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February 2011

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Subject:
From:
Cedric ORAIN <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Cedric ORAIN <[log in to unmask]>
Date:
Thu, 17 Feb 2011 20:52:40 +0100
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text/plain (172 lines)
Do you mean between Ni and AL ?

-----Message d'origine-----
De : TechNet [mailto:[log in to unmask]] De la part de Eric Christison
Envoyé : jeudi 17 février 2011 17:53
À : [log in to unmask]
Objet : Re: [TN] Voids issue on Aluminium base plate

Cedric,

Maybe a bit tangential to your question but don't you have a bad 
combination of metals in the joint? I'm wondering if you're in danger of 
setting up a galvanic cell which will lead to the aluminium corroding.

Regards,



On 17/02/2011 16:27, Phil Bavaro wrote:
> Cedric,
>
> Lots of things come to mind....plating thicknesses, paste patterns,
> wetting, profiles.
>
> Is there any pattern to the voiding? Does it resemble the printed paste
> shape?
>
> I have soldered lots of RF transistor bases down, but I haven't ever
> soldered them to NiAg plated aluminum (always to Ni/Au plated copper
> slugs).
>
> You don't mention the paste patterns used but that will contribute to
> large voiding if you don't give the gases a path to get out.  I would
> reduce the solder paste coverage to 45%, use a checkerboard pattern of
> dots, and then observe the voiding pattern.
>
> This assumes that the voiding is not relative to wetting as that will
> change everything.  To do this, check the solderability of both surfaces
> being soldered to independently.
>
>
> Phil
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Cedric ORAIN
> Sent: Thursday, February 17, 2011 6:26 AM
> To: [log in to unmask]
> Subject: [TN] Voids issue on Aluminium base plate
>
> Dear Technetters,
>
> We have to solder a RF power transistor onto an aluminium base plate and
> we
> are facing with a very challenging issue.
>
> We encountered a high voids rate (>30% or 40%) underneath the component
> body
> (which is about 35x10mm). This is not acceptable for this application.
>
> The component is Nickel/gold plated whereas the aluminium baseplate is
> plated 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
> voids
> rate. We are now wondering if the solderability of the Ni/Ag plating is
> good
> enough and even if it is convenient for that purpose.
>
> Is somebody could give us advises? How to enhanced NiAg plating
> solderability (acid ?!, ...)? Which flux could help to compensate the
> poor
> wettability? Which kind of plating would be preferable? ...
>
> Thanks and regards,
>
> Cedric
>
>
>
>
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-- 
Eric Christison
Consumer&  Micro group
Imaging Division

STMicroelectronics (R&D) Ltd
33 Pinkhill
Edinburgh EH12 7BF
United Kingdom

Tel:	+44 (0)131 336 6165
Fax:	+ 44 (0)131 336 6001

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