Evaluating underfill material for flip chip ball grid array package

Flip chip technology is appearing in a variety of package format since it w as introduced by IBM 30 years ago. Earlier format of FCBGA (nip chip ball g rid army package) often uses classic C4 (controlled collapse chip connectio n) ceramic package. This type of package shows excellent electrical perform ance with shortest possible leads, lowest inductance, highest frequency, be st noise control, highest density, greatest number of inputs/outputs (I/O), smallest device footprints, and lowest profile when compared with other po pular interconnect methods [1]. With the substrate technology driving towar d the cheaper but still reliable organic substrate, FCBGA is being increasi ngly used for a wide range of applications, implantable devices and automot ive applications. This paper outlines the methodology used to screen for hi gh reliability underfill in evaluation study. The goal was to rank several commercially available underfill materials based on several processability and reliability criteria. The chosen material was used to manufacture sampl es of FCBGA devices for further testing. Finite element analysis was performed to determine the optimum fillet shape for underfill. The stress distribution of chip and underfill itself was co mpared to obtain the optimization. Material properties effects of underfill were also studied. Underfill modulus and CTEs (coefficient of thermal expa nsion) were parameters in this study. Experiments were carried to verify th e finite element results.