Curable organosiloxane compositions and semiconductor devices

• US 5,804,631 A
• Filed: 07/30/1996
• Issued: 09/08/1998
• Est. Priority Date: 08/04/1995
• Status: Expired due to Fees

• Current Assignee: Dow Corning Toray Company Limited (Dow, Inc.)
• Original Assignee: Dow Corning Toray Company Limited (Dow, Inc.)
• Inventors: Nakayoshi, Kazumi, Mitani, Osamu, Mine, Katsutoshi, Tazawa, Rikako
• Primary Examiner(s): Marquis, Melvyn I.
• Application Number:
  US08/688,456
• Time in Patent Office: 770 Days
• Field of Search: 257/783, 528/15, 528/16, 528/17, 524/780, 524/785, 524/440, 427/387
• US Class Current: 524/440
• CPC Class Codes: C08G 77/12 containing silicon bound to hydrogen C08G77/045 takes precedence
• CPC Class Codes: C08G 77/18 to alkoxy or aryloxy groups
• CPC Class Codes: C08G 77/20 containing silicon bound to unsaturated aliphatic groups C08G77/045 takes precedence
• CPC Class Codes: C08K 3/08 Metals
• CPC Class Codes: C08L 83/00 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
• CPC Class Codes: C08L 83/04 Polysiloxanes
• CPC Class Codes: C09J 183/04 Polysiloxanes
• CPC Class Codes: H01L 2224/29 of an individual layer connector
• CPC Class Codes: H01L 2224/29099 Material
• CPC Class Codes: H01L 2224/29101 the principal constituent melting at a temperature of less than 400°C
• CPC Class Codes: H01L 2224/2919 with a principal constituent of the material being a polymer, e.g. polyester, phenolic based polymer, epoxy
• CPC Class Codes: H01L 2224/29191 The principal constituent being an elastomer, e.g. silicones, isoprene, neoprene
• CPC Class Codes: H01L 2224/29199 Material of the matrix
• CPC Class Codes: H01L 2224/2929 with a principal constituent of the material being a polymer, e.g. polyester, phenolic based polymer, epoxy
• CPC Class Codes: H01L 2224/29298 Fillers
• CPC Class Codes: H01L 2224/29299 Base material
• CPC Class Codes: H01L 2224/32225 the item being non-metallic, e.g. insulating substrate with or without metallisation
• CPC Class Codes: H01L 2224/32245 the item being metallic
• CPC Class Codes: H01L 2224/45124 Aluminium (Al) as principal constituent
• CPC Class Codes: H01L 2224/45144 Gold (Au) as principal constituent
• CPC Class Codes: H01L 2224/45147 : Copper (Cu) as principal constituent
• CPC Class Codes: H01L 2224/48091 : Arched
• CPC Class Codes: H01L 2224/48227 : connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2224/48247 : connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2224/48472 : the other connecting portion not on the bonding area also being a wedge bond, i.e. wedge-to-wedge
• CPC Class Codes: H01L 2224/73265 : Layer and wire connectors
• CPC Class Codes: H01L 2224/8319 : Arrangement of the layer connectors prior to mounting
• CPC Class Codes: H01L 2224/83205 : Ultrasonic bonding
• CPC Class Codes: H01L 2224/83805 : involving forming a eutectic alloy at the bonding interface
• CPC Class Codes: H01L 2224/8385 : using a polymer adhesive, e.g. an adhesive based on silicone, epoxy, polyimide, polyester
