Thanks for the input.  We've used a helium leak detector..  A good
technician spent an hour checking the tube and pretty well pinpointed the
leak - it's through a soft soldered joint.  We're fairly sure it's not
outgassing, the needle on the vac-ion pump goes up 15 seconds after we pass
the probe over the suspected leak area.  We're not sure whether it's a
porosity problem, an adhesion problem or even a leakage through the cold
rolled steel.  This tube has always been produced before with no problems
of this type.  That's what makes this leak puzzling.  Right now I'm
wondering if it's an adhesion problem, and if I could heat up the joint
inside of a bell jar (in vacuum) to get the adhesion voids to bubble out.
All input welcome.

Thanks,

Sam



>Have you ruled out the possibility of it being outgassing, rather than a
>real leak? Have the materials in this location been used with success
>before or are the materials new? A couple things to try to help figure
>this out is to use a Helium leak detector or even a bakeout (in case the
>source is from residue that's outgassing). Good luck.
>
>Regards,
>
>Paul Terranova
>Analytical and Environmental Test Services Lab
>
> Digital Equipment Corporation
> 200 Forest Street
> Mail Stop: MRO3-1/D2
> Marlboro,  MA  01752-3085
>
>'    Phone: (508)467-3109
>* Fax: (508)467-6796
>* Email: [log in to unmask]
>WebSite: http://www.digital.com/lab-services
>
>               -----Original Message-----
>               From:   Samuel Flores [mailto:[log in to unmask]]
>               Sent:   Sunday, May 10, 1998 7:56 PM
>               To:     [log in to unmask]
>               Subject:        [TN] Leakage paths through soft solder
>joints
>
>               Is anyone familiar with gas leakage paths through soft
>soldered joints?
>               Part of a vacuum electron device which I am working with
>has a puzzling
>               leak.  It occurrs only when the device is at a temp of
>85C or above.  The
>               joint is between a cold-rolled steel piece and a
>Carpenter-42 piece.  We
>               suspect it is either in the solder itself or in the
>interface between the
>               solder and the cold rolled steel.  Appreciate all input.
>
>               Thanks,
>
>               Sam
>
>
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