Metallographic analysis of laser soldered chip resistors

During the last decade laser material processing has been used in more and more fields of electronics technology. Among these techniques laser soldering processes showed great improvements and they offer several advantages mainly in terms of localized heating, rapid rise and fall in temperature, non-contact and easily automated process. This paper presents a systematic experimental investigation, which was aimed at finding relation between the most significant laser soldering parameters (soldering time and average power) and the intermetallic layer thickness and the microstructure of the solder joint. We applied defocused frequency tripled Nd:YAG laser beam on simple SMD chip resistors. The solder joints were qualified by resistance measurements, X-ray micrographs, shear tests, and the microstructure of the solder joint was analyzed with SEM on cross-section samples.