A Fracture Mechanics-Based Approach to Simulate Die Pick-up Process

Sandeep Shantaram, Ph.D., Yi Hsuan Tsai, Yao Jung Chang
NXP Semiconductors Inc.
TX, USA

Integrated circuit die pick-up event is an important process step in advanced packages such as wafer level chip scale packages (WLCSP). The productivity is sensitive to 3 primary factors which include die-crack risk due to ejection process, die knocking to the neighboring dies, unsuccessful delamination of the chip-on-substrate structure. This paper provides a procedure to simulate die pick-up process based on contact-debonding fracture mechanics approach. Also, ejection height predicted by the model will be compared with the empirical findings for various needle configuration. Finally, needle selection rule for WLCSP family will be provided.

WLCSP which is extensively used in the semiconductor industry pose challenges during the electronic assembly. And one such challenge includes handling thin semi-conductor silicon dies during the die pick up assembly step. The productivity is sensitive to 3 primary factors which include die-crack risk due to ejection process, die knocking to the neighboring dies, unsuccessful die-pickup event.

This paper provides step-by-step procedure on how to simulate die-pick up process step using cohesive zone contact debonding fracture mechanics approach. Models have been validated with empirical data in-terms of ejection height, delamination initiation and crack growth path. Modeling result also used to evaluate the potential die crack risk due to over stressing and die-knocking effects. Based on the current study it is recommend to use multiple needle (4+) over single needle for die-ejection to mitigate the die-crack risk. Also, for multi-needle scenario by keeping needle alignment within spec, needles pitch can be set to half of the die size to reduce die-knocking risk and to improve the success rate of the die-ejection event.