Thermoplastic fluxing underfill composition

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 thermoplastic fluxing underfill solution for application between an integrated circuit device and a circuit board to assist in solder assembly of the integrated circuit device to the circuit board and to provide shock resistance after said solder assembly of the integrated circuit device to the circuit board, the thermoplastic fluxing underfill solution comprising:
 a thermoplastic resin having a glass transition temperature within the range of about −25° C. to about 60° C., and thermal stability such that the thermoplastic resin loses less than about 10% of its weight upon exposure to soldering conditions comprising a temperature of about 250° C. for about 90 seconds;   a solvent which dissolves the thermoplastic resin having said thermal stability; and   a fluxing agent for fluxing a solder in solder assembly of the integrated circuit device to the circuit board.   
     
     
         2 . The thermoplastic fluxing underfill solution of  claim 1  wherein the thermoplastic resin has a melt temperature that is between about 50° C. and about 150° C. 
     
     
         3 . The thermoplastic fluxing underfill solution of  claim 1  wherein the glass transition temperature is between about −15° C. and about 40° C. and the thermoplastic resin has a melt temperature that is between about 60° C. and about 150° C. 
     
     
         4 . The thermoplastic fluxing underfill solution of  claim 1  wherein the glass transition temperature is between about 20° C. and about 40° C. and the thermoplastic resin has a melt temperature that is between about 80° C. and about 100° C. 
     
     
         5 . The thermoplastic fluxing underfill solution of  claim 1  wherein the glass transition temperature is between about 25° C. and about 35° C. and the thermoplastic resin has a melt temperature that is between about 85° C. and about 95° C. 
     
     
         6 . The thermoplastic fluxing underfill solution of  claim 1  wherein the glass transition temperature is between about −5° C. and about 10° C. and the thermoplastic resin has a melt temperature that is between about 50° C. and about 65° C. 
     
     
         7 . The thermoplastic fluxing underfill solution of  claim 1  wherein the thermoplastic resin has a molecular weight that is between about 30,000 and about 55,000 daltons. 
     
     
         8 . The thermoplastic fluxing underfill solution of  claim 1  wherein the thermoplastic resin has a molecular weight that is between about 30,000 and about 40,000 daltons. 
     
     
         9 . The thermoplastic fluxing underfill solution of  claim 1  wherein the thermoplastic resin has a viscosity that is less than about 30,000 cP at a temperature that is between about 220° C. and about 260° C. 
     
     
         10 . The thermoplastic fluxing underfill solution of  claim 1  wherein the thermoplastic resin has 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. 
     
     
         11 . The thermoplastic fluxing underfill solution of  claim 1  wherein the thermoplastic resin has a viscosity that is between about 3,000 and about 300 cP at a temperature that is between about 180° C. and about 240° C. 
     
     
         12 . The thermoplastic fluxing underfill solution of  claim 1  wherein the thermoplastic resin is a phenoxy resin having about 20 weight percent of caprolactone grafted onto the backbone hydroxyl groups that has a molecular weight of about 39,000 daltons, a glass transition temperature of about 30° C., and a viscosity that is between about 7,000 and about 2,500 cP at a temperature that is between about 220° C. and about 260° C. 
     
     
         13 . The thermoplastic fluxing underfill solution of  claim 1  wherein the solvent is a polar solvent selected from the group consisting of a ketone, an ester, an alcohol, and combinations thereof. 
     
     
         14 . The thermoplastic fluxing underfill solution of  claim 1  wherein the solvent is selected from the group consisting of ethyl-ethoxypropionate, methyl ethyl ketone, and cyclohexanone. 
     
     
         15 . The thermoplastic fluxing underfill solution of  claim 1  wherein 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. 
     
     
         16 . The thermoplastic fluxing underfill solution of  claim 1  the fluxing agent is selected from a monocarboxylic acid having more than 20 carbon atoms per molecule, a dicarboxylic acid having more than 12 carbon atoms per molecule, or a combination thereof that is liquid at room temperature and is soluble in a polar solvent. 
     
     
         17 . The thermoplastic fluxing underfill solution of  claim 1  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. 
     
     
         18 . The thermoplastic fluxing underfill solution of  claim 1  wherein the underfill solution comprises a wetting agent selected from the group consisting of a silane, a fluorocarbon, and an acrylate resin at a concentration that is between about 0.005 and about 2.0 weight percent of the underfill solution. 
     
     
         19 . The thermoplastic fluxing underfill solution 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. 
     
     
         20 . The thermoplastic fluxing underfill solution 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.