SMTA International Conference Proceedings


Can a Cyanide Free Immersion Gold Bath be a Viable Option in the Existing Final Finish Production Environments?

Authors: Rick Nichols, Sandra Heinemann, Robert Spreemann, and Gustavo Ramos
Company: Atotech Deutschland GmbH
Date Published: 10/14/2018   Conference: SMTA International


Abstract: Due to increasing environmental awareness, the use of products or processes that are deemed harmful, is becoming more restricted, banned, or simply less desirable. In a number of countries, the use of cyanide in open processes tanks, such as those used in plating applications, is now seen as a concern, so a cyanide-free gold bath is seen as a preferred and eco-friendly solution for plating.

In this paper, a cyanide-free gold plating solution is tested in combination with different electroless nickel baths, specifically a mid-phosphorous electroless nickel (MP) and a high-phosphorous electroless nickel (HP). All results will be benchmarked against the industry representative cyanide containing immersion golds.

The two distinct nickel types were selected in order to represent distinct production environments. The MP represents the well-established market workhorse, which has been cemented in place by the perceived relationship between HP and ‘black pad’. HP has been selected as a contender to fulfil the requirement of the newly released IPC 4552a specification in terms of corrosion resistance, and also over turn the negative perception and show that HP is a truly viable option for high corrosion resistance HDI production. Experience has shown that environmental advantages alone are not sufficient to justify the introduction of a new process into the highly conservative final finish production arena. In this paper a novel cyanide free matrix for an immersion gold bath will be pitted against a traditional immersion gold process in terms of solderability. Not only is the bath able to perform equally as well as the cyanide containing gold baths as a main stream functional finish on MP electroless nickel, the cyanide free gold bath has performance and life time benefits over the cyanide containing gold baths for life times when capping HP nickel. Today HP nickel is being championed by several significant mobile device OEMs.

The evaluation includes Cold Ball Pull tests (CBP), Ball Shear testing (BS), proprietary/ in-house solderability testing (solder indicator and solder spread) and wetting balance evaluations. The goal of this paper is to demonstrate that a cyanide free immersion gold bath has a technically founded position in a technically demanding and historically conservative production environment.

Key Words: 

MP electroless nickel, HP nickel, Ball shear testing, Proprietary/ in-house solderability testing , Wetting balance, Corrosion resistance



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