Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/54—Silicon-containing compounds
  • C08K5/541—Silicon-containing compounds containing oxygen
  • C08K5/5415—Silicon-containing compounds containing oxygen containing at least one Si—O bond
  • C08K5/5419—Silicon-containing compounds containing oxygen containing at least one Si—O bond containing at least one Si—C bond
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
  • C08G77/04—Polysiloxanes
  • C08G77/06—Preparatory processes
  • C08G77/08—Preparatory processes characterised by the catalysts used
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/0091—Complexes with metal-heteroatom-bonds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/04—Oxygen-containing compounds
  • C08K5/05—Alcohols; Metal alcoholates
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/04—Oxygen-containing compounds
  • C08K5/14—Peroxides
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/56—Organo-metallic compounds, i.e. organic compounds containing a metal-to-carbon bond
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L83/00—Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon only; Compositions of derivatives of such polymers
  • C08L83/04—Polysiloxanes
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
  • C08G77/04—Polysiloxanes
  • C08G77/12—Polysiloxanes containing silicon bound to hydrogen
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
  • C08G77/04—Polysiloxanes
  • C08G77/14—Polysiloxanes containing silicon bound to oxygen-containing groups
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
  • C08G77/04—Polysiloxanes
  • C08G77/14—Polysiloxanes containing silicon bound to oxygen-containing groups
  • C08G77/18—Polysiloxanes containing silicon bound to oxygen-containing groups to alkoxy or aryloxy groups
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
  • C08G77/04—Polysiloxanes
  • C08G77/20—Polysiloxanes containing silicon bound to unsaturated aliphatic groups
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
  • C08G77/70—Siloxanes defined by use of the MDTQ nomenclature
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
  • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
  • H01L2224/42—Wire connectors; Manufacturing methods related thereto
  • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
  • H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
  • H01L2224/484—Connecting portions
  • H01L2224/48463—Connecting portions the connecting portion on the bonding area of the semiconductor or solid-state body being a ball bond
  • H01L2224/48465—Connecting portions the connecting portion on the bonding area of the semiconductor or solid-state body being a ball bond the other connecting portion not on the bonding area being a wedge bond, i.e. ball-to-wedge, regular stitch
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]
  • Y10T428/31652—Of asbestos
  • Y10T428/31663—As siloxane, silicone or silane

Definitions

• the present invention relates to heat curable silicone compositions . More particularly, the present invention relates to low temperature, fast curing silicone compositions which include a rhodium catalyst.
• Silicone compositions are * known to cure through a variety of mechanisms. For example, moisture cure, photocure and heat cure mechanisms are commonly used. In many applications, such as in the electronics industry, the use of heat cured mechanisms has limitations due to the heat sensitivity of the electronic components. For example, in electronic sealing applications, such as the sealing of electronic module boxes containing electronic components, the use of high temperature sealants to seal the module can deleteriously affect the electronic components. For such applications, moisture curing or photocuring compositions have been found to be more appropriate. Moisture curing compositions, however, are slower to reach full cure than other mechanisms. Photocure compositions often do not have sufficient cure-through-volume (“CTV”) and are therefore combined with moisture curing mechanisms to ensure full cure.
• CTV cure-through-volume
• thermal management an increasingly important consideration, particularly with respect to packaging issues. For instance, heat build-up in electronic products tends to reduce reliability, slow performance and reduce power-handling capabilities. There is, therefore, a desire generally to reduce power consumption of electronic components, while increasing their number on semi-conductor chips which are reduced in size. Also, chip-on-board technology, where semiconductor chips are mounted directly to printed circuit boards, creates further demands on thermal management because of the more efficient use of the surface area, creating increased chip density. Numerous heat curable silicone compositions are disclosed in the patent literature. Many of these compositions disclose cure temperatures which are either too high for use in electronic applications, or disclose relatively low cure temperatures (e.g.
