Mike and all -
The 33 g/ square inch ratio I had used for years (and appears in my older course material) was originated by a fellow who was with Motorola and eventually went to Delco.  I used it for years.  Later on, I experimented with higher mass and made it up to 44 g/ sq. in.  I discussed this with Bob Willis and I believe he did some further experimentation as well as quoted me.  We both feel very comfortable with 44 g/ in sq but, of course, one should experiment with the subject component first before subjecting it to production.  By the way, this includes most QFPs, SOICs, PLCCS below 84 pin, most BGAs and other non-ceramic bodied parts, particularly fine-ptich.

As far as the "mixed metaphors" of measurement - never got around to figuring it out in metric (and apparently, neither has Bob W).  Old habits die hard - I still find myself referring to wave-solder pot temps in degrees F though I always refer to reflow in degrees C. 

Regards,

Phil Zarrow

ITM Consulting 
Durham, NH  USA
www.ITM-SMT.com
T: (603) 868-1754
F: (603) 868-3623
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