Letter 9038

Hydrogen Bake-out for Kovar 

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I am interested in developing a hydrogen bake-out process for machined Kovar parts prior to Ni/Au plating. Does anyone know what temperature ranges are tyically used? I have evidence that 200hrs @ 150C has been used but I would like to shorten up the cycle by going to a higher tmeperature.

Thanks,

Dale Christensen
- Portland, OR, USA

Hello Dale!

So why are you trying to get rid of hydrogen BEFORE plating? Sounds odd, since Kovar is a vacuum melted alloy that shouldn't have much if any H in it to begin with. Further, it also doesn't have a phase change (it's a low expansion glass sealing alloy, for Pete's sake) so you can heat it up to whatever temp you want, providing you protect it from carbon contamination. My CarTech brochure notes the permeability you get after annealing at 1000 C and 1100 C, so bake away, my friend!

Good luck!

Lee Gearhart
- East Aurora, NY

Kovar is annealed in liquid hydrogen during the manufacturing process and it is difficult to remove all of the hydrogen from all of the grain boundries, but you can try 300 or 350 deg. C bake (higher temp. may be ok, depending upon whether you plan further machining or not). If you can do it in nitrogen in a vacuum it is better. If you do the bake in standard air, you will oxidize the surface and it will be more difficult to plate or process. When you plate the kovar you must do something to eliminate it from the gold plating because there will be a lot of hydrogen in that.
Hope this helps a little.

Nancie Barker
Hybrid Semiconductors - Morgan Hill, CA, USA

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