• This patent discloses a heat curable, thermally conductive silicone composition having a crosslinkable polyorganosiloxane, a polyorganohydrogensiloxane crosslinking agent, an alumina powder having an average particle size in the range of 2. O ⁇ to lO ⁇ and an oil absorption of ⁇ 15mL/g, and a platinum catalyst. These compositions can be cured by heating under ambient conditions at temperatures of about 250° to 450°C. Other platinum-group catalysts such as rhodium, iridium, ruthenium, and osmium are disclosed as useful.
• U.S. Patent No. 5,312,885 discloses curable organosiloxane compositions which contain a vinylsilyl-terminated perfluoropolyalkylene or perfluropolyalkylene polyether compound as the reactive resin and employ specific rhodium catalysts for cure.
• the use of the rhodium catalysts is reported to impart greater storage stability without viscosity increases as compared to platinum- based catalysts.
• These compositions are directed toward stable compositions which do not use inhibitors.
• These compositions are disclosed as being curable when heated at temperatures from 70° to 150°C, though preferably at temperatures greater than 110°C.
• 5,008,307 discloses relatively low temperature curing compositions which require long cure times. Cure temperatures of 100°C for one hour and 80°C for four hours are disclosed.
• This patent discloses thermally conductive silicone compositions which include an organopolysiloxane capable of reaction with an organohydrogenpolysiloxane having at least two SiH bonds, two types of aluminum powders which are a mixture of different sized spherical shaped particles, and a platinum catalyst.
• Platinum and rhodium catalysts are commonly recited in prior patent documents directed toward heat curing silicone compositions. Generally, such prior patent documents often disclose them in a list of useful catalysts, along with others from the platinum group of the periodic table.
• U.S. Patent No. 5,552,506 discloses the production of acrylic-modified organopolysiloxanes using rhodium catalysts.
• the resulting reactive compounds are disclosed as being useful as radiation curable lacquers or coating compositions, or as additives in such systems. These compounds are also disclosed as being thermally curable with the addition of peroxides.
• U.S. Patent No. 5,629,399 discloses room temperature curing organosiloxane compositions which have an alkenyl-containing polyorganosiloxane, an organohydrogensiloxane, a platinum catalyst, a methylvinylcyclosiloxane and an acetylenic alcohol.
• the platinum catalyst is generally used in amounts of 5 to 250 parts by weight of platinum metal per million parts of the combined weights of the other components.
• the methylvinylcyclosiloxane component is disclosed as effecting the working time of the composition and the demold time, i.e., the time between when the composition is mixed and poured into a mold and the time when the resulting elastomer can be removed from the mold without permanent deformation.
• the acetylenic alcohol is used in amounts of 0.002 to 0.11% by weight.
• This component is also disclosed as effecting the working time and the demold time of the resulting composition.
• Reinforcing fillers such as finally divided silica and non- reinforcing fillers such as quartz alumna, mica and calcium carbonate are also disclosed as being useful in this composition.
• compositions are designed for and disclosed as being room temperature curing compositions, with longer working time and shorter demolding time.
• U.S. Patent No. 5,270,457 discloses one part curable compositions having a curable polyorganosiloxane containing at least two alkenyl radicals per molecule, an organohydrogensiloxane crosslinker having at least two silicone bonded hydrogen atoms per molecule, a hydrosilation catalyst chosen from the platinum-group of the periodic table, and an adhesion promoting composition consisting of essentially of an epoxy-substituted silane and a cure inhibitor, such as cyclic methylvinylsiloxane, and an acetylenic alcohol containing at least six carbon atoms.
• compositions are disclosed as curing at temperatures below 100°C.
• the present invention provides rapid, curing silicone compositions, capable of curing in a commercially acceptable time frame at temperatures lower than have been used in the past.
• These compositions can be used in a variety of applications, for example, in the electronics industry (such as in underfill, glob top and dam and fill applications in circuit board assembly) , sealing applications, such as the sealing of electronic modules, potting applications, conformal coatings, thermal and electrical conductive applications, as well as adhesive applications, are among those for which the inventive compositions are useful.
