Advanced Wire Bonding Technology: Materials, Methods, and Testing

Wirebonding is the most dominant form of first-level chip or integration circuit interconnect method used throughout the world-wide electronics industry today. Many trillion of wirebonds are made annually using automated machines. Wirebonding is reliable, flexible, and low cost when compared to other forms of first-level microelectronic interconnection. Failures are typically at the single digit parts per million level or below. As the number of interconnections on the integrated circuit grows with increased functionality, the bonding pads are becoming much smaller and closer together. Similarly rigid inorganic substrates and package structures have given way to their more flexible organic counterparts. Everywhere in the microelectronic industry new applications, materials, and structures are appearing and challenging the performance and, hence, the dominance of wirebonding. This chapter focuses on the basic wirebonding methods, the materials, and the testing techniques required to produce high quality wirebonds. It addresses the organic substrate problem, stacked chip bonding, and interconnection over extreme temperature ranges. Reliability of the wirebonded interconnect is explored along with testing and control methods designed to improve bond quality. High frequency bonding and the bonding to soft substrates are given special attention. Wire properties are considered along with the changing bond shapes and sizes as the number of chip’s inputs and outputs increase. Methods for chip bumping using a wirebonding machine are also presented.