Study on moisture behavior in flip chip BGA packages and bake process optimization

Abstract

The Lead-Free (LF) and Halogen-Free (HF) "green" initiatives are driving the advanced packaging manufacturers to develop new generation materials and assembly technologies. However, the moisture related reliability issues become the significant technical challenge to meet stringent reliability and quality standards comparing to the previous Lead and Halogen technology. In this study, the moisture absorption and desorption performance of Halogen Free and Lead Free material were investigated. The experimental data revealed that after fully baked process there was still some resident moisture which was mainly contained at substrate level. The modeling data of moisture absorption and desorption behavior with 125°C bake comparison was discussed and was fully aligned with experimental data. Moreover, a 'soft bake' method via Nitrogen and dry air was introduced. In low RH effect test, under 25°C / 60%RH precondition process, all the moisture absorbed for 1100 hours can be removed by 'soft' bake. This indicates that not only no moisture absorption in low RH environment, but also an additional 'soft bake' process occurring during the storage time. The results demonstrated that the storage of moisturesensitive material in the optimized environment is an attractive facility solution which can reduce the risk of popcorn and cracking problems.

Moisture Diffusion Inside the BEOL of an FC-PBGA Package

“…A higher temperature (>100 • C) is required to remove the residual bound water [9], [10]. Dai et al [11] described this residual bound water as being mostly localized inside the substrate; hence, most of it is not detected by the sensors located within the BEOL. A standard duration of 24 h at 130 • C completely dries the BEOL of an FC-PBGA module without underfill; it also demonstrates the robustness of the sensors after multiple measurements.…”