A MOISURE INDUCED FAILURE IN FCBGA PACKAGES DURING MULTIPLE REFLOW
Author: Fay Hua Company: Hewlett Packard Company Date Published: 8/23/1998
Surface Mount International
Abstract: Flip chip BGA (FCBGA) packages usually undergo multiple reflows after being underfilled as required by second level assembly and rework processes. During the re- reflow process, the eutectic Pb-Sn solder bumps melt and expand (4%) against the underfill; thermal stresses are also induced due to the difference in thermal expansion coefficients of materials, and/or expansion of gases trapped within the underfill. This paper reports the observation of mechanical failure of FCBGA packages during multiple reflow process. The failure depends on moisture level in the package and on the reflow temperature. The failure mechanisms were analyzed by C-SAM (C-mode Scanning Acoustic Microscopy), X-ray topography, metallographic cross-section, and SEM (Scanning Electronic Microscopy). Solution for the problem will also be discussed.