February 7, 2004

Folks, we have an OEM who is having problems making a good solder connection from 18 gauge nickel plated stranded wire to a gold plated standoff terminal.  The OEM is getting what appears to me to be severe non-wetting or exposure of an oxide layer under the top gold layer when the gold is melted by the solder.

The wire is MIL-W-22759/2 18 gauge, nickel coated stranded copper.  The standoff terminal, which is assembled in a molded terminal block, is brass per QQ-B-626, Composition 22, 1/2 hard with 0.000020 inch gold per MIL-G-45204.

Two different plating shops are used for the gold plating.  One shop plates the gold over a nickel flash.  I don't believe the other shop uses nickel flash.  

Solder used is Sn96 Kester flux core 282 (RMA)(24-7050-7420).  Kester indicated that this FLUX can be used to make an acceptable connection to gold plated brass with a nickel flash, but not to gold gold plate with no nickel flash.  Kester recommended an RA flux cored solder (Kester 44).

The OEM was able to make good solder joints using Kester flux 282 cored solder when he soldered to gold plated standoff terminals that were plated by a different vendor.

I suspect the problem may be related to the plating process used for the standoff terminal since one vendor part would solder OK but the other would not, using the same 282 flux cored solder for both.

However, I recommended the OEM do the following to help solve the problem:

1. Do solderability test on the as-received terminals per the IPC Standard.
2. Remove all gold from the terminals by dipping.
3. Tin the nickel stranded wire.

There may be other factors involved.  For example the size of the soldering iron used (wattage rating), tip temperature, soldering time, etc.

What wattage iron should be used for soldering the 18 gauge wire to the terminal?  What tip temperature? How long to make the connection?  Since the solder is Sn96 it would take higher temp and possibly more time than soldering to Sn63.


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Any help on solving this problem would be appreciated.  Thanks