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April 1999

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Subject:
From:
Seth Goodman <[log in to unmask]>
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Date:
Thu, 15 Apr 1999 12:47:10 -0500
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Roberto,

If by PQFP240 you mean the 0.5mm lead pitch package that has lead width of
0.3mm max, IPC-782 recommends a pad of 1.6 X 0.3mm (63 X 12 mils).  This
only leaves 8 mils between pads, which is not really enough to get solder
mask between pads (3 mil mask width, 2.5 mils pad clearance).  Your 10 mil
pad width will just barely get you mask between pads with most vendors (4
mil mask width, 3 mils pad clearance).  But the package maximum lead width
is 2 mils bigger than the 10 mil pad!  Talk to your pc board fabricator and
see if he can do the mask between the 12 mil pads.  If not, you're stuck at
10 mils.  The last choice would be to ask your process people if they'd
allow you to do 12 mil pad width without solder mask in between, but that is
asking for trouble.

Hope this helps.

Seth Goodman
Goodman Associates
7687 Leta Way
Verona, WI 53593-8631
Tel (608)833-9933
Fax (608)833-9966


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