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November 2009

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Subject:
From:
"Braddock, Iain (UK)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Braddock, Iain (UK)
Date:
Mon, 9 Nov 2009 11:27:19 +0000
Content-Type:
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A few years ago we had some capped, planarized via's on a rather
challenging board, the capping was planarised by linishing; several
batches down the line we found during sectioning they had managed to
locally remove most of the Cu.

Regards,
	Iain.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: 07 November 2009 09:16
To: [log in to unmask]
Subject: Re: [TN] Via fill for heat transfer

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Kevin,
how do you perform the planarization in practice?
/Inge


----- Original Message -----
From: "Glidden, Kevin" <[log in to unmask]>
To: "TechNet E-Mail Forum" <[log in to unmask]>; "Inge" 
<[log in to unmask]>
Sent: Friday, November 06, 2009 8:37 PM
Subject: RE: [TN] Via fill for heat transfer


Inge,

I would fill the vias completely, and have them planarized and capped.
This 
prevents the solder thieving and eliminates air pockets in the fill, or
the 
risks of a tented via on one side.  I am not sure of the limitation on 
plugging in such a small via - what is the aspect ratio?  Smaller vias
might 
be candidates for electroplating plugging.


-----Original Message-----
From: Inge [mailto:[log in to unmask]]
Sent: Friday, November 06, 2009 1:18 PM
To: [log in to unmask]
Subject: Re: [TN] Via fill for heat transfer

Hey there,

I've a q about via fill for LGA, small ones, package 5x5 millimeters and
8
I/Os, teflon one layer on thick brass back. Heat transfer vias 0.5 mm.
How
do you fill them before mounting the LGAs? Halfways, even or overfilled?
If
the solder volume is too meagre, there will not be a good SJ against the
LGA
heat sink (under side), if you  have too much solder, you may get
overbridging. There are five vias for the contact with the heat sink,
four
vias in a square and one in the middle. We solder same size of packages
with
J-leads on the same board, and they become perfect, but the LGAs get
varying
result.

/Inge

PS. I regret the deplorable incident in Austin. Bad, very bad in many
aspects, both socially and politically. The human nature is really
unpredictable.

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