• a heat-curable silicone composition which includes: (a) a reactive silicone having at least two unsaturated functional groups; (b) a silicone crosslinker having at least two reactive silicon hydride functional groups;
• rhodium-based catalyst system of the present invention has been found to reduce the cure temperature of the inventive silicone compositions, as compared to traditional catalysts used with heat cure silicone compositions such as those based on platinum. Moreover, it has further been discovered that the use of rhodium catalysts in combination with platinum catalysts gives a more rapid cure, at a lower temperature, than using platinum alone and further improves the cure- through-volume of the cured reactive product.
• a heat-curable silicone composition which includes :
• an encapsulating composition for use on semi-conductors which includes:
• a silicone crosslinker having at least two silicon hydride functional groups (b) a silicone crosslinker having at least two silicon hydride functional groups; (c) a catalytically effective amount of a catalyst system including a rhodium-based catalyst or a combination of a rhodium-based catalyst and a platinum-based catalyst;
• a flow modification agent which includes a dense metal oxide material, such as alumina, desirably in a generally spherical shape.
• a silicone crosslinker having at least two silicon hydride functional groups (b) a silicone crosslinker having at least two silicon hydride functional groups; and (c) a catalyst system including in combination a rhodium and platinum catalyst.
• a heat curable silicone which in addition to the aforementioned reactive silicone and silicone crosslinker components, further includes in combination a peroxide and an acetylenic compound as a stabilizing or inhibitor system.
• inventive compositions also include flow modification agents which serve to enhance or otherwise control the flowability and/or viscosity of the final composition.
• the flow modification agents also serve to lower the coefficient of thermal expansion of the total composition and may also provide conductivity.
• the present invention further includes a method of providing a low temperature-curing, rapid seal on a fixture such as an electronic part, the steps of which include administering to a surface of a fixture compositions of the present invention set forth therein, and permitting said compositions to cure.
• Figure 1 is a perspective view of a chip-on-board electronic device showing the components encapsulated with the inventive silicone composition in a "glob top” application.
• Figure 2 is a perspective view of a chip-on-board electronic device showing the components encapsulated with the inventive silicone composition in a "dam and fill” application.
• the reactive silicones in the present invention have at least two unsaturated functional groups to permit cross- linking of the composition. While the unsaturated group are desirably vinyl, other unsaturated groups may be employed.
• Useful reactive silicones may be generally represented by the following formula:
• R 1 , R 2 , R 3 , R 4 and R 5 may be the same or different and may be hydrogen, alkyl, alkenyl, aryl, alkoxy, alkenyloxy, aryloxy, (meth)acryl or (meth) acryloxy provided that at least two of R 1 , R 2 , R 3 , R 4 and R 5 have up to 12 carbon atoms (C ⁇ _ ⁇ 2 ) and include an unsaturated group; and n is an integer between about 100 and 1,200.
• the reactive silicone is a vinyl terminated polydimethylsiloxane, which may be represented by the following formula:
• R 1 , R 2 , R 3 and R 4 may be selected from alkyl, alkoxy, alkenyloxy, aryloxy, aryl, methacryl, methacryloxy and combinations thereof and n is between 100 and 1,200.
• the reactive silicone is generally present in amounts sufficient to achieve the structural integrity required of the specific application chosen. In general, the reactive silicone may be present in amounts of about 15% to about 90%, and desirably about 20% to about 50% by weight of the total composition.
• the reactive organopolysiloxanes of the present invention may optionally contain one or more hydrolyzable groups, in addition to the two unsaturated groups.
• the silicone composition can then be made to cure using a mechanism other than heat.
• moisture curing groups can be placed on the reactive silicone to impart moisture cure properties.
• hydrolyzable groups include amino, oxime, hydroxyl, alkoxy, aroloxy, alkaroloxy, aralkoxy and the like.
