Hi Trent,
What I have been doing, and it seems to work pretty well, is to place the
vias in the center (usually about 9) on a fill. Then I place smaller squares
in the paste mask layer in between the vias. This gives about 50% coverage.
I define the solder mask opening with a fill also.
At 12:46 PM 9/6/2005 +0000, [EMAIL PROTECTED] wrote:
Message: 1
Date: Tue, 6 Sep 2005 11:33:16 -0500
From: <[EMAIL PROTECTED]>
Subject: [PEDA] QFN Footprint, Solder mask for the center pad
To: "Protel EDA Discussion List" <[email protected]>
Message-ID: <[EMAIL PROTECTED]>
Content-Type: text/plain; charset="us-ascii"
I have a question about footprints for QFN packages. Specifically the
solder paste/mask for the center thermal pad
I am using my first QFN package and I thought I would read up on it a little
since I didn't want any problems during production. I came across the
following two documents on the web.
http://www.wolfsonmicro.com/uploads/documents/WAN0118.pdf
http://www.ssec.honeywell.com/microwave/appnotes/QFNsolder-AN310.pdf
Both documents state that the center pad on the QFN should be only be %50
covered by solder paste and the Wolfson document stated that the solder
paste should be in a star shape and that any via's should not be covered by
the solder paste.
Are they correct, only have %50 of the pad covered with solder paste or does
it matter?
Also if they are correct how do I change the solder mask in Protel 99 SE?
For the solder mask I always just place a pad and let Protel do the work.
In case you are curious I am using a Maxim footprint, 16-QFN thin 5x5x0.8mm.
As far as QFN's go it is pretty forgiving with a pad width of 0.3mm (not the
center pad) and a pad spacing of 0.8mm
(http://www.maxim-ic.com/cgi-bin/packages?Type=Max)
Trent
-Bob
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Robert Ritchey
Quest Engineering & Development
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