Introduction of PCB OSP surface treatment

What is the OSP process principle?

OSP means organic copper surface protector. 

The principle of the process is to form a protector coating film through a chemical reaction with imidazole and the surface of the metal copper. It is a uniform, extremely thin, transparent organic coating, the coating has excellent heat resistance, the thickness of the protective film is usually 0.2-0.5μm.

At present, SYS Tech requires that the thickness of OSP can meet the requirements of twice reflow soldering and once wave soldering. PCB Manufacturers normally do 0.2~0.35μm thickness OSP. During soldering, the protective film decomposes, volatilizes, and melts into the solder paste or acid flux, exposing the copper surface, making the solder and clean copper reacts. Because of its low production cost and mature technology, it has been widely used.

Advantages of OSP process

flat and cheap, OSP only loves copper surfaces, it has no affinity for other surfaces such as solder mask, and will not adhere to its surface, so it is widely used.

Disadvantages of OSP process

① The storage time is short, and the storage period is 3 months under vacuum packaging conditions. When storing, keep away from acidic substances and the temperature should not be too high, otherwise it will volatilize.

② Difficult to detect, colorless and transparent.

③ OSP itself is insulated, and Imidazole OSP forms a thicker coating, which will affect electrical testing and cannot be used as a coating for electrical contact surfaces such as golden fingers, keyboard keys, test points, etc.

④ Reflow soldering cannot be performed multiple times, generally 3 times. It needs to be considered in double-sided reflow soldering and rework. After several generations of improvements, its heat resistance, storage life, and flux compatibility have been greatly improved.

⑤ The soldering temperature is relatively increased to 225℃, and a stronger (acidic component) flux must be added to eliminate the protective film during the soldering process, otherwise it will cause soldering defects.

Applications of OSP process

OSP process (Organic Solderability Preservatives) has a wide range of applications in the field of electronic manufacturing, mainly used for surface treatment of printed circuit boards (PCBs). The OSP process forms a thin and uniform organic protective film on the surface of the PCB to improve its solderability and oxidation resistance.

⑴ Multilayer PCB board: Multilayer PCB boards usually have complex circuit structures and high densities. OSP coating can protect exposed copper wires and provide good soldering performance.

⑵ Ultra thin PCB board: commonly used in mobile devices, tablets, and other small electronic devices, OSP coating can provide protection and soldering performance.

⑶ Flexible PCB board: Used in applications that require bending or folding, OSP coating can provide a thin protective layer and has good solderability.

⑷ Consumer electronics and communication equipment: OSP technology is widely used in the field of consumer electronics and communication equipment, and can meet the assembly needs of general electronic products.