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Specification for Immersion Tin Plating for Printed Circuit Boards - Amendment 1
1 SCOPE
This specification sets the requirements for the use of Immersion Tin (ISn) as a surface finish for printed circuit boards. It is intended for use by supplier, manufacturer, contract manufacturer (CM) and original equipment manufacturer (OEM).
1.1 Description
ISn is a metallic finish deposited by a chemical displacement reaction that is applied directly over the basis metal of the PCB, that is, copper. ISn is primarily used as a solderable surface. It has been used in press fit connections and as the interface for Zero Insertion Force (ZIF) edge connectors.
The ISn protects the underlying copper from oxidation over its intended shelf life. Copper and tin however have a strong affinity for one another. The diffusion of one species into the other will occur inevitably, directly impacting the shelf life of the deposit and the performance of the finish. Various ISn formulations designed specifically for use as surface finishes for PCBs utilize various methods of retarding the diffusion process, including the use of co-deposition of organics, the use of another metal as a diffusion barrier or the use of grain structure refining. It is recommended that the user of the deposit clearly understand the different methods of copper migration retardation and that the supplier know the positive and negative impacts of the system chosen.
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