Issue link: https://iconnect007.uberflip.com/i/1161956
96 SMT007 MAGAZINE I SEPTEMBER 2019 Summary/Conclusions The successful soldering to PCBs is less- ened with time and exposure to environmental conditions—most notably heat and moisture. Excessive exposure renders boards unsuitable for final fabrication/assembly based on poor solderability resulting in disposal before— or worse, after—expensive components have been mounted. Enhanced soldering reliabil- ity is achieved by rendering heat and humidity ineffectual in reducing solderability. Steam aging per IPC J-STD-002 and J-STD- 003 is a convenient and low-cost method of evaluating the shelf-life of finishes used on PCBs that takes minimal time. Two finishes— ENIG and EPIG—were tested for solder wetting pre- and post-steam stressing exposure. Test data shows that the steam stressing had little influence on the EPIG board surface finish sol- derability while ENIG board surface finish rap- idly becomes unsolderable. The swift oxidation of the nickel layer by steam is thought to be the cause. Supporting evidence was provided by applying a secondary organic anti-tarnish coat to the ENIG samples before steam stress- ing. Oxidation of the nickel layer was then sup- pressed. The organic film reduced nickel oxi- dation after steam stressing with improved solder wetting. SMT007 References 1. Morris, G.K., Luukaszewski, R.A, and Genthe C., "Envi- ronmental Contamination and Corrosion in Electronics: The Need for an Industrial Standard and Related Acceler- ated Test Method That Makes Sense," IEEE, 2017. 2. O'Brian, G., chairman of 5-23A, responsible for IPC J-STD-003. Verbal communication. 3. Milad, G., Bengston, J. and Gudeczauskas, D., "The Mechanism of Nickel Corrosion in ENEPIG Deposits and How to Mitigate It," SMTA International, 2017. 4. Yokomine, K., Shimiizu, N., Miyamoto, Y., Iwata, Y., Love, D., and Newmam, K., "Development of Electroless Ni/ Au Plated Build-Up Flip Chip Package with Highly Reliable Solder Joints," IEEE, Electronic Components and Technol- ogy Conference, 2001. This paper was first presented at the IPC APEX EXPO 2019 Technical Conference and published in the 2019 Technical Conference Proceedings. Jon Bengston is research and development manager for Uyemura-America in Southington, Connecticut, USA. Richard DePoto is business development manager for Uyemura-America in Southington, Connecticut, USA. Table 2: Compilation of test conditions, positive wetting time, and maximum wetting force (from Figure 7–12).