Production of via hole in flexible circuit printable board

Abstract

A flexible circuit printable board can be favorably produced by a process composed of steps of forming in a polyimide film having a metal coat on each surface side a via hole penetrating at least one metal coat and the polyimide film; and applying a mixture of liquid and abrasive grains under pressure onto the via hole, whereby smoothing an edge of the via hole and cleaning the via hole.

1 . A process for producing a flexible circuit printable board which comprises the steps of: 
 forming in a polyimide film having a metal coat on each surface side a via hole penetrating at least one metal coat and the polyimide film; and    applying a mixture of liquid and abrasive grains under pressure onto the via hole, whereby smoothing an edge of the via hole and cleaning the via hole.    
   
   
       2 . The process of  claim 1 , wherein the via hole is a blind via hole formed by means of a laser.  
   
   
       3 . The process of  claim 2 , wherein the laser is a carbon dioxide laser, a UV-YAG laser, or an excimer laser.  
   
   
       4 . The process of  claim 1 , wherein the via hole is a through-hole formed by means of a punch or a drill.  
   
   
       5 . The process of  claim 1 , the polyimide film having a metal coat on each surface side is produced by placing a metal film on each surface side of a multilayer polyimide film having on each side a thermoplastic polyimide layer.  
   
   
       6 . A flexible circuit printable board produced by the process of  claim 1 .  
   
   
       7 . A process for producing a flexible circuit printed board which comprises the steps of: 
 forming in a polyimide film having a metal coat on each surface side a via hole penetrating at least one metal coat and the polyimide film;    applying a mixture of liquid and abrasive grains under pressure onto the via hole, whereby smoothing an edge of the via hole and cleaning the via hole;    plating an inside of the via hole with metal so as to electrically connect the metal coat on one surface side to the metal coat on another surface side; and    etching each of the metal coat to form a predetermined circuit pattern.    
   
   
       8 . The process of  claim 7 , wherein the via hole is a blind via hole formed by means of a laser.  
   
   
       9 . The process of  claim 8 , wherein the laser is a carbon dioxide laser, a UV-YAG laser, or an excimer laser.  
   
   
       10 . The process of  claim 7 , wherein the via hole is a through-hole formed by means of a punch or a drill.  
   
   
       11 . The process of  claim 7 , which further comprises a step of forming a solder mask on the circuit pattern.  
   
   
       12 . The process of  claim 11 , which further comprises a step of forming an opening on the solder mask and a step of plating a gold layer on the metal layer in the opening.  
   
   
       13 . The process of  claim 11 , wherein the solder mask is formed by laminating on the circuit pattern a photosensitive resist film under vacuum and subjecting the laminated resist film to predetermined patterning.  
   
   
       13 . A flexible circuit printed board produced by the process of  claim 7 .  
   
   
       14 . A flexible circuit printed board produced by the process of  claim 11.