Hi Rick & all

     We as a company have experienced the observation you mentioned along
     with I guess a million other users.  A while ago we carried a
     collaborative assembly exercise along with several other companies for
     the National Physical Laboratory looking at the effects of using
     Palladium coated components.

     The results of this exercise are due out at their SSTC autumn meeting
     on the 22nd October.  Early indications are that the wetting effect or
     lack of as the case may be (that cause of the muddy footprint
     phenomena) is down to the dissolution rate of Palladium.  As with
     conventionally coated SnPb components there is a solderable medium
     already on the component which melts & merges with the solderpaste
     enabling good wetting, all othet things being right.

     With Palladium coated components, melting of the Palladium doesn't
     occur (it req's >1000C to melt) soldering relies on dissolution of the
     Palladium to enable connection to the underlying material.  It's a
     trade off between a very thin coating of Pd allowing quicker
     dissolution against a thicker coating which provides less porosity but
     won't allow a good soldering action, either way their isn't sufficient
     energy in the paste to provide a similar wetting effect to SnPb coated
     components.

     Having said all this the interesting fact must be is it a problem wrt
     joint failure, the answer to that is wait and see the outcome of the
     report - I don't want to steal their thunder!

     There are a lot more interesting points noted & spelled out in more
     detail in the NPL report so it's probably worth contacting them for a
     copy.  Try - [log in to unmask]

     Regards Iain.


______________________________ Reply Separator _________________________________
Subject: [TN] Soldering Palladium plated leads
Author:  rthompson ([log in to unmask]) at Internet
Date:    10/2/98 3:39 PM


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Hi,

With all the current discussion of solderability issues, I'm hoping some of
you may be able to apply your expertise and give me some insight into a
problem we seem to consistently have.  When soldering components with
palladium plated leads, we do not seem to get any wetting on the leads.  It
kind of looks like the 'footprint in mud' affect.  On pcb's where we have
this condition, all other components have soldered fine with good fillets and
wetting.  Checks of the oven profile indicate a good profile for the paste
we're using (Kester R598, water soluble).  Currently we've only found this on
components from TI, so I don't know if it's only their components or the
plating in general.

Question: Are there any recommendations for profile, paste, process, etc.
that differ from 'standards' when working with these types of components?

Thanks.

                Rick Thompson
                Ventura Electronics Assembly
                2665A Park Center Dr.
                Simi Valley, CA 93065

            [log in to unmask]

                (805) 584-9858 voice
                (805) 584-1529 fax

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