In order to solder the tab ribbons to the solar cell, PV manufacturers apply soldering flux to the tab ribbon. This is done to remove any oxidation and it will make sure that the ribbons will stick to the solar cell perfectly. On the photo below you see tab ribbons in a bath of soldering flux.
The cells are soldered to a 160 μm x 1.6 mm copper ribbon with SnPbAg-coating in a commercially available tabber stringer. The soldering method is infrared soldering. The strings are cut into single soldered cells to obtain 40 solar cells. The rear side of the each cell is attached to a rigid substrate to avoid cell cracking at high peel forces.
The first test to qualify the interconnection of crystalline silicon solar cells after soldering is the peel test. The interconnector ribbons are peeled off from the solar cell measuring the force. This easy and fast method is used to accept or reject new cells in a module production line and to optimize the soldering process of a tabber stringer.
As mentioned above, it depends on the melting temperature of the solder on the tab ribbons. The hotter the soldering iron, the faster you can work. However, it is important not to overheat the solar cells, which will make the cells brittle and will definitely damage the cell.
In this research, we develop eddy current soldering as a non-contact soldering technique for tabbing the ribbon of PV cells under a layer of glass. The performance of eddy current soldering was studied in detail by changing an induction coil distance to the treated sample from 2 to 4 mm and varying exposure time.
J. Wendt et al., "Improved quality test method for solder ribbon interconnects on silicon solar cells", 12th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm), (2010).