PCB surface finish - OSP

OSP (Organic Solderability Preservative) stands for organic solderability protective film, which is a kind of printed circuit board surface treatment technology. The following is a detailed introduction:

OSP is a process of applying a very thin organic coating on the copper surface of the PCB. This coating can form a stable chemical bond with the copper surface to form a protective film. This film has anti-oxidation, heat shock resistance, and moisture resistance. It can protect the copper surface from rusting in a normal environment, but in the subsequent high temperature of welding, it can be easily removed by the flux quickly, so that the exposed clean copper surface can be immediately combined with the molten solder in a very short time to form a solid solder joint.

Process flow

Degreasing>Secondary water washing>Micro etching>Secondary water washing>Acid washing>DI water washing>Filming air drying>DI water washing>Drying

1. Degreasing: Remove oil stains on the surface of the PCB to ensure the quality of subsequent film formation. The degreasing effect directly affects the uniformity of the film thickness.

2. Secondary water washing: Wash away the degreasing agent and surface impurities.
3. Micro-etching: forming a rough copper surface, which is convenient for film formation. The micro-etching thickness is generally controlled at 1.0-1.5μm.
4. Secondary water washing: washing the micro-etching solution to prevent it from affecting the subsequent film formation.
5. Pickling: further removing the surface oxide layer and improving the activity of the copper surface.
6. DI water washing: using deionized water for washing to prevent impurities in the water from contaminating the film-forming solution.
7. Film-forming air drying: immersing the PCB in the film-forming solution, controlling the film-forming time and temperature, so that a uniform organic protective film is formed on the copper surface, and the film thickness is generally controlled at 0.2-0.5μm3.
8. DI water washing: washing away the residual film-forming solution on the surface, the pH value should be controlled between 4.0-7.0.
9. Drying: removing the moisture on the surface of the PCB to obtain the final OSP-treated board.

Advantages

1. Good solderability: OSP coating can effectively protect the copper surface, maintain good solderability, facilitate the welding process of electronic components and PCBs, and reduce the occurrence of welding defects.
2. Low cost: Compared with some other surface treatment processes, the material cost and processing cost of OSP process are relatively low, which helps to reduce the production cost of PCBs.
3. Simple process: OSP process is relatively simple, does not require complex equipment and multiple process steps, can improve production efficiency and reduce production time.
4. Good flatness: It can maintain the flatness of the copper surface, which is beneficial to subsequent welding and assembly processes.
5. Good heat shock resistance: Suitable for lead-free process and single and double-sided board processing, and compatible with any solder.
6. Environmental protection and energy saving: No toxic substances are involved, less pollution, easy to automate production lines, and less energy is used during processing.

Disadvantages

1. Limited shelf life: OSP coating has a certain shelf life, generally can be stored for 6 months under vacuum packaging. Over time, the coating may be damaged or the protective effect may be reduced. Therefore, PCBs treated with OSP need to be soldered in time.
2. Sensitive to high temperature and high humidity: OSP coating is sensitive to high temperature and high humidity environment, which will affect its protective effect and solderability.
3. Not suitable for some high-end applications: In some high-end electronic products that require high reliability and long-term stability, the OSP process may not meet all requirements.
4. Poor wear resistance: OSP is relatively thin and is easily scratched and worn.
5. Difficult to detect: The OSP layer is transparent, and it is difficult to tell whether the PCB has been coated with OSP, which increases the difficulty of quality control during the production process.
6. Inconvenient electrical testing: OSP itself is insulated and non-conductive. When conducting electrical testing, the test point must open the steel mesh and print solder paste to remove the original OSP layer before contacting the pin point for electrical testing.

Application:

1. Consumer electronics: such as mobile phones, computers, TVs and other products. These products require good solderability and relatively low production costs, and OSP PCBs can meet these requirements.
2. General electronic products: such as household appliances, toys, electronic tools, etc. This type of product does not have particularly high requirements for reliability and service life, and OSP PCB can be used to reduce costs.
3. Communication equipment: PCB boards in equipment such as base stations, routers, and switches.
4. Automotive electronics: PCB boards in engine control units, in-vehicle entertainment systems, etc.