Solder alternative: contact resistance improvements for SMCAs. II

Surface Mount Conductive Adhesives (SMCA) provide an alternative to traditional solders currently used in the electronics industry. SMCAs currently show a benefit over solders on temperature sensitive substrates, in fine pitch applications, and in thermal cycling performance. The two major limitations of SMCAs have been their instability on common electronic metals such as copper and tin/lead solder and their performance under impact testing. Much progress has been made in identifying the causes for these limitations. Recent experimental work published by National Starch Corporate Research in collaboration with Georgia Institute of Technology has shown that the unstable contact resistance of SMCAs on copper and solder is due to electrochemical corrosion of these metals under adverse conditions. Emerson and Cuming has used this information to develop some new silver filled adhesives which show exceptional contact resistance on previously unstable metal surfaces. These surfaces include OSP copper, tin/lead alloys and even 100 percent tin. In the process of this development, various tests have been run using actual boards and components to validate these findings. In the area of impact testing or drop test performance, much progress has also been made. Early work within the National Starch companies discovered new methods for improving the impact performance of these SMCAs. However, these early materials exhibited a drop in contact resistance performance. Recent advances in contact resistance have now been incorporated along with the advances in impact performance to create novel materials. These novel materials exhibit both improved contact resistance as well as improved impact resistance. This report is the second update on progress made in the development of novel SMCAs