Immersion silver

Immersion silver is cheaper than immersion gold. Immersion silver would be a good choice if PCB has connection functional requirements and needs to reduce costs. With good flatness and contact, immersion silver process should be chosen.

Immersion silver is widely used in communication products, automobiles, computer peripherals and high-speed signal design. Immersion silver can also be used in high frequency signals because of its excellent electrical properties that other surface treatments cannot achieve.

Immersion silver is recommended due to it is easy to assembly and has good checkability. However, the growth of immersion silver is slow (but not decreasing) due to defects such as loss of luster and void in solder joints.

Advantages:

RoHS complaint

Planar

Fine pitch

Cost effective

Good alternative to ENIG

High stability

Disadvantages:

Tarnishes

Silver Whiskering

Some systems cannot throw into microvias aspect ratios of > 1:1

High friction coefficient/not suited for compliant-pin intertion (Ni-Au Pins)

Process：

Immersion silver is divided into the following three steps: pre-preg, immersion and final deionized water washing. There are three purposes for the establishment of pre-preg. One is to use it as a sacrificial solution to prevent the copper and other substances from being contaminated by the micro-etching tank to contaminate the silver deposit. The same chemical environment and pH value in the silver solution. Since the composition of the pre-preg is the same as the silver sink (except for metallic silver), the third function of this process is to automatically replenish the silver sink. The only thing consumed in the immersion silver reaction is metallic silver. The change in the content of the organic components in the immersion silver solution is only the loss caused by the bath liquid, and the pre-preg and the immersion silver solution have the same composition. The amount is equal to the amount brought out by the silver sink, so the silver sink liquid will not accumulate unnecessary organic matter. The silver sink reaction is carried out by a substitution reaction between copper and silver ions. The copper surface that has been micro-roughened by the micro-etching solution can ensure that a uniform and consistent silver deposit layer can be slowly generated at a controlled silver deposit speed. The slow silver deposition speed is conducive to depositing a dense crystal structure, avoiding the growth of particles due to precipitation and agglomeration, and forming a high-density silver layer. This compact structure and moderate thickness (6-12u") silver layer not only has high corrosion resistance, but also has very good electrical conductivity. The silver sink solution is very stable, having a long life cycle, and insensitive to light and trace halide.