Reliability Study of MCM-L with High I/Os Flip Chip and Laminated Board with Stacked vias in Build-up Layers

摘要

The reliability of MCM-L with high I/Os flip chip and build-up laminate with stacked vias was investigated in this paper. Accelerated thermal cycling(ATC) tests and failure analysis for six specimens with different structures and materials were conducted firstly to determine the fatigue life and failure mechanisms of the package. The results revealed that the CTE of board and underfill observably affected the fatigue life of the solder joints even when encapsulated with underfill, while the size of chip had little effect. For the specimens with single layer PI substrate, cracks all existed in upper solder joint near the chip, while for the specimens with build-up laminate, there existed two phenomena: for the specimens with lower CTE underfill, cracks mainly existed in upper solder joint near the chip, and the drum profile of the solder joints were destroyed to a certain extend, for specimens with higher CTE underfill, cracks not only existed in upper solder joint but also existed in the interface between solder joint and copper pad on the substrate, and the drum profile of the solder joints were kept well. Another phenomenon was that although there existed inner voids or air bubbles within the underfill after curing, no further delamination was found to propagate near these defects with the increased thermal cycles. Global-local FEA were then conducted to analyze the mechanical behavior of the package. The simulation results revealed that for the specimens with stacked vias, higher CTE underfill and board, solder joints underwent higher von Mises stress and strain, and then led to lower fatigue life, which showed that the simulation results could accounted for ATC tests results well. A fatigue life model in related with accumulated strain energy density of solder joint was built to estimate the solder joint fatigue life of the package, and the empirical constants were determined by fitting simulation and ATC tests results.