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Coating under Mil connector....

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#38658

Coating under Mil connector.... | 22 December, 2005

How is everyone coating under these connectors? Is RTV covering the outside so nothing can get in an answer? Or very thin silicone to wick under...

http://img302.imageshack.us/img302/1728/dscn24450ac.jpg

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#38660

Coating under Mil connector.... | 22 December, 2005

Off the Cuff Answer: Wow, nice big ugly connector! Thought we were the only ones using these things designed during the Korean war. Actually it really depends on the customers print. If they want conformal coating, they should know exactly where they want it. If it's your design, then you can redesign it using a better design connector.

Proces Answer: It all depends on your process equipment. Some coaters can turn 90 degrees to spray, but I doubt this would work on such an ugly connetor - they generally only work on the beautiful ones. Why not dip the unit? Or else you'll need to apply by hand. It's fun for about the first dozen or so....

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#38662

Coating under Mil connector.... | 22 December, 2005

Josh: Room Temperature Vulcanizing (RTV) is Dow Corning's trade name for it's family of silicone cure sealants. RTV is about the worst kind of coating there is. Its chemistry is highly ionic and it requires atmospheric humidity absorbed to "complete" its polymerization. Many types depend even on strong acetic acid to work. We've gone off on RTV several times previously here on SMTnet. So, we'll spare the regulars [some eye-rolling, "there they go again", rude sounds, etc] and suggest that you search the fine SMTnet Archives, if you want more.

We agree with Ms Chunky that: * This one very coo connector. * Dipping probably will allow a thinned conformal coating to underflow the connector. It will be a little tricky to dip the connector and not entrap air under the connector though.

We Question: * Why you want to conformal coat under the connector? * Would an encapsulant meet your customer specification? * What is the purpose [goal] of applying conformal coating? * Returning to your picture, what is that nasty looking bluish/greenish stuff on the connector?

IPC-HDBK-830, Guidelines for Design, Selection and Application of Conformal Coatings says:

A conformal coating may have several functions depending on the type of application. The most common are: * Inhibit current leakage and short circuit due to humidity and contamination from service environment. * Inhibit corrosion. * Improve fatigue life of solder joints to leadless packages. * Inhibit arcing, corona and St. Elmo's Fire. * Provide mechanical support for small parts that cannot be secured by mechanical means, to prevent damages due to mechanical shock and vibration.

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MikeF

#38785

Coating under Mil connector.... | 3 January, 2006

If you know you have cleaned any flux residues that were under there you could consider a bead of an electronic grade RTV, such as RTV3145. If you trap any uncleaned residues under there you could have long term reliability problems.

But, like DaveF asked, what are your requirements for the coating?

If you have to coat under the connector, an option is to thin an acrylic or polyurethane conformal coating so it will flow under there. I don't think dipping will get a good coating due to trapped air. If you need a complete coating on every solder joint I believe you will have to tip the board about 45 degrees and flow a thin coating under the connector and let it drain off the side of the board. My preference would be to use acrylic, much easier to rework than polyurethane.

By the way, be glad those are not filtered connectors, they run about $500 to $600 each. I will be building some boards with that style connector in a couple of months. A mistake with those really hurts.

Mike F

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#38805

Coating under Mil connector.... | 4 January, 2006

Dow 3145 or 3140 is exactly what I was going to use on these connectors. Our requirement is to protect every solder joint in our product basically. This connector, being power input and signal out all in one is very important and needs to be protected by something. I think ill get as much as possible with the acrylic and then Ill try the 3145. Thanks guys

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