Immersion Tin (ImSn) is a metallic coating of‘Tin’, which is deposited directly over the top copper layer of a PCB that produced by PCB supplier china, which  using an electroless chemical bath process. PCB finishes are used to protect the copper tracks and pads on printed circuit boards while in storage. Immersion Tin forms a dense uniform coating (0.8 to 1.2 micrometers) with good hole wall lubricity. Its appearance is usually White, so it is also called‘White Tin‘ during PCB supplier china .

Immersion Tin is not a usual displacement process; it is self-limiting and depends on the exchange between Copper and Tin. It can only take place in the presence of thiourea, which is a carcinogen, with health implications, so the process needs to be highly controlled.

Advantages of Immersion Tin Surface Finish:

• Shelf-life: 6 months
• Easy to rework (but rework should be limited)
• Due to its planarity (flatness), suitable for fine-pitch/ BGA/ small components placement
• Not expensive coomparing other finish in PCB supplier china
• Good for backplane panels, which are assembled using press fit pin insertion
• Offers good solderability after exposure to various thermal cycles 

Disadvantages of Immersion Tin Surface Finish:

• Not durable, sensitive to handle
• Tin Whiskering: Tin Whiskering is an internal defect developed during Tin Deposition. Due to this, some material protrudes out of the structure, creating whiskers. These ‘Whiskers’ grow outwards and create a shorting problem with the adjacent connections.
• Environmental concerns with Thiourea (carcinogen) used during processing
• Not good for PTH