. After a predetermined number of thermal cycles, the sample was subjected to a continuity test to confirm the interity of the electrical connection between the CSP and the circuit board. The samples were considered to be acceptable if they passed 500 cycles L-L. Table 3 below shows collected data: Table 3 As shown in Table 3, these samples are all acceptable with the type of chips tested. Reworkability Using a hot air generator, the area around the CSP, fixed to the circuit board with the compositions of Sample Nos. 1-2 and 4-5, should be heated by applying hot air at a temperature of about 215°C for a period of time of 1 minute. Then, the CSP may be easily removed by pulling or twisting the semiconductor chip from the circuit board using tweezers . Thermosetting resin composition prepared without the epoxy compound having at least one thermally cleavable linkage represented by formula III , with the balance of the epoxy resin component coming from the RS-404-S epoxy resin, which was dispensed and cured as above, does not allow for removal in the manner so described. Reliability of Replaced Chip The cured composition left on the curcuit board after the so-described process can be removed by using physical scrapping procedures, such as using a dremel with a rotating bristle at about 30,000 rpm. The site of the failed semiconductor chip should then be fluxed and a new semiconductor chip may be attached using conventional flip chip technology. Then, the thermosetting resin composition of this invention may be applied around the periphary of the newly-replaced semiconductor chip and cured by heating to a temperature of about 165°C for a period of 7 minutes. Electrical connections were securely established on the so-repaired CSP-mounted circuit board. This new board assembly was again submitted to L-L and A-A thermal cycling tests. Observed results for Sample No. 5 are given below in Table 4. Table 4 The samples described above are presented as illustrative, rather than limiting, examples of the inventive compositions. Many additional embodiments thereof are included in the spirit and scope of the invention.

Claims: What Is Claimed Is; 1. A thermosetting resin composition capable of sealing underfilling between a semiconductor device including a semiconductor chip mounted on a carrier substrate and a circuit board to which said semiconductor device is electrically connected, reaction products of which are capable of softening and losing their adhesiveness under exposure to temperature conditions in excess of those used to cure the composition, said composition comprising: (a) an epoxy resin component, a portion of which comprises an epoxy compound having at least one thermally cleavable linkage; (b) optionally, an inorganic filler component; and (c) a curing agent component comprising a member selected from the group consisting of anhydride compounds, amine compounds, amide compounds, imidazole compounds, and combinations thereof. 2. The composition according to Claim 1, wherein the epoxy compound having at least one thermally cleavable linkage may be chosen from those within the following formula : where each R is independently selected from hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert butyl, Cι_ alkoxy, halogen, cyano and nitro, and each R 3 is independently selected from hydrogen, methyl, ethyl, propyl, and isopropyl, Ri and R 2 are each independently selected from hydrogen, methyl, ethyl and propyl, provided that both Ri and R 2 cannot be hydrogen and m is 0 or 1. 3. The composition according to Claim 2, wherein the epoxy compound having at least one thermally cleavable linkage is a member selected from the group consisting of O 00/56799 - - 4. The composition according to Claim 2, wherein the epoxy compound having at least on thermally cleavable linkage is: 5. The composition according to Claim 1, further comprising a flowability agent. 6. The composition according to Claim 5, wherein the flowability agent is a member selected from the group consisting of silanes, titanates and combinations thereof. 7. The composition according to Claim 1, further comprising an adhesion promtor. 8. The composition according to Claim 7, wherein the adhesion promoter is a member selected from the group consisting of glycidyl trimethoxysilane, gamma-amino propyl triethoxysilane, and combinations thereof. 9. The composition according to Claim 1, further comprising a cyanate ester. 10. The composition according to Claim 9, wherein the cyanate ester is a member selected from the group consisting of dicyanatobenzenes, tricyanatobenzenes, dicyanatonaphthalenes, tricyanatonaphthalenes, dicyanato- biphenyl, bis (cyanatophenyl) methanes and alkyl derivatives thereof, bis (dihalocyanatophenyl) propanes, bis (cyanatophenyl) ethers, bis (cyanatophenyl) sulfides, bis (cyanatophenyl) propanes, tris (cyanatophenyl) phosphites, tris (cyanatophenyl) phosphates , bis (halocyanatophenyl) methanes, cyanated novolac, O 00/56799 - - bis [cyanatophenyl (methylethylidene) ] benzene, cyanated bisphenol-terminated thermoplastic oligomers, and combinations thereof. 11. The composition according to Claim 1, wherein the inorganic filler component may be selected from the group consisting of materials constructed of or containing reinforcing silicas, aluminum oxide, silicon nitride, aluminum nitride, silica-coated aluminum nitride, boron nitride, and combinations thereof. 