PCB Surface Treatment——Immersion Silver

　　As an environmentally friendly surface treatment process, Immersion silver is to deposit a layer of silver with a thickness of 6-18u” on the surface of copper to ensure the reliable soldering of electronic devices on the circuit board.

　　Immersion silver is a process carried out after electrical and visual inspection. The specific process is as follows:

　　Immersion Silver Process:

　　The Advantage of Immersion Silver: The thickness of the sinking silver has a protective function on the copper surface. Immersion silver can provide superior and reliable welding points for lead-free soldering; it has good corrosion resistance and low ion pollution; It cost less than the ENIG process and it’s flatter than the tin-plated surface. Its flat surface is suitable for the production of high-density circuit boards, SMT (Surface Mount) with dense pitch, BGA (Ball Grid Array) and direct wafer mounting. And immersion silver’s process is simple. Its contrasting color makes it easy to check, and it is also a natural alternative to HASL in soldering. Based on these advantages, immersion sliver is more used in the surface treatment of PCBs.

　　The Disadvantages of Immersion Silver: It cannot be exposed to sulfur-containing substances. Its surface is easily contaminated and discolored, which will affect the welding performance and its appearance, and may be silver migration.

　　Common Problem Analysis and Processing:

　　Causes of contaminated exposed copper: Glue, grease

　　Improvement Method: 1. Avoid adhesive tape on the board surface and use clean rubber separator in each process ; 2. Clean equipment (e.g. beer machine, E-TEST) before making immersion silver PCB; 3. Soak the board with degumming water before immersion silver.

　　Cause of Silver Surface Oxidation:  1. It stays in the air for too long; 2. The silver surface is contaminated and in contact with sulfur-containing substances.

　　Improvement Method: 1. The immersion silver PCB must be vacuum packed within 8 hours; 2. Strengthen the training of the operating staff and standardize the operation.

OSP Process