Silicone composition for sealing semiconductor

Abstract

The silicone composition for sealing a semiconductor, comprises: (A) 100 parts of a polyorganosiloxane having one or more alkenyl groups, obtained by reacting (a1) 60 to 99 parts of an organosiloxane containing at least a trifunctional siloxane unit not taking part in a hydrosilylation reaction, with (a2) 40 to 1 parts of an organosiloxane containing a bifunctional siloxane unit having an alkenyl group and/or a monofunctional siloxane unit having an alkenyl group; (B) an amount of a polyorganohydrogensiloxane having two or more hydrogen atoms having a viscosity at 25° C. of 1 to 1000 mPa·s so that an amount of the hydrogen atoms is 0.5 to 3.0 mol per mol of the alkenyl groups; and (C) a platinum-based catalyst, wherein a decrease in storage modulus of a cured product thereof from 25° C. to 50° C. is 40% or more.

What is claimed is: 
     
         1 . A silicone composition for sealing a semiconductor, comprising:
 (A) 100 parts by weight of a polyorganosiloxane having one or more alkenyl groups, on average, per molecule, obtained by reacting (a1) 60 to 99 parts by weight of an organosiloxane containing at least a trifunctional siloxane unit represented by a formula: R 1 SiO 3/2  (where R 1  represents an alkyl group or an aryl group) and not taking part in a hydrosilylation reaction, with (a2) 40 to 1 parts by weight of an organosiloxane containing a bifunctional siloxane unit represented by a formula: R 2   2 SiO 2/2  (where R 2  represents an alkenyl group, an alkyl group, or an aryl group, and at least one of groups in a molecule is an alkenyl group) and/or a monofunctional siloxane unit represented by a formula: R 2   3 SiO 1/2  (where R 2  is as described above);   (B) an amount of a polyorganohydrogensiloxane having two or more hydrogen atoms bonded to silicone atoms per molecule and having a viscosity at 25° C. of 1 to 1000 mPa·s so that an amount of the hydrogen atoms bonded to the silicon atoms is 0.5 to 3.0 mol per mol of the alkenyl groups bonded to silicon atoms in the (A) component; and   (C) a catalyst amount of a platinum-based catalyst,   wherein a decrease in storage modulus of a cured product thereof from 25° C. to 50° C. is 40% or more.   
     
     
         2 . The silicone composition for sealing a semiconductor according to  claim 1 ,
 wherein the decrease in storage modulus of the cured product of the silicone composition for sealing a semiconductor from 25° C. to 50° C. is 70% or more.   
     
     
         3 . The silicone composition for sealing a semiconductor according to  claim 1 ,
 wherein a nonvolatile content of the (A) component after heating at 150° C. for 1 hour is 97 weight % or more.   
     
     
         4 . The silicone composition for sealing a semiconductor according to  claim 1 ,
 wherein 20 to 70 mol % of all of organic groups bonded to silicon atoms in the (a1) component are phenyl groups.   
     
     
         5 . The silicone composition for sealing a semiconductor according to  claim 1 ,
 wherein the polyorganosiloxane being the (A) component is a polymer obtained by reacting a first organosiloxane represented by an average unit formula:   (R 1 SiO 3/2 ) a (R 1   2 SiO 2/2 ) b (R 1 SiO (3−n)/2 Y n ) c (R 1   2 SiO (2−m)/2 Y m ) d  a second organosiloxane represented by a formula: (R 2   3 SiO 1/2 ) 2  (R 2   2 SiO 2/2 ) e  and a third organosiloxane represented by a formula: (R 2   2 SiO 2/2 ) f  at a weight ratio (%) of g:h:i,   (where, R 1  represents an alkyl group or an aryl group, R 2  represents an alkenyl group, an alkyl group, or an aryl group, Y represents an alkoxy group or a hydroxyl group, n is 1 or 2, m is 1, a is a positive number, b is a positive number, c is 0 or a positive number, and d is 0 or a positive number, which are numbers satisfying a+b+c+d=1.0, 0.2<(a+c)/(a+b+c+d)<0.8, 0.2<(b+d)/(a+b+c+d)<0.8, 0≦c/(a+b+c+d)<0.15, 0≦d/(a+b+c+d)<0.15. Further, e is 0 or a positive number, and f is a positive number, which are numbers satisfying 0≦e≦100, 3≦f≦20. Furthermore, g, h, i are numbers satisfying 60≦g≦99, 0≦h≦20, 0≦i≦20, and g+h+i=100.)   
     
     
         6 . The silicone composition for sealing a semiconductor according to  claim 5 ,
 wherein the polyorganosiloxane being the (A) component is obtained by subjecting, in a step (2), a linear organosiloxane (II) containing an alkenyl group and/or a cyclic organosiloxane (III) containing an alkenyl group to block polymerization or graft polymerization and equilibration reaction with a polyorganosiloxane (I) obtained in a following step (1):
 the step (1) of polymerizing, in the presence of a basic catalyst, a polyorganosiloxane obtained by hydrolyzing or partially hydrolyzing, under acid condition, a silane compound represented by a formula: R 1 SiX 3  and R 1   2 SiX 2  (where R 1  represents an alkyl group or an aryl group, X represents a halogen group, an alkoxy group, or a hydroxyl group), to obtain the polyorganosiloxane (I) represented by an average unit formula: 
   (R 1 SiO 3/2 ) a (R 1   2 SiO 2/2 ) b (R 1 SiO (3−n/2 Y n ) c (R 1   2 SiO (2−m)/2 Y m ) d  (where, Y represents an alkoxy group or a hydroxyl group, n is 1 or 2, m is 1, a is a positive number, b is a positive number, c is 0 or a positive number, and d is 0 or a positive number, which are numbers satisfying a+b+c+d=1.0, 0.2<(a+c)/(a+b+c+d)<0.8, 0.2<(b+d)/(a+b+c+d)<0.8, 0≦c/(a+b+c+d)<0.15, 0≦d/(a+b+c+d)<0.15); and
 the step (2) of subjecting the linear polyorganosiloxane (II) containing an alkenyl group represented by a formula: (R 2   3 SiO 1/2 ) 2  (R 2   2 SiO 2/2 ) e  (where R 2  represents an alkenyl group, an alkyl group, or an aryl group, and e is 0 or a positive number satisfying 0≦e≦100) and/or the cyclic polyorganosiloxane containing an alkenyl group represented by a formula: (R 2   2 SiO) f  (where R 2  is as described above, and f is a positive number satisfying 3≦f≦20) to block polymerization or graft polymerization and equilibration reaction, in the presence of a basic catalyst, with the polyorganosiloxane (I).