• CPC Class Codes: H01L 2224/85201 : Compression bonding
• CPC Class Codes: H01L 2224/85205 : Ultrasonic bonding
• CPC Class Codes: H01L 23/49513 : having bonding material between chip and die pad
• CPC Class Codes: H01L 24/29 : of an individual layer connector
• CPC Class Codes: H01L 24/32 : of an individual layer connector
• CPC Class Codes: H01L 24/45 : of an individual wire connector
• CPC Class Codes: H01L 24/48 : of an individual wire connector
• CPC Class Codes: H01L 24/73 : Means for bonding being of different types provided for in two or more of groups H01L24/10, H01L24/18, H01L24/26, H01L24/34, H01L24/42, H01L24/50, H01L24/63, H01L24/71
• CPC Class Codes: H01L 24/83 : using a layer connector
• CPC Class Codes: H01L 2924/00 : Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/00011 : Not relevant to the scope of the group, the symbol of which is combined with the symbol of this group
• CPC Class Codes: H01L 2924/00012 : Relevant to the scope of the group, the symbol of which is combined with the symbol of this group
• CPC Class Codes: H01L 2924/00013 : Fully indexed content
• CPC Class Codes: H01L 2924/00014 : the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/01005 : Boron [B]
• CPC Class Codes: H01L 2924/01006 : Carbon [C]
• CPC Class Codes: H01L 2924/0101 : Neon [Ne]
• CPC Class Codes: H01L 2924/01012 : Magnesium [Mg]
• CPC Class Codes: H01L 2924/01013 : Aluminum [Al]
• CPC Class Codes: H01L 2924/01014 : Silicon [Si]
• CPC Class Codes: H01L 2924/01019 : Potassium [K]
• CPC Class Codes: H01L 2924/0102 : Calcium [Ca]
• CPC Class Codes: H01L 2924/01028 : Nickel [Ni]
• CPC Class Codes: H01L 2924/01029 : Copper [Cu]
• CPC Class Codes: H01L 2924/0103 : Zinc [Zn]
• CPC Class Codes: H01L 2924/01033 : Arsenic [As]
• CPC Class Codes: H01L 2924/0104 : Zirconium [Zr]
• CPC Class Codes: H01L 2924/01047 : Silver [Ag]
• CPC Class Codes: H01L 2924/01077 : Iridium [Ir]
• CPC Class Codes: H01L 2924/01078 : Platinum [Pt]
• CPC Class Codes: H01L 2924/01079 : Gold [Au]
• CPC Class Codes: H01L 2924/01082 : Lead [Pb]
• CPC Class Codes: H01L 2924/0132 : Binary Alloys
• CPC Class Codes: H01L 2924/01322 : Eutectic Alloys, i.e. obtained by a liquid transforming into two solid phases
• CPC Class Codes: H01L 2924/014 : Solder alloys
• CPC Class Codes: H01L 2924/0665 : Epoxy resin
• CPC Class Codes: H01L 2924/0715 : Polysiloxane
• CPC Class Codes: H01L 2924/07802 : not being an ohmic electrical conductor
• CPC Class Codes: H01L 2924/09701 : Low temperature co-fired ceramic [LTCC]
• CPC Class Codes: H01L 2924/10253 : Silicon [Si]
• CPC Class Codes: H01L 2924/1301 : Thyristor
• CPC Class Codes: H01L 2924/14 : Integrated circuits
• CPC Class Codes: H01L 2924/15747 : Copper [Cu] as principal constituent
• CPC Class Codes: H01L 2924/181 : Encapsulation
• CPC Class Codes: H01L 2924/19041 : being a capacitor
• CPC Class Codes: H01L 2924/19043 : being a resistor
• CPC Class Codes: H01L 2924/19105 : in a side-by-side arrangement on a common die mounting substrate
• CPC Class Codes: H01L 2924/3025 : Electromagnetic shielding

