Ball bumping and coining operations for TAB and flip chip

Abstract

The process of using a ball bonder to form bumps on a chip, for subsequent TAB or Flip Chip attachment to a substrate, has now reached the production stage. A number of companies are using the process for full scale production. Other companies are using the process for rapid prototyping and limited quantity production. The advantages of the ball bumping process are that it requires no expensive masks or wet processing. It also uses existing equipment, experienced personnel, and it has the flexibility and ease of manufacturing associated with wire bonding. The yields and reliability of wire bonding are well established, and the ball bumping process is the same as the ball bonding portion of the wire bond process. Similar yields are expected. In many cases ball bumping provides the most cost effective method for depositing bumps on chips. Two process variations are prevalent. 1. Bumping and coining, is a process where a normal ball bond with a short ductile fracture tip protruding from the top of the ball is bonded to the device. Optionally, the bumps are then coined flat by a second stage operation. 2. The stud bumping process produces a short loop with the crescent bond placed on the shoulder of the ball.