On Wed, Sep 13, 2006 at 10:18:50PM -0400, Xiaofan Chen wrote:
> The QFNs with a center ground pad are really hard to solder even with
> hot air rework station...

two tricks that make hand soldering QFN's a _lot_ easier:

1) Make pad footprints long enough to stick out 1mm from the package - let the solder wicking to the hard work for you

2) Use plated thru-holes to 'stitch' the (usually) GND paddle to the GND plane - wick solder up thru the holes from the bottom

Take care,
-Chris

-- 
| Christopher Cole, Cole Design and Development               cole@coledd.com |
| Embedded Electronics and Software Design                  http://coledd.com |
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