Thermoplastic fluxing underfill method

Abstract

A flip chip having solder bumps and an underfill that is thermoplastic and fluxing, as well as methods for making such a device. The resulting device is well suited for a simple one-step application to a printed circuit board, thereby simplifying flip chip manufacturing processes.

1 . A method for forming an integrated circuit assembly for attachment to a circuit board by soldering, the method comprising:
 applying an underfill solution comprising a thermoplastic resin, a solvent, and a fluxing agent to an integrated circuit device having at least one solder bump on a surface thereof such that the underfill solution is in contact with the at least one solder bump and with the surface of the integrated circuit device; and   removing at least a portion of the solvent from the applied underfill solution to thereby yield the integrated circuit assembly for attachment to a circuit board, wherein the integrated circuit assembly comprises the integrated circuit device, the at least one solder bump, and a thermoplastic fluxing underfill in contact with the integrated circuit device surface and in contact with the at least one solder bump.   
   
   
       2 . The method of  claim 1  wherein removing at least a portion of the solvent from the applied under fill solution yields a cured thermoplastic fluxing underfill in contact with the integrated circuit device surface. 
   
   
       3 . The method of  claim 1  wherein the thermoplastic resin has a viscosity between about 2,500,000 cP and about 100,000 cP at a temperature between about 80° C. and about 125° C. 
   
   
       4 . The method of  claim 1  wherein the thermoplastic resin has a viscosity between about 100,000 cP and about 500,000 cP at a temperature between about 80° C. and about 125° C. 
   
   
       5 . The method of  claim 1  wherein the thermoplastic resin has a viscosity of less than about 30,000 cP at a temperature between about 220° C. and about 260° C. 
   
   
       6 . The method of  claim 1  wherein the thermoplastic resin has a glass transition temperature that is between about −25° C. and about 60° C., a molecular weight that is between about 30,000 and about 50,000 daltons, and a viscosity that is between about 10,000 and about 1,000 cP at a temperature that is between about 220° C. and about 260° C. 
   
   
       7 . The method of  claim 6  wherein the thermoplastic resin is a phenoxy resin having about 20 weight percent of caprolactone grafted onto the backbone hydroxyl groups, the solvent is a polar solvent selected from the group consisting of a ketone, an ester, and an alcohol, and the fluxing agent is selected from the group consisting of a monocarboxylic acid having more than 20 carbon atoms per molecule, and a dicarboxylic acid having more than 12 carbon atoms per molecule that are liquid at room temperature and are soluble in the solvent. 
   
   
       8 . The method of  claim 7  wherein the underfill solution comprises a concentration of the thermoplastic resin that is between about 20 and about 60 weight percent, a concentration of the solvent that is between about 40 and about 80 weight percent, and a concentration of the fluxing agent that is between about 1 and about 10 weight percent. 
   
   
       9 . The method of  claim 2  wherein the thermoplastic resin has a viscosity between about 2,500,000 cP and about 100,000 cP at a temperature between about 80° C. and about 125° C. 
   
   
       10 . The method of  claim 2  wherein the thermoplastic resin has a viscosity between about 100,000 cP and about 500,000 cP at a temperature between about 80° C. and about 125° C. 
   
   
       11 . The method of  claim 2  wherein the thermoplastic resin has a viscosity of less than about 30,000 cP at a temperature between about 220° C. and about 260° C. 
   
   
       12 . The method of  claim 2  wherein the thermoplastic resin has a glass transition temperature that is between about −25° C. and about 60° C., a molecular weight that is between about 30,000 and about 50,000 daltons, and a viscosity that is between about 10,000 and about 1,000 cP at a temperature that is between about 220° C. and about 260° C. 
   
   
       13 . The method of  claim 12  wherein the thermoplastic resin is a phenoxy resin having about 20 weight percent of caprolactone grafted onto the backbone hydroxyl groups, the solvent is a polar solvent selected from the group consisting of a ketone, an ester, and an alcohol, and the fluxing agent is selected from the group consisting of a monocarboxylic acid having more than 20 carbon atoms per molecule, and a dicarboxylic acid having more than 12 carbon atoms per molecule that are liquid at room temperature and are soluble in the solvent. 
   
   
       14 . The method of  claim 13  wherein the underfill solution comprises a concentration of the thermoplastic resin that is between about 20 and about 60 weight percent, a concentration of the solvent that is between about 40 and about 80 weight percent, and a concentration of the fluxing agent that is between about 1 and about 10 weight percent. 
   
   
       15 . The method of  claim 1  wherein removing at least a portion of the solvent from the applied underfill solution dries the applied underfill solution and the process further comprises the steps of:
 placing the integrated circuit assembly onto the circuit board to yield a circuit board with the integrated circuit assembly placed thereon; and   heating the circuit board with the integrated circuit assembly placed thereon to a reflow temperature to thereby solder the integrated circuit device to the circuit board while the fluxing agent fluxes the solder and to flow the cured thermoplastic fluxing underfill thereby yielding a circuit board having the integrated circuit device attached thereto with a metallic solder connection and the cured thermoplastic underfill between and bonded to the circuit board and the integrated circuit device.   
   
   
       16 . The method of  claim 2  wherein removing at least a portion of the solvent from the applied underfill solution dries the applied underfill solution and the process further comprises the steps of:
 placing the integrated circuit assembly onto the circuit board to yield a circuit board with the integrated circuit assembly placed thereon; and   heating the circuit board with the integrated circuit assembly placed thereon to a reflow temperature to thereby solder the integrated circuit device to the circuit board while the fluxing agent fluxes the solder and to flow the cured thermoplastic fluxing underfill thereby yielding a circuit board having the integrated circuit device attached thereto with a metallic solder connection and the cured thermoplastic underfill between and bonded to the circuit board and the integrated circuit device.   
   
   
       17 . A method for forming an integrated circuit assembly for attachment to a circuit board by soldering, the method comprising:
 applying a cured underfill film comprising a thermoplastic resin and a fluxing agent to an integrated circuit device having at least one solder bump on a surface thereof such that the cured underfill film is in contact with the at least one solder bump and with the surface of the integrated circuit device; and   adhering the cured underfill film to the integrated circuit device to yield the integrated circuit assembly for attachment to a circuit board, wherein the integrated circuit assembly comprises the integrated circuit device, the at least one solder bump, and the cured thermoplastic fluxing underfill adhered to the integrated circuit device surface and the at least one solder bump.   
   
   
       18 . The method of  claim 17  wherein the thermoplastic resin has a viscosity between about 2,500,000 cP and about 100,000 cP at a temperature between about 80° C. and about 125° C. 
   
   
       19 . The method of  claim 17  wherein the thermoplastic resin has a viscosity of less than about 30,000 cP at a temperature between about 220° C. and about 260° C. 
   
   
       20 . The method of  claim 17  wherein the thermoplastic resin has a glass transition temperature that is between about −25° C. and about 60° C., a molecular weight that is between about 30,000 and about 50,000 daltons, and a viscosity that is between about 10,000 and about 1,000 cP at a temperature that is between about 220° C. and about 260° C., and the fluxing agent is selected from the group consisting of a monocarboxylic acid having more than 20 carbon atoms per molecule, and a dicarboxylic acid having more than 12 carbon atoms per molecule.