Laser soldering for fine-pitch leads in SMT assembly

Abstract

This paper describes the development of a new laser soldering technique for surface mount assemblies. The new technique, using a focused YAG laser beam, has superior performance. It can be applied to tape carrier package (TCP) assemblies for fine pitch leads and offers a no-bridge soldering process.In this paper, the performance of the new technique is evaluated experimentally. First, the new technique is compared with the conventional laser-soldering technique for TCP assemblies, and the no-bridge soldering concept is proved. Second, to obtain more flexibility in assembly, the solder flow is investigated by beam scanning. The beam-resting time on the pads of the printed circuit board (PCB), is optimized by the theoretical and experimental analysis of the volume of melted solder. The reducing atmosphere (H2-N2gas) is considered to achieve a no-clean soldering process. From these experiments, the new laser soldering technique offers the ability to assemble high lead count, fine pitch ICs such as TCPs.This paper describes the development of a new laser soldering technique for surface mount assemblies. The new technique, using a focused YAG laser beam, has superior performance. It can be applied to tape carrier package (TCP) assemblies for fine pitch leads and offers a no-bridge soldering process.In this paper, the performance of the new technique is evaluated experimentally. First, the new technique is compared with the conventional laser-soldering technique for TCP assemblies, and the no-bridge soldering concept is proved. Second, to obtain more flexibility in assembly, the solder flow is investigated by beam scanning. The beam-resting time on the pads of the printed circuit board (PCB), is optimized by the theoretical and experimental analysis of the volume of melted solder. The reducing atmosphere (H2-N2gas) is considered to achieve a no-clean soldering process. From these experiments, the new laser soldering technique offers the ability to assemble high lead count, fine pitch ICs such as TCPs.