Reliability analyses for new improved high performance flip chip BGA packages

High pin count and superior thermal dissipation are the main driving factors for high performance IC packages. Flip chip interconnects technology can generally achieve I/O count of more than 500, and large amounts of heat in the silicon chip can be dissipated efficiently through metal heat spreader attachment. A one-piece cavity lid flip chip BGA package with high pin count and targeted reliability has recently been developed by UTAC. However it was found that solder joint reliability could be compromised due to the rigidity resulted by the one-piece cavity lid. A new design of flip chip BGA package (patent pending) has been looked into for improved board level performance. In this new design, the flip chip is over-molded (with the die top surface exposed) before the lid is attached. With the new single flat lid mounted onto the mold compound, the package substrate is thus less rigid under thermal loading. Hence, solder joint integrity enhancement is expected. The structural differences between the two flip chip BGA designs are discussed in this paper along with detailed package reliability results.