Bonding flexible film circuit and electronic circuit board

Abstract

Two circuit bearing substrates, such as a rigid electronic circuit board and a flexible circuit film, each having large arrays or multiple arrays of surface contact pads or traces, are mechanically and electrically joined without relocating the substrates during the bonding process by using a bonding apparatus with multiple working tools or bond shoes. The bonding apparatus includes a fixture for holding the circuit bearing substrates with a joining layer between them, and two or more independently operated heated bond shoes that compress different portions of the circuit bearing substrates with the joining layer, such as a layer of anisotropic conductive film.

We claim:  
     
         1 . A bonding apparatus for electrically joining a first circuit bearing substrate having a first array of conductive surface traces to a second circuit bearing substrate having a second array of conductive surface traces, the bonding apparatus comprising: 
 a fixture having a fixture surface;    first and second bond shoes; and    one or more tool presses connected to the first and second working tools for selectively pressing the first bond shoe toward a first portion of the fixture surface and for selectively pressing the second bond shoe toward a second portion of the fixture surface.    
     
     
         2 . The bonding apparatus of  claim 1 , wherein: 
 a first tool press is connected to the first working tool;    a second tool press is connected to the second working tool;    the first tool press has a tacking mode of operation in which the first tool press presses the first bond shoe toward the first portion of the fixture surface with a tacking force; and    the second tool press has a bonding mode of operation in which the second tool press presses the second bond shoe toward the second portion of the fixture surface with a bonding force, which bonding force is greater than the tacking force.    
     
     
         3 . The bonding apparatus of  claim 2 , wherein: 
 the first tool press additionally has a bonding mode of operation in which the first tool press presses the first bond shoe toward the first portion of the fixture surface with the bonding force; and    the second tool press additionally has a tacking mode of operation in which the second tool press presses the second bond shoe toward the second portion of the fixture surface with the tacking force.    
     
     
         4 . The bonding apparatus of  claim 1 , wherein the first and second portions of the fixture surface do not overlap.  
     
     
         5 . The bonding apparatus of  claim 4 , wherein the first and second portions of the fixture surface are substantially adjacent one another.  
     
     
         6 . The bonding apparatus of  claim 5 , wherein: 
 the first bond shoe has a first face that opposes the first portion of the fixture surface;    the second bond shoe has a second face that opposes the second portion of the fixture surface; and    the first and second bond shoe faces are separated from one another by no more than 0.25 inch.    
     
     
         7 . The bonding apparatus of  claim 6 , wherein: 
 the first bond shoe face has a length of less than 5 inches; and    the second bond shoe face has a length of less than 5 inches.    
     
     
         8 . The bonding apparatus of  claim 7 , wherein the first and second portions of the fixture surface have a combined length of at least 7 inches.  
     
     
         9 . The bonding apparatus of  claim 1 , wherein: 
 the first portion of the fixture surface has a first surface contour;    the first bond shoe has a first face having the complement of the first surface contour;    the second portion of the fixture surface has a second surface contour;    the second bond shoe has a second face having the complement of the second surface contour.    
     
     
         10 . The bonding apparatus of  claim 9 , wherein the first and second surface contours are planar.  
     
     
         11 . The bonding apparatus of  claim 10 , wherein: 
 the first bond shoe face has a length of less than 5 inches; and    the second bond shoe face has a length of less than 5 inches.    
     
     
         12 . The bonding apparatus of  claim 1 , wherein each of the bond shoes includes a heater opening for receiving a heater element.  
     
     
         13 . The bonding apparatus of  claim 12 , wherein each of the bond shoes includes a sensor opening for receiving a temperature sensor.  
     
     
         14 . A method of electrically joining a first circuit bearing substrate having a first array of conductive surface traces to a second circuit bearing substrate having a second array of conductive surface traces, the method comprising: 
 positioning on a fixture surface the first circuit bearing substrate with the first array of conductive surface traces facing away from the fixture surface;    positioning the second circuit bearing substrate on the first circuit bearing substrate, with the second array of conductive surface traces facing the first array of conductive surface traces; and    compressing different sections of the arrays of conductive surface traces between first and second working tools and the fixture surface.    
     
     
         15 . The method of  claim 14 , wherein compressing different sections of the arrays of conductive surface traces between first and second working tools and the fixture surface comprises: 
 pressing the first working tool against a section of the second circuit bearing substrate; and    pressing the second working tool against a different section of the second circuit bearing substrate.    
     
     
         16 . The method of  claim 15 , additionally comprising positioning a joining material between the first and second circuit bearing substrates.  
     
     
         17 . The method of  claim 16 , wherein the step of positioning the joining material is conducted before the step of positioning the second circuit bearing substrate.  
     
     
         18 . The method of  claim 17 , wherein the step of positioning the joining material comprises positioning an anisotropic conductive film between the first and second circuit bearing substrates.  
     
     
         19 . The method of  claim 18 , additionally comprising heating the first and second working tools during the compressing step.  
     
     
         20 . The method of  claim 15 , additionally comprising heating the first and second working tools during the compressing step.  
     
     
         21 . A method of electrically and mechanically joining a flexible circuit film having electrically conductive film surface traces to an electronic circuit board having electrically conductive board surface traces, the method comprising: 
 positioning the electronic circuit board on a fixture surface with the board surface traces facing away from the fixture surface;    positioning a joining layer on the electronic circuit board;    tacking the joining layer to the electronic circuit board;    positioning the flexible circuit film on the joining layer, with the film surface traces facing and aligned with the board surface traces; and heating first and second working tools to a bonding temperature;    pressing the heated first working tool against one section of the flexible circuit film with a bonding force; and    pressing the heated second working tool against a different section of the flexible circuit film with a bonding force.    
     
     
         22 . The method of  claim 21 , wherein the electronic circuit board and flexible circuit film remain stationary between the step of pressing the first working tool with the bonding force and the step of pressing the second working tool with the bonding force.  
     
     
         23 . The method of  claim 22 , wherein the step of pressing the first working tool with the bonding force and the step of pressing the second working tool with the bonding force overlap in time.  
     
     
         24 . The method of  claim 23 , wherein the step of pressing the first working tool with the bonding force and the step of pressing the second working tool with the bonding force occur simultaneously.  
     
     
         25 . The method of  claim 21 , wherein tacking the joining layer to the electronic circuit board comprises: 
 heating the first and second working tools to a tacking temperature;    pressing the heated first working tool against one section of the flexible circuit film with a tacking force; and    pressing the heated second working tool against a different section of the flexible circuit film with a tacking force.