I wish we could attach photo's but the server will not pass them on to us...

You need to find a spot where you can publish them like Steve's website or
Webshots or something like that....
Then include a link where we can go look at them.

Bill Brooks - KG6VVP
PCB Design Engineer , C.I.D.+, C.I.I.
Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510
e-mail:[log in to unmask]
http://www.dtwc.com
http://pcbwizards.com


-----Original Message-----
From: - Bogert [mailto:[log in to unmask]]
Sent: Monday, March 14, 2005 4:12 PM
To: [log in to unmask]
Subject: [TN] Capacitor Terminal Silver Braze Problem

March 14, 2005

Folks, the attached photographs show some type of problem with a silver to
ceramic braze joint.  The joint provides a seal around a capacitor terminal.
The manufacturer rejected the terminal due to the noted conditions.

In the photo titled top view, the white area on the outer diameter is a 90%
Alumina ceramic.

Next to the ceramic is the silver braze connection that connects the ceramic
to 304 stainless steel using Ag 2.5 silver solder (i.e., 97.5PbAg2.5).

In the middle of the top view photo is a copper terminal.

The other three photos show the top view enlarged in the 8 o'clock, 4
o'clock and 10 o'clock positions.

As you can tell from the photographs, the silver braze joint appears
corroded.  Also, there appears to be poor or non-wetting to the 304 SST, or
otherwise a crack formed.

We used a knife in the area from the one o'clock position to about the 2
o'clock position and were able to easily scrape away the top surface of the
braze down to about a 1/64 inch or > depth till we got to solid braze area.

We had an analysis performed that did not show any chlorides, just silver
and lead.  It could be that the stuff we were able to scrape away is some
form of lead oxide, not sure.

I note that the historical QQ-S-571 specification in section 6 indicates
that Ag2.5 solder is subject to corrosion in a humid environment, as is
Ag5.5.  However, the QQ spec indicates that Ag1.5, which is used
interchangeably with Ag2.5, has better shelf life and will not develop a
black surface deposit.  I don't know if the corrosion for Ag2.5 means just a
black deposit, or if the solder joint will fail due to other type of
corrosion.  I note that J-STD-006 does not include the same information as
does section 6 of QQ-S-571.

During our qualification testing, we subjected a capacitor to high humidity
at high temp for an extended period of time with no evidence of corrosion.


Can you folks please answer the following questions?

1.  What caused the conditions shown in the photographs?  What are the
photographs showing?

2.  Would brazing (probably a furnace braze, not sure) at too high or too
low a temperature cause the condition?

3.  Will Ag2.5 corrode in a humid environment? If so, what type of
corrosion, and why can it occur?  Is it a black surface condition?, or can
the corrosion ultimately cause failure of the braze joint?  What is the
physical science basis for the corrosion?  Why does it only occur for
certain % of silver content, and not for all % of silver?

4.  Why doesn't J-STD-006 have the same info as QQ-S-571 regarding corrosion
of Ag2.5 and Ag5.5 solder?

5.  Will the corrosion continue?

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