Advantages and disadvantages of OSP surface treatment

OSP namely Organic Solderability Preservatives, the biggest advantage of an OSP finished board is the price. OSP boards tend to be cheaper than those fabricated with other surfaces such as HASL, Immersion Tin, Immersion Silver or ENIG. Another advantage that OSP has, particularly as compared to HASL finished boards, is the flatness of the pads.

The primary drawbacks are related to solderability, shelf life, re-use of misprinted boards, and multiple heating cycles. The solderability/shelf life is the issues need to be considerate for OSP PCB; if the OSP degrades through shelf life (typically less than 1 year), the Copper underneath oxidizes fairly easily and prevents the board from being generally easy to solder. If the PCB passed 6 months after manufacturing, then it should be baked before SMT.

The re-use of misprinted boards can also be an issue with OSP since alcohol and other solvents used to clean misprinted boards will also remove the OSP, leaving the Copper surface very easy to oxidize. Misprinted boards that are cleaned need to be sent back through the print/place/reflow processes quickly to avoid this issue.

Finally, OSP boards can be susceptible to solderability problems when subjected to multiple heating cycles; this occurs as a result of the OSP itself being degraded by the heating processes.