Direct attach chip scale package

Abstract

A reliable, chip scale or flip chip semiconductor device which can be directly attached to a PC board without the use of an underfill material to absorb stress on the solder joints interconnecting the device and board is provided by a silicon chip, having the substrate thinned until the chip thickness is in the range of 50 to 250 microns, attaching a backing or cap layer with specific thermal properties to approximate those of a printed circuit board (PCB), and providing solder bump contacts attached to the input/output terminals.

1 - 9 . (canceled)  
   
   
       10 . A method of forming a direct attach semiconductor device including the following steps: 
 a) providing a semiconductor wafer with a plurality of integrated circuits fabricated on the first surface, and thinning said wafer from the second surface to about 50 to 250 microns thick,    b) laminating a backing layer, comprising a material having an expansion coefficient similar to that of a printed circuit board, onto the second surface of said wafer,    c) dicing said wafer into individual chips,    d) affixing a flex film interposer preformed to the chip size and shape to the active surface of said chip,    e) thermally processing the assemblage to cross-link adhesives of both the backing and interposer layers, and    f) attaching solder balls to input/output lands on the interposer.    
   
   
       11 . A method of fabricating a direct attach semiconductor device as in  claim 11  wherein a backing layer is molded onto the second surface of said diced chips.  
   
   
       12 . A method of fabricating a direct attach semiconductor device wherein an interposer is fabricated on the first surface of said wafer by thin film metallization patterned on a thin film dielectric layer to reroute input/output contacts to a preselected area array, 
 b) thinning said wafer from the backside to a thickness of 50 to 250 microns,    c) laminating a backing layer comprising a material having an expansion coefficient similar to that of a printed circuit board onto the second surface of said wafer,    d) dicing said wafer into individual chips,    e) thermally processing the assemblage to cross-link adhesives of the backing layer, and    f) attaching solder balls to input/output lands on the interposer.    
   
   
       13 . A method of fabricating a direct attach semiconductor device wherein an interposer is fabricated on the first surface of said wafer by thin film metallization patterned on a thin film dielectric layer to reroute input/output contacts to a preselected area array, contacts to a preselected area array, 
 b) thinning said wafer from the backside to a thickness of 50 to 250 microns,    c) molding a backing layer having an expansion coefficient similar to that of a printed circuit board onto the second surface of said wafer,    d) attaching solder balls to input/output lands on the interposer, and    e) dicing said wafer into individual chips.