PCB surface treatment of Immersion Tin

According to IPC, the association Connecting Electronics industry, Immersion Tin is a metallic finish deposited by a chemical displacement reaction that is applied directly over the basis metal of the printed circuit boards, that is, copper. The technology of Immersion Tin protects the underlying copper from oxidation over its intended shelf life.

Copper and tin, however, has a strong affinity for each other, which will inevitably spread a metal to another metal inside. This will directly affect the shelf life of deposit and the performance of finish.

Advantages include:

  1. Smooth surface
  2. Do not contain lead(Pb)
  3. Can be re-workable

Disadvantages include:

  1. Handling damage easily
  2. Process use a kind of carcinogenic substance (thiourea)
  3. Tin exposed outside may be corroded in final pcb assembly
  4. Tin whiskers
  5. Unsuitable for multiple reflow soldering and assembly
  6. Thickness is difficult to be measured

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