PCB surface finishing OSP is abbreviation of Organic Solderability Preservatives. It grows a layer of organic film on clean bare copper surface through chemical method.This layer film has features like anti-oxidation,heat shock,moisture resistance, it can protect the circuit board copper don’t be oxidized or vulcanized,etc.But the protective film must be cleared instantly in the subsequent high temperature welding,so that the exposed clean copper immediately combines into to a solid solder joints with melting solder in a very short time.

The process of OSP:

Degreasing—>Washing—>Micro-Etching—>Washing—>Pickling—>Pure water washing—>OSP—>Pure water washing—> Drying

OSP Principle:

An organic film is formed on the surface of printed circuit board,firmly protects the fresh copper surface,and also be anti-oxidation and pollution at high temperatures.OSP film thickness is generally controlled at 0.2-0.5 microns.

Features of OSP:

Good flat,no IMC between printed circuit board and OSP film.
Good wetting,allow welding of solder and circuit board copper direct welding.
Low cost,low temperature processing technology, it can reduce the use of energy when processing.
Extensive using, it can be used in low-tech circuit board,also be used in high-density chip package substrate.
The types of OSP

Rosin
Active Resin
Azole
Disadvantages

Appearance inspection is difficult,it doesn’t suit for multiple reflow(generally no more than three times)
OSP film is easy to scratch
Strict environment requirement for storage
Storage time is shorter
Storage method and time

Vacuum packaging for 6 months(temperature 15-35℃,humidity RH≤60%)

SMT site requirements

OSP Printed circuit boards should be stored in low temperature and low humidity(temperature 15-35℃,humidity RH≤60%),and avoid exposure to acid-rich environments.OSP packs are assembled within 48 hours after unpacking.
Suggest to use it in 48 hours and save it in a low temperature cabinet without vacuum packaging.
Suggest finish DIP within 24hours after two sides SMT(surface mount technology) completed.