Advice needed

[GF2277]

I need some advice. An RF Eng. onsite wants to solder a Glass-bead feedthru into an AL housing. I have no experience with these; however from purely a thermal/mechanical nature... this seems very risky. From very limited information I can get, Silver epoxy seems to be the preferred method.

Any comments?

 

[biff44]

Well, people have been using glass bead feedthrus on hermitic military projects for decades, so I do not see what your problem is. Epoxy is not hermetic, solder is. Epoxy will flow all over the place during curing, possibly shorting out the RF center conductor, while solder will not wick over the glass portion of the bead. There are issues that have to be properly addressed, such as the aluminum housing has to be plated to become solderable, and the "glass bead" will have to have a plated metal ring around its outside, probably made of kovar, to solder to.

Properly done, a soldered glass bead will maintain a 10^-8 leak rate after 1000 temperature cycles from -55 to + 125 deg. c. Do you have an epoxy that can do that?

 

[biff44]

Look up a company like ThunderlineZ for installation procedures.

 

[biff44]

You're in luck, thunderline has a soldering guide to show you how to do it:

http://www.thunderlinez.com/