My guess at the reason for the failure is improper cleaning of the mold release compound. A good epoxy bond should grab the surface of the case. Even with a 100 degree elevated temperature, the internal pressure would only be about 1.3x normal, and the area of the tiny hole to the interior (at the center of the plug) is less than 1mm^2. This would provide very little force to pop the plug. By teasing the plugs with a "pointy thing" (a technical term), I was able to pop the plugs out without much trouble.
Regardless of the failure mechanism, and no matter what actually defines "sealed", my paranoid conclusion still stands . . .
Don't wash sealed relays!
Later,
Carl
Carl B. Van Wormer, P.E., AE7GD
Senior Hardware Engineer
Cipher Engineering LLC
21195 NW Evergreen Pkwy Ste 209
Hillsboro, OR 97124-7167
503-617-7447x303
[log in to unmask] http://cipherengineering.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Creswick
Sent: Friday, March 20, 2015 4:21 PM
To: [log in to unmask]
Subject: Re: [TN] Sealed relays fail after water wash - story #2
Carl,
The component manufacturing design and assembly process is especially critical with UV cure 'seal' materials. It seems that some organizations get wrapped up in the 'speed' and 'rapidity' of UV cure materials and they don't take the effort to actually study the materials involved.
Generally, these materials have near room temp Tg's, and large CTE's because they are unfilled materials. I posit that the large CTE is evidenced by the way the 'seal' extruded from the 'seal cavity' in the side views in the first group of images.
Their mechanical properties also are not as mechanically robust as a filled material can be, so even if the materials adhesive properties are sufficient enough, its bulk cohesive, or tensile properties may not...
I argue, that the seal design needs to be more than 'a dollop of glue' ON TOP OF A HOLE. Your best opportunity to 'seal' with this type of material property is to create a dumb-bell shaped seal where there is a mechanical plug on the inside of the hole as well. This is likely best accomplished using 'dual cure', or supplemental latent cure materials.
On the other hand, I've known automotive 'quasi-sealed' components that are 'sealed' with a decal of Kapton tape/acrylic adhesive over the vent hole... and that actually worked quite well!
I believe that you are accepting too much responsibility when you say, "failures caused by our assembly process". Sounds more like a case of false advertising, or exaggerated capabilities.
Happy Spring!
Steve C
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