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February 2011

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Subject:
From:
Dennis Fritz <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Dennis Fritz <[log in to unmask]>
Date:
Thu, 17 Feb 2011 12:49:02 -0500
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Ioan, I think you have the right idea, but maybe not the exact solution.  Aluminum is very sensitive to plating solutions of any type - most are very corrosive to the aluminum - think sulfuric acid.  There most probably is a barrier over the aluminum to facilitate further plating.  For instance, aluminum hard drives are treated with a zinc solution (zincate) before electroless nickel is applied.  Literally billions of aluminum core hard disk drives are produced this way each year. I think there is fair chance this heat slug is first electroless nickel plated, and then finished with either electroplated or immersion silver. 

Cedric - can you get TechNet the details of the nickel and the silver on your heat sink?  Many of us have experience soldering to electroless nickel (ENIG) or electroplated nickel - active flux.  The silver goes into solution in the solder almost instantly, so you are really dealing with a nickel soldering issue. 

Denny Fritz





-----Original Message-----
From: Ioan Tempea <[log in to unmask]>
To: TechNet <[log in to unmask]>
Sent: Thu, Feb 17, 2011 12:07 pm
Subject: Re: [TN] Voids issue on Aluminium base plate


Bonjour Cédric,
Maybe you should try playing with the finishes. The first question coming 
hrough my mind is why Ni/Ag on top of the Al? Ni wets slower than Cu, so why 
ot going for a Cu/Ag plating on the Al...? Also, Cu instead of Ni might help 
he RF performance. Maybe you should also try tinning the Ni/Au of the 
omponent.
Bonne chance,
Ioan Tempea, ing.
ngénieur Principal de Fabrication / Senior Manufacturing Engineer
 | 450.967.7100 ext.244
 | [log in to unmask] 
 | www.digico.cc
N'imprimer que si nécessaire - Print only if you must
-----Original Message-----
rom: TechNet [mailto:[log in to unmask]] On Behalf Of Cedric ORAIN
ent: Thursday, February 17, 2011 6:26 AM
o: [log in to unmask]
ubject: [TN] Voids issue on Aluminium base plate
Dear Technetters,
We have to solder a RF power transistor onto an aluminium base plate and
e
re facing with a very challenging issue.
We encountered a high voids rate (>30% or 40%) underneath the component
ody
which is about 35x10mm). This is not acceptable for this application.
The component is Nickel/gold plated whereas the aluminium baseplate is
lated with Nickel and Silver and then cleaned with solvent.
We tried to change/adapt:
 soak time of the profile, 
 2 difference solder pastes (SAC305), 
 change the screen design and thickness
Finally none of these parameters looks to have significant effect on
oids
ate. We are now wondering if the solderability of the Ni/Ag plating is
ood
nough and even if it is convenient for that purpose.
Is somebody could give us advises? How to enhanced NiAg plating
olderability (acid ?!, ...)? Which flux could help to compensate the
oor
ettability? Which kind of plating would be preferable? ...
Thanks and regards,
Cedric

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