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I have a embedded computer design which uses a low profile micro sd card socket as an extra option in addition to an on board solid state disk as storage/booting mediums. In manufacture the board is coated with conformal coating but i'm in a bit of a pickle regarding the SD card socket and the coating.

The SD card socket should be masked i assume before coating is applied, otherwise it may seep into the connector i suspect, but then i am creating a bit of a weakness against moisture. It seems this particular weakness is inherent to the SD card socket.

Has anyone found a good solution for this on a professional level, or are these two things simply incompatible (card sockets and coatings/materials). Have you operated exposed sd card sockets in moist environments with a long durability ?.

What i'm mostly afraid of is that if i have the pin connections protruding from the chassis coated, the coating will seep into the socket. Expecting workers to be careful while hand coating stuff like this is probably too much and asking for trouble later.

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    \$\begingroup\$ Masking boot? conformalcoating.co.uk/Conformal_Coating_Masking_Boots.php \$\endgroup\$
    – Some Hardware Guy
    Oct 22, 2014 at 20:47
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    \$\begingroup\$ Apart from masking boots or peelable mask (tricky), the other alternative is to mask the SD socket solder pads, concoat the board, and fit the socket as a second build stage. \$\endgroup\$
    – user16324
    Oct 23, 2014 at 10:41
  • \$\begingroup\$ Use EMMC instead? \$\endgroup\$
    – user3528438
    May 3, 2017 at 17:42
  • \$\begingroup\$ Connector contacts cannot really be conformal coated so the goal here is to decide if the rest of the connector should be gummed up (there is often a write protect switch that must be protected) or if the whole connector needs to be moved or eliminated (see my answer below) \$\endgroup\$
    – KalleMP
    May 22, 2017 at 20:59

2 Answers 2

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You could try loading a dummy card while coating to act as a mask for the contacts. In my experience, SD cards themselves are quite hardy to moisture but unless you seal the SD card into the socket you'll have a potential for water ingress to the contacts. I've only dealt with conformal coatings a few times and usually the boards only have pigtails to avoid this sort of issue with connectors.

That said, I have potted boards with connectors installed for prototype systems and the epoxy never broke the contact. You might be fine installing the final SD cards prior to coating as long as you don't intend to access/remove them.

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    \$\begingroup\$ It would be a nightmare to try and trouble-shoot an intermittent fault resulting from a thin film of conformal coating that separates, at random intervals, the spring contacts from the card pads. \$\endgroup\$
    – KalleMP
    May 3, 2017 at 16:58
  • \$\begingroup\$ I agree totally. They could maybe make a tool to scrape the contacts post coating but still seems better to remove the part and use a large flash IC. It might be doable with lots of testing but it would be expensive... \$\endgroup\$
    – kkemper
    May 4, 2017 at 17:33
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Perhaps you could surface mount the microSD card permanently onto the board like in this example http://hackaday.com/2015/08/18/reflow-solder-your-micro-sd-to-ensure-it-doesnt-go-anywhere/

Or otherwise have the connector on a pigtai that is soldered to the board and protected from the coating like this http://www.babiwa.com/images/Simcard-Micro-Sim-Connector-Linker/Genuine-Luxury-Type8-SD-TO-MICROSD-CONVERTER-Extender-1.jpg mentioned on Reddit here https://www.reddit.com/r/Android/comments/42hju9/hardware_modification_marshmallow_supports/

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