SGER: High Temperature Pb-Free Joints for Flip Chip Technology

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This small grant for exploratory research (SGER) award by the Division of Materials Research to University of California is to study new approaches to replace high lead solder joints. By designing an ultra-fast reaction between the lead-free eutectic Tin-Silver-Copper (SnAgCu) solder and Palladium (Pd), an intermetallic joint of Palladdium-Tin compound can be formed that has the high melting point required by industrial processing. The intermetallic joint can be formed by a reflow step at a temperature of 250o C, and after the joint is formed, it will not melt at 250o C. The innovative concept is that in forming the intermetallic joint an ultra-fast reaction between eutectic SnAgCu solder and Pd is used and a joint of 50 to 100 micron size is formed at 250o C in just a few minutes. After formation, there no solder left. Since this type of joint has not been studied before, this is considered to be a high-risk project. Due to environmental concerns, there are four anti-lead bills pending in the US Congress. One of them is from the Environmental Protection Agency (EPA). The European Union has already passed a law to ban the use of lead in electronic products by July 1, 2006. In mainframe computers, a high melting point (above 300o C) high-lead (97Pb3Sn) solder has been used to connect silicon chips to ceramic modules. The National Electronic Manufacturing Initiative (NEMI) has recommended eutectic SnAgCu solder to replace low temperature eutectic SnPb solder, but there is no lead-free solder available to replace the higher temperature 97Pb3Sn solder. For this reason, the US mainframe computer companies have obtained an exemption from the EPA to continue the use of high-lead solder in manufacturing until 2010. This situation has resulted in an urgent need to develop a high temperature lead-free solder. Research on this problem could impact the future of our information technology and enhance US leadership in global competition in high-end technology. From an educational point of view, the SGER project supports two domestic students, including a female student.