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.

Soldering is different from welding as the parent metal is not melted in soldering. Only the filler metal melts and on solidification, it forms a joint whereas in welding both the parent metals melts and forms a weld pool. This weld pool upon solidification forms a tough joint which is as strong as the parent metal itself. In past, lead based filler metals were used, but currently, lead free filler metal is used in the wake of eco-friendly technological advancement.

Soldering finds application in plumbing, metal working, electronics and jewelry. Soldering gives an option to reverse the connection between copper pipes in plumbing system as it can be reversible even though they act as permanent joints. It is used in sheet metal industry for manufacturing food cans, rain gutters, roof flashing and automobile radiation industry.

Silver soldering process, a higher temperature laser soldering process, is used to assemble and repair jewelry components, machine tools and some plumbing and refrigeration components. Soldering can also be used to make a semi-permanent patch to stop the leakage in containers. Laser soldering is also used to solder minute electrical circuits in the printed circuit boards with accuracy.

Laser soldering is a very good example of technological advancement when it comes to comparing it with the other conventional processes. Conventional cutting takes a lot of time as either it is manual or it requires manual monitoring where as laser soldering takes almost no time to perform its task. It is easy to operate and the accuracy level of this machine is very high. The error band of laser soldering is very thin and the accuracy level of conventional process is beyond comparison when it is compared to the laser soldering process. The accuracy level of laser solder is close to unity where as the conventional processes have a decent accuracy of more than three-fourth of unity.

Laser solders can perform very minute operations to huge operations with same efficiency where as conventional processes need specialized workmanship for each sort of soldering. The lasers can solder in any axis and can draw any design, however complex it may be but it is quite impossible for non mechanized techniques to create some of these designs on the workpiece.

Laser solders are economical when it comes to calculate the operating cost. The manual workmanship charge is higher than a skilled operator of the laser soldering machine. Overall a laser solder is accurate, versatile, economical, technically advanced, has better performance, takes less time and is clean in operation.

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