Failure Analysis of Full Delamination on the Stacked Die Leaded Packages

Abstract

There has been significant demand for stacked die technology during the past 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 stacked die construction was built into the leaded package. It was found that the test vehicles had full delamination at the lead-frame paddle/mold compound interface after 100 temperature cycles (−65°C to 150°C) with moisture preconditioning at level 3 (60°C at 60% relative humidity for 40 h) although the electrical test passed 1000 temperature cycles. The fishbone 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 evaluation 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 lead-frame 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 scanning acoustic microscope. It demonstrated that excellent package integrity could be obtained by applying the void-free die attach paste and improving the adhesion strength at the lead-frame paddle level.