OSP (Organic Solderability Preservatives), Chinese translation for organic solder protection film, also known as copper protection agent and anti-oxidation. It is a kind of surface treatment in order to protect the copper surface of the solder joint with good soldering performance during the production of the circuit board.

Simply put, OSP is to chemically grow an organic film on the clean bare copper surface. This layer of film has anti-oxidation, thermal shock, moisture resistance, to protect the copper surface from rusting (oxidation or vulcanization, etc.) in the normal environment; that is to say, this layer of organic film can resist the attack of moisture in the air , can withstand the test of high temperature, and maintain good activity, easy to be dissolved and broken by flux, and can maintain good tinning ability.

And there will be no residue. However, in the subsequent high temperature of soldering, this protective film must be easily and quickly removed by the flux, so that the exposed clean copper surface can be immediately combined with the molten solder to form a strong solder joint in a very short time.