Multilayer printed wiring board and a process of producing same

Abstract

A multilayer printed wiring board which permits the formation of fine wiring patterns, thereby increasing the density of wiring patterns. Using photosensitive glass having a coefficient of thermal expansion close to that of a copper film as a core substrate, a through hole is formed in the photosensitive glass by photolithography, a sputtering silicon oxide layer and a sputtering silicon nitride layer are formed to prevent leak of alkali metal ions from the photosensitive glass, a sputtering chromium layer, a sputtering chromium-copper layer and a sputtering copper layer are formed to enhance the adhesion strength between the copper film and the sputtering silicon oxide layer, and a copper film of 1 to 20 μm thick is formed. With resin filled into the interior of the through hole, a wiring layer is patterned by etching, an insulating layer is formed, and the surface is covered with a surface treatment layer and a cover coat.

What is claimed is:  
     
         1 . A multilayer printed wiring board comprising: 
 a glass substrate having a through hole connecting opposite surfaces thereof;    a plurality of insulating layers and wiring layers formed on the surfaces of said glass substrate; and    a conducting portion having a conductive film formed on an inner wall surface of the through hole and providing conductor connection between the opposite surfaces of said glass substrate,    wherein the conductive film has a thickness of 1 to 20 μm.    
     
     
         2 . A multilayer printed wiring board comprising: 
 a glass substrate having a through hole connecting opposite surfaces thereof;    a plurality of insulating layers and wiring layers formed on the surfaces of said glass substrate; and    a conducting portion having a conductive film formed on an inner wall surface of the through hole and providing conductor connection between the opposite surfaces of said glass substrate,    wherein a protective layer is formed so as to cover at least the conductive film.    
     
     
         3 . The multilayer printed wiring board according to  claim 1  or  2 , wherein the conductive film comprises a film continuous with the wiring layer.  
     
     
         4 . The multilayer printed wiring board according to any one of claims  1  through  3 , wherein the wiring layer has a land width of 10 μm or less.  
     
     
         5 . The multilayer printed wiring board according to any one of claims  1  through  4 , wherein the through hole is filled with a protective film.  
     
     
         6 . The multilayer printed wiring board according to any one of claims  1  through  5 , wherein the through hole has a diameter of 30 to 150 μm.  
     
     
         7 . The multilayer printed wiring board according to any one of claims  1  through  6 , wherein the surfaces of the glass substrate and at least part of the wall surface of the through hole are covered with an ion blocking layer mainly comprising an insulating film.  
     
     
         8 . The multilayer printed wiring board according to any one of claims  1  through  7 , wherein an adhesion-reinforcing layer is interposed between the wiring layer and the glass substrate to enhance force of adhesion between the wiring layer and the glass substrate.  
     
     
         9 . The multilayer printed wiring board according to any one of claims  1  through  8 , wherein the glass substrate comprises photosensitive glass.  
     
     
         10 . The multilayer printed wiring board according to any one of claims  1  through  9 , wherein a wiring pattern formed of the wiring layer has a line width of 3 to 50 μm.  
     
     
         11 . A process of producing a multilayer printed wiring board, comprising the steps of: 
 forming a through hole in a glass substrate so as to connect opposite surfaces thereof;    forming a plurality of insulating layers and wiring layers on the surfaces of the glass substrate;    coating the through hole with a conductive film to provide conductor connection between the opposite surfaces of the glass substrate; and    covering the conductive film with a protective layer.    
     
     
         12 . The process according to  claim 11 , wherein the through hole formation step is performed by laser beam machining.  
     
     
         13 . The process according to  claim 11 , wherein the through hole formation step is performed by photolithography.  
     
     
         14 . The process according to any one of claims  11  through  13 , further comprising the step of modifying the glass substrate.  
     
     
         15 . The process according to  claim 14 , wherein the glass substrate is modified by crystallizing the entire glass substrate.  
     
     
         16 . The process according to  claim 15 , wherein the crystallization of the entire glass substrate is performed following the through hole formation step.  
     
     
         17 . The process according to any one of claims  11  through  16 , wherein the step of covering the conductive film with a protective layer is performed by screen printing.  
     
     
         18 . The process according to any one of claims  11  through  17 , further comprising the step of dealkalizing the glass substrate.  
     
     
         19 . The process according to any one of claims  11  through  18 , wherein the conductive film and the wiring layer are formed in an identical step.  
     
     
         20 . The process according to any one of claims  11  through  19 , wherein, prior to the formation of the wiring layer, an adhesion-reinforcing layer comprising at least one layer is formed in advance to enhance force of adhesion with the wiring layer.  
     
     
         21 . The process according to any one of claims  11  through  20 , further comprising the step of polishing at least one of the opposite surfaces of the glass substrate after the conductive film is covered with resin.  
     
     
         22 . The process according to any one of claims  11  through  21 , further comprising the step of forming a barrier layer on the wiring layer to protect the wiring layer.  
     
     
         23 . The process according to any one of claims  11  through  22 , further comprising the step of forming a wiring pattern of the wiring layer by photolithography, the wiring pattern having a line width of 3 to 50 μm.  
     
     
         24 . The process according to any one of claims  11  through  23 , wherein the insulating layer is formed on one surface of the glass substrate at a time.