Abstract

A curable organosiloxane composition useable as a silicone die attach adhesive, an electrically conductive silicone rubber composition each comprising a composition that cures through both addition and condensation reactions, that will not impair wire bondability to a semiconductor chip or lead frame after the semiconductor chip has been bonded to a substrate or package; and semiconductor devices in which the semiconductor chip is bonded to its substrate or package using the curable organosiloxane composition and in which the semiconductor device that evidences high reliability by virtue of the use of the curable organosiloxane composition.

Claims

1. A curable organopolysiloxane composition consisting essentially of:

(A) 100 weight parts of a mixture of

(a) 5 to 95 weight % of an alkoxy-substituted organopolysiloxane having a viscosity at 25°

C. of 20 to 200,000 mPa.s and containing an average of at least two silicon-bonded alkoxy groups per molecule, and wherein the alkoxy-substituted organopolysiloxane is free of silicon-bonded alkenyl groups; and

(b) 95 to 5 weight % of an alkenyl-substituted organopolysiloxane having a viscosity at 25°

C. of 20 to 200,000 mPa.s and containing an average of at least two silicon-bonded alkenyl groups per molecule, and wherein the alkenyl-substituted organopolysiloxane is free of silicon-bonded alkoxy groups; and

(B) a polyorganosiloxane having a viscosity at 25°

C. of 2 to 20,000 mPa.s and containing an average of at least two silicon-bonded hydrogen atoms per molecule, in a quantity that affords a value of 0.5 to 20 for the molar ratio of silicon-bonded hydrogen atoms in component (B) to silicon-bonded alkenyl groups in component (b);

(C) 0.01 to 10 parts by weight of a condensation reaction catalyst selected from the group consisting of organotitanium, organozirconium, and organoaluminum condensation reaction catalysts; and

(D) platinum catalyst in a catalytic quantity.

2. The curable organosiloxane composition of claim 1 further comprising

(E) 50 to 2000 weight parts of an electrically conductive filler.

3. The curable organosiloxane composition of claim 2 wherein component (E) is present in an amount ranging from 300 to 1000 parts by weight per 100 parts by weight of component (A).

4. The curable organosiloxane composition of claim 2 wherein component (E) is selected from the group consisting of gold micropowder and silver micropowder.

5. The curable organosiloxane composition of claim 4 wherein component (E) is silver micropowder.

6. The curable organosiloxane composition of claim 1 wherein the silicon-bonded alkoxy groups of component (a) are individually selected from the group consisting of methoxy, ethoxy, propoxy, butoxy, methoxymethoxy and methoxyethoxy.

7. The curable organosiloxane composition of claim 6 wherein the silicon-bonded alkoxy groups of component (a) are methoxy.

8. The curable organosiloxane composition of claim 1 wherein the viscosity of at 25°

C. of component (a) is from 100 to 100,000 mPa.s.

9. The curable organosiloxane composition of claim 1 wherein the silicon-bonded alkenyl groups of component (b) are individually selected from the group consisting of vinyl, allyl, butenyl, pentenyl and hexenyl.

10. The curable organosiloxane composition of claim 9 wherein the silicon-bonded alkenyl groups of component (b) are vinyl.

11. The curable organosiloxane composition of claim 1 wherein the viscosity of at 25°

C. of component (b) is from 100 to 100,000 mPa.s.

12. The curable organosiloxane composition of claim 1 wherein component (C) is present in an amount ranging from 0.1 to 5 weight parts per 100 weight parts component (A).

13. A product prepared by admixing materials consisting essentially of:

(A) 100 weight parts of a mixture of

(a) 5 to 95 weight % of an alkoxy-substituted organopolysiloxane having a viscosity at 25°

C. of 20 to 200,000 mPa.s and containing an average of at least two silicon-bonded alkoxy groups per molecule, and wherein the alkoxy-substituted organopolysiloxane is free of silicon-bonded alkenyl groups; and

(b) 95 to 5 weight % of an alkenyl-substituted organopolysiloxane having a viscosity at 25°

C. of 20 to 200,000 mPa.s and containing an average of at least two silicon-bonded alkenyl groups per molecule, and wherein the alkenyl-substituted organopolysiloxane is free of silicon-bonded alkoxy groups; and

(B) a polyorganosiloxane having a viscosity at 25°

C. of 2 to 20,000 mPa.s and containing an average of at least two silicon-bonded hydrogen atoms per molecule, in a quantity that affords a value of 0.5 to 20 for the molar ratio of silicon-bonded hydrogen atoms in component (B) to silicon-bonded alkenyl groups in component (b);

(C) 0.01 to 10 parts by weight of a condensation reaction catalyst selected from the group consisting of organotitanium, organozirconium, and organoaluminum condensation reaction catalysts; and

(D) platinum catalyst in a catalytic quantity.

