I would like to utilize this board Dual Axis Magnetic Sensor Eval Board - Honeywell HMC1052L sku: SEN-00761 (or something similar) in a device that would be lowered to the bottom of a water well (i.e., it will get wet).
I anticipate that I would encase it in some sort of epoxy or silicon caulk as a water-proofing. Would this provide sufficient protection and keep the unit within the humidity specs provided there is no breach in the epoxy?
Thanks,
Dale
P.S.: Sorry about this being a duplicate post, but it might be more appropriate here.
There’s plently of products for coating / potting PCBs, but a major issue is water entering where wiring penetrates through the potting. After a while, the adhesion of the wiring to the encapsulant can weaken, allowing water in. Not impossible to deal with, but something to keep in mind.
As said before, wire flex is a significant issue. Also be aware that epoxy can put major strain on the board and components as it is curing. There are specialty epoxies available which are designed for whole-device potting. Either way, you will likely have some failures after potting.
I would prefer to use a silicon caulk rather than an epoxy. I planned on slathering it on thick and placing it in its final position before it sets and cures. If the device is completely immobilized, then wire flex shouldn’t be as big an issue, correct?
The other concern is whether the magnetic sensor will generate heat that won’t dissipate when encased in silicon.
Anyone have any insight on silicon caulk over epoxy and the heat the sensor might generate?
I’ve sucessfully used silicone sealant (hardware store stuff) to pot high voltage circuits, but you MUST use the NON-Acid cure type (check the label). If it smells like vinegar, do NOT use it!!
I can’t vouch for silicone in your application. As with epoxy, the adhesion to the wiring would be the critical aspect. I’ve seen pretty reasonable adhesion of silicone sealant to wire insulation so you may be OK.
The other thing you need to remember is that hardware store silicone is the air-cure type, so you can’t apply it too thick or you’ll be waiting forever. Check the label, but you may need to apply it in several stages depending on your application. You can get 2-part silicones that get around this problem if needed.
From what I can see, I wouldn’t worry about overheating because of the heat generated by the circuit. Silicone isn’t a particularly good thermal insulator. Do some calcs using the specified thermal resistance in the silicone datasheet, but I wouldn’t worry.
Thanks for the advice on the varieties of silicon. I understand about the sealing around the wiring part of it, but once it gets encased, it should be immoble with no stress or strain on those wires. Thanks for the wires.
You’re certainly not going to complain about spending the extra $35 if it doesn’t fail. You’ll have to evaluate whether or not it’s worth the money to you, though, but how much is your time and the equipment worth?
Wire traces out will be the sealing “challenge”. Either pot the unit with a waterproof connector, or be very careful about how you get the wires out of the enclosure.
I’ve done a lot of designs for very acidic environments, and most of my PCB houses call the epoxy they use a conformal coating.
It’s basically an epoxy (probably the same as the post above), but I’ve never had any heat or stress problems.
It does give cost problems though - the PCB manufacturers HATE it because it gets into connectors. So the moral is to attach all cables (make sure your crimps are good ) before applying the coating.
In another medical product I have been using hot glue. It strain relieves and protects a solder joint where a coax cable is soldered to a PCB. It protects against blood, bleach and all manner of crusty stuff.
We made up a small two part mold and inject glue using a normal hot glue gun - works a treat.
) before applying the coating.