Hi Leo! Interesting numbers. I can add on more potential source of sulfur
that hits many of facilities even closer - use of nonelectric vehicles in
the factories. Many companies have nonelectrical forklifts and package/mail
delivery vehicles that run up and down the isles and the emissions coming
out of the mufflers isn't kind to silver finishes.
Dave
Leo Higgins
<Leo_Higgins@asat
.com> To
"'TechNet E-Mail Forum'"
03/02/2006 10:00 <[log in to unmask]>,
PM "[log in to unmask]"
<[log in to unmask]>
cc
Subject
RE: [TN] Black "crud" on connector
solder connections causing
electrical short-circuit
- Need Help Please
Further comments on solderability of Ag......Doing some work on the
solderability shelf life of silver palladium thick film material in low
temp
cofired ceramic substrates for IC assembly for a customer program, I came
across a reference that said the in North America the typical hydrogen
sulfide (H2S) level in the air is 7 ppb, but can be much higher near
industrial, coal burning power generation, and heavy duty agricultural
sites
(live stock waste, etc.). Levels in China, especially in highly industrial
zones is commonly as high as 800 - 1200 ppb due in large part to the very
heavy dependence on coal burning for power generation. Unless special air
handling systems (scrubbers) are used, these levels can find there way into
cleanroom atmospheres, where the relative humidity is typically held at 50%
at a typical 25C. Such conditions can tarnish Ag with formation of silver
sulfide quite nicely. In typical non-cleanroom EMS site atmospheres the
temperatures, and humidity levels can be considerably higher. It is
expected that extended exposure time (TBD) of Ag surfaces to these
atmospheres can cause problems with solderability, and gold wire bonding on
the silver spot-plating on leadframes.
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
The information contained in this electronic message is CUSTOMER/SUPPLIER
PRIVILEGED AND CONFIDENTIAL INFORMATION intended only for the use of the
individual or entity named above. If the reader of this message is not the
intended recipient, you are hereby notified that any dissemination,
distribution and copying of this communication is strictly prohibited. If
you have received this communication in error, please immediately notify
the
sender by electronic mail. Thank you.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of David D. Hillman
Sent: Thursday, March 02, 2006 1:22 PM
To: [log in to unmask]
Subject: Re: [TN] Black "crud" on connector solder connections causing
electrical short-circuit - Need Help Please
Hi Ramon! Yes, silver plating such as fine silver and jewelry does darken
when exposed to air. The real question that needs answered is "what is in
the air that would cause the tarnishing?". The "air" around us contains
many more things than just oxygen and nitrogen - there can be significant
contributions from sulfur and chloride species especially if you are living
near a marine environment or just down wind from a metal working plant.
Dave
"Dehoyos, Ramon"
<ramon.dehoyos@NG
C.COM> To
Sent by: TechNet [log in to unmask]
<[log in to unmask]> cc
Subject
03/02/2006 12:11 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
"Dehoyos, Ramon"
<ramon.dehoyos@NG
C.COM>
Hi David:
I found this on:
http://www.chem.umn.edu/services/lecturedemo/info/Silver_oxide.html'
Doesn't silver darken when heavily oxidized? I am talking
about silverware and other silver items like earring, bracelets....The
color of silver changes from grayish white to dark gray. I know that
some are not pure silver, but some are and darken.
Regards,
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Thursday, March 02, 2006 12:38 PM
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
The information contained in this electronic message is
CUSTOMER/SUPPLIER PRIVILEGED AND CONFIDENTIAL INFORMATION intended only
for the use of the individual or entity named above. If the reader of
this message is not the intended recipient, you are hereby notified that
any dissemination, distribution and copying of this communication is
strictly prohibited. If you have received this communication in error,
please immediately notify the sender by electronic mail. Thank you.
-----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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