Case Filling: Epoxy; thin consistency and thermally conductive

[ACharnley]

Hi all,

I have a small PCB going into a small case approximately 70mm long, 11mm wide 5.5mm high (internal). The PCB must be waterproofed and ideally the cables need protection against being pulled (there is no room for knotting the cable to relief on the case).

I investigated neutral cure silicone but have found it develops a skin of 5mm then stops curing. It's also a little too flexible.

Standard epoxy adhesive is good once it's cured but is too thick to inject into the case. It's also expensive.

Essentially I need "runny" epoxy which I can inject with a syringe. Thermally conductive would be a bonus. Any recommendations?

The alternative is to fill the case as the PCB is going in, but it'll be messy and I have 1,000+ units to do!

Thanks, Andrew

 

[Nigel Goodwin]

Try looking for 'potting compound', there are a great many types available - many syringe injectable.

 

[ACharnley]

Something like this (epoxy for fibreglass)? **broken link removed**

 

[ACharnley]

Try looking for 'potting compound', there are a great many types available - many syringe injectable.

How hard to do they get though? If silicone based I'd expect a little flex and cable could rip through?

edit: ok, I see they're epoxy based as well. Looks good. https://www.ebay.co.uk/itm/Potting-...04C-1Kg-Encapsulation-Compound-/291550744336?

 

[spec]

**broken link removed**

http://www.ebay.co.uk/itm/Potting-Compound-Twin-Pack-Resin-and-Hardener-50g/291472247231?_trksid=p2047675.c100010.m2109&_trkparms=aid=222007&algo=SIC.MBE&ao=1&asc=35923&meid=29b9cd57a1f94e09bc6ec804758cadc6&pid=100010&rk=1&rkt=4&sd=121342616487

You need some compliance or the potting can stress the components and interconnections especially with vibration a and temperature. Particular care needs to be taken with surface mount components.

You also need a potting compound that can be removed or the unit will be written off in the case of a failure.

spec

 

[ACharnley]

The unit shouldn't fail but if it did it would be written off. I've bought 1kg of PX700k and shall see what the viscosity is like.