A New Approach for No-Underfill Flip Chip Package Design

摘要

This research proposes a new approach for flip chiprntype packages with no-underfill structure. Previousrnresearch has shown that flip-chip type packages withrnorganic substrate require underfill for adequate reliabilityrnperformance. Although underfill encapsulant is critical tornthe reliability of the flip chip solder joint interconnects,rnthe shortcoming of underfilling process is well-known,rnsuch as, it will increase the difficulty of the reworkabilityrnand will decrease the manufacturing throughput.rnGenerally, the shear/equivalent strain of the solder jointsrnbetween the chip and the substrate is generated by thernmismatch in the coefficient of thermal expansion. Basedrnon this physical characteristic, a feasible way to increasernthe reliability of solder joint is to minimize the thermalrnmismatch between the silicon die and the organicrnsubstrate. This research proposes a structure usingrnceramic-like (CTE close to silicon) material mounted onrnthe backside of the substrate to constrain the thermalrnexpansion of the organic substrate. The ceramic-likernmaterial could make the thermal mismatch betweenrnsilicon die and substrate more compliant, therebyrnenhancing the reliability life of the solder joint. Thernresults show that this new structure could achieve thernsame range of reliability life of solder joints as thernunderfill material. Furthermore, using flip chip withoutrnunderfill could easily solve the reworkbility problem,rncould enhance the thermal capability and could alsornsignificantly increase the manufacturing throughput.