Soldering with solid state and diode lasers: Energy coupling, temperature rise, process window

The increasing number of electrical contacts in automobiles in combination with more complex and miniaturized components leads to higher requirements for the joining technologies. In that context, laser soldering represents an interesting alternative to conventional techniques. So far, solid state lasers [Nd:yttrium–aluminum–garnet (YAG)] and CO2 lasers have been successfully applied in industrial production. Recently, the development of high power diode lasers has offered a new laser source for soldering with technological advantages. Absorptivity of laser radiation on metals, generally increases with shorter wavelength and, consequently, diode lasers may lead to a higher process efficiency compared to Nd:YAG lasers. The absorptivity of copper alloys with different surface conditions has been measured at 808 nm (diode) and 1064 nm (Nd:YAG). When heating up the solder joint, the intensity distribution of the different laser spots becomes important, too. This effect is demonstrated by means of process modeling and temperature measurements for a typical joint geometry. For the case of soldering strip-to-strip joints, the effects of the different energy absorption on the process are pointed out.