• a silicone having at least two reactive silicon hydride functional groups As a second component of the heat-curable silicone compositions of the present invention, there is included a silicone having at least two reactive silicon hydride functional groups. This component functions as a cross-linker for the reactive silicon. In the presence of the hydrosylization catalyst, the silicon-bonded hydrogen atoms in the cross-linking component undergo an addition reaction, which is referred to as hydrosilation with the silicon-bonded alkenyl or unsaturated groups in the reactive silicone component. This results in cross-linking and curing of the compositions . Since the reactive silicone component contains at least two unsaturated functional groups, the silicone cross-linking component should also contain at least two silicon-bonded hydrogen atoms to achieve the final cross- linked structure in the cured product.
• the silicon-bonded organic groups present in the silicone cross-linking component may be selected from the same group of substituted and unsubstituted monovalent hydrocarbon radicals as set forth above for the reactive silicone component, with the exception that the organic groups in the silicone cross-linker should be substantially free of ethylenic or acetylenic unsaturation.
• the silicone cross-linker may have a molecular structure that can be straight chained, branched straight chained, cyclic or networked.
• the silicone cross-linking component may be selected from a wide variety of compounds, that desirably conforms to the formula below:
• R 7 , R 8 and R 9 are H; otherwise R 7 , R 8 and R 9 can be the same or different and can be a substituted or unsubstituted hydrocarbon radical from C ⁇ - 2 o such hydrocarbon radicals including those as previously defined for formula I above; thus the SiH group may be terminal, pendent or both; R 10 can also be a substituted or unsubstituted hydrocarbon radical from C ⁇ _ 2 o such hydrocarbon radicals including those as previously defined for R 7 , R 8 and R 9 , and desirably is an alkyl group such as methyl; x is an integer from 10 to 1,000; and y is an integer from 1 to 20. Desirably R groups which are not H are methyl.
• the silicon hydride crosslinker should be present in amounts sufficient to achieve the desired amount of crosslinking and desirably in amounts of about 1 to about 10% by weight of the composition.
• the third component of the inventive compositions includes a rhodium catalyst, which is effective for catalyzing the addition reaction between the silicon-bonded hydrogen atoms in the silicon crosslinker and the unsaturated groups in the reactive silicone.
• rhodium catalysts include, but are not limited to, rhodium hydrocarbon complexes, such as tris (tributylsulfide) rhodium trichloride, (acetylacetonato) di-carbonylrhodium, tri (triphenylphosphine) rhodium chloride having the formula (Ph 3 P) 3 RhCl, rhodium acetate dimer having the formula [ (CH 3 COO) 2 Rh] 2 f and rhodium acetylacetonate having the formula Rh(ACAC) 2 in which ACAC is the acetylacetonato group forming a ring structure with the rhodium atom.
• rhodium hydrocarbon complexes
• Rhodium-containing transition metal complex may be used as the rhodium catalyst and chosen from a variety of organometallic materials or metallocenes. Those materials of particular interest herein may be represented by metallocenes within structure II:
• Ri and R 2 may be the same or different and may occur at least once and up to as many four times on each ring in the event of a five-membered ring and up to as many as five times on each ring in the event of a six-membered ring;
• Ri and R 2 may be selected from H; any straight- or branched-chain alkyl constituent having from 1 to about 8 carbon atoms, such as CH 3 , CH 2 CH 3 , CH 2 CH 2 CH 3 , CH(CH 3 ) 2 , C(CH 3 ) 3 or the like; acetyl; vinyl; allyl; hydroxyl; carboxyl; -(CH 2 ) n -OH, where n may be an integer in the range of 1 to about 8; - (CH 2 ) n -COOR 3 , where n may be an integer in the range of 1 to about 8 and R 3 may be any straight- or branched-chain alkyl constituent having from 1 to about 8 carbon atoms; H; Li; or Na; -(CH 2 ) n -OR 4 , wherein n may be an integer in the range of 1 to about 8 and R 4 may be any straight- or branched-chain alkyl constituent having from 1 to about 8 carbon atoms; or - (
• the element represented by M e may have additional ligands -- Yi and Y 2 -- associated therewith beyond the carboxylic ligands depicted above .
