Practical application of laser soldering in electronics assembly

The use of laser energy to heat solder joints, although not a new technique, is one which now has the potential to make a major contribution to certain aspects of electronics manufacturing. This increased applicability is a result of both improved laser technology, and in particular the availability of low cost, high power, semiconductor lasers, and a greater understanding of the way in which laser energy interacts with materials used in soldering. This paper considers the requirements for a typical laser soldering system and the types of laser which may be used, with particular emphasis on the relevant characteristics of semiconductor lasers. It then considers the ways in which laser energy interacts with the different materials used and how heat is transferred within joints. It is shown that an understanding of the heat transfer processes is essential to the successful application of the technique. The range of applicability of laser soldering is illustrated by the description of three industrial laser soldering systems developed by the authors and by consideration of the potential for future applications.