[time-nuts] HP 5065A rubidium lifetime (soldering kovar)

[Joseph M Gwinn]

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