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December 2005

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From:
"David D. Hillman" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Fri, 2 Dec 2005 15:48:58 -0600
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Hi Kevin! I could give you the standard Doug Paul's response "it depends"
but then I would owe him another Mt. Dew royalty! There are two prevailing
groups of thought on flux selection for pretinning and you described both
sides of the coin very well. IMHO I think that the water soluble solution
is best choice with one very big qualifier- you must absolutely insure that
the post pretinning cleaning process effectively neutralizes/removes any
non-reacted flux material. There are some component types that you can not
insure complete cleaning and therefore the rosin flux choice is more
appropriate. I would not recommend using the "stock time-frame" as a
screening method to see if corrosion is going to take place. Ion
Chromatography is a good way to measure the effectivity of the post
pretinning cleaning process. My vote is for the water soluble choice. Ok
the count is water soluble: 2, rosin: 1. Next!

Dave Hillman
Rockwell Collins
[log in to unmask]




             Kevin Glidden
             <[log in to unmask]
             COM>                                                       To
             Sent by: TechNet          [log in to unmask]
             <[log in to unmask]>                                          cc

                                                                   Subject
             12/02/2005 03:36          [TN] Pre-tinning wire & components
             PM


             Please respond to
             [log in to unmask]
                    om






Hello all,

Question on pre-tinning of components and wires.  We are in a debate here.

Is it desirable to pre-tin wires and components with a water soluble (high
activity) or an RMA (low activity)?

My position is that water soluble (high activity) is the preffered flux
type
over RMA to provide better pre-tin and also ease of cleaning.

Others are arguing that there is significant risk in using the water
soluble
due to the corrosive residues, particularly if they are able to wick up the
wire and under the insulation.  They state rosin is to be used for
pre-tinning to mitigate that risk. My issue with this method (aside from
the
lower activity level potentially yielding a lower quality pre-tin) is that
our termination process can call for either rosin flux or water soluble
flux, depending on the application or product, and I am concerned that any
rosin residues from the pre-tin (more difficult to remove than water
soluble) could negatively impact the termination solder joint.

Another thing to consider is that we stock pre-cut and pre-tinned wires at
point-of-use, so there could be a significant time-frame between
pre-tinning
and termination.   Depending on your view, this could be time for the water
soluble residue to work it's corrosive magic or for RMA residue to nicely
harden.

Thoughts?

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