Vibration-Assisted Method for Underfilling Flip-Chip Electronic Devices

Abstract

A semiconductor assembly comprising an integrated circuit chip with a first plurality of metallic contact pads exposed, having a pitch center-to-center of less than 180 μm. A metallic bump of reflowable metal is attached to each of these contact pads. The assembly further has an electrically insulating substrate with a second plurality of metallic terminal pads in locations matching the locations of the contact pads. Each of the bumps also attached to these matching terminal pads, respectively, whereby the chip is interconnected with the substrate spaced apart by a gap. An adherent polymeric encapsulant fills the gap so that the encapsulant is free of voids. It is a pivotal feature in the method that vibration energy, up to ultrasonic frequencies, is used while the encapsulant is still in a low-viscosity precursor state in order to ensure the void-free spreading of the precursor throughout the gap between chip and substrate. The vibration energy ensures uniform underfill distribution even when the gap and the bump pitch are narrow, with uniform distribution of any fillers, and enhanced adhesion to chip, substrate and bumps.

1 . A method for forming an electronic assembly, comprising the steps of: 
 providing an integrated circuit chip having a first plurality of metallic contact pads;    attaching a metallic bump to each of the contact pads;    providing an insulating substrate having a second plurality of metallic terminal pads in locations matching the locations of the contact pads;    attaching the metallic bumps to the matching terminal pads on the substrate, thereby connecting the chip to the substrate, spaced apart by a gap;    vibrating the electronic assembly, while filling the gap with an adherent polymeric precursor; and    curing the polymeric precursor.    
     
     
         2 . The method according to  claim 1 , in which the steps of curing the polymeric precursor comprise heating the assembly.  
     
     
         3 . The method according to  claim 1 , in which the step of vibrating comprises applying vibration energy of frequencies between about 50 Hz and 25 kHz, and amplitudes between about 1.0 μm and 1.0 mm.  
     
     
         4 . The method according to  claim 1 , in which the step of vibrating comprises applying vibration energy of frequencies between about 120 Hz and 1000 Hz, and amplitudes between about 1.0 and 100 μm.  
     
     
         5 . The method according to  claim 1 , in which the step of attaching the metallic bumps to the matching terminal pads on the substrate comprises: 
 heating the substrate and the chip to melt the metallic bumps;    reducing the heating to allow the metallic bumps to solidify; and    maintaining the temperature of the assembly at an elevated temperature until the end of the curing step.