Superior, whisker‐reduced immersion tin technology

Abstract

Purpose

To provide information about latest product developments to address and take away the fear of whisker formation on pure immersion tin surface finishes on PCBs.

Design/methodology/approach

This paper summarises the latest findings on whisker formation of pure tin surface finishes and describes an effective methodology for whisker suppression in combination with other benefits for the use of this new immersion tin generation.

Findings

Whisker formation is a typical feature of pure tin when coated, e.g. on copper and is a threat to the PCB industry, because of the risks of shortcuts involved. The main driving force for whiskers is an accumulation of internal stress created by diffusion at the boundary of copper and tin. A nano layer deposited from an organic metal‐based pre‐dip significantly reduces the diffusion by creating a unique sandwich layer with smooth concentration gradients. A drastic reduction of diffusion and stress was found, eliminating the driving force for whisker formation and prolonging the layer's shelf life and temperature stability at the same time.

Practical implications

Whenever whisker formation on immersion tin is regarded as a potential risk, e.g. by OEMs, a whisker‐reduced process is available and should be chosen to meet the market's specifications.

Originality/value

This paper takes the edge off the whisker threat discussions, leading to a hesitant implementation of immersion tin surface finish technology for PCBs, which disregard its excellent features with respect to future lead‐free soldering. Whisker‐reduced immersion tin is a viable and preferable alternative solderable surface finish for the lead‐free era.

Citation

Schroeder, S. (2005), "Superior, whisker‐reduced immersion tin technology", Circuit World, Vol. 31 No. 4, pp. 42-46. https://doi.org/10.1108/03056120510603134