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silicone conformal coat and electrical contacts

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rw

#47025

silicone conformal coat and electrical contacts | 26 January, 2007

We are developing a new product that requires conformal coating on the motor controller. We selected a silicone based conformal coat due to its ease of use. There has been disagreement among engineers as to its impact on the motor. We have contacted the motor supplier who indicates that silicone volatile is an issue especially if the motor brushes spark. I don't believe that this will have an effect due to the board with conformal coating is not encapsulating the motor thus allowing the volatiles to vent to the atmosphere. Has anybody had experience with this?

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#47033

silicone conformal coat and electrical contacts | 26 January, 2007

IMHO I would avoid sprayed silicones like the plague. They can travel around your facility and cause solder wetting issues that you will never know the root cause for.

Also found this e-drive article on using silicones around motors and relays. Looks like there may be a viable product now in the market, but as others always say on this forum, do your due diligence with any new chemistry.

http://www.e-driveonline.com/images/DowCorning.pdf

Personally, I would coat with UV cure urethane or acrylic way before silicone.

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#47085

silicone conformal coat and electrical contacts | 29 January, 2007

We allow no silicone in our shop, because they ruin solderability.

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blnorman

#47105

silicone conformal coat and electrical contacts | 30 January, 2007

We use nothing but silicones and have for at least the last 7 years. We don't have relays, but we do have motors. No issues with soldering, but our lines are constructed such that the last solder operation is a good distance from the coating or potting station. Our Dow rep has pushed the controlled volatility silicones, but we haven't had a chance to work with them yet.

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#47111

silicone conformal coat and electrical contacts | 30 January, 2007

Hose and/or Dave,

Please elaborate of how the silicone can affect soldering. Material itself or fumes?

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#47112

silicone conformal coat and electrical contacts | 30 January, 2007

NASA Internal Advisory: NASA-Issued Return to Flight Wristbands Contaminated with Silicone [snip] 10. PROBLEM DESCRIPTION: Recently we have been made aware of a silicone problem associated with the "Return to Flight" wristbands. These wristbands are contaminated with silicone. Silicone is used in the manufacture of numerous products, mainly as a release agent, which aids in the removal of casted or molded plastics from the mold's surface. The problem with silicone is that a small amount goes along way. Silicone is easily transferred (cross contamination) and inhibits bonding. Less than .250 mg/ft2 causes a shift in failure modes. Silicone is an issue in electrical fabrication and inspection and test areas. If you get silicone on the leads of a piece part, the silicone impairs the soldering process and gives a bad solder joint. Conformal coating will not stick to silicone either and will cause the parts on the board not to accept the conformal coating. What you need to know is that all of these type wristbands (Lance Armstrong's, Breast Cancer Awareness, and Return to Flight) use virtually the same production techniques, meaning that they are all contaminated with silicone. Therefore, caution should be exercised when wearing these wristbands. If your operation is sensitive to silicone contamination, then these wristbands should not be worn in or during these operations. A picture of a typical wristband and its original packaging are included on the second page. While the example is green, this problem exists on wristbands of various colors. 11. ACTION TAKEN: Please do not wear these in our facilities and keep your eyes open for others that do not get this message. A Quality Alert has been issued at our Wasatch Facilities due to the serious nature of what silicone can do to our processes. 12. NAME/TITLE OF ORIGINATOR: Jennifer McCarter NASA Headquarters 13. ORIGINATOR PHONE NUMBER: 202-358-1639 14. DATE PREPARED: May 5, 2005

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#47127

silicone conformal coat and electrical contacts | 31 January, 2007

Material, fumes, cured or uncured, all are suspect. Silicone gets on an operator's hands, that operator handles components ( even a day or more later ) silicone is transferred to the solder connections = contamination. Process and workcell control procedures must be strictly enforced even when dispensing RTV gel / high viscosity materials.

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rw

#47129

silicone conformal coat and electrical contacts | 31 January, 2007

I'm not that concerned about the solderability of the motor. Our customer is concerned about the outgassing of the conformal coat effecting the motor brushes. Silicone will break down into SiO2 and SiC will result from a spark between the brushes and rotor on the motor. This SiC is like a little piece of glass in the motor which will destroy it. But I believe this will only happen say if you put the silicone in the motor itself. Not on the PCB surrounding ECU which is located about 1 inch below the motor. Because silicone is in the air all the time. I think that it would have to be directly applied into the motor for this to happen.

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#47141

silicone conformal coat and electrical contacts | 1 February, 2007

NASA is concerned about outgassing in high-vacuum environments. They select materials to minimize outgassing. http://outgassing.nasa.gov/og_desc.html

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blnorman

#47142

silicone conformal coat and electrical contacts | 1 February, 2007

Especially VCM - volatile condensable materials. Strictly verboten around optics.

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CK Flip

#47166

silicone conformal coat and electrical contacts | 2 February, 2007

Wow, I cut first cut my teeth in the Industrial motor control industry. My 1st company made motor control products like variable speed drives, solid state overload relays, soft starts, etc. and in our shop, we used nothing BUT Dow Corning silicone products. Granted our controllers and relays were enclosed in NEMA-rated enclosures, so I'm not sure if the volatiles would have escaped out of the enclosure and onto the motors.

For our hi-volume product, we used to use a dip coating process with silicone in the tank. It used to get everywhere and would wick up into unsealed components. I recommended going to a spray process using polyurethane UV-curable, but then a big German company bought us out and got rid of our manufacturing. :-(

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