Multi-layer circuit board and method of making the same

Abstract

To provide a simplified method of making a multi-layer circuit board capable of observing a high density surface mounting of electronic parts, a method is provided for making a multi-layer circuit board including a first film (A) and at least two more films, second and third films (B and C), each being made of thermoplastic polymer capable of forming an optically anisotropic melt phase. The first film (A) has a low melting point (Tm 1 ), and the second and third films (B and C) have respective melting points (Tm 2 B and Tm 2 C) higher than the melting point (Tm 1 ) of the first film (A). And at least one of the second and the third films have a circuit pattern thereon. The first to third films (A to C) are thermo compressed together with the first film (A) interposed between the second and third films (B and C). The method includes causing at least one of the circuit patterns (D) on one of the second and third films (B and C) to contact an opposing surface of the other of the second and third films (B and C) through the first film (A) during the thermo compression bonding of the first to third films (A to C).

What is claimed is:  
     
         1 . A method of making a multi-layer circuit board, said multi-layer circuit board comprising a first film and at least two more films, second and third films, each being made of a thermoplastic polymer capable of forming an optically anisotropic melt phase, the first film having a low melting point, the second and third films having respective melting points higher than the melting point of the first film and at lest one of the second and the third films having a circuit pattern thereon, said first to third films being thermo compressed together with said first film interposed between the second and third films, said method comprising: 
 causing at least one of the circuit patterns on one of the second and third films to contact an opposing surface of the other of the second and third films through the first film during the thermo compression bonding of the first to third films.    
     
     
         2 . The method of making a multi-layer circuit board as claimed in  claim 1 , wherein, prior to the thermo compression bonding, the first film has a thickness within the range of ⅕ to 1.5 times a height of the circuit pattern which will penetrate the first film.  
     
     
         3 . The method of making a multi-layer circuit board as claimed in  claim 1 , wherein each of the respective melting points of the second and third films is higher than the melting point of the first film by 15° C. or more.  
     
     
         4 . The method of making a multi-layer circuit board as claimed in  claim 1 , wherein one or both of the second and third films have at least one micro-via.  
     
     
         5 . The method of making a multi-layer circuit board as claimed in  claim 1 , wherein each of the second and third films has a thermal deformation temperature higher than that of the first film by 20° C. or more.  
     
     
         6 . The method of making a multi-layer circuit board as claimed in  claim 1 , wherein each of the first to third films is substantially isotropic.  
     
     
         7 . A multi-layer circuit board, which comprises: 
 a first film and at least two more films, second and third films, each being made of thermoplastic polymer capable of forming an optically anisotropic melt phase, the first film having a low melting point, and the second and third films having respective melting points higher than the melting point of the first film;    said first to third films being thermo compressed together with said first film interposed between the second and third films; and    a circuit pattern formed in one or both of the second and third films, at least one of the circuit patterns on one of the second and third films being held in contact with the opposing surface of the other of the second and third films through the first film.    
     
     
         8 . The multi-layer circuit board as claimed in  claim 7 , wherein each of the respective melting points of the second and third films is higher than the melting point of the first film by 15° C. or more.  
     
     
         9 . The multi-layer circuit board as claimed in  claim 7 , wherein each of the second and third films has a thermal deformation temperature higher than that of the first film by 20° C. or more.  
     
     
         10 . The multi-layer circuit board as claimed in  claim 7 , wherein one or both of the second and third films have at least one micro-via.  
     
     
         11 . The multi-layer circuit board as claimed in  claim 7 , wherein each of the first to third films is substantially isotropic.