Cedric

I echo Inge's comments with respect to 'drying' the elements and George,
Richard and Paul's on the possibilities of volatiles and suggested use of
pre-tinning and minimal flux.  Definitely Denny's on wetting to the Ni.

Since you are seeing lot to lot differences - the first thing I would
attempt is to pre-tin!  Answer your Ni wetting question once and for all.
By pre-tinning, you should be able to force it to wett!  ... then clean it.

The channels which Paul mentions DO work, and don't have to be extremely
macroscopic... but you likely can not do that with these parts.

Somewhat surprised that no one commented on Thorsten's suggestion for
(vacuum) vapor phase reflow.  
I my days of making power devices I had the luxury of a vacuum
reflow/brazing system using conduction heating via graphite tooling.  You
would be surprised at how much 'gas & crap' [technical terms] you can pull
out of a plated metal under vacuum - to Inge's comment.  Having pre-wetted
components and no flux [could purge with a forming gas] and ability to
over-pressurize would result in essentially void free joints.

I can see that the vapor phase approach could drastically lessen/eliminate
the need for a flux - assuming the surfaces are clean.  I realize you don't
have one, but maybe for this project, you could go to someone that does -
depending upon whether this was a one shot deal, or will be a recurring
project/nightmare.

What I am not familiar with however, is .... is there such a thing as a
vacuum vapor phase??  
How does that work, or was that just a 'typo'?  
I would like to learn more about that particular piece of equipment if there
is such a critter.

Sincerely,
Steve Creswick
http://www.linkedin.com/in/stevencreswick






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