Transparent molding compound study and leadframe design improvement for ambient light and proximity sensor packaging

This paper discusses the material selection of a transfer moldable clear compound to be used for packaging Ambient Light Sensors and Proximity Sensors. Several grades of clear molding compound were characterized for their relevant material properties. Carsem´s in-house materials lab was utilized to test the different clear compounds and generate data on glass transition temperature (Tg), coefficient of thermal expansion (CTE), saturated moisture concentration (CSAT) and the coefficient of moisture expansion (CME) - a critical material property not usually found in supplier data sheets. After material characterization, stress modeling using Finite Element Analysis was used to study the shear stress versus adhesion strength at the critical interfaces which are prone to delamination. The stress modeling was also extended to study the effect of different leadframe features on the package robustness after MSL before eventually finalizing the leadframe design. Finally, some reliability data is shared towards the end of the paper. This paper demonstrates how material characterization coupled with stress modeling can greatly accelerate the introduction of new products in an ever-changing and dynamic market place.