Thinner semiconductor package is becoming popular especially in consumer electronics applications. As package becomes thinner, it is more vulnerable to package crack when subjected to external load. It is important to ensure that the package is strong enough to resist package cracking. This paper presents the study of package flexural strength under different epoxy mold compound curing condition. A 3-point bend test was done to characterize the breaking strength of the package that was subjected to post-mold curing. It was then compared to the strength of the package not subjected to post-mold curing (PMC). Results of the bend testing showed that the package flexural strength is much lower when the package is not subjected to post-mold curing. This study demonstrates that the measurement of flexural strength can be used to determine if the package has undergone post-mold curing or not. Performing the right post-mold curing of the thin molded package is required to ensure higher flexural strength.
This study focuses on eliminating the lead pullback problem in an automotive quad flat no lead (QFN) package in order to meet the non-negotiable requirement to have a solder wettable or solderable lead sidewall. It involves using a non-traditional approach of Monte Carlo tolerance analysis to determine the final leadframe and singulation blade design solution. It was found out that the zero lead pullback could be achieved by reducing the leadframe lead to lead distance from 0.275 mm to 0.225 mm and increasing the blade thickness from 0.325 mm to 0.350 mm. Actual results from 10 line stressing lots all showed zero pullback validating the effectiveness of the final design and the use of Monte Carlo tolerance analysis technique. Costly investment for a lead pullback inspection system was avoided and the 100% manual inspection eliminated.
Die fracture strength measurement is important to assess the robustness of a specific silicon die such that it is strong enough to resist die crack. There are several methods used to measure the strength of silicon die and 3-point bend test is the most common. However, the impact of the loading anvil shape on die strength results needs to be investigated. This paper discusses the comparison of die strength characterization using different loading anvil shapes in a 3-point bend test. The anvil shapes considered were wedge shape and needle shape. Die strength calculations were all done using the standard 3-point bend formula for flexural stress. Statistical analysis of the results revealed that die strength measured using wedge shape loading anvil is not significantly different from the strength measured using the needle shape loading anvil. Therefore, using the needle shape loading anvil in a 3-point bend test could still provide die strength results comparable with the results using the standard wedge shape loading anvil.
Package delamination is one of the problems in semiconductor packaging. Understanding the delamination mechanism in a specific situation is very important to identify the root cause and implement robust solution. In this study, package deformation modeling was done to analyze the deformation of the substrate or package at different thermal conditions. The modeling result was compared with the actual package deformation of the package with delamination problem. It was found out that the observed deformation through actual cross-section analysis matched with the modeling result at reflow temperature condition. Thus, it could be concluded that the delamination happens during package reflow and not after post mold cure or the preceding processes.
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