Substrate for mounting element and process for its production

Abstract

To provide a substrate for mounting element having sulfurization resistance improved by increasing planarity of the surface of a thick conductor layer. The substrate 10 for mounting element of the present invention has such a structure that on a surface of a LTCC substrate or ceramics substrate as an inorganic insulating substrate 1 , a thick conductor layer 2 is formed as an element connection terminal. The thick conductor layer 2 is made of a metal composed mainly of silver (Ag) or copper (Cu) and formed by printing and firing a metal paste. This thick conductor layer has its surface planarized by wet blast treatment to a surface roughness Ra of at most 0.02 μm. A Ni/Au-plated layer 3 is formed on the thick conductor layer 2 , so that the surface of the thick conductor layer 2 is completely covered without any space.

1 . A substrate for mounting element, which comprises:
 an inorganic insulating substrate made of an inorganic insulating material,   a thick conductor layer formed on the inorganic insulating substrate and made of a metal composed mainly of silver (Ag) or copper (Cu), and   an electroconductive metal-plated layer formed on the thick conductor layer, wherein the thick conductor layer has its surface planarized by wet blast treatment and has a surface roughness Ra of at most 0.02 μm.   
     
     
         2 . The substrate for mounting element according to  claim 1 , wherein the inorganic insulting substrate is a low temperature co-fired ceramics substrate. 
     
     
         3 . The substrate for mounting element according to  claim 1 , wherein the inorganic insulting substrate is a ceramics substrate. 
     
     
         4 . The substrate for mounting element according to  claim 3 , wherein the ceramics substrate contains alumina or aluminum nitride as the main component. 
     
     
         5 . The substrate for mounting element according to  claim 1 , wherein the electroconductive metal-plated layer is a nickel (Ni)/gold (Au)-plated layer. 
     
     
         6 . A process for producing a substrate for mounting element, which comprises:
 a step of forming a thick conductor layer-provided substrate having a thick conductor layer made of a metal composed mainly of silver (Ag) or copper (Cu), on a surface of an inorganic insulating substrate made of an inorganic insulating material,   a step of applying wet blast treatment to the thick conductor layer to planarize the surface of the thick conductor layer to a surface roughness Ra of at most 0.02 μm, and   a step of forming a nickel (Ni)/gold (Au)-plated layer on the thick conductor layer having the surface planarized by the wet blast treatment.   
     
     
         7 . The process for producing a substrate for mounting element according to  claim 6 , wherein the step of forming a thick conductor layer-provided substrate comprises:
 a step of printing a metal paste composed mainly of silver (Ag) or copper (Cu) on a surface of a substrate made of a glass ceramics composition comprising a glass powder and a ceramics powder, to form a conductor pattern, and   a step of firing the substrate having the conductor pattern formed to sinter the glass ceramics composition and fire the metal paste thereby to form the thick conductor layer made of a metal composed mainly of silver (Ag) or copper (Cu).   
     
     
         8 . The process for producing a substrate for mounting element according to  claim 6 , wherein the step of forming a thick conductor layer-provided substrate comprises:
 a step of firing a ceramics composition comprising a ceramics powder and a sintering aid to obtain a ceramics substrate,   a step of printing a metal paste composed mainly of silver (Ag) or copper (Cu) on a surface of the ceramics substrate to form a conductor pattern, and   a step of re-firing the ceramics substrate having the conductor pattern formed to form, from the metal paste, the thick conductor layer made of a metal composed mainly of silver (Ag) or copper (Cu).   
     
     
         9 . The process for producing a substrate for mounting element according to  claim 6 , wherein an abrasive to be used for the wet blast treatment is a ceramics powder having a particle size of from 25 to 150 μm, and a medium is water. 
     
     
         10 . The process for producing a substrate for mounting element according to  claim 9 , wherein the mixing ratio of the abrasive is from 20 to 60 vol % based on the total amount of the abrasive and the water. 
     
     
         11 . The process for producing a substrate for mounting element according to  claim 9 , wherein in the wet blast treatment, the blast force of a blast liquid comprising the abrasive and the water is from 1.2 to 1.8 kg/cm 2 .