Paper Title
Method for Controlling the Circular type Micro Hole Size on Stainless Steel Thin Film by Photoresist Etching

Fast development of wafer level packing (WLP) in recent years is mainly owing to the advances in integrated circuit fabrication process and the market demands for devices with high electrical performance, small form factor, low cost etc. Evaporating and electroplating are the two wafer solder bump processes in production today. Evaporating is high cost, and can not produce eutectic solder bumps due to the Sn and Pb vapor pressure difference. Electroplating is a relatively low cost option, but it requires photoresists steps that add to the cost and plated bump composition is not easy to control due to differences in Sn and Pb electrochemical behavior. Stencil print technology is a well established process used in surface mount board assembly. Technology advances in solder paste, stencil fabrication, and printing equipment make it possible to print Sn/Pb solder paste onto wafer to form bumps. Nowadays, there are three types of stencils available, chemical etching, laser cut and electroformed. Chemical etch stencils are cheap, but has the dimension and accuracy limitation. In this study, for improving the dimension and accuracy of stencil hole size, the etching conditions and methods for controlling the circular type micro hole size on 50μm thickness stainless steel has been investigated. For controlling the machined hole size with etching method, the relationship between dry film photoresist coating size after exposure and development and machined hole size has been compared. And also, the hole size machining limitation of etching method has been confirmed. Keywords - Stencil Printing, Stencil Mask, Stainless Steel Thin Film, Etching