Comprehensive study in mold compound, thermal residual stress, package & leadframe geometry influence towards convex cavity package warpage

Higher demand of Rds(on) in power MOSFET package introduces the copper clip is used as interconnect material, this package construction increase CTE mismatch with mold compound. Warpage can be categorised as convex warpage (leadframe warpage in cavity molding) and concave warpage (mold compound warpage in map molding). This paper focus on convex leadframe warpage, where leadframe jamming & damage are observed at molding offloading tracks which subsequently effecting yield. Mold parameter, mold compound formulation, package outline, leadframe design, thermal residual stress characterizations are essential to minimize convex warpage.[1] Four TDSON packages single heatsink, dual heatsink, singles heatsink fused lead and single heatsink fused lead LTI has been studied. Copper material within package outline increase > 2.34% in fused lead packages, increasing CTE mismatch between copper-die-mold compound warpage start to be seen. To maintain current fused lead packages outline, optimization of leadframe design focusing at non-functional area is studied and the correlation of warpage versus copper material is established. Result shows reduction of warpage of the single heatsink fused lead from 5 mm to minimal of 1.4mm. Selection of basic resin, filler loading, warpage additive in mold compound plays an important role in thermal & chemical shrinkage. Lower Tg improves convex warpage, addition of short molecular chain biphenyl & LMW into Multi-Aromatic is needed. Increment of CTE to 14ppm/dC alone reduce warpage from 5mm to minimal 3mm, addition of Warpage Relief Additive (abbreviated as WRA) reduces convex warpage to 1.5mm. Correlation of WRA with mold shrinkage & convex warpage are established, result reveals addition of WRA to max 4.6% reduces warpage by 3.5mm. Addition of unreactive WRA reduces mold compound curability. Our studies also show thermal residual stress relief identified can improve convex warpage, this paper focus on of leadframe cooling time and design of degating cooling station. Study show cooling station tubing position, blowing direction and cooling mechanism contribute for different equipment contribute to 20% warpage magnitude.