Package crack resolution through low stress dambar punch design: A six sigma DMAIC approach

Package micro-crack has been a stern problem in ON Semiconductors Philippines Inc (OSPI) Trim and Form (T&F) process. That despite numerous studies to eliminate the problem it still persist. Package micro-crack was of concern as it has a high chance to escape assembly inspection control and electrical test. And potentially will contribute to the product failure upon application of stress. This study aspires to close the gap between numerous Trim and Form process studies and aimed to zero out package micro-crack occurrence. To achieve the goal the study utilized the Define, Measure, Analyze, Improve and Control or DMAIC a component of six sigma methodology. DMAIC revealed the most affected product line which became the focus of investigation to map and measure the defect signature. The resulting data were consolidated in a Kepner-Trego table were used in the analysis of the potential micro-crack mechanism. Each of the potential micro-crack producing mechanism was set-up on the machine used to process the most affected product, Intercon or ICT Trim and Form machine, outlined in a simple experiment design matrix. In parallel, the study made use of Finite Elemental Analysis software (FEA) to theoretically validate some of the potential failure mechanism. Experiment samples were all subject to Scanning Acoustic Microscopy or SAM testing to determine if the set-up mechanism can reproduce similar failure signature as that of the customer returned failed units. Then, replication experiments were performed to turn the problem 'on' and 'off' using the observed micro-crack producing set-up. And finally, solutions were derived to eliminate package micro-crack. Result showed that die inserts with planarity difference of ≥ 5mils during set-up will produce package micro-crack. FEA also revealed that the current dambar punch design induces high stress. Other observations noted in the study showed that response also varies depending on the mold compound type and leadframe design. Micro-crack was observed to be prevalent on mold compound with the lowest flexural strength compared to other mold compound types. To be able to control the mechanism that will lead to package micro-crack, die insert planarity was ensured to be below 5 mils and the die punch was redesigned to reduce stress on package during the dambar cutting.