A brief introduction of Surface treatment Technology for PCB OSP

     OSP is on the clean surface of bare copper, chemical method to grow a layer of organic film, this film has oxidation resistance, heat shock resistance, moisture resistance. Used to protect the circuit board copper surface in the normal environment no longer oxidation or vulcanization and so on; However, in the subsequent welding high temperature, the protective film must be easily removed by the flux, so that the exposed clean copper surface can be immediately bonded with the molten solder to form a solid solder joint in a very short period of time.


       1. Process: deoiling. →Water washing. →Micro erosion. →Water washing. →Pickling. →Pure water washing. →OSP. →Pure water washing. →Dry.

       2. Principle: a layer of organic film is formed on the copper surface of the circuit board, which firmly protects the fresh copper surface, and can also prevent oxidation and pollution at high temperature. The thickness of the OSP film is generally controlled at 0.2-0.5 μ m.

       3. Features: smooth surface, no IMC is formed between OSP film and circuit board copper pads, allowing welding solder and circuit board copper welding (wettability), processing technology of low temperature, low cost (less than HASL), the processing of less energy use can be used in low technology and so on. The content of the circuit board, but also can be used in high density chip package substrate.

       4. OSP material type: Rosin. OSP materials used in deep coupling circuits are currently the most widely used azoles.

       5. Insufficient: (1) the appearance inspection is difficult and is not suitable for multiple reflow welding (general requirement is three times);(2)The surface of 2OSP film is vulnerable to scrape (3) the requirement of storage environment is high; (4) short storage time;

      6, storage mode and time: vacuum packaging for 6 months (temperature 15-35 ℃, humidity RH ≤ 60).


The advantages of OSP can be summarized as:

• Simple process and reusable: PCB manufacturers can easily change OSP coated boards so that once the PCB assembler finds that the coating is damaged, it can use a new coating.

• Good wettability: OSP coated sheets perform better in solder wetting when flux encounters vias and pads.

• Environmentally friendly: Because waterborne compounds are used to generate OSP, they do not pose a hazard to the environment and only fall into the green world. Therefore, OSP is consistent

The best choice for electronic products such as RoHS.

• PCB cost effectiveness: Due to the simple compounding and simple manufacturing processes used in the OSP manufacturing process, OSP is very costly in all types of surface treatments. Its formation

This is lower, resulting in a lower cost of the final board.

• Reflow soldering of double-sided SMT assembly: With the continuous development and advancement of OSP, it has been accepted by single-sided SMT assembly and double-sided SMT assembly, greatly expanding its application fields.

• Solder mask ink requirements are lower

• Long storage time