• metallocene structure I_I may be modified to include materials such as those within structure III below:
• Ri, R 2 , Yi, Y 2 , A, A', m, m' and M e are as defined above.
• a particularly desirable example of such a material is where Ri and R 2 are each H; Yi and Y 2 are each CI; A and A' are each N; m and m' are each 2 and M e is Rh.
• well-suited metallocene materials may be chosen from within metallocene structure IV :
• rhodium complexes are those disclosed in U.S. Patent No. 3,890,359, the subject matter of which is incorporated herein by reference.
• such complexes include RhCl 3 (EtSCH 2 SiMe 3 ) 3 , RhCl 3 (n-BuSCH 2 SiMe 3 ) 3 , RhCl 3 (PhSCH 2 SiMe 3 ) 3 and RhCl 3 [ (Me 3 SiCH 2 ) 2 S] 3 , wherein Me, Et, Bu and Ph represent methyl, ethyl, butyl and phenyl radicals respectively.
• the rhodium catalysts should be used in an amount effective to induce curing at an appropriate temperature, which is lower than that which is ordinarily required with non-rhodium heat cure catalysts.
• the catalyst is present in amounts of about 0.00001% to about 1.0% by weight, and more desirably about 0.00002% to about 0.001% and even more desirably in amounts of about 0.00005% to about 0.005% by weight of the total composition.
• compositions of the present invention provide for faster curing at low temperatures, e.g., at temperatures of about 100°C or less.
• the compositions of the present invention can be formulated to fully cure at temperatures of about 60 °C to about 100 °C, in time periods of about 2 to about 30 minutes.
• tack-free cure can be obtained in a period of time of about 6-10 minutes at a temperature of about 75 °C to about 100 °C.
• the catalyst system which may employ a combination of rhodium and platinum, provides a means of achieving faster, low temperature cure, while simultaneously achieving a commercially acceptable shelf-life.
• the catalyst system when the combination of rhodium and platinum are used, avails itself of the best properties of each of the metal catalysts, without the disadvantages of the individual catalysts when used alone.
• Enhanced surface cure and cure- through can be achieved using a lower total amount of catalyst.
• at low temperatures, such as about 100°C better adhesion is achieved than compositions which use just platinum or platinum-based catalysts.
• platinum or platinum-containing complexes such as the platinum hydrocarbon complexes described in U.S. Patent Nos. 3,159,601 and 3,159,662; the platinum alcoholate catalysts described in U.S. Patent No. 3,220,970, the platinum complexes described in U.S. Patent No. 3,814,730 and the platinum chloride-olefin complexes described in U.S. Patent No. 3,516,946, are useful.
• platinum or platinum-containing complexes such as the platinum hydrocarbon complexes described in U.S. Patent Nos. 3,159,601 and 3,159,662; the platinum alcoholate catalysts described in U.S. Patent No. 3,220,970, the platinum complexes described in U.S. Patent No. 3,814,730 and the platinum chloride-olefin complexes described in U.S. Patent No. 3,516,946, are useful.
• platinum or platinum-containing complexes such as the platinum hydrocarbon complexes described in U.S. Patent Nos. 3,159,
• rhodium-based catalyst to platinum-based catalyst may range from about 1:100 to about 10:1.
• other catalysts may be used in combination with the rhodium and rhodium/platinum catalyst combinations.
• complexes of ruthenium, palladium, oznium and arridium are also contemplated.
• ferrocenes i.e., where M e is Fe
• M e ferrocene
• vinyl ferrocenes ferrocenes
• ferrocene derivatives such as butyl ferrocenes or diarylphosphino etal-complexed ferrocenes [e.g., 1,1-bis (diphenylphosphino) ferrocene-palladium dichloride]
• titanocenes i.e., where M e is Ti
• bis(rj 5 -2,4 ⁇ cyclopentadien-1-yl) -bis- [2, 6-difluoro-3- ( lH-pyrrol-1- yl)phenyl] titanium which is available commercially from Ciba Specialty Chemicals, Tarrytown, New York under the tradename "IRGACURE" 784DC, and combinations thereof.
