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Greetings, I was wondering if anyone out there is familiar with this standard and/or know of a coating that can be used on PCBs to protect them from potentially corrosive gases and airborne contaminents. The standard specifically deals with process measurement and control systems. Thanks, DB GE Industrial Systems Daniel Biggs Test Engineer Hardware Design Services GE Fanuc Automation PO Box 8106 Charlottesville, VA 22906 PH: (804) 978-6946 Fax: (804) 978-5588

Daniel: I am not familiar with the standard mentioned. In the past, I have used silicone-based conformal coatings on printed circuit boards to isolate them from the environment. I believe GE is one of the manufacturers of these materials. Regards, Jacob Z. Schanker, P.E. Director of Agency Compliance Adaptive Broadband Corporation 615 Fishers Run Victor, NY 14564 +716 742 6154 (voice) +716 742 6102 (fax) +716 820 7364 (US cellphone) +0777 992 5368 (UK cellphone) jschanker@adaptivebroadband.com

I can't comment expressly about the ISA standard but conformal coatings on PCB's are very common. Talk to any serious industrial electronics manufacturer and they will advise you. There are various types available right up to potting compounds. You will probably have to choose one that is UL/CSA approved. The compound is applied to the PCB by brush or spray. If there are any connectors or potentiometers on the PCB, these will have to be masked (can use a removable paint-on silicon rubber) before spraying. Best regards, Alastair Fordyce REA, NZCE,CQA Systems Engineer Bremca Industries Limited www.bremca.co.nz PO Box 7169 Christchurch NEW ZEALAND tel +64 (3) 332 6370 fax +64 (3) 332 6377 e-mail alastair.fordyce@bremca.co.nz

Dow Corning make silicone based conformal coatings which would fit the bill.

Daniel, Do you mean conformal coating, such as?: <http://www.chemtronics.com/catalog/catalog.cgi?action=list_product s&category=8> My new washing machine has electronic controls, for example, and the PCB is conformal coated--it looks like it was in an ice storm. Hope this helps, Eric M. Klintworth, PE Columbus, Ohio USA

For Corrosive constituents like SO2 gases the coating standard to be followed is G3.

Ananth Could you enlighten abit more on G3 Nilanjan > For Corrosive constituents like SO2 gases the coating standard to be followed is G3.

If G3 environment requires conformal coating then what is required for G1 and G2 environment? Are the PCB tracks have more width or height to be suitable for G1 and G2 class? Why this is not possible for G3 class?

In regard to this standard, special systems are typically installed to prevent circuit corrosion from corrosive gases. Its very common at refineries, paper mills, smelters, etc. These systems keep the room pressurized with purified air. Temperature and humidity control are critical as well. There is typically not a need to coat boards when ISA-S71.04 is followed.

If you have further questions, please feel free to contact me at kjameson@pureairfiltration.com

GE product range uses these conformal coating for GE Multilin Products. GE Multilin products - http://www.geindustrial.com/multilin/products/ur_v48/hecc.pdf

S anjay Satpute

HumiSeal has provided conformal coatings to all national and international standards for the last 50 years.
see http://www.humiseal.com