Hello Wolfgang,

You will find that mechanical dimensions vary considerably between QFP's
of different pin counts and between different manufacturers of the same
package type.  My preference is to make sure that the lands after
etching are just large enough to contain the solder fillets and
worse-case lead variations for the part and part manufacturers that will
actually be used.

Here are the guidelines that I follow:

IPC-SM-782 Surface Mount Design and Land Pattern Standard
http://search.ipc.org/SM782/default.asp
EMPF RB0009 Solder Joint Volume Calculations Using a Spreadsheet
http://www.empf.org/forms/techpub.html
Designer's Notebook, Conductor Width, Part 2, PCD Magazine, Nov'97
http://www.pcdmag.com/reprint.html
And my interpretation of IPC-SM-782 for gull wing land design
attachment: gw_lands.doc, Word 6.0 document

You should get many good responses to your question and my reply.  All
are welcome and appreciated.

John Balchunas