• a particularly desirable metallocene is ⁇
• bis-alkylmetallocenes for instance, bis- alkylferrocenes (such as diferrocenyl ethane, propanes, butanes and the like) are also desirable for use herein.
• Examples of such materials include cobalt (II) acetylacetonate ( "Co (II) ACAC” ) , cobalt (III) acetylacetonate ( “Co (III) ACAC” ) , nickel (II) acetylacetonate ("NiACAC”), iron (II) acetylacetonate ("Fe (II) ACAC”) , iron (III) acetylacetonate ( "Fe (III) ACAC” ) , chromium (II) acetylacetonate ( “Cr (II) ACAC” ) , chromium (III) acetylacetonate ( "Cr (III) ACAC”) , manganese (II) acetylacetonate ( "Mn (II) ACAC”) , manganese (III) acetylacetonate ( "Mn (III) ACAC”) and copper (II) acetylacet
• an inhibitor system which includes a combination of an acetylenic compound, such as an acetylenic alcohol and a peroxide.
• peroxides which are known to initiate free radical curing mechanisms present in heating curing silicone compositions, have been found to increase the shelf stability of the inventive compositions, alone or in combination with an acetylinic compound.
• a desirable inhibitor system includes the combination of an acetylene compound such as an acetylenic alcohol or ester, such as octynol, and a peroxide.
• an acetylene compound such as an acetylenic alcohol or ester, such as octynol
• the amount of acetylenic compound useful in the inhibitor system ranges from about 0.01% to about 2.0% by weight of the total composition, and desirably about 0.1% to about 1.0% by weight of the total composition.
• Useful peroxides for inclusion in the inhibitor system include cumene ⁇ hydroperoxide (“CHP”) , tertiary butyl hydroperoxide (“TBH”) and the like. Other peroxides may of course be employed.
• the amount of peroxide compounds used in the inhibitor system ranges from about 0.001% to about 1% by weight of the total composition, and desirably about 0.01% to about 0.1% by weight of the total composition.
• flow modifying agents may be incorporated into the inventive compositions to influence flowability and viscosity of the composition.
• the present invention provides low temperature heating-curing silicone compositions having controlled flowability.
• the flow modifiers are generally spherically shaped to increase flow properties, but other shapes may be chosen as well, to suit application needs .
• Flowability and viscosity control are particularly of concern in electronic applications .
• Flow modifying agents useful include relatively dense metal oxides, such as alumina, zinc oxide and the like. As previously mentioned, desirably these agents are spherical in shape and have an average particle size of about 1 to about lO ⁇ .
• Another aspect of the invention relates to heat curing silicone compositions which have relatively low coefficients of thermal expansion (“CTE") .
• This aspect of the invention also provides silicone compositions which, notwithstanding very high amounts of flow modifying agents, e.g., 50% to 90% by weight, exhibit excellent flowability in the uncured state, have a commercially acceptable shelf-life and relatively stable viscosity over time.
• the particular flow modifying agents are chosen to achieve flowable materials having low CTE .
• dense metal oxides such as alumina have been found to be extremely effective in achieving such flowable compositions having low CTE properties.
• Alumina particles are desirably spherical in shape, the combination of the density and shape of the material enhancing the flowability properties of the silicone composition.
• the average particle size of spherical alumina found to be particularly useful is in the range of about l ⁇ to lO ⁇ . Smaller particle sizes of the flow modifier may additionally be incorporated to help maintain the larger particles in suspension. Desirably, spherically shaped alumina particles of about l ⁇ or less are incorporated as suspension stabilizers for the larger diameter alumina particles .
• the reactive silicone component when cured tends to expand significantly more than the metal oxide flow modifiers. Incorporating the flow modifiers in the aforementioned amounts provides cured compositions which are less influenced by the forces of thermal expansion. Minimizing thermal expansion is particularly important when the compositions are used as encapsulants for electronic parts. Less thermal expansion of the cured composition results in less stress on electronic parts adjacent thereto.
