Unfortunately, the supplier who achieved the plating closed recently and we
have no details about the process. We will perhaps perform a micro-section
for that reason. If we do so, we will have also the answer about whether it
is a matter of wetting or a matter of outgasing.
My conviction is that we are facing with a wetting issue because we made an
other production run with other parts and other Al baseplate that work well
(15-20% voiding rate, having the paste and profile the same and a paste
pattern very similar).
Here are my comments and answer about your post:
*** 1 *** WETTING :
Ioan, I wonder if cooper plating over aluminium will not lead to galvanic
corrosion problem. I've read zincate process should be a better choice for
that reason as Denny outlined.
Denny, the nickel plating issue is one of the causes I'm suspecting. The
other is perhaps an oxide layer in silver, but I have poor experience with
silver finition. What do you think about this hypothesis? And how the oxide
layer could be removed to make a test?
*** 2 *** Flux outgasing
Torsten,
Thanks for your advise. Unfortunately we do not have any vapour phase oven
but I will think further about your suggestion regarding reducing the flux
rate in solder paste and use Nitrogen.
Richard,
Your suggestion: 'Can you plate the part surface with solder, and pre-solder
the area on the aluminum? This will eliminate voids induced from the solder
paste.'
-> Not too difficult, I will set up a test.
Phil,
We tested 2 paste patterns, it wasn't relevant. Nevertheless we do not
reduce as much as 45% of the area neither we experimented a checkerboard of
dots.
Regards,
Cedric
-----Message d'origine-----
De : TechNet [mailto:[log in to unmask]] De la part de Dennis Fritz
Envoyé : jeudi 17 février 2011 18:49
À : [log in to unmask]
Objet : Re: [TN] Voids issue on Aluminium base plate
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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