Cure shrinkage characterization and its implementation into correlation of warpage between simulation and measurement

Abstract

In this work, a new approach was proposed to characterize the cure shrinkage of EMC by using the EMC/Cu bi-layer strip specimens. The warpage of bi-layer strip was measured at different temperature using Shadow Moire. The results show that warpage at molding temperature was non-zero and zero-warpage temperature shifted from molding temperature (175 degc) to higher temperature due to cure shrinkage effect. From Timoshenko's beam theory, the cure shrinkage was calculated as 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> order approximation theoretically either from the warpage at molding temperature or from zero- warpage temperature. The determined cure shrinkage together with thermal shrinkage obtained from TMA tests was used to predict the warpage of the different EMC/Cu strips. Good correlation was observed in the wide temperature range. As comparison, direct measurement of the cure shrinkage was also done using long rectangular bar specimens. Cure shrinkage was determined by extracting thermal shrinkage from total shrinkage. Cure shrinkage of 2 EMCs were characterized and then applied to PBGA matrix. Warpage of the PBGA EMC/substrate maps was measured using Shadow Moire and simulated as well for the molding compounds (EMCs) after 3 different processes, i.e. after transfer molding (TM), post mold cure (PMC) and PMC + Reflow at 260 degc for 3 times (RF260X3). Consistence between simulation and experiments was found when cure shrinkage was considered. The presented data show the necessity and importance of cure shrinkage in warpage prediction simulation.