Helium Bombing Adhesive

[wumbo6]

I have a bonded part that I subject to helium vacuum bombing/pressurization and perform leak detection using a mass spectrometer using the helium as a tracer gas. The adhesive I'm using is absorbing the helium during the bombing cycle and releasing it during the detection cycle creating a virtual leak. Can anybody recommend an adhesive or coating that would prevent helium absorption?

 

[ScottyUK]

The epoxies used in the semiconductor industries for die bonding have low outgassing and low absorbtion. Whether these are of any use in your application is wholly unclear because we don't know what you're assembling. Die bonding adhesives are very high purity and used in tiny quantities, so for a large component they could be prohibitively expensive.

 

[Compositepro]

No organic material is impervious to helium to the degree you require. The helium atom is small enough to diffuse through any polymer. That is why ultra high vacuum systems use copper gaskets. Another reason for copper is that they can withstand the several hundred degrees temperature that is used to bake-out vacuum systems to remove gasses that have been adsorbed onto metal surfaces. Can you use brazing instead of adhesive?

 

[epoxybot]

As Compositepro states. No organic material is impervious to helium but some companies are of a class that they have permeability data because they have spent years working with the Aerospace Industry. Also the proper term might be sealant regardless of the adhesive action you desire. A google search will yield infinity more results.

Here is a data sheet from Henkel - LOCTITE SI 5055
Link