14. A product prepared by admixing materials consisting essentially of:

(A) 100 weight parts of a mixture of

(a) 5 to 95 weight % of an alkoxy-substituted organopolysiloxane having a viscosity at 25°

C. of 20 to 200,000 mPa.s and containing an average of at least two silicon-bonded alkoxy groups per molecule, and wherein the alkoxy-substituted organopolysiloxane is free of silicon-bonded alkenyl groups; and

(b) 95 to 5 weight % of an alkenyl-substituted organopolysiloxane having a viscosity at 25°

C. of 20 to 200,000 mPa.s and containing an average of at least two silicon-bonded alkenyl groups per molecule, and wherein the alkenyl-substituted organopolysiloxane is free of silicon-bonded alkoxy groups; and

(B) a polyorganosiloxane having a viscosity at 25°

C. of 2 to 20,000 mPa.s and containing an average of at least two silicon-bonded hydrogen atoms per molecule, in a quantity that affords a value of 0.5 to 20 for the molar ratio of silicon-bonded hydrogen atoms in component (B) to silicon-bonded alkenyl groups in component (b);

(C) 0.01 to 10 parts by weight of a condensation reaction catalyst selected from the group consisting of organotitanium, organozirconium, and organoaluminum condensation reaction catalysts;

(D) platinum catalyst in a catalytic quantity; and

(E) 50 to 2000 parts by weight of an electrically conductive filler.

15. A curable organosiloxane composition, which is curable via both addition and condensation reactions, said curable organopolysiloxane composition consisting essentially of:

(A'"'"') 100 parts by weight of an alkenyl-substituted organopolysiloxane having a viscosity at 25°

C. of 20 to 200,000 mPa.s and containing an average of at least two silicon-bonded alkenyl groups per molecule;

(B'"'"') a polyorganosiloxane having a viscosity at 25°

C. of 2 to 20,000 mPa.s, and containing an average of at least two silicon-bonded hydrogen atoms per molecule in a quantity that affords a value from 0.5 to 20 for the molar ratio of silicon-bonded hydrogen atoms in component (B'"'"') to silicon-bonded alkenyl groups in component (A'"'"');

(C) 0.01 to 10 parts by weight of a condensation reaction catalyst selected from the group consisting of organotitanium, organozirconium, and organoaluminum condensation reaction catalysts; and

(D) platinum catalyst in a catalytic quantity;

with the proviso that at least one of components (A'"'"') and (B'"'"') contains an average of at least two silicon-bonded alkoxy groups per molecule.

16. The curable organosiloxane composition of claim 15 wherein the silicon-bonded alkenyl groups of component (A'"'"') are individually selected from the group consisting of vinyl, allyl, butenyl, pentenyl, hexenyl, and heptenyl.

17. The curable organosiloxane composition of claim 16 wherein the silicon-bonded alkenyl groups of component (A'"'"') are vinyl.

18. The curable organosiloxane composition of claim 15 wherein the viscosity of at 25°

C. of component (A'"'"') is from 100 to 100,000 mPa.s.

19. The curable organosiloxane composition of claim 15 wherein component (C) is present in an amount ranging from 0.1 to 5 weight parts per 100 weight parts component (A'"'"').

20. The curable organosiloxane composition of claim 15 further comprising (E) 50 to 2000 weight parts of an electrically conductive filler.

21. The curable organosiloxane composition of claim 20 wherein component (E) is present in an amount ranging from 300 to 1000 parts by weight per 100 parts by weight of component (A).

22. The curable organosiloxane composition of claim 20 wherein component (E) is selected from the group consisting of gold micropowder and silver micropowder.

23. The curable organosiloxane composition of claim 22 wherein component (E) is silver micropowder.

24. A product prepared by admixing materials consisting essentially of:

(A'"'"') 100 parts by weight of an alkenyl-substituted organopolysiloxane having a viscosity at 25°

C. of 20 to 200,000 mPa.s and containing an average of at least two silicon-bonded alkenyl groups per molecule;

(B'"'"') a polyorganosiloxane having a viscosity at 25°

C. of 2 to 20,000 mPa.s, and containing an average of at least two silicon-bonded hydrogen atoms per molecule in a quantity that affords a value from 0.5 to 20 for the molar ratio of silicon-bonded hydrogen atoms in component (B'"'"') to silicon-bonded alkenyl groups in component (A'"'"');

(C) 0.01 to 10 parts by weight of a condensation reaction catalyst selected from the group consisting of organotitanium, organozirconium and organoaluminum condensation reaction catalysts; and

(D) platinum catalyst in a catalytic quantity;

with the proviso that at least one of components (A'"'"') and (B'"'"') contains an average of at least two silicon-bonded alkoxy groups per molecule.

