Underfill process for flip-chip device

Abstract

The present invention relates to a method of packaging a microelectronic device that, in one embodiment, uses a vacuum-assisted underfill process. One embodiment of the method uses a curing process with a tacky film disposed over the device to prevent wicking of the underfill material after the underfill material is in place. One embodiment of the method uses a curing process that utilizes a non-tacky tacky film with a curing process to prevent wicking of the underfill material after the underfill material is in place.

What is claimed is:  
     
         1 . A method of forming a package, comprising: 
 placing a film against a flip-chip assembly, wherein the flip-chip assembly includes a die, an electrical connection, and a mounting substrate;    underfilling the die with underfill material;    curing the underfill material; and    after beginning curing the underfill material, removing the film.    
     
     
         2 . The method according to  claim 1 , wherein the film includes a tacky film.  
     
     
         3 . The method according to  claim 1 , wherein the film includes a tacky film, and wherein curing the underfill material is carried out under heat that causes the tacky film to release from the flip-chip assembly.  
     
     
         4 . The method according to  claim 1 , wherein after beginning curing the underfill material and removing the film, curing includes: 
 curing the underfill material that is in contact with the film;    removing the film; and thereafter    curing the underfill material that is between the die and the mounting substrate.    
     
     
         5 . The method according to  claim 1 , wherein after beginning curing the underfill material and removing the film, curing includes: 
 curing the underfill material that is in contact with the film by conductive heat transfer from a mold press;    removing the film; and thereafter    curing the underfill material that is between the die and the mounting substrate by placing the package into a curing oven.    
     
     
         6 . The method according to  claim 1 , wherein after beginning curing the underfill material and removing the film, curing includes: 
 heating the package in a curing oven under conditions to cause the tacky film to release from the flip-chip assembly.    
     
     
         7 . The method according to  claim 1 , wherein after beginning curing the underfill material and removing the film, curing includes: 
 heating the package in a curing oven under conditions to cause the tacky film to release from the flip-chip assembly, wherein heating includes a first temperature ramp to a temperature range from about 100° C. to about 180° C., a temperature hold at a temperature in this range, a second temperature ramp to a temperature range from about 140° C. to about 260° C., and cooling.    
     
     
         8 . The method according to  claim 1 , wherein after beginning curing the underfill material and removing the film, curing includes: 
 heating the package in a curing oven under conditions to cause the tacky film to release from the flip-chip assembly, wherein heating includes a single step temperature ramp to a temperature in a range from about 140° C. to about 240° C.; and    cooling.    
     
     
         9 . The method according to  claim 1 , wherein the underfill material has a viscosity that causes it to draw between the die and the mounting substrate without the assistance of a pressure differential.  
     
     
         10 . The method according to  claim 1 , wherein the underfill material has a viscosity that causes it to draw between the die and the mounting substrate, further including: 
 flowing the underfill material from a first edge of the die to an opposite, second edge of the die by a pressure differential.    
     
     
         11 . A method of forming a package, comprising: 
 stretching a flexible film over die that is mounted on a mounting substrate to seal the flexible film thereupon;    flowing underfill material between the die and the mounting substrate with a source and a vent;    heating the underfill material to a first curing temperature; and    after reaching the first curing temperature, removing the flexible film.    
     
     
         12 . The method according to  claim 11 , wherein the film is selected from a non-tacky film and a tacky film.  
     
     
         13 . The method according to  claim 11 , wherein the film includes a tacky film, and wherein heating the underfill material to a first curing temperature is carried out to cause the underfill material to cure, and wherein the first curing temperature is reached to a temperature range from about 100° C. to about 180° C.; and 
 wherein the second curing temperature causes the tacky film to release from the die and mounting substrate, and wherein the second curing temperature is reached to a temperature range from 140° C. to about 260° C.  
 
     
     
         14 . The method according to  claim 11 , wherein the film is a non-tacky film and wherein after heating the underfill material to a first curing temperature and removing the film, curing includes: 
 gelling the underfill material that is in contact with the film;    removing the film; and the process further including: 
 curing the underfill material that is between the die and the mounting substrate.  
   
     
     
         15 . The method according to  claim 11 , wherein heating the underfill material to a first curing temperature includes: 
 heating along a first temperature ramp to a first temperature range from about 100° C. to about 180° C.; and further including: 
 holding the first temperature;  
 heating along a second ramp to a temperature range from about 140° C. to about 260° 0  C.; and  
 cooling.  
   
     
     
         16 . The method according to  claim 11 , wherein the underfill material has a viscosity that causes it to draw between the die and the mounting substrate, further including: 
 flowing the underfill material from a first edge of the die to an opposite, second edge of the die by a pressure differential.    
     
     
         17 . A chip package comprising: 
 a die;    a mounting substrate;    an electrical connection disposed between the mounting substrate and the die;    a cured underfill material including a fillet portion, and an interstitial portion disposed between the die and the mounting substrate, wherein the fillet portion includes a surface roughness and pattern that is characteristic of an interstitial film surface roughness and pattern.    
     
     
         18 . The chip package according to  claim 17 , wherein the interstitial film surface roughness and pattern is derived from a film selected from a tacky film and a non-tacky film.  
     
     
         19 . The chip package according to  claim 17 , wherein the fillet portion exhibits a single-stage solidification profile in cross section.  
     
     
         20 . The chip package according to  claim 17 , wherein the fillet portion exhibits a symmetrical rectilinear or other controllable footprint on the mounting substrate.  
     
     
         21 . The chip package according to  claim 17 , wherein the fillet portion exhibits a concave curvilinear cross-sectional profile.  
     
     
         22 . The chip package according to  claim 17 , wherein the electrical connection disposed between the mounting substrate and the die is selected from a ball grid array, a collapsed ball grid array, and a pin grid array.  
     
     
         23 . A chip-packaging process system comprising: 
 a die;    a mounting substrate;    an electrical connection disposed between the mounting substrate and the die;    a tacky film that is disposed over the die and stretched onto the mounting substrate;    a mold press that gives a shape to the film;    an underfill material disposed between the die and the mounting substrate; and    an underfill inlet and outlet system that communicates through the film.    
     
     
         24 . The chip-packaging process system according to  claim 23 , wherein the underfill inlet and outlet system includes an underfill conduit and a vent.  
     
     
         25 . The chip-packaging process system according to  claim 23 , wherein the underfill material includes a fillet shape disposed between the die and the mounting substrate, and wherein the a mold press that gives shape to the film includes a heater element disposed at the fillet.  
     
     
         26 . The chip-packaging process system according to  claim 23 , further including: 
 a first heating source for ramping the temperature of the underfill material to a first cure state; and    a second heating source for causing the tacky film to release from the die, the fillet, and the mounting substrate.