Organic solderability preservative

Organic solderability preservative or OSP is a method for coating of printed circuit boards. It uses a water-based organic compound that selectively bonds to copper and protects the copper until soldering.
The compounds typically used are from the azole family such as benzotriazoles, imidazoles, benzimidazoles. These adsorb on copper surfaces, by forming coordination bonds with copper atoms and form thicker films
through formation of copper (I) – N–heterocycle complexes. The typical film thickness used is in the tens to hundreds of nanometers.