Au-Sn microsoldering on flexible circuit

Portable communication products such as cellular phones and pagers are changing rapidly towards product miniaturization. With the increased product complexity and features, this leads to the requirement for higher density IC packaging. This fine-pitch high-density IC packaging requires very fine line substrates and current rigid board PCBs are not able to meet this requirement. Chip-on-film (COF) is one of the latest flip-chip technologies which offers fine-pitch mounting capability on a flexible substrate. This technology is able to meet the requirements of a low-cost fine-pitch assembly. This paper discusses the COF technology using the Au-Sn micro-soldering method and its application to displays and semiconductor packaging such as chip-scale packaging (CSP). The challenges of this interconnect technology, encompassing the bonding of the gold-to-tin metallurgy, bumping specifications and substrate plating requirements, is discussed. Reliability testing is also presented and discussed.