Effect of Dry Degumming and Wet Etching Process on Uniformity of Solder Bumps Height and Size

摘要

One of the important developments to reduce cost and manufacturability in integrated circuits is the solder bumps technology applied in flip chip, in which reliability is especially important. The uniformity of solder ball shape must be closely monitored during production, which is a basic requirement for high-quality solder bumps manufacturing processes and is a controlling factor for interconnection yield during flip chip assembly. In this paper, we use a commonly used plating deposition solder process with a polymer photoresist mask to control volume and alignment and the bumps after plating are reflowed to form solder bumps. The subsequent etching uniformity is improved by increasing the wet degumming time to fully degumming. The etching rate is accelerated by adding dry degumming before etching and undercuts caused by overetching are prevented from subsequent nonuniformity of solder bumps. The interface of the solder bumps was studied by scanning electron microscope and focused ion beam analysis. The results show that the dry degumming and wet etching process improve the solder bumps process and significantly improve the uniformity of solder bumps height and size. Automated Optical Inspection shows the yield of solder bumps effected by dry degumming and wet etching process is up to 99.5 %. The solder bumps shear test shows strength of the solder bumps effected by dry degumming and wet etching process passes the industry standards , which is over 2.5 g/mil²。