Laser soldering is a method of joining two strips of a metal with the help of another filler metal which has lower melting point than the strips. The parent strips do not melt in this process where as the filler metal melts and appends the two strips after solidification.
In laser soldering, a 30-50 W laser is used to melt the electric connection junction and solder it with the help of diode laser systems which are based on semiconductor junctions. It was patented by Suzanne Jenniches in 1980.
The wavelength of laser lies between 808 nm and 980 nm. An optical fiber of diameter 800 µm or smaller is used to deliver the beam to the workpiece. As soon as the beam comes out of the fiber, it diverges rapidly. To control this divergence, lenses are used to focus the beam coherently onto the workpiece at a suitable working distance. Solder filler is supplied to the setup with the help of a wire feeder.
Soldering can be done on both lead-tin and silver-tin arrangement. The process differs on the basis of the composition of the alloys. Power level of 10 Watt for about 1 second is adequate for soldering on chip carriers. Incomplete wetting and void formation takes place when low power level laser is used. These defects can weaken the joints and reduce the efficiency of the product.