• FIG. 1 shows a perspective view of a chip- on-board device.
• substrate 10 also commonly referred to as a circuit board
• semi-conductor chip 14 also commonly referred to as a die.
• Electrical wires or leads 16 connect the circuit board to the semi-conductor chip 14 at connections 18 and 18a.
• the chip and wire connections are then encased or encapsulated with the inventive silicone composition, which is then subjected to relatively low heat to cure.
• the cured composition serves to protect the electronic components. This configuration is often referred to as a "glob top" application.
• FIG 2 is also a perspective view of a chip-onboard electronic device, with a configuration commonly referred to as a "dam and fill” application.
• the semiconductor chip 14 ' is located on circuit board 10', which in turn are connected to each other by wire leads 16' at locations 18' and 18a'.
• a reservoir or dam area having walls 20 is shown about semi-conductor chip 14'. This dam area provides a volume in which the inventive composition can be applied or filled.
• compositions of the present invention may also include one or more amino-containing silane compounds which act as adhesion promoters. These amino-containing silane compounds are present in amounts of about 0.1 percent by weight of the composition to about 5.0 percent by weight of the composition. Desirably, these compounds are present in amounts of about 0.74 percent by weight of the composition to about 1.4 percent by weight of the composition.
• Amino- containing silane compounds which are useful in the present invention include, but are not limited to, silane compounds containing amino-alkyl groups, such as gamma- ureidopropyltrimethoxy silane, 3-aminopropyl trimethoxysilane, N,N'-bis (3-trimethoxy silylpropyl) urea, gamma- aminopropyltrimethoxysilane, N- (2-aminoethyl) -3- aminopropyltriethoxysilane, N- (2-aminoethyl) -3- aminopropyltrimethoxysilane , trimethoxysilylpropyldiethylene triamine, tertiary alkyl carbamate silane, and aminoethyl-3- aminopropyl-methyl-dimethylsilane .
• amino-alkyl groups such as gamma- ureidopropyltrimethoxy silane, 3-amin
• amino- containing silane compounds include silane compounds containing amino-cycloaliphatic groups such as methyl tris (cyclohexylamino) silane and silane compounds containing amino- aromatic groups such as methyl tris- (N-methylbenzamido) silane .
• Adhesion promoters may be present in amounts of up to about 5%, and desirably up to about 2% by weight.
• adhesion promoters examples include octyl trimethoxysilane (commercially available from Witco Corporation, Greenwich, Connecticut under the trade designation A-137), glycidyl trimethoxysilane (commercially available from Witco under the trade designation A-187), methacryloxypropyl trimethoxysilane (commercially available from Witco under the trade designation of A-174), vinyl trimethoxysilane, tetraethoxysilane and its partial condensation products, and combinations thereof.
• octyl trimethoxysilane commercially available from Witco Corporation, Greenwich, Connecticut under the trade designation A-137
• glycidyl trimethoxysilane commercially available from Witco under the trade designation A-187
• methacryloxypropyl trimethoxysilane commercially available from Witco under the trade designation of A-174
• vinyl trimethoxysilane tetraethoxysilane and its partial condensation products
• inventive compositions may also contain other additives so long as they do not interfere with the curing mechanisms or intended use.
• additives such as fillers, promoters, pigments, moisture scavengers, inhibitors and the like may be included.
• Fillers such as fumed silica or quartz are contemplated, as are moisture scavengers such as methyltrimethoxysilane and vinyl trimethoxysilane.
• fillers examples include zirconium silicate, hydroxides such as hydroxides of calcium, aluminum, magnesium, iron and the like.
• Other fillers such as diatomaceous earth, carbonates such as sodium, potassium, calcium and magnesium carbonates may be employed.
• Calcium clay, graphite and synthetic fibers may also be incorporated. Mixtures of fillers are contemplated.
• Conductive — thermally and/or electrically -- fillers may also be included in the inventive compositions.
