MODELING OF WHOLE FIELD VAPOR PRESSURE DURING REFLOW FOR FLIP CHIP BGA AND WIRE BOND PBGA PACKAGES

Abstract

ABSTRACT In this paper, FEA models are built for bothflip chip BGA (FCBGA) and wire bond PBGApackages to predict the moisture distribution,followed by the calculation of vapor pressuredistribution in the package using the micro-mechanics approach with consideration of themicro-void effect. Results show that the vaporpressure saturated much faster than the moisturediffusion, and a near uniform vapor pressure isreached in the package. The vapor pressure isstrongly dependent on the temperature and itsmagnitude can’t exceed the saturated pressureat the corresponding temperature, even whenmore moisture is added in. The vapor pressureintroduces additional mismatch to the packagebesides the CTE thermal mismatch. Vaporpressure-induced expansion is directly related tothe vapor pressure distribution, rather than themoisture distribution. Moisture desorptionduring reflow is also studied and it hassignificant effect on the moisture distribution,but not on the vapor pressure distribution. 1. INTRODUCTION