25. A product prepared by admixing materials consisting essentially of:

(A'"'"') 100 parts by weight of an alkenyl-substituted organopolysiloxane having a viscosity at 25°

C. of 20 to 200,000 mPa.s and containing an average of at least two silicon-bonded alkenyl groups per molecule;

(B'"'"') a polyorganosiloxane having a viscosity at 25°

C. of 2 to 20,000 mPa.s, and containing an average of at least two silicon-bonded hydrogen atoms per molecule in a quantity that affords a value from 0.5 to 20 for the molar ratio of silicon-bonded hydrogen atoms in component (B'"'"') to silicon-bonded alkenyl groups in component (A'"'"');

(C) 0.01 to 10 parts by weight of a condensation reaction catalyst selected from the group consisting of organotitanium, organozirconium, and organoaluminum condensation reaction catalysts;

(D) platinum catalyst in a catalytic quantity; and

(E) 50 to 2000 parts by weight of an electrically conductive filler;

with the proviso that at least one of components (A'"'"') and (B'"'"') contains an average of at least two silicon-bonded alkoxy groups per molecule.

26. A semiconductor device comprising

(A) a semiconductor chip;

(B) a substrate; and

(C) a silicone die attach adhesive prepared by curing a curable organosiloxane composition which is curable via both addition and condensation reactions;

wherein the semiconductor chip is bonded to the substrate with the silicone die attach adhesive.

27. The semiconductor device of claim 26 wherein the curable organosiloxane composition consists essentially of:

(A) 100 weight parts of a mixture of

(a) 5 to 95 weight % of an alkoxy-substituted organopolysiloxane having a viscosity at 25°

C. of 20 to 200,000 mPa.s and containing an average of at least two silicon-bonded alkoxy groups per molecule, and wherein the alkoxy-substituted organopolysiloxane is free of silicon-bonded alkenyl groups; and

(b) 95 to 5 weight % of an alkenyl-substituted organopolysiloxane having a viscosity at 25°

C. of 20 to 200,000 mPa.s and containing an average of at least two silicon-bonded alkenyl groups per molecule, and wherein the alkenyl-substituted organopolysiloxane is free of silicon-bonded alkoxy groups; and

(B) a polyorganosiloxane having a viscosity at 25°

C. of 2 to 20,000 mPa.s and containing an average of at least two silicon-bondedhydrogen atoms per molecule, in a quantity that affords a value of 0.5 to 20 for the molar ratio of silicon-bonded hydrogen atoms in component (B) to silicon-bonded alkenyl groups in component (b);

(C) 0.01 to 10 parts by weight of a condensation reaction catalyst selected from the group consisting of organotitanium, organozirconium, and organoaluminum condensation reaction catalysts; and

(D) platinum catalyst in a catalytic quantity.

28. The semiconductor device of claim 26 wherein the curable organosiloxane composition consists essentially of:

(A) 100 weight parts of a mixture of

(a) 5 to 95 weight % of an alkoxy-substituted organopolysiloxane having a viscosity at 25°

C. of 20 to 200,000 mPa.s and containing an average of at least two silicon-bonded alkoxy groups per molecule, and wherein the alkoxy-substituted organopolysiloxane is free of silicon-bonded alkenyl groups; and

(b) 95 to 5 weight % of an alkenyl-substituted organopolysiloxane having a viscosity at 25°

C. of 20 to 200,000 mPa.s and containing an average of at least two silicon-bonded alkenyl groups per molecule, and wherein the alkenyl-substituted organopolysiloxane is free of silicon-bonded alkoxy groups; and

