Novel Wet-Chemical Processing for Sidewall Plating of High Reliability Bottom-Terminated Packages

The use of bottom-termination IC packages, like Quad-Flat No leads (QFN) devices in the automotive industry grows rapidly. The high automotive reliability standards require tin solder plating on the copper sidewalls exposed after singulation of a QFN lead frame. Without a wettable flank, a solder fillet does not form, which reduces the solder joint reliability and impedes automatic optical inspection. This contribution presents novel wet chemical processes addressing failure modes and reliability issue in current approaches for exposed sidewall tin plating of bottom-terminated packages. Firstly, a wet-chemical deburr process compatible with high through-put continuous tin electroplating to reduce tin flaking solderability failures due to roughness and burr formation during step-cut singulation. Secondly, an autocatalytic immersion tin process achieving a 2–3 µm tin layer that passes industrial solderability standards.