Unique high density leadframe development for SOT23

Abstract

With a drive of leading lower cost and higher productivity of Small Outline Surface Mounting (SOSM) packages, high density leadframe introduction was launched in the market since 21st century. But almost all factories use more expensive spot silver (Ag) plated and less than 60mm width leadframe. This paper presents the challenges faced and success in the development of unique high density copper (Cu) plated leadframe at more than 70 mm width and less than 0.11mm thicknesses for SOT23 packages. Due to the unique leadframe design, some considerations and solutions were developed: (1) Thermo-mechanical die stress simulation per package assembly process, reflow and temperature cycling for verifying the leadframe designs; (2) Bonder Equipment and process optimization though DOE experiments for eliminating leadframe oxidation and assuring the copper plated leadframe be workable; (3) Special through-gate design for increasing mold compound usage or yield; (4) Development of modeling and special de-gate tool design for broken the sub-gate to remove the leadframe warpage and coilset; (5) Special air blowing device design which was patented in China to stabilize thinner leadframe for passing through plating cells smoothly without leadframe jamming and damaging. The results show high density copper plated leadframe at more than 70mm width and less than 0.11mm thicknesses are applicable for mass production based on special assembly process design and development. It benefits with lower capital investment, leadframe cost saving, mold compound saving and lower production floor spacing.