SMTA International Conference Proceedings

Immersion Tin Surface Finish - Reviewing the Past and a Look to the Future

Authors: Mustafa Oezkoek, Dipl.-Ing., Hubertus Mertens, and Maren Bruder
Company: Atotech Deutschland GmbH
Date Published: 9/28/2014   Conference: SMTA International

Abstract: In 1999 The Immersion Tin surface finish was introduced to the market. The industry at that time was mainly using ENIG (Electroless Nickel), HASL (Hot Air Solder Leveling with SnPb) and OSP (Organic Solder Preservative). At that stage more than 60% of the market in terms of square meter used HASL, mainly for wave soldering with eutectic SnPb solder. But market conditions were changing over time and new requirements such as the growth of the Surface Mount Technology (SMT) and the introduction of new regulations such as RoHS and WEEE had resulted in the fact that alternative surface finishes were required to fulfill the new challenges towards more flat surfaces compared to HASL (Thickness 1-40µm) or for the assembly of SMD (Surface Mount Device) parts, which were getting gradually smaller and smaller. In addition to meet the new ecological requirements from RoHS and WEEE, lead free surface finishes become paramount in many industries. New surface finishes such as Immersion Tin and Immersion Silver entered the market and steadily gained ground. One of the major concerns regarding Immersion Tin in the past was the potential for whisker growth. In 2002 the new Anti-Whisker-Additive was introduced for Immersion Tin which solved this problem and new qualifications in the automotive industry, industry electronics, the server infrastructure, enhanced the growth of Immersion Tin over the years.

When time passed by those OEM´s and assemblers who changed from HASL to Immersion Silver were confronted with corrosion failures form the field (creep corrosion and silver migration). Furthermore solder joint reliability issues caused by champagne voids. Both impacts was leading to the situation that the Immersion Silver market nowadays is not much growing and even for the future more and more assemblers are changing either to OSP or Immersion Tin whereas other OEMs still keep Immersion Silver as a surface finish by doing additional efforts like more properly sealing the electronics from the environment e.g. better sealed housing or by improved conformal coatings. It was not considered by some OEMs that their products are losing the corrosion resistance of the full assembled package when changing from HASL towards Immersion Silver. Immersion Tin did not suffer this problem because of the good corrosion resistance comparable to the HASL finish. Further developments of the Immersion Tin process such as continuous chemistry regeneration, the improvement of soldermask compatibility and other features lead to the fact that nowadays Immersion Tin is growing year by year. This paper will also provide an outlook to the future of Immersion Tin.

Key Words: 

Immersion Tin, Surface Finish, Immersion Sn

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