Hermetic seals of metal housings with over-molded plastic?

[spiri]

Does anyone have any experience with creating a hermetic seal on metal housings that are sandwiching a thin metal membrane? Specifically with the fluid leak path between the metal and the plastic.

 

[trurle]

I think your design may be related to metal membrane fuel tanks used in rocketry. In brief, either use two o-rings an a lot of bolts around membrane, or weld the membrane to housing. Over-molding with plastic may work as replacement for bolts in case of design utilizing o-rings though.
http://www.northropgrumman.com/Capa...s/Documents/technicalPapers/AIAA2007-5559.pdf

 

[essenmein]

Does anyone have any experience with creating a hermetic seal on metal housings that are sandwiching a thin metal membrane? Specifically with the fluid leak path between the metal and the plastic.

If you are talking overmolding metal parts with plastic and then sealing that metal to plastic joint then yes, its there, and very difficult to avoid due to large CTE differences and typically overmolding thermoplastics doesn't create much adhesion if any at all.

Common techniques are longer labyrinth, eg T slot or similar, depending on how you are forming the metal, maybe coining (we typically protrude electrical leadframes out plastic housings, so coining is a suitable way of forming), or casting etc.

However if you have to maintain seal over large temperature swings this will not work, the only reasonable way (ie cost effective) we found is encapsulating the joint on the inside with compliant material (RTV, sil gel etc) to prevent leaks.