Enhancing Drop Test Efficacy for Product Quality Improvement through Interconnection Shear Tests

Abstract

Comparison of data from high speed shear and drop test of four different tin based BGAs, DIP 34, DIP 33, DIP 18C and DIP 18B show that there is a good correlation between these two tests. The test performance ranking of the alloys from the drop test is DIP 33 > DIP 18C > DIP 18B > DIP 34 and that from the shear test is DIP 33 ~ DIP 18C > DIP 18B > DIP 34. There was a good matching of the failure mechanisms observed during these two tests. In addition, this article shows that by increasing the shear test speed, a better correlation with the drop test can be achieved.For the shear tests, there was a clear difference in the failure modes between samples having the lowest and highest shear strength values. In all the sample sets, the weakest link appears to be the component side IMC layer.This article will show that the shear test can be used as a proxy to the drop test to evaluate quality of components that are assembled in a mobile electronic product. IntroductionDrop tests are commonly employed to assess the reliability of mobile electronic products under mechanical impact loading. The tests are performed both at the board and product level. At the board level, the drop tests provide information on the quality of incoming components. The product level drop test can assess the reliability of a component taking into account the effects of the product casing. However, the data from the drop test is attribute (data which is in the form of pass/fail, and which is not directly measured) and therefore, does not lend itself to rapid root cause analysis and quality improvement. In addition, these tests are time consuming. There is a need to find a test method that mirrors the drop test behavior but one that yields continuous data (data which is directly measured and has a range of values) to provide timely inputs for corrective actions and quality improvement. The package to board interconnection shear test, which was developed earlier to assess the quality of the interconnection, is an attractive candidate for this purpose [1].However, there are conflicting reports in the literature about the correlation of interconnection shear strength with drop test performance. A study performed to understand the effect of thermal aging on the board level reliability of Pb free BGA's reported that there was no correlation between the drop and ball shear tests failure locations [2]. In another study involving characterization of different substrate finishes for flip chips, the ball shear test failed to reproduce the failure mode normally seen during mechanical shock loading conditions [3]. Solder joints with ENIG pad finish failed at the component/solder interface during the drop test. However, the failure location during the ball shear test was in the bulk