12. The composition according to Claim 1, wherein the inorganic filler component has a low ion concentration and a particle size in the range of about 2-10 microns. 13. The composition according to Claim 1, wherein the anhydride compounds of the curing agent component may be selected from the group consisting of hexahydrophthalic anhydride, methyl hexahydrophthalic anhydride, 5- (2,5- dioxotetrahydrol) -3-methyl-3- cyclohexene-1, 2-dicarboxylic anhydride, and combinations thereof . 14. The composition according to Claim 1, wherein the amine compounds of the curing agent component may be selected from the group consisting of dicyandiamide, diethylenetriamine, triethylenetetramine, diethylaminopropylamine, m-xylenediamine, diaminodiphenylamine, isophoronediamine, menthenediamine, polyamides, and combinations thereof. 15. The composition according to Claim 1, wherein the amide compounds of the curing agent component may be selected from the group consisting of dicyandiamide and combinations thereof. 16. The composition according to Claim 1, wherein the imidazole compounds of the curing agent component may be selected from the group consisting of imidazole, - - isoimidazole, 2 -methyl imidazole, 2 -ethyl-4 -methylimidazole, 2, 4-dimethylimidazole, butylimidazole, 2-heptadecenyl-4- methylimidazole, 2 -methylimidazole, 2-undecenylimidazole, 1- vinyl-2-methylimidazole, 2-n-heptadecylimidazole, 2- undecylimidazole, 2-heptadecylimidazole, 2 -ethyl 4- methylimidazole, 1-benzyl-2 -methylimidazole, l-propyl-2- methylimidazole, l-cyanoethyl-2-methylimidazole, 1- cyanoethyl-2 -ethyl-4 -methylimidazole , 1-cyanoethyl-2 - undecylimidazole, 1-cyanoethyl-2 -phenylimidazole, 1- guanaminoethyl-2-methylimidazole, addition products of an imidazole and trimellitic acid, addition products of an imidazole and 2 -n-heptadecyl-4-methylimidazole, phenylimidazole, benzylimidazole, 2 -methyl-4 , 5- diphenylimidazole, 2 , 3 , 5-triphenylimidazole, 2- styrylimidazole, 1- (dodecyl benzyl) -2 -methylimidazole, 2- (2- hydroxyl-4-t-butylphenyl) -4 , 5-diphenylimidazole, 2- (2- methoxyphenyl) -4, 5-diphenylimidazole, 2- (3-hydroxyphenyl) -4- , 5-diphenylimidazole, 2- (p-dimethylaminophenyl) -4,5- diphenylimidazole, 2- (2 -hydroxypheny1) -4,5- diphenylimidazole, di (4 , 5-diphenyl-2-imidazole) -benzene-1, 4 , 2-napnthyl-4 , 5-diphenylimidazole, l-benzyl-2- methylimidazole, 2-p-methoxystyrylimidazole, and combinations thereof. 17. The composition according to Claim 1, wherein the curing agent component is used in an amount of from about 3 to about 60 parts by weight, per 100 parts by weight of the epoxy resin. 18. The composition according to Claim 1, wherein the curing agent component is used in an amount of from about 5 to about 40 parts by weight, per 100 parts of the epoxy resin. 19. The composition according to Claim 5, wherein the flowability agent is selected from octyl trimethoxy silane, methacryloxy propyl trimethoxy silane, titanium IV tetrakis [2 , 2-bis [ (2-propenyloxy) methyl] -l-butanolato-0] [bis (ditridecylphosphito-O) , dihydrogen] 2 , and combinations thereof . 20. The composition according to Claim 5, wherein the flowability agent is used in an amount up to about 2 parts by weight, per 100 parts of the epoxy resin. 21. The composition according to Claim 1, having a viscosity in the range of about 500-70,000 cps. 22. A thermosetting resin composition capable of sealing underfilling between a semiconductor device including a semiconductor chip mounted on a carrier substrate and a circuit board to which said semiconductor device is electrically connected, reaction products of which are capable of softening and losing their adhesiveness under exposure to temperature conditions in excess of those used to cure the composition, said composition comprising: (a) an epoxy resin component, a portion of which comprises an epoxy compound having at least one thermally cleavable linkage, in an amount within the range of about 20 to 65 weight percent, based on the total weight of the composition; (b) an inorganic filler component in an amount up to about 60 weight percent, based on the total weight of the composition; (c) a curing agent component in an amount within the range of 2 to about 50 weight percent, based on the total weight of the composition; and (d) a flowability agent in an amount up to about 0.5 weight percent, based on the total weight of the composition. 23. Reaction products formed from the compositions according to any one of Claims 1-22. 24. An electronic device comprising a semiconductor device and a circuit board to which said semiconductor device is electrically connected assembled using a thermosetting resin composition according to any one of Claims 1-21 as an underfill sealant between the semiconductor device and the circuit board, wherein reaction products of the composition are capable of softening and losing their adhesiveness under exposure to temperature conditions in excess of those used to cure the composition.

Inventors: CRANE LAWRENCE N, KONARSKI MARK M, SZCZEPANIAK ZBIGNIEW A, TORRES-FILHO AFRANIO, CRANE, LAWRENCE, N., KONARSKI, MARK, M., SZCZEPANIAK, ZBIGNIEW, A., TORRES-FILHO, AFRANIO
Applicants: CRANE LAWRENCE N, KONARSKI MARK M, LOCTITE CORP, SZCZEPANIAK ZBIGNIEW A, TORRES FILHO AFRANIO, CRANE, LAWRENCE, N., KONARSKI, MARK, M., LOCTITE CORPORATION, SZCZEPANIAK, ZBIGNIEW, A., TORRES-FILHO, AFRANIO
Application year: 2000
Main classification: C08G59
IPC codes: C08G59, C08K3, C08L63, C08L79, H01L21, H01L23