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Soldering Immersion Tin
Soldering Immersion Tin
This paper focuses on awareness of factors attributed to soldering i-Sn including IMC formations in relation to reflow cycles and solderability performance.
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Authored By:
Rick Nichols and Sandra Heinemann - Atotech Deutschland GmbH

Summary
The stimulating impact of the automotive industry has sharpened focus on immersion tin (i-Sn) more than ever before. Immersion tin with its associated attributes, is well placed to fulfill the requirements of such a demanding application.

In an environment dominated by reliability, the automotive market not only has very stringent specifications but also demands thorough qualification protocols. Qualification is ultimately a costly exercise. The good news is that i-Sn is already qualified by many tier one OSATs.

The focus of this paper is to generate awareness of the key factors attributed to soldering i-Sn. Immersion tin is not suitable for wire bonding but ultimately suited for multiple soldering applications. The dominant topics of this paper will be IMC formations in relation to reflow cycles and the associated solderability performance.
Under contamination free conditions, i-Sn can provide a solderable finish even after multiple reflow cycles. The reflow conditions employed in this paper are typical for lead free soldering environments and the i-Sn thicknesses are approximately 1 micrometer.

Conclusions
Whilst i-Sn can be shown to be a reliable final finish for soldering even after multiple thermal ageing tests that could feasibly be encountered in production, uncontrolled external influences can result in poor results. These are not only problematic to i-Sn final finishes and can be eliminated by good practice.

The production environment is a complex one where controls and good practice can help to ensure high yields. This paper proves that i-Sn can provide a reliable solderable finsh with a long shelf life and a compatibility to realistically challenging production environments.

Initially Published in the IPC Proceedings

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