Re: gEDA: *QFP* footprint naming conventions

[Wojciech Kazubski <wk@ire.pw.edu.pl>]

Hi all!

The L in LQFP may stand for "Low profile" as they are about 1.6mm thick, which 
is less than standard 2.5 to 3.6mm for QFPs. TQFP "thin" packages are even 
thinner, about 1.2mm.
Both families have the same pin length (1mm) so they can share the same 
footprint.
Standard QFP have a bit longer leads, usually 1.6mm, except the rectangular 
package 14x20mm which has 1.9mm pins.

I decided to make footprints for both LQFP/TQFP and QFP packages to save some 
space in dense designs. There is also possible to make an universal footprint 
for all *QFPs by extending pads a bit.

The dimensions I used for LQFP/TQFP came from Philips recommendations:
http://www-us.semiconductors.philips.com/acrobat/packages/footprint/FOOTPRINT-HTQFP-HLQFP-LQFP-REFLOW.pdf
(in simplified form)

Another question: Some QFPs have a heatsink on the bottom side that has to be 
soldered to the board. Do they need a separate footprint (heatsinks can have 
different size) or can the heatsink pad be added manually as copper zone?

W. Kazubski