[time-nuts] HP 5065A rubidium lifetime (soldering kovar)
Joseph M Gwinn
gwinn at raytheon.com
Mon Mar 22 21:56:51 UTC 2010
time-nuts-bounces at febo.com wrote on 03/21/2010 10:43:40 PM:
> From:
>
> Bob Camp <lists at rtty.us>
>
> To:
>
> Discussion of precise time and frequency measurement
<time-nuts at febo.com>
>
> Date:
>
> 03/21/2010 10:52 PM
>
> Subject:
>
> Re: [time-nuts] HP 5065A rubidium lifetime
>
> Sent by:
>
> time-nuts-bounces at febo.com
>
> Hi
>
> One thing to be careful about with all this tinning of strange
materials:
>
> There is indeed a way to get it *almost right". The lead wets
> with solder and the lead will indeed pass a tug test. Thermo-
> cycle the lead a dozen times and you can pull it right out of
> the solder.
>
> If you are going to do this on any "mission critical" devices,
> it's best to check the result fairly carefully until you are
> sure of your materials and technique.
>
> --------------------
>
> While I have no direct experience with a problem, I also
> suspect you would want to keep your stash of phosphoric acid
> away from any un-tinned kovar leads. Kovar it's self will not
> solder, but it's oxide will. Strip the oxide and you have a
> significant problem. You have to get the stuff very hot to re-
> form the oxide you need.
I'm surprised by this. In the 1970s, I had the kovar leads on some nixie
tubes become unsolderable (probably due to minor corrosion - the leads
looked OK), and solved the problem by dipping the leads in dilute sulfuric
acid (battery acid diluted 10:1, so about 2% strength) for a few seconds
and washing off in tap water. I would assume that the acid pickling
removed an offending oxide layer.
Joe Gwinn
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