Bonding material for semiconductor devices
A semiconductor device is provided which has internal bonds which do not melt at the time of mounting on a substrate. A bonding material is used for internal bonding of the semiconductor device. The bonding material is obtained by filling the pores of a porous metal body having a mesh-like structure and covering the surface thereof with Sn or an Sn-based solder alloy.
1. A solder bonding material comprising:
an electrically conductive porous metal body having a mesh-like structure with pores, and
Sn or an Sn-based lead-free solder alloy which impregnates the pores of the porous metal body and covers a surface of the porous metal body, the porous metal body having a porosity expressed as a proportion of the cross-sectional area of the pores with respect to a cross-sectional area of the porous metal body of 20-30%,
wherein in a state before the solder bonding material is heated to bond the solder bonding material to another member, the Sn or the Sn-based lead-free solder alloy is bonded to the porous metal body by an intermetallic compound layer.
2. A solder bonding material as claimed in claim 1 wherein the porous metal body is made of at least one material which is selected from Cu, Ni, Ag, and Cu alloys having a Cu content of at least 90 mass % and which forms an intermetallic compound by a reaction with Sn.
3. A solder bonding material as claimed in claim 1 wherein the 20-30% by area of the porous metal body is occupied by the Sn or Sn-based lead-free solder alloy.
4. A solder bonding material as claimed in claim 1 wherein the thickness of the porous metal body is at least 0.1 mm and at most 0.2 mm and the overall thickness of the solder bonding material including the Sn or Sn-based lead-free solder alloy is 0.15-0.3 mm.
5. A method of manufacturing a solder bonding material as claimed in claim 1 comprising immersing a porous metal body having a pore structure which communicates from an interior to a surface of the porous metal body in a molten bath of molten Sn or a molten Sn-based lead-free solder alloy to impregnate the interior of the pore structure of the porous metal body and coat the surface of the porous metal body with the molten Sn or the molten Sn-based lead-free solder alloy, removing the porous metal body from the molten bath, and solidifying the molten Sn or Sn-based lead-free solder alloy which impregnates the pore structure of the porous metal body and coats the porous metal body.
6. A semiconductor device comprising an insulating substrate and a semiconductor element which is bonded to the insulating substrate by a solder bond formed by the solder bonding material as claimed in claim 1 .
7. A semiconductor device as claimed in claim 6 wherein an elemental Sn phase is consumed in the solder bond.
8. A semiconductor device as claimed in claim 6 wherein the solder bond does not melt at 260° C.
9. A solder bonding material as claimed in claim 1 wherein the porous metal body is a porous sintered body.
10. A solder bonding material as claimed in claim 1 wherein the porous metal body is formed by a method selected from (a) plating expanded urethane and removing the urethane by heating, (b) foaming a metal powder slurry containing expanded urethane and then performing grease removal sintering, and (c) applying a metal powder slurry to expanded urethane and performing sintering to remove the urethane.
11. A method of performing internal bonding of a semiconductor device comprising performing fluxless bonding of a semiconductor element to an insulating substrate using a solder bonding material as claimed in claim 1 by heating in an atmosphere selected from an inert gas atmosphere, a reducing gas atmosphere, and a reduced pressure atmosphere for at least 5 minutes at a temperature of 300°-350° C.