OSP Process of PCB Board
Organic solderability preservative, abbreviated as OSP, is known as anti-oxidants in the PCB industry. The general OSP composition includes alkylbenzimidazole, organic acids, copper chloride, deionized water, etc.
Limitations of OSP are listed as follows:
1.OSP is transparent and colorless, so it is difficult to check. It is also hard to distinguish whether a PCB board is coated OSP or not.
2.OSP itself is insulated, it does not conduct electricity. OSP of Benzotriazoles type are relatively thin thus may not affect the electrical test, while for OSP of Imidazoles type, the final protective film is thicker which can affect the electrical test.
3.OSP requires a stronger Flux when soldering, otherwise the protective film can not be removed which may result in soldering defects.
4.In the storage process, OSP surface can not be exposed to acidic substances, the temperature can not be too high, otherwise OSP will evaporate.
OSP process of PCB board: oil remove-> secondary washing-> micro etching-> secondary washing-> pickling-> DI washing-> film drying-> DI washing-> drying
Of course OSP also has its shortcomings like various actual formulations, different performance, etc. This means that the supplier's certification and selection work needs to be done well. The OSP technique has no IMC isolation of other materials between the Cu of the pad and the Sn of the solder. In lead-free technology, SnCu in solder joints with high Sn content increases rapidly which affects the reliability of solder joints.