Gerald,
I've been involved in similar tasks decades ago. You have a classical
and dramatic picture, which can be 'analyzed' as follows:
Pins are likely to be Kovar which is common for glass feedtrues
(FeNiCo).
The pins are probably copper plated with a nickel barrier and then gold
plated for solderability.
The wires are probably ogygen free copper with a barrier and finally
silver finish for solderability.
So, you have a nice chain of electrochemical aspirants: Iron, Nickel,
Cobalt, Silver, Gold, Copper, Tin, Lead plus movable ions from flux
residues. This combination has caused our company some real problems
with connectors and inductive loads in the past. If your application is
airborne or navy, we are even closer.
First, I know that it use to be a problem to get a perfect plating in
the pin-to-glass interface. Oftenly, there is a small gap, or there will
be when you scratch the pins to get a better surface for soldering. This
little gap is a trap! I think your equipment has been exposed to water
condensation, which is not unusual for mil cans (Viet Nam, Korea etc).
The presence of ions will start migration in seconds (Copper, Silver,
Iron etc...yum-yum)and you will get a bridge of metal products between
the pins. And, finally, arcing. The DC bias voltage creates the
corrosive actions and the coil you mentions may give sparks. This can go
on until there is no Iron left in the pin-to-glass interface, and the
pins falls off!!
To minimize the risks, we ordered glass connectors without gold plating,
just tinned to decrease the electromotoric potential. The pins must not
be scratched or bent. And only tinned wires for this kind of
application. The wires are secured against stretching or moving. The
flux residues are extremly well removed and sometimes, silicon is
applied.
I bet the 'corrosion bridge' at your photos is Lead with some Copper.
Ingemar Hernefjord
Ericsson Microwave Systems
PS. I'm not so active at the moment because of illness, but this topic
woke me up.
-----Ursprungligt meddelande-----
Från: TechNet [mailto:[log in to unmask]] För - Bogert
Skickat: den 2 mars 2006 00:51
Till: [log in to unmask]
Ämne: [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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