Trent,
Here is some more info. regarding QFN's. It's a long link so you
may have to copy and paste.
http://www.carsem.com/services/Drwgs&Data/CSM-MLP%20apps%20note-4-23-200
2-300dpi.pdf
Also, I have some general info. regarding center thermal pads.
http://focus.ti.com/lit/an/slma002/slma002.pdf
If you can't access the second link, let me know and we'll figure out
how to get it to you or whoever else may be interested.
Dan Enslen
The only reason time exists is so
everything doesn't happen all at once.
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
On Behalf Of [EMAIL PROTECTED]
Sent: Tuesday, September 06, 2005 9:33 AM
To: Protel EDA Discussion List
Subject: [PEDA] QFN Footprint, Solder mask for the center pad
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
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