(B) a polyorganosiloxane having a viscosity at 25°

C. of 2 to 20,000 mPa.s and containing an average of at least two silicon-bonded hydrogen atoms per molecule, in a quantity that affords a value of 0.5 to 20 for the molar ratio of silicon-bonded hydrogen atoms in component (B) to silicon-bonded alkenyl groups in component (b);

(C) 0.01 to 10 parts by weight of a condensation reaction catalyst selected from the group consisting of organotitanium, organozirconium, and organoaluminum condensation reaction catalysts;

(D) platinum catalyst in a catalytic quantity; and

(E) 50 to 2000 weight parts of an electrically conductive filler.

29. The semiconductor device of claim 26 wherein the curable organosiloxane composition consists essentially of:

(A'"'"') 100 parts by weight of an alkenyl-substituted organopolysiloxane having a viscosity at 25°

C. of 20 to 200,000 mPa.s and containing an average of at least two silicon-bonded alkenyl groups per molecule;

(B'"'"') a polyorganosiloxane having a viscosity at 25°

C. of 2 to 20,000 mPa.s, and containing an average of at least two silicon-bonded hydrogen atoms per molecule in a quantity that affords a value from 0.5 to 20 for the molar ratio of silicon-bonded hydrogen atoms in component (B'"'"') to silicon-bonded alkenyl groups in component (A'"'"');

(C) 0.01 to 10 parts by weight of a condensation reaction catalyst selected from the group consisting of organotitanium, organozirconium, and organoaluminum condensation reaction catalysts; and

(D) platinum catalyst in a catalytic quantity;

with the proviso that at least one of components (A'"'"') and (B'"'"') contains an average of at least two silicon-bonded alkoxy groups per molecule.

30. The semiconductor device of claim 26 wherein the curable organosiloxane composition consists essentially of:

(A'"'"') 100 parts by weight of an alkenyl-substituted organopolysiloxane having a viscosity at 25°

C. of 20 to 200,000 mPa.s and containing an average of at least two silicon-bonded alkenyl groups per molecule;

(B'"'"') a polyorganosiloxane having a viscosity at 25°

C. of 2 to 20,000 mPa.s, and containing an average of at least two silicon-bonded hydrogen atoms per molecule in a quantity that affords a value from 0.5 to 20 for the molar ratio of silicon-bonded hydrogen atoms in component (B'"'"') to silicon-bonded alkenyl groups in component (A'"'"');

(C) 0.01 to 10 parts by weight of a condensation reaction catalyst selected from the group consisting of organotitanium, organozirconium, and organoaluminum condensation reaction catalysts;

(D) platinum catalyst in a catalytic quantity; and

(E) 50 to 2000 weight parts of an electrically conductive filler;

with the proviso that at least one of components (A'"'"') and (B'"'"') contains an average of at least two silicon-bonded alkoxy groups per molecule.

31. A method for making a semiconductor device, said method comprising the steps of:

(A) providing a semiconductor chip;

(B) providing a substrate;

(C) applying a curable organopolysiloxane composition, which is curable via both addition and condensation reactions, to at least one of said semiconductor chip and said substrate; and

(D) curing said curable organopolysiloxane composition.

32. The method of claim 31 wherein the curable organosiloxane composition consists essentially of:

(A) 100 weight parts of a mixture of

(a) 5 to 95 weight % of an alkoxy-substituted organopolysiloxane having a viscosity at 25°

C. of 20 to 200,000 mPa.s and containing an average of at least two silicon-bonded alkoxy groups per molecule, and wherein the alkoxy-substituted organopolysiloxane is free of silicon-bonded alkenyl group; and

(b) 95 to 5 weight % of an alkenyl-substituted organopolysiloxane having a viscosity at 25°

C. of 20 to 200,000 mPa.s and containing an average of at least two silicon-bonded alkenyl groups per molecule, and wherein the alkenyl-substituted organopolysiloxane is free of silicon-bonded alkoxy groups; and

(B) a polyorganosiloxane having a viscosity at 25°

C. of 2 to 20,000 mPa.s and containing an average of at least two silicon-bonded hydrogen atoms per molecule, in a quantity that affords a value of 0.5 to 20 for the molar ratio of silicon-bonded hydrogen atoms in component (B) to silicon-bonded alkenyl groups in component (b);

(C) 0.01 to 10 parts by weight of a condensation reaction catalyst selected from the group consisting of organotitanium, organozirconium, and organoaluminum condensation reaction catalysts; and

(D) platinum catalyst in a catalytic quantity.

