I think the reference to double tinning probably stems from the use of
solder pots to remove gold from component leads in a dipping process. This
was quite common on packaged devices which, before selective plating,  were
generously gold plated for MIL apps. 
First pot/station would remove gold into pot, but naturally leave behind a
slightly gold enriched coat. Amount of gold gradually increases. A dip into
second pot would leave virtually pure solder.
After a time the first pot is emptied and the second pot becomes the first
and the empty pot is refilled to be the second station.
Now write that out into Speclish and add some numbers.
Now it's solidified into a specification all similar processes will be done
that way so as to be compliant with a spec.
Wicking or sucking solder out of cups would qualify as similar, the
difference is that you can't accumulate gold on the work surface. 
If that explanation is not accepted.......
Suggest an interpretation/SOP would be to remove the gold with wick or
whatever and then "redress the cup with fresh solder as/if required". As
meaning is in the eye of the beholder, that should satisfy whoever it is
saying do double dip without actually requiring you to do it. Or if you're
subsequently required to do it, not have to rewrite your operator SOP. Or am
I being too cynical?
A double removal would seem superfluous and result in 3 heat cycles which
could be damaging.

Best Wishes
 
 
 
Mike

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gumpert, Ben
Sent: Friday, May 03, 2013 4:31 PM
To: [log in to unmask]
Subject: [TN] How to Tin (remove gold from) Solder cups

Technetters,

It looks like from the archives that we all agree that removing the gold
from solder cups is necessary to get a good joint. So that leaves me with a
couple of questions:

1. Does anyone have some recommendations on a good method to ensure adequate
gold removal, especially on really small cups? Is adding solder and then
removing it with a solder wick the standard method?

2. What does a double-tinning method really mean (i.e. what do I need to do
to meet the requirement of J-STD-001E Para. 4.5.1?)

A single tinning process would be to fill the cup with solder wire and then
reflow that solder to 'tin' the cup, followed by the installation of a wire.
So does a double tinning just mean that the solder is removed ONCE and the
cup tinned a second time with the solder that will be used to create the
final joint? I have had some people tell me that the solder had to be
removed TWICE to be considered 'double-tinning'. (Of course the main goal
should be to get rid of the gold and the process should be based on
achieving that goal, but that may be a different discussion.)

Ben

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