Fabrication on uniform plating-based flip chip solder bumps after reflow process using a polishing mechanism

Abstract: This paper presents an innovative polishing process aimed at leveling rough surface of plating-based flip chip solder bumps so as to get uniform coplanarity across the whole substrate after both electroplating and reflow processes. This polishing mechanism is characteristic of combining mechanical-dominated polishing force with slight chemical reaction together. A large number of extremely but inevitably rugged mushroom-like structures after electroplating are drastically smoothed down with the help of this newly-developed polishing process. Nearly 70μm solder bumps in height with two different profiles as square and circle on the substrates reach as flatly as ±3μm between different substrates after reflow process; ±2.5μm in single substrate; and even ±1μm in die, respectively. Besides, surface roughness among the solder bumps is simultaneously narrowed down from Ra 0.6 to Ra 0.03 along with the coplanarity improvement. Excellent uniformity and smooth surface roughness in solder bumps are absolutely beneficial to pile up and deposit in the following steps in MEMS and semiconductor fields. [Copyright &y& Elsevier]