CAPILLARY UNDERFILL PHYSICAL LIMITATIONS FOR FUTURE PACKAGES
Authors: Horatio Quinones and Tom Ratledge Company: ASYMTEK Date Published: 1/26/2010
Pan Pacific Symposium
Abstract: The capillary underfill (CUF) although a well established manufacturing assembly process, is being challenged as die thickness diminishes, the interconnection (bumps) get smaller and their number increases. Denser populated packages demand very tight tolerances for keep out zones (KOZ); the total package thickness challenges the process throughput since die contamination from underfill fluid is not allowed and multiple fluid dispense passes may be needed. All this challenges translate in lower capillary surface energies, increase in fluid flow drag, smaller particle size fluid that often results in increase in viscosity and therefore slow flow-out-times. The present work addresses these issues. A series of mathematical models based on surface energy evolution for CUF accounting for these new geometries and processes is proposed. In particular the problem of component proximity is and the gap topology issues are studied. Experimental data for CUF in the presence of these future assembly demands is shown. Although there are practical physical limitations for the CUF as experienced today if one were to implement it for future packages, new hybrid CUF methods that overcome such shortcoming are recommended.