Electroless Nickel/Immersion Silver—A New Surface Finish PCB Applications

Electroless nickel/immersion gold (ENIG) has been the primary, high-performance surface finish used in the PCB industry for some decades now. Market research confirms that in terms of processed surface area per year, ENIG useage is second only to organic solderability preservatives (OSP) [1]. ENIG is typically described as a surface finish which is labor intensive to work with at the fabrication level, but its high-performance characteristics mitigates this fact to a great extent. Electroless nickel/immersion gold is designed to deliver a highly corrosion resistant and superior solderable surface. This finish is also commonly used for aluminum wire bond applications.

With significant volatility in precious metal pricing and the constant demand for better products at cheaper prices, original equipment manufacturers (OEM's) are being driven to search for ways to reduce cost whilst not sacrificing quality. The layer of gold metal on an ENIG-treated surface, although thin, adds a prohibitively high premium to the cost of this finish.

MacDermid has developed an electroless nickel/immersion silver (ENImAg) process that delivers the performance characteristics afforded by ENIG and eliminates the concern associated with the use of a high priced metal, such as gold. This change, from using gold to silver, also has the added benefit of eliminating a cyanide-containing process from the fabrication house. Applying, qualifying for and maintaining a cyanide license is a cost adder for the ENIG process.

This paper expands on the work conducted in 2010's “A New Surface Finish for the Electronics Industry [2].” Process flow and the associated chemical steps will be discussed to alleviate concerns of fabrication difficulties. This work will detail additional performance characterization and discuss the surface finish performance on a production scale. The test data presented will include solderability, tarnish and corrosion resistance, aluminum wire bonding and contact performance.