Underfill method

Abstract

A process for selectively depositing a filled underfill material onto a die surface without covering solder bumps present on the die. The process entails microjetting a polymer matrix material, a filler material, and optionally a fluxing material onto the die surface. Together, the polymer matrix and filler materials define the filled underfill material in which the filler material is dispersed to reduce the coefficient of thermal expansion of the underfill material. The resulting underfill material surrounds but does not cover the solder bumps. The die is then placed on a substrate on which a second underfill material is present, forming a composite underfill layer that completely fills the space between the die and substrate and forms a fillet on a peripheral wall of the die.

1 . A method of underfilling a flip chip component, the method comprising the steps of: 
 microjetting a polymer matrix material and a filler material onto a surface of the component on which solder bumps are present, the polymer matrix material and the filler material defining a filled underfill material in which the filler material is dispersed to reduce the coefficient of thermal expansion of the filled underfill material, the polymer matrix material and the filler material being selectively deposited so that the filled underfill material surrounds and does not cover the solder bumps;    depositing a second underfill material on a substrate having bond pads on a surface thereof, the second underfill material being substantially free of a filler material;    registering the solder bumps on the component with the bond pads on the substrate so that the filled underfill material and the second underfill material fill in a space defined by and between the component and the substrate, the second underfill material extending onto a peripheral wall of the component;    heating the substrate, the solder bumps, the filled underfill material and the second underfill material so that the solder bumps melt and so that the filled underfill material and the second underfill material form a composite underfill layer having discrete filled and unfilled portions; and then    cooling the molten solder bumps and the composite underfill layer so that the molten solder bumps form solid electrical connections that are metallurgically bonded to the bond pads, the composite underfill layer encapsulates the connections, the unfilled portion of the composite underfill layer defines a fillet that extends onto the peripheral wall of the component, and the space between the component and the substrate is free of voids.    
     
     
         2 . The method according to  claim 1 , wherein the microjetting step is performed at wafer-level, the component is one of a plurality of dies separated by scribe lines on a surface of a wafer, and the filled underfill material does not cover the scribe lines.  
     
     
         3 . The method according to  claim 1 , wherein the microjetting step further comprises microjetting a flux material onto the surface of the component so as to contact the solder bumps, the polymer matrix material and the filler material are selectively deposited so that the filled underfill material surrounds the flux material, and the solder bumps are fluxed by the flux material during the heating step.  
     
     
         4 . The method according to  claim 1 , wherein the filler material is deposited on the component prior to the polymer matrix material, and the polymer matrix material and the filler material combine in situ to form the filled underfill material.  
     
     
         5 . The method according to  claim 4 , wherein the filler material is deposited while suspended in a volatile solvent, and the polymer matrix material is deposited after evaporating the volatile solvent from the surface of the component.  
     
     
         6 . The method according to  claim 1 , wherein the polymer matrix material and the filler material are combined prior to the microjetting step, such that the filled underfill material is microjetted directly onto the component  10 .  
     
     
         7 . The method according to  claim 6 , wherein the filler material consists essentially of nanoparticles.  
     
     
         8 . The method according to  claim 1 , wherein the second underfill material contains a flux compound.  
     
     
         9 . The method according to  claim 1 , wherein the microjetting step is performed with a microjetting apparatus programmed to selectively deposit the polymer matrix material and the filler material on the surface of the component.  
     
     
         10 . A method of underfilling a flip chip die, the method comprising the steps of: 
 microjetting a filled underfill material onto a surface of a wafer on which individual dies are delineated and separated by scribe lines, each of the dies having solder bumps associated therewith, the filled underfill material comprising a polymer matrix material and a dispersion of particulate filler material that reduces the coefficient of thermal expansion of the filled underfill material, the filled underfill material being selectively deposited between the solder bumps and not over the solder bumps or the scribe lines;    singulating the dies from the wafer along the scribe lines;    depositing an adhesive on a substrate having bond pads on a surface thereof, the adhesive being substantially free of a filler material;    registering the solder bumps of one of the dies with the bond pads on the substrate so that the filled underfill material and the adhesive fill a space defined by and between the die and the substrate and the adhesive extends onto a peripheral wall of the die;    heating the substrate, the solder bumps, the filled underfill material and the adhesive so that the solder bumps melt and so that the filled underfill material and the adhesive form a composite underfill layer having discrete filled and unfilled portions; and then    cooling the molten solder bumps and the composite underfill layer so that the molten solder bumps form solid electrical connections that are metallurgically bonded to the bond pads, the composite underfill layer encapsulates the connections, the unfilled portion of the composite underfill layer defines a fillet that extends onto the peripheral wall of the die, and the space between the die and the substrate is free of voids.    
     
     
         11 . The method according to  claim 10 , wherein the microjetting step further comprises microjetting a flux material onto the surface of the wafer so as to contact the solder bumps, the filled underfill material is selectively deposited so as to surround and contact the flux material, and the solder bumps are fluxed by the flux material during the heating step.  
     
     
         12 . The method according to  claim 10 , wherein the filler material consists essentially of nanoparticles.  
     
     
         13 . The method according to  claim 10 , wherein the adhesive flows onto at least some of the bond pads.  
     
     
         14 . The method according to  claim 13 , wherein the adhesive contains a flux compound.  
     
     
         15 . A method of underfilling a flip chip die with a composite underfill layer comprising filled and unfilled regions, the method comprising the steps of: 
 microjetting a particulate filler material onto a surface of a wafer on which individual dies are delineated and separated by scribe lines, each of the dies having solder bumps associated therewith, the filler material being selectively deposited so as to surround the solder bumps and not cover the solder bumps or the scribe lines;    microjetting a polymer matrix material onto the filler material, the polymer matrix material being selectively deposited between the solder bumps and not over the solder bumps or the scribe lines, the polymer matrix material wetting the filler material so as to form in situ a filled underfill material in which the filler material is dispersed to reduce the coefficient of thermal expansion of the filled underfill material;    singulating the dies from the wafer along the scribe lines;    depositing an adhesive on a substrate having bond pads on a surface thereof, the adhesive being substantially free of a filler material;    registering the solder bumps of one of the dies with the bond pads on the substrate so that the filled underfill material and the adhesive fill a space defined by and between the die and the substrate and the adhesive extends onto a peripheral wall of the die;    heating the substrate, the solder bumps, the filled underfill material and the adhesive so that the solder bumps melt and so that the filled underfill material and the adhesive form a composite underfill layer having discrete filled and unfilled portions; and then    cooling the molten solder bumps and the composite underfill layer so that the molten solder bumps form solid electrical connections that are metallurgically bonded to the bond pads, the composite underfill layer encapsulates the connections, the unfilled portion of the composite underfill layer defines a fillet that extends onto the peripheral wall of the die, and the space between the die and the substrate is free of voids.    
     
     
         16 . The method according to  claim 15 , further comprising the step of microjetting a flux material onto the surface of the wafer so as to contact the solder bumps, wherein the polymer matrix material and the filler material are selectively deposited so that the filled underfill material surrounds and contacts the flux material, and the solder bumps are fluxed by the flux material during the heating step.  
     
     
         17 . The method according to  claim 15 , wherein the filler material is deposited while suspended in a volatile solvent, and the polymer matrix material is deposited after evaporating the volatile solvent from the surface of the wafer.  
     
     
         18 . The method according to  claim 15 , wherein the adhesive flows onto at least some of the bond pads.  
     
     
         19 . The method according to  claim 18 , wherein the adhesive contains a flux compound.