There has been significant demand for stacked die technology during the paste few years. The stacked die devices are mainly used in portable consumer products. This kind of silicon integration technology provides flexibility in space reduction, weight savings and excellent electrical functionality. In this article, the samples with stacked die construction were built into the leaded package. It was found that one of the test vehicles had full delamination at the leadframe paddle/mold compound interface after 100 temperature cycles (-55C to 150C) with moisture preconditioning at level 3 (60C/60%RH for 40 hours) although the electrical test passed 1000 temperature cycles. The fish bone diagram was used to identify the possible failure root causes. The material, process and design factors were extensively evaluated by the experiments and finite element analysis. The ealuation results showed that die attach paste voids were major factors affecting the package integrity, and could produce the delamination initiation at the edge of the die attach paste and propagate down to the leadframe paddle/mold compound interface due to high stress concentration and weak adhesion strength. The finite element analyses were implemented to address the stress distribution in the stacked die package and verified by the actual C-SAM results. It demonstrated that the excellent package integrity could be achievable by applying the void-free die attach paste and improving the adhesion strength at the leadframe paddle level.
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