An organic solder mask is formed on the clean bare copper surface of the circuit board to protect the copper surface from oxidation, rust, heat shock, moisture resistance, and corrosion resistance. In the later soldering, flux is added and after the soldering is heated, This layer of film will evaporate, which is more convenient for welding. The thickness of OSP film is generally 0.2-0.5μm. Computer keyboard PCB and computer motherboard PCB, in many cases will choose OSP process, PCB area is relatively large, if you choose gold plating process, the cost is higher. It is estimated that 25-30% of PCBs currently use OSP, and its process control is easier than other surface treatments. If the PCB surface does not require connection functions or the storage period is too long, OSP is an ideal choice.

(1). OSP Function:

Protect the surface of bare copper from oxidation, rust, heat and thermal shock, moisture resistance, and corrosion resistance.
(2). Advantages& disadvantages:

1). Good coplanarity, can be used on high-density PCB;

2). It can pass the RoHS standard and can be stored for 6 months in vacuum packaging (environmental temperature 15-35℃, environmental humidity RH≤60%);

3.)Lower cost than HASL

4). The surface is flat and the weld-ability is good (in the case of not being oxidized)

Disadvantages:

1). OSP is transparent and colorless, it is difficult to distinguish whether OSP has been applied;

2) The OSP film surface is easy to scratch, and the storage environment requires high (keep away from acidic environment);

3). Compared with ENIG and HASL, the storage time is also shorter;

(3). Process flow:

Remove oil→Water washing→Micro Etching→cleaning with pure water→Pickling→cleaning with pure water→OSP→washing with pure water→drying