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:

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