• Such fillers include by way of example inorganic or metallic materials, for instance iron, aluminum, zinc, silver, gold, lead, nickel, magnesium, boron, barium, platinum, palladium, copper, zirconium, titanium, uranium, vanadium, niobium, tungsten, silicon and conductive derivatives thereof, such as oxides and nitrides, as well as carbon, graphite, silicon carbide, and the like, and combinations thereof.
• metals such as is commercially available from
• magnesium oxide such as is commercially available from Kaopolite Incorporated, Union, New Jersey or Harbison-Walker Refractories Company, Pittsburgh, Pennsylvania
• aluminum oxide such as is available commercially from Whittaker, Clark & Daniels, Inc., South Plainfield, New Jersey
• zinc oxide such as is available commercially from Zinc Corporation of America, Monaca, Pennsylvania
• silver flake such as is available commercially from Zinc Corporation of America, Monaca, Pennsylvania
• the conductive filler should be used in an amount effective to conduct electricity or heat to an extent appropriate for the end use application.
• a conductive filler may be present in an amount within the range of about 40 to about 85 weight percent of the total composition.
• Heat curable silicone compositions were prepared as set forth in Table I, below. A premix of the vinyl-terminated PDMS and the catalysts were prepared separately and added to the additional components, with mixing.
• Composition A is a control composition and employs only a platinum catalyst.
• Compositions B-G are all representative of the invention.
• Compositions B-D are representative of the low temperature, fast curing compositions of the present invention which employ either a rhodium catalyst alone (B) or a combination of rhodium and platinum catalysts (C-D) .
• Compositions A-D each employ a combination of peroxide and an acetylenic compound as a stabilizing system.
• compositions E-G demonstrate the aspect of the invention which employs a rhodium catalyst in combination with a significant amount of a flow modifying agent to provide a flowable, low temperature curing and low CTE composition.
• Compositions A-D A variety of physical properties were tested for Compositions A-D. These are set forth in Table II, below. In particular, Compositions C and D exhibited as good or better cure-through time using lower total amount of catalyst as compared to Composition A (control) . Additionally, DSC measurements indicated a maximum exotherm peak for Compositions C and D at 1.09 and 1.0 minutes respectively, as compared to Composition A (control) which exhibited the maximum peak at 1.53 minutes. These measurements are also indicative of faster cure times of the inventive composition. It should be noted that each of the Compositions A-D were prepared in the same manner and are substantially identical but for the catalysts.
• compositions B , C and D were also measured for tensile strength. As indicated in the table, Compositions B-D had significant improvement in tensile strength after 1 hour at 100°C cure, as compared to Composition A (control) . From these test results, it can be seen that inventive Compositions B-D have distinct advantages in cure speed, cure-through time and tensile speed when cured at 100 °C, as compared to substantially the same composition containing only a platinum catalyst.
• compositions E-G were each tested for suspension stability of the flow modifying agent, flowability of the uncured composition, as well as viscosity stability. These formulations were found to have acceptable suspension stability and good flowability. Upon storage at room temperature for 4 days, the viscosity remained substantially the same, i.e. 43,590 cps after 1 day and 43,220 cps after 4 days .
• Table III identifies a heat curable silicone composition, prepared using only a rhodium catalyst.
• Composition H represents a control with no stabilizer system.
• Compositions I and J contain only a peroxide or an acetylenic compound but not the combination.
• Composition K represents the inventive combination of a peroxide and an acetylenic compound as a stabilizer system.
• composition H The initial viscosity of each composition is shown in the last row of the composition with no stabilizers (Composition H) gelled in 14 days.
• Composition I shows the addition of only CHP to an otherwise identical formulation to Composition H. After 21 days its viscosity increased 51%.
• Composition J shows the addition of only the acetylenic compound octynol to an otherwise identical formulation to Composition H. After 11 days its viscosity doubled.
• Inventive Composition K which contained a combination of cumene hydroperoxide and octynol, only increased 33% in viscosity in 21 days.

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