We did some testing of design parameters when we switched to lead-free, and 
found that the lead-hole ratio is more critical.  We also found that top side 
pad size is irrelevant for hole fill, but large bottom side pads can adversly 
affect hole fill.  Using this chart, we are able to achieve 75% with regularity 
(and we do not have the best process controls in our plant):

Lead Range	Pad Size	Hole Size
.000-.017	0.05	0.026
.018-.022	0.06	0.035
.023-.027	0.07	0.04
.028-.032	0.07	0.046
.033-.042	0.08	0.052
.043-.052	0.09	0.062
.053-.063	0.1	0.073
.064-.076	0.11	0.086
.077-.086	0.12	0.096
.087-.106	0.14	0.116
.107-.115	0.15	0.125
(dimensions in inches)

standard plane connects are thermal relief, using (4) .008" spokes.

This testing was done only to establish design parameters, there are plenty of 
process parameters that will affect hole fill.  But if your design parameters 
aren't good, all the process tweaks in the world won't fix trhe problem.

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