Porous insulating film and its laminates

Abstract

A porous insulating film comprising a highly heat resistant resin film having a fine porous structure with a mean pore size of 0.01-5 μm in at least the center of the film, and a porosity of 15-80%. A laminate is prepared by forming a heat resistant adhesive layer or a conductive metal layer or an inorganic or metal substrate on one or both sides of the porous insulating film or by forming an inorganic or metal substrate on one side of the porous insulating film and a conductive metal layer on the other side.

What is claimed is:  
     
         1 . A porous insulating film comprising a highly heat resistant resin film having a fine porous structure with a mean pore size of 0.01-5 μm in at least the center of the film, and having a porosity of 15-80%.  
     
     
         2 . A porous insulating film according to  claim 1 , wherein the mean pore size is 0.05-1 μm.  
     
     
         3 . A porous insulating film according to  claim 1 , wherein the porosity is 30-80%.  
     
     
         4 . A porous insulating film according to  claim 1 , which has a thickness of 5-150 μm.  
     
     
         5 . A porous insulating film according to  claim 1 , wherein the fine porous structure consists of fine continuous pores.  
     
     
         6 . A porous insulating film according to  claim 1 , which is fabricated by a film casting method.  
     
     
         7 . A porous insulating film according to  claim 1 , wherein the dielectric constant is no greater than 2.5.  
     
     
         8 . A porous insulating film according to  claim 1 , wherein the highly heat resistant resin film is a polyimide film.  
     
     
         9 . A porous insulating film according to  claim 1 , wherein the porous structure has fine continuous pores reaching to both surfaces.  
     
     
         10 . A porous insulating film according to  claim 9 , which has a porosity of 30-80%, a maximum pore size of no greater than 10 μm, a film thickness of 5-100 μm, a resistance to passage of air of from 30 sec/100 cc to 2000 sec/100 cc, a heat resistance temperature of 200° C. or above and a heat shrinkage of no greater than ±1%.  
     
     
         11 . A porous insulating film according to  claim 1 , wherein the porous structure has a dense layer on both surfaces of the film.  
     
     
         12 . A laminate prepared by forming a heat resistant adhesive layer on one or both sides of a porous insulating film according to  claim 1 .  
     
     
         13 . A laminate prepared by laminating a conductive metal layer for an electronic circuit on one or both sides of a porous insulating film according to  claim 1 , either directly or via a heat resistant adhesive layer.  
     
     
         14 . A laminate prepared by laminating an inorganic or metal substrate onto one side of a porous insulating film according to  claim 1  and a conductive metal layer onto the other side, each via a heat resistant adhesive layer.