Immersion Tin, or Chemical Tin, it’s a RoHS Compliant metallic finish deposited by a chemical displacement reaction that is applied directly over the basis metal of the circuit board, the immersion Tin protects the underlying copper from oxidation over it’s intended shelf life, copper and tin however have a strong affinity for one another, the diffusion of one metal into the other will occur inevitably, directly impacting the shelf life of the deposit and the performance of the finish. The negative effects of tin whiskers growth are well described in industry related literature and topics of several published papers.
The typical thickness of Immersion Tin is ≥1.0UM and the shelf life is 6 months. The cost of Immersion Tin is more expensive than HASL but less expensive than Immersion Gold PCB and close to Immersion Silver. Similar to Immersion Silver, Immersion Tin is also sensitive in handling and storage, it requires PCB manufacturers to control and pack PCBs with Imm Tin more carefully.
The advantages of Immersion Tin
● Excellent flatness
● Mid range cost for lead free finish
● Good for fine pitch / BGA / smaller components
● Top choice for press fit technology
The disadvantages of Immersion Tin
● Very sensitive to handling – gloves must be used
● Exposed Tin on final assembly can corrode
● Not good for multiple reflow/assembly processes
● Aggressive to soldermask – soldermask dam should be more than 5mil
● Baking prior to use can have a negative effect
A-TECH is capable of using Immersion Tin, we make the profile and electrical test before the process of Immersion Tin finish, and we use papers to separate each piece of boards to avoid scratches during package and transportation.
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