How to Choose Ssurface Treatment Process (2)

3. Electroless Nickel/Immersion Gold
The process of electroless nickel/immersion gold is different from organic coating. It is mainly used on boards that have functional requirements for connection and a longer storage period, such as mobile phone keypads and router housings. The edge connection area of ​​the chip processor is elastically connected to the electrical contact area. Due to the flatness problem of hot air leveling and the removal of organic coating flux, electroless nickel/immersion gold was widely used in the 1990s. Later, due to the appearance of black disks and brittle nickel-phosphorus alloys, electroless nickel plating, the application of immersion gold process has decreased. But at present, almost every high-tech PCB factory has electroless nickel plating/immersion gold wire. Considering that the solder joints will become brittle when removing the copper-tin intermetallic compound, there will be many problems in the relatively brittle nickel-tin intermetallic compound. Therefore, portable electronic products (such as mobile phones) almost all use copper-tin intermetallic compound solder joints formed by organic coating, immersion silver or immersion tin, and electroless nickel/immersion gold is used to form the key area, contact area and EMI shielding area. It is estimated that about 10%-20% of PCBs currently use electroless nickel/immersion gold processes.

4. Immersion Silver
Immersion silver is cheaper than electroless nickel/immersion gold. If the PCB has connection functional requirements and needs to reduce costs, immersion silver is a good choice. Plus the good flatness and contact of immersion silver, then should choose immersion silver process. There are many immersion silver applications in communication products, automobiles, and computer peripherals, and immersion silver has also been applied in high-speed signal design. Because immersion silver has good electrical properties that other surface treatments cannot match, it can also be used in high-frequency signals. EMS recommends using the immersion silver process because it is easy to assemble and has better checkability. However, due to defects such as tarnishing and solder joint voids, the growth of immersion silver has been slow (but not decreased). It is estimated that about 10%-15% of PCBs currently use the immersion silver process.

5. Immersion Tin
Tin has been introduced into the surface treatment process in the past ten years, and the emergence of this process is the result of the requirements of production automation. Immersion tin does not bring any new elements into the solder joints, which is especially suitable for backplanes for communication. Tin will lose its solderability beyond the storage period of the board, so immersion tin requires better storage conditions. In addition, the immersion tin process has been restricted in its use due to the carcinogenic substances contained in it. It is estimated that about 5%-10% of PCBs currently use the immersion tin process.

Concluding Remarks:
As customer requirements are getting higher and higher, environmental requirements are getting stricter and more and more surface treatment processes are increasing. In the end, the choice of surface treatment process with development prospects and greater versatility seems to be a little bit Dazzling and confusing. Where the PCB surface treatment process will go in the future cannot be accurately predicted now. In any case, meeting customer requirements and protecting the environment must be done first!