March 2, 2006
Hi Dave. I just sent the attached photos to Steve to post on his site. Any comments?
----- Original Message -----
From: David D. Hillman<mailto:[log in to unmask]>
To: [log in to unmask]<mailto:[log in to unmask]>
Sent: Thursday, March 02, 2006 6:45 PM
Subject: Re: [TN] Black "crud" on connector solder connections causing electrical short-circuit - Need Help Please
Hi Greg! I have been using SERA testing to get a better handle on the
relationship of tarnish color, surface species, and solderability impact.
The SERA methodology uses electrochemical reduction to differentiate the
silver oxide, silver chloride and silver sulfide species. The technique is
not perfect as there are some signal overlap issues and some other
confounding surface species. My testing of "good looking, clear colored"
immersion silver pwbs shows only silver oxide. However, as the immersion
silver finish begins to "yellow' I see both silver oxide and silver
chloride. And the immersion silver pwbs which have a brown or black
appearance show little silver oxide but strong indications of either silver
chloride or silver sulfide. Immersion silver pwbs which have been exposed
to sulfur containing cardboard also show very strong indications of silver
sulfide. Using a "cleanable no clean flux" I have not had too many issues
soldering clear or yellowed immersion silver finishes but silver sulfide
(black) causes me lots of problems. Don Cullen, MacDermid, published a
paper some time back that also showed that up to around 500 A of surface
species (yellow in appearance) the finish solderability was not
significantly impacted. Looks like my testing results match up fairly well
with your past electrochemical experiences. I view the tarnish reaction of
immersion silver is an advantage - when immersion tin goes bad there is
often no visual indication that a loss of solderability has occurred.
Dave
"Munie, Gregory"
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m> To
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03/02/2006 03:57 <[log in to unmask]<mailto:[log in to unmask]>>,
PM <[log in to unmask]<mailto:[log in to unmask]>>
cc
Subject
RE: [TN] Black "crud" on connector
solder connections causing
electrical short-circuit -
Need Help Please
Dave
My memory may be fuzzy after all these years but it seems to me that under
special circumstances (whatever those may be as I did this
electrochemically a LONG time ago) you can produce Ag+2 oxide which is dark
in color. (I would assume SERA could pick up +1 and +2 if both were there.)
If this unit has been powered up maybe the circumstances are right for the
"dark side" of silver to appear. Otherwise I agree that the pure Ag+ oxide
should be light/transparent. Or it could be a sulfide as George has noted.
I'd be interested in hearing commentary: I did this work 34 years ago and
am depending on my very defective memory bank.
Greg
________________________________
From: TechNet on behalf of David D. Hillman
Sent: Thu 3/2/2006 11:37 AM
To: [log in to unmask]<mailto:[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<mailto:ramon.dehoyos@ng>
c.com> To
"TechNet E-Mail Forum"
03/02/2006 09:37 <[log in to unmask]<mailto:[log in to unmask]>>,
AM <[log in to unmask]<mailto:[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]<mailto:[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]<mailto:[log in to unmask]>
Leo Higgins
<Leo_Higgins@ASAT<mailto:Leo_Higgins@ASAT>
.COM>
To
Sent by: TechNet [log in to unmask]<mailto:[log in to unmask]>
<[log in to unmask]<mailto:[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]<mailto:[log in to unmask]>>
; Please respond
to
Leo Higgins
<Leo_Higgins@ASAT<mailto: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]<mailto:[log in to unmask]>
www.asat.com<http://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]<mailto:[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]<mailto:[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]<mailto:[log in to unmask]<mailto:[log in to unmask]>>
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