33. The method of claim 31 wherein the curable organosiloxane composition consists essentially of:

(A) 100 weight parts of a mixture of

(a) 5 to 95 weight % of an alkoxy-substituted organopolysiloxane having a viscosity at 25°

C. of 20 to 200,000 mPa.s and containing an average of at least two silicon-bonded alkoxy groups per molecule, and wherein the alkoxy-substituted organopolysiloxane is free of silicon-bonded alkenyl groups; and

(b) 95 to 5 weight % of an alkenyl-substituted organopolysiloxane having a viscosity at 25°

C. of 20 to 200,000 mPa.s and containing an average of at least two silicon-bonded alkenyl groups per molecule, and wherein the alkenyl-substituted organopolysiloxane is free of silicon-bonded alkoxy groups; and

(B) a polyorganosiloxane having a viscosity at 25°

C. of 2 to 20,000 mPa.s and containing an average of at least two silicon-bonded hydrogen atoms per molecule, in a quantity that affords a value of 0.5 to 20 for the molar ratio of silicon-bonded hydrogen atoms in component (B) to silicon-bonded alkenyl groups in component (b);

(C) 0.01 to 10 parts by weight of a condensation reaction catalyst selected from the group consisting of organotitanium, organozirconium, and organoaluminum condensation reaction catalysts;

(D) platinum catalyst in a catalytic quantity; and

(E) 50 to 2000 weight parts of an electrically conductive filler.

34. The method of claim 31 wherein the curable organosiloxane composition consists essentially of:

(A'"'"') 100 parts by weight of an alkenyl-substituted organopolysiloxane having a viscosity at 25°

C. of 20 to 200,000 mPa.s and containing an average of at least two silicon-bonded alkenyl groups per molecule;

(B'"'"') a polyorganosiloxane having a viscosity at 25°

C. of 2 to 20,000 mPa.s, and containing an average of at least two silicon-bonded hydrogen atoms per molecule in a quantity that affords a value from 0.5 to 20 for the molar ratio of silicon-bonded hydrogen atoms in component (B'"'"') to silicon-bonded alkenyl groups in component (A'"'"');

(C) 0.01 to 10 parts by weight of a condensation reaction catalyst selected from the group consisting of organotitanium, organozirconium, and organoaluminum condensation reaction catalysts; and

(D) platinum catalyst in a catalytic quantity;

with the proviso that at least one of components (A'"'"') and (B'"'"') contains an average of at least two silicon-bonded alkoxy groups per molecule.

35. The method of claim 31 wherein the curable organosiloxane composition consists essentially of:

(A'"'"') 100 parts by weight of an alkenyl-substituted organopolysiloxane having a viscosity at 25°

C. of 20 to 200,000 mPa.s and containing an average of at least two silicon-bonded alkenyl groups per molecule;

(B'"'"') a polyorganosiloxane having a viscosity at 25°

C. of 2 to 20,000 mPa.s, and containing an average of at least two silicon-bonded hydrogen atoms per molecule in a quantity that affords a value from 0.5 to 20 for the molar ratio of silicon-bonded hydrogen atoms in component (B'"'"') to silicon-bonded alkenyl groups in component (A'"'"');

(C) 0.01 to 10 parts by weight of a condensation reaction catalyst selected from the group consisting of organotitanium, organozirconium, and organoaluminum condensation reaction catalysts;

(D) platinum catalyst in a catalytic quantity; and

(E) 50 to 2000 weight parts of an electrically conductive filler;

with the proviso that at least one of components (A'"'"') and (B'"'"') contains an average of at least two silicon-bonded alkoxy groups per molecule.