Reliability study of high-pin-count flip-chip BGA

Abstract

A family of 1.0-mm pitch full-array flip-chip BGAs were developed. These packages vary from 27 to 45 mm in package size, 15 to 25 mm in die size, and 672 to 1020 in ball count. With dies and packages so large, solder joint fatigue failure and underfill delamination, induced by thermal expansion mismatch, are a major concern. Finite element analysis was set up for efficient reliability analysis. Two substrates, hi-CTE ceramic (12/spl times/10/sup -6///spl deg/C) and BT (17/spl times/10/sup -6///spl deg/C), are compared. Hi-CTE ceramic substrate has a better CTE match with die (2.6/spl times/10/sup -6///spl deg/C), therefore, it was surmised that hi-CTE ceramic would improve component-level reliability yet with satisfactory board-level reliability. To validate it, several die and package combinations were modeled using both substrates. Both component-level stresses and board-level solder joint fatigue life were compared. In addition, design of experiment (DOE) was used to study the effect of properties and dimensions of underfill and heat spreader on solder joint fatigue life. The effect of pad opening size was also quantified. Finally, the effect of underfill on interface stress between underfill and die was investigated.