Good Morning! I recommend focusing on the components surface finishes
before I would begin chasing soldering iron questions. A couple of
potential trouble spots:

a) You listed the terminal block as brass overplated with gold. Gold over a
copper (e.g. brass)  has historically not been a stable solderable surface.
Secondly, the zinc in the brass can diffuse into the gold forming some
wonderfully weird combinations which I doubt are solderable. A nickel flash
between the gold and the brass would prevent having zinc diffusion issues.
I recommend you run a JSTD-002B solderability test to determine wetting
characteristics.

b) You listed the wire as nickel plated copper. Nickel oxide is really
stable and doesn't like to allow solder wetting without using a reasonably
active flux composition. You will need to find a flux composition that is
tailored for wetting a nickel surface. Again,  a JSTD-002B solderability
test to determine wetting characteristics is a good approach.

Good Luck.

Dave Hillman
Rockwell Collins
[log in to unmask]



                      - Bogert
                      <[log in to unmask]>        To:       [log in to unmask]
                      Sent by: TechNet         cc:
                      <[log in to unmask]>        Subject:  [TN] Seeking help on hand soldering problem please


                      02/07/2004 08:54
                      AM
                      Please respond to
                      "TechNet E-Mail
                      Forum."; Please
                      respond to -
                      Bogert






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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