iNEMI releases creep corrosion risk guidelines.

HERNDON, VA - iNEMI (inemi.org) in June published a position paper outlining limits of temperature, humidity and gaseous contamination in data centers and telecommunication rooms to avoid creep corrosion on printed circuit boards.

These recommendations were developed by the consortium's Creep Corrosion Project, which has been investigating factors that influence creep corrosion since 2009.

"Corrosion of electronics is a significant issue," said Bill Bade; CEO of iNEMI. "However, there is very little agreement on the test methods and conditions that should be used to simulate the environmental conditions and to predict potential failures. This project team has surveyed the electronics manufacturing industry to identify leading factors in creep corrosion and is working to understand the sensitivities of those factors. They have conducted, and are continuing to conduct, very valuable testing to help extend industry's understanding of the issues surrounding creep corrosion."

Creep corrosion is a process in which solid corrosion products (typically sulfide and chloride) migrate over a surface without the influence of an electric field. Creep corrosion is highly surface-specific, and a given corrosion product can only migrate on a specific type of surface. Commonly seen in polluted environments rich in sulfur, this kind of corrosion has predominantly been observed on PCBs with lead-free surface finishes such as ImAg and OSP. In these cases, the corrosion product (typically copper sulfide) creeps onto the solder mask surface and causes short circuits between adjacent pads and traces. Creep corrosion on printed circuit boards is promoted by the residue of certain types of fluxes, and is also affected by temperature and humidity in the environment.

iNEMI's position statement defines the temperature, humidity and copper and silver corrosion rate limits within which PCBs will perform reliably in the field with respect to creep corrosion. Existing studies indicate that the most effective way to protect electronic hardware from creep corrosion is to ensure that environmental conditions are within the modified severity level G1 of ANSI/ISA-71.04-1985, Environmental Conditions for Process Measurement and Control Systems: Airborne Contaminants (ISA 1985):

* A copper reactivity rate of less than 30nm/month.

* A silver reactivity rate of less than 20nm/month.

The recommended ranges for temperature and humidity are based on white papers from the American Society of Heating, Refrigerating and Air-Condition-ing Engineers (ASHRAE):

* Temperature within 18[degrees] to 27[degrees]C.

* Relative humidity less than 60%.

* Dew point within the range of 5.5[degrees] to 15[degrees]C.

iNEMI members supporting this position statement are Agilent, HP, Alca-tel-Lucent, Huawei, Cisco, IBM, Dell, Intel, DfR Solutions, Dow Chemical, and IST-Integrated Service Technology Inc.

Phase 3 of iNEMI's Creep Corrosion Project is currently performing laboratory-based experiments to further investigate the sensitivities of the influencing factors, including surface finish, flux, solder mask geometry, solder paste coverage, reflow and wave soldering, and mixed flowing gas (MFG) test conditions (corrosive gas concentration, humidity, temperature).--MB

EDITED BY MIKE BUETOW