Soldermask, or solder resist, is a lacquer-like layer that provides a permanent protective coating for the copper traces of a printed circuit board (PCB) and prevents solder from bridging between conductors, thereby preventing short circuits. Soldermask was created primarily to facilitate wave soldering used in mass assembly.
The soldermask process includes a number of steps. After a pre-cleaning step, in which the printed circuit boards are degreased and the copper surface is either mechanically or chemically roughend, the soldermask is applied. There are several applications like curtain coating, screen-printing or spraycoating available. After the PCBs have been coated with soldermask, the solvent needs to be flashed-off in a tack-drying step. The next step in the sequence is exposure. In order to structure the soldermask, artwork (silverfilm or diazo) is used.The boards are exposed with a typical 360 nm lightsource. The exposed areas will polymerize while the covered areas will remain monomer. In the developing process the exposed areas are resistant, and the unexposed (monomer) areas will be washed out. The final curing (polymerisation) is done in a batch or tunnel oven. After the final curing, an additional UV cure may be needed for increasing the mechanical and chemical properties of the soldermask.
Main benefits :
- Cost-effective coating tailored to the customer's needs
- High quality soldermasks with good performance in final surface applications like ENIG and immersion Sn
- Excellent mechanical and chemical properties