The Study of Process Enhancements to Improve Flash Removal Performance for Power Packages

For majority of the backend assembly of microelectronic devices, epoxy molding compounds (EMC) have been and will continue to be the mainstream of encapsulation materials in view of their cost and productivity advantages. Normally after mold encapsulations, some flashes will be remained on the leadframes/heatsink and to be cleaned by the subsequent deflash process. Based on research, found that Chemical Deflash (CD) provide better delamination performance compare with conventional Electrolytic Deflash (ED). However, the deflash performance for CD is not as good as ED. The parameter that can be optimized for CD also limited to only soaking time and temperature; this creates a challenge to achieve a good deflash quality. Therefore, the study of this paper is to focus on various CD process enhancements to improve the deflash performance which the main target is to reduce the Flash Along Lead (FAL) and Pad Flash (PF). There are 2 flat power packages chosen for this evaluation. The 1st package (Package A) with typical flash along lead (FAL) while the 2nd package (Package B) with open heatsink which will typically having the pad flash (PF) defect. The samples were assembled through typical assembly process except CD process, which need to have various runs with different process enhancements such as improve the chemical circulations and with acoustic signal. After completion, the samples submitted for 100% visual inspection (VI), solderability test and C-SAM (C-Mode Scanning Acoustic Microscopy). The results revealed that all the process enhancements improved the deflash performance. While the run with acoustic signal at low frequency showed most superb improvement. All runs passed the solderability test and delamination check without any abnormalities.