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March 2006

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Subject:
From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Thu, 2 Mar 2006 14:30:03 -0600
Content-Type:
text/plain
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text/plain (329 lines)
You are 95% correct. The silver saver paper is simply a sulpher-free
paper. Oxygen can and will tarnish the immersion silver finish on PWBs,
but much more tarnishing will take place if a sulpher-laden paper is
used (nearly all paper is made with sulpher). To really keep the boards
from tarnishing, use the silver saver paper liners and hermetically wrap
the brick of boards with a vacuum-seal low-outgassing wrap.

But Mr. Bogert's problem has nothing to do with immersion silver
finishes on the pwb.

In his particular case, the black oxides showing up on the silvercoated
wires are not from the silver finish on the wire strands, but from the
PREVIOUS flux residue used to tin the wires at the OEM. The note from
Mr. Bogert references the tinning process using 63/37 solder done by the
OEM. When you leach some of that flux back out from under the
insulation, add some different flux to it from the WRMAP 10 wire solder,
and try to solder silver-finished wires to a gold ring that has 50
uinches of gold on it, you can bet your supper it will have poor wetting
and black crud. The poor wetting is from too much gold. The black crud
is from a reaction between the WRMAP flux and the ORH1 or ORH0 flux the
OEM probably used. 
One should never tin wires with any flux other than a no-clean or RMA
flux, and never mix flux chemistries when soldering. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Thursday, March 02, 2006 11:38 AM
To: [log in to unmask]
Subject: Re: [TN] Black "crud" on connector solder connections causing
electrical short-circuit - Need Help Please

Hi Ramon - I have several  references show that silver oxide is
transparent, silver chloride is yellow/brown , and silver sulfide as
black.
The reference you cited (where did that information come from?) shows
that the oxidation reaction is associated with a color change which I
don't believe is correct. Also, when "silver saver" paper is used,
silver finishes do not tarnish and I know that the "silver saver" paper
does not prevent oxygen from the surface of the silver plating. Ok
TechNetees (George W., Rudy, George M, Gerard O., John B.etc.) what do
your references information say?

Dave



             "Dehoyos, Ramon"
             <ramon.dehoyos@ng
             c.com>
To
                                       "TechNet E-Mail Forum"
             03/02/2006 09:37          <[log in to unmask]>,
             AM                        <[log in to unmask]>
 
cc

 
Subject
                                       RE: [TN] Black "crud" on
connector
                                       solder connections causing
                                       electrical         short-circuit
-
                                       Need Help Please











             Read below:

             Silver metal will oxidize spontaneously upon exposure to
free oxygen. This process is commonly referred to as "tarnishing". The
chemical reaction describing this proces is shown below.
4 Ag  (s)  +  O2 (g) (r) 2 Ag2O  (s)
Silver metal is a grayish white color, silver oxide is a black color.
This contrast in colors makes tarnished silver appear much different in
appearence than untarnished silver. This explains why so much physical
and chemical effort is spent in removing the tarnish from silver
objects.

Thermodynamic Constants of Compounds of Interest [1] Compound DHof
(kJ/mol) DGof (kJ/mol) So (J/mol.K)
Ag (s) 0 0 42.6
O2 (g) 0 0 205.2
Ag2O (s) -31.1 -11.2 121.3







-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Thursday, March 02, 2006 10:29 AM
To: [log in to unmask]
Subject: Re: [TN] Black "crud" on connector solder connections causing
electrical short-circuit - Need Help Please

Hi Leo! I might be mistaken but I thought that silver oxide (Ag2O) was
transparent (e.g clear). The other species you mentioned my references
show as black or other various colors.

Dave Hillman
Rockwell Collins
[log in to unmask]




             Leo Higgins
             <Leo_Higgins@ASAT
             .COM>
To
             Sent by: TechNet          [log in to unmask]
             <[log in to unmask]>
cc


Subject
             03/01/2006 10:37          Re: [TN] Black "crud" on
connector
             PM                        solder connections causing
                                       electrical         short-circuit
-
                                       Need Help Please
             Please respond to
              TechNet E-Mail
                   Forum
             <[log in to unmask]>
             ; Please respond
                    to
                Leo Higgins
             <Leo_Higgins@ASAT
                   .COM>






Might be a coincidence that the 'crud'in the referenced, but not seen,
photos is black, but Ag2O, Ag2CO3, Ag2S, AgCl, and AgNO3 are all black.


Best regards,
Leo

Leo M. Higgins III, Ph.D.
Vice President, Technical Support Operations ASAT, Inc.
3755 Capital of Texas Highway, Suite 100
Austin, Texas     78704

office phone   512-383-4593
mobile           512-423-2002
[log in to unmask]
www.asat.com


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-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Richard Kraszewski
Sent: Wednesday, March 01, 2006 8:01 PM
To: [log in to unmask]
Subject: Re: [TN] Black "crud" on connector solder connections causing
electrical short-circuit - Need Help Please


I don't see any photos.

Rich K / KEDS
260.925.8719

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of - Bogert
Sent: Wednesday, March 01, 2006 6:51 PM
To: [log in to unmask]
Subject: [TN] Black "crud" on connector solder connections causing
electrical short-circuit - Need Help Please

March 1, 2006

Folks, the three attached photographs show some problems an OEM of ours
is having.  Specifically, he hand solders two MIL-W-16878 silver coated
stranded wires to a MIL SPEC connector that has solder eyelets plated
with 50 microinch of gold.  Sn10 WRMAP flux cored solder is used with no
additional flux added.  The OEM has had recent rash of failures in
fielded equipment.  We do not know the cause yet.  We are having the
black residue shown sent out for analysis but no results yet.

The solder joints do not appear to be acceptable to me.  One can see
exposed gold on the gold-plated connector contact eyelets.  Appears to
be non-wetting???  Also, appears to be excess solder since strands are
not always visible in the joint.  The OEM tins the stranded wire with
Sn63 prior to soldering.

Do you folks have any ideas on what the problem could be?  There is
detailed info on the photographs on the application of the product.  The
connector provides power to a solenoid that actuates a valve.

The application is hermetic sealed by welding the connector to a metal
housing that contains the solenoid winding.  The wires connecting to the
connector are the MIL-W-16878 silver coated stranded lead wires that
connect from the gold plated connector pins on one end to the MIL SPEC
magnet wires on the solenoid on the other end.  The solenoid is
varnished (DIP process, no vacuum).

I am aware that silver plated wire in an SO2 environment can cause
corrosion, but we use a lot of silver coated wire in other product with
no known corrosion problems.

The connector housing has a small vent port into which air is applied to
do a pressure seal test.  After the pressure test is completed, the vent
hole plug is welded closed.  We are checking to see if the air could
have had moisture in it.

Dielectric strength, insulation resistance and functional testing is
done on the solenoid after assembly is completed and all tests passed.
However, failures occur in the field.

Since the flux used in the SN10 flux-cored solder is RMA, one would
normally not expect the black residue to be due to RMA flux but I am not
sure.  We will probably know for certain after we get the test results
on the black crud.

Any insight you may have into into this problem would be appreciated.

Please e-mail your response to following e-mail address:

[log in to unmask]<mailto:[log in to unmask]>

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