Heat transfer sheet and heat dissipation structure

Abstract

A heat transfer sheet of the present invention includes a heat transfer layer having a first portion and a second portion provided in a position different from the first portion in a planar view of the heat transfer layer, the second portion being capable of expanding and contracting in a thickness direction of the heat transfer layer at an expansion ratio larger than that of the first portion depending on temperature changes in an object from which heat is to be dissipated. In a state that the heat transfer sheet is used, in the case where a temperature of the heat transfer layer is a predetermined temperature or lower, thermal conductivity between the object and a dissipation member is lowered due to creation of a gap between the second portion and the object and/or the dissipation member, whereas in the case where the temperature of the heat transfer layer is a predetermined temperature or higher, the thermal conductivity between the object and the dissipation member is increased due to substantial elimination of the gap.

1 . A heat transfer sheet being adapted to be used by being provided between an object from which heat is to be dissipated and a dissipation member for transferring the heat between the object and the dissipation member, comprising:
 a heat transfer layer having a first portion and a second portion provided in a position different from the first portion in a planar view of the heat transfer layer, the second portion being capable of expanding and contracting in a thickness direction of the heat transfer layer at an expansion ratio larger than that of the first portion depending on temperature changes in the object,   wherein in a state that the heat transfer sheet is used, in the case where a temperature of the heat transfer layer is a predetermined temperature or lower, thermal conductivity between the object and the dissipation member is lowered due to creation of a gap between the second portion and the object and/or the dissipation member, whereas in the case where the temperature of the heat transfer layer is a predetermined temperature or higher, the thermal conductivity between the object and the dissipation member is increased due to substantial elimination of the gap.   
   
   
       2 . The heat transfer sheet as claimed in  claim 1 , wherein a thermal expansion coefficient of the second portion in the thickness direction of the heat transfer layer is larger than that of the first portion, and a heat transfer rate of the second portion in the thickness direction of the heat transfer layer is higher than that of the first portion. 
   
   
       3 . The heat transfer sheet as claimed in  claim 1 , wherein one of the first and second portions includes a plurality of portions arranged so as to be separated from each other in the planar view of the heat transfer layer, and the other portion is provided so as to be embedded between the separated portions of the one portion. 
   
   
       4 . The heat transfer sheet as claimed in  claim 3 , wherein the separated portions of the first or second portion are arranged so as to be uniformly dispersed within the heat transfer layer in the planar view thereof. 
   
   
       5 . The heat transfer sheet as claimed in  claim 4 , wherein the separated portions of the first or second portion are regularly arranged in a tetragonal lattice or houndstooth check manner in the planar view of the heat transfer layer. 
   
   
       6 . The heat transfer sheet as claimed in  claim 3 , wherein the second portion includes the plurality of separated portions, and the first portion is provided so as to be embedded between the separated portions of the second portion. 
   
   
       7 . The heat transfer sheet as claimed in  claim 6 , wherein each of the separated portions of the second portion has a columnar structure extending along the thickness direction of the heat transfer layer. 
   
   
       8 . The heat transfer sheet as claimed in  claim 1  further comprising a support layer that supports the heat transfer layer by fixing or uniting the support layer to the second portion. 
   
   
       9 . The heat transfer sheet as claimed in  claim 8 , wherein a constituent material of the support layer is the same as that of the second portion. 
   
   
       10 . The heat transfer sheet as claimed in  claim 1 , wherein the first portion is formed by penetrating a resin composition containing a curable resin and an inorganic filler into a fiber base member. 
   
   
       11 . The heat transfer sheet as claimed in  claim 10 , wherein the curable resin is cyanate resin. 
   
   
       12 . The heat transfer sheet as claimed in  claim 11 , wherein fibers constituting the fiber base member include glass fibers. 
   
   
       13 . The heat transfer sheet as claimed in  claim 1 , wherein the second portion is formed of a metal as a major component thereof. 
   
   
       14 . The heat transfer sheet as claimed in  claim 13 , wherein the metal constituting the second portion is aluminum or an alloy containing aluminum. 
   
   
       15 . The heat transfer sheet as claimed in  claim 1 , wherein an occupation ratio of an area of the second portion with respect to a total area of the heat transfer layer in the planar view thereof is in the range of 50 to 85%. 
   
   
       16 . A heat dissipation structure, comprising:
 an object from which heat is to be dissipated;   a dissipation member; and   the heat transfer sheet defined by  claim 1 ,   wherein the heat can be dissipated from the object by transferring the heat from the object to the dissipation member through the heat transfer sheet.   
   
   
       17 . The heat dissipation structure as claimed in  claim 16 , wherein the heat transfer sheet further comprises a support layer that supports the heat transfer layer by fixing or uniting the support layer to the second portion, and the heat transfer sheet is provided so that the support layer is positioned on a side of the object.