Wire bonding-towards 6- sigma yield and fine pitch

Abstract

The author describes the problems as well as the solutions required to wire bond high lead-count chips to their packages at the required high yields. the elements for achieving 6 sigma wire bond yields can be summarized as follows: (1) the choice of metallization on the chip as well as on the package is critical; (2) an appropriate cleaning procedure (which in some circumstances may be at the wafer level) and/or special storage and shipping containers are necessary: (3) factorial bonder setup and proper bond test methods are required; (4) uniform, reproducible wire and bonding machine characteristics are essential; and (5) both the chip bond pads and the package pads must be designed with full awareness of the limitations and tolerances of the chosen bonder and its bonding method. Wafer-testing probe cards currently limit the minimum wire bond pad pitch on high-end devices to about 100 mu m. However, 75- mu m pitch wedge bonding can be performed with current (modified) autobonders, and 40- mu m pitch bonding has been reported. Almost every aspect of fine-pitch bonding requires more planning and coordination and is more expensive to achieve than bonding at normal pitch. >