Organic Solderability Preservative
OSP is a water-based, organic surface finish that is typically used for copper pads. It selectively bonds to copper and protects the copper pad before soldering.
Advantages: simple process, very smooth surface, suitable for lead-free welding and SMT. Easy rework, easy production operation, suitable for horizontal line operation. Boards are suitable for multiple processes (e.g. OSP+ENIG). Low cost, environmentally friendly.
Disadvantages: limited number of reflow soldering (multiple welding thickness, film will be damaged, basically no problem for 2 times). Not suitable for compression bonding technology, wire binding. Visual inspection and electrical inspection are inconvenient. N2 gas protection is required for SMT. SMT rework is not suitable. Storage requirements are high.
Immersion Tin (ISn) is a good surface finish for planar, fine pitch products and is popular with press fit and backplanes.
Advantages: suitable for horizontal line production. Suitable for fine line processing, lead-free welding, especially for compression welding technology. Very good flatness, suitable for SMT.
Disadvantages: good storage conditions are required, preferably no more than 6 months to control tin whisker growth. Not suitable for contact switch design. In the production process, there is a high requirement for the soldering film process, otherwise the film will fall off. N2 gas protection is preferred for multiple welds. Electrical measurement is also a problem.