immersion tin pcb (ImSn) PCB Finish
Immersion Tin (ImSn) is a metallic coating of ‘Tin’, which is deposited directly over the top copper layer of a PCB 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’.
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
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
Immersion Tin PCBs
Immersion Tin VS Immersion Silver VS HASL
HASL
Lead-Free HASL is similar to standard HASL, but with an obvious difference… It doesn’t use Tin-Lead solder. Instead, Tin-Copper, Tin-Nickel or Tin-Copper-Nickel Germanium may be used. This makes Lead-Free HASL an economical and RoHS compliant choice. But like standard HASL it is not ideal for smaller components.
Immersion Silver
Immersion silver is a non-electrolytic chemical finish applied by immersing the copper PCB into a tank of silver ions. It is a good choice finish for circuit boards with EMI shieldingand is also used for dome contacts and wire bonding. The average surface thickness of the silver is 5-18 microinches.
Comparison With These Surface Finishes
The features of immersion silver as surface finish place it in between OSP and immersion gold. Even when exposed to humidity, heat, and pollution, immersion silver continues to provide good solderability and electrical connection, although it will tarnish. Immersion gold has a layer of nickel under it, which provides it with physical strength. As there is no nickel layer under immersion silver, its physical strength is lower than that of immersion gold.
Immersion silver requires more care for storage and handling than immersion tin does. However, immersion silver is safer for the environment than immersion tin is.
Immersion silver is easier to use compared to Organic Solder Preservative or OSP is.
Immersion silver offers a more planar surface than HASL does.
It is important to select the appropriate surface finish for your project by considering the various options while factoring in performance requirements and material costs.
Premier Manufacturer of Immersion Tin PCB
What need to pay much attention when do immersion tin pcb?
Features of Immersion Tin
Features of Immersion Tin
1.1 Baked at 155 for 4 hours (i.e., equivalent to a year of storage), or after 8 days of high temperature and high humidity test (45, 93% relative humidity), or after three reflow soldering still has excellent solderability.
1.2 Sink tin layer smooth, flat, dense, more difficult to form copper-tin metal interdigitates than electroplated tin, sink tin layer thickness up to 0.8-1.5μm, can withstand multiple lead-free soldering impact.
1.3 Stable solution, simple process, can be used continuously by analysis of the replenishment, no need to change the cylinder,suitable for both vertical and horizontal processes. The cost of sinking tin is lower than nickel gold.
1.4 Suitable for fine line high density IC package hard board and flexible board,suitable for surface mount (SMT) or press-fit (Press-fit) mounting process.Lead-free and fluorine-free, no pollution to the environment, free recycling of waste liquid.
Factors affect the tin sinking rate?
Factors affect the tin sinking rate?
Tin concentration: The settling rate of tin increases with the increase of tin concentration. The appearance of settling layer does not change with increasing tin concentration, so increasing tin concentration can effectively improve settling rate.
Influence of organic sulfonic acid concentration: The sedimentation rate of tin increases with the increase of organic sulfonic acid concentration. The rate remained constant when the organic sulfonic acid content exceeded 110g/L, but when the organic sulfonic acid concentration was below 50ml/L, the tin layer formed would fog.
Effect of thiourea concentration: The rate of tin deposition increases with the increase of thiourea concentration. If the thiourea density up then 250g/L, the appearance of the tin layer becomes rough and foggy.
Temperature: During the range of 40℃ ~ 80℃, the deposition rate of tin increases as temperature rising.The thickness of tin layer increases with time, but stabilizes after 20 minutes at 60℃. Therefore, in production, choose 60℃ for 10-12 minutes, can get 1.5μm thick tin layer.
What need to pay much attention when do Immersion Tin pcb?
What need to pay much attention when do Immersion Tin pcb?
The coating requires a precise handle – gloves should be used when assembling. Corrosion may occur when making soldermask jumpers (less than 5 mm). Plugging the holes on one side, using a stripping mask and leaded solder is not recommended during application.
Unlike sink gold/sink silver, sink tin is less common and is rarely used in the production of printed circuit boards. In addition, this surface treatment can lead to an increase in intermetallic compounds and short circuits in the landing area associated with whiskers.
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