Printed circuit boards must be protected in several ways to ensure their effective performance. Since copper tends to be oxidized in the air, it is difficult to bond with solder and the conductive quality is lowered as the same time. Thus solder mask is widely used as a cheap way to cover untapped copper surfaces on PCB with the help of resins and paints.
PCB tinning is the process of applying a layer of tin on copper traces to prevent any possible degradation. Tin plating also helps to mask copper traces when the circuit board is etched. By doing this, the manufacturing process is simplified and unwanted etching is prevented thanks to the industrial process use highly concentrated solvents like sodium sulphate.
PCB tinning is able to increase the current carrying capacity of traces for high-power rails. Choosing a thicker copper cladding for smaller high-current areas can make the circuit board more expensive. So PCB tinning is ideal for bridging high current paths. It is mainly done by concentrating the deposition with solder on a specific area.
PCB tinning process uses pure tin, or solder with a 60:40 mixture of lead and tin.
There are many ways to tin a printed circuit board, but the most common one is to place the circuit board in a tin plating solution and introduce the tin electrode into a controlled current plating process. The second coating is done after the last fabrication step.
The solder layer can be deposited either by hand or by a hot solder extruder that can deposit the solder blob on to the area. Tin itself will oxidize when exposed to the outside environment and therefore can not completely and reliably keep the printed circuit board unmasked, thereby applying a solder mask is necessary.