Author: G. Bartlett Company: Mercury Computer Systems Date Published: 4/28/1997
Surface Mount International
Abstract: Ball Grid Arrays (BGAs) have proliferated as popular micropackaging options because of their packaging density, relative ease of assembly, and inherent physical integrity, among other things. Standard commercial environments pose no rigorous stresses on them, but the same cannot be said for harsher environments. Unfortunately, the distinction between the two is ill-defined and requires extensive testing and analysis be performed for each specific application. Both ceramic BGAs (CBGAS) and plastic BGAs (PBGAs) that house Mercury Computer Systems’ custom ASIC chips have been found to be generally resilient to such stresses, with the exception of large vibrational stresses which caused premature failure of susceptible solder joints during qualification testing. A variety of techniques were investigated to ruggedize these joints. Application of a compliant underillling epoxy with viscosity levels tailored for two package types, CBGAS and PBGAs, was found to provide the best combination of performance, cost, ease of use, and reworkability. Furthermore, this material is compatible with other materials and processes used in electronics assembly.