Investigation and Optimization of Mold Flow Impact to Leadless SMD Package Delamination

An interesting phenomenon on the effect of mold flow to leadless SMD package delamination was observed in this study. Delamination on molded package interface was detected on the saw singulated units coming from different locations of the map molded strip. To further investigate the impact of mold flow and seek possible optimization, an experimental design with different molding parameter, sawing parameter and BOM material was proposed. C-SAM was used to measure the delamination level in different areas of the molding block. Mold flow effect was investigated by changing the mold transfer speed process parameter, samples coming from the mold gate and vent area examined under high magnification after cross-section revealed the filler distribution difference. Results showed that slower transfer speed was able to minimize the mold flow impact, improve fluidity, and mitigate uneven filler distribution within the molded strip. Meanwhile faster transfer speed resulted to migration of fillers towards the vent area. Mold flow impact on delamination during saw singulation process was also investigated by changing the cooling water speed parameter. Experimental results showed that the delamination on the gate and vent slightly improved with faster cooling water speed, and the delamination difference from gate to vent was more evident. Furthermore, the EMC and leadframe material properties were optimized to eliminate the stress difference during saw singulation process. The surface morphology and roughness of normal and rough leadframe was characterized by SEM and AFM. The adhesion of the EMC to the leadframe was characterized by button shear test. Generally, with the higher adhesion EMC, the delamination was reduced especially in the vent area where the delamination trend is less than gate, however in molding gate where the sawing stress is higher, the impact is relatively minimal. Moreover, using rough leadframe with stronger mold interlock, the sawing stress can be sustained, making the molded leadless package more robust against delamination. The result of this study reveals a very interesting correlation between mold flow and package delamination level in leadless SMD package, it creates a new perspective to semiconductor industry for material and process development.