Ning-Cheng Lee, Indium Corporation
Assembly of components with large pads such as high brightness LEDs often is soldered with preform, mainly due to a lower voiding and lower flux fume generated when compared with solder paste. This is particularly true when the joints are to be formed within a cavity. Although lower than solder paste, the voiding in the solder joint is still a concern for high reliability and high performance devices. In this study, voiding behavior of large pad devices was simulated with Cu coupon to Cu coupon sandwiches. Its assembly using flux coated preform was studied, with variation in solder alloy type, quantity of flux coated on solder preform, Cu coupon pre-oxidation extent, reflow temperature, and pressure exerted onto the sandwich during reflow. Voiding of Sn63 was the lowest, followed by 57Bi42Sn1Ag, with SAC305 being the highest. Higher oxidation caused a higher voiding. With increasing flux quantity, the voiding increased when reflowed at temperature below activation temperature, but decreased when reflowed at above activation temperature. With increasing reflow temperature, the voiding increased at low temperature range, then decreased due to better wetting, but increased again due to excessive outgassing. Higher pressure resulted in a lower voiding due to constrained mobility of liquid solder.
Dr. Ning-Cheng Lee, is the Vice President of Technology of Indium Corporation. In addition, he is also an SMTA Member of Distinction.
Dr. Lee has been with Indium Corporation since 1986. Prior to joining Indium, he was with Wright Patterson Air Force Base Materials Laboratory, Morton Chemical, and SCM. Dr. Lee has two decades of experience in the development of fluxes and solder pastes for SMT industries.
Dr. Lee has more than three decades of experience in the development of fluxes and solder pastes for SMT industries. Dr. Lee has more than 30 years of experience in the development of fluxes and solder pastes for SMT applications. In addition, he also has very extensive experience in the development of high-temperature polymers, encapsulants for microelectronics, underfills, and adhesives. His current research interests cover advanced materials for interconnects and packaging for electronics and optoelectronics applications, with emphasis on both high performance and low cost of ownership.
Dr. Lee received his Ph.D. in polymer science on structure-property relationships from the University of Akron in 1981, and a BS in chemistry from the National Taiwan University in 1973. He also studied Organic Chemistry at Rutgers University. He has served on the advisory boards of Soldering and Surface Mount Technology and Global SMT and Packaging magazines.