We designed a test PCB with various hole sizes and several rows had a DIP pattern where each hole had a wagon wheel ground pad connecting to the inner layers. The wave process used the same temperature profile 225-230F for Pb-free boards and the same conveyor speed. We also tested the difference in contact time and wave dynamics between the Electrovert wave with the chip wave of the original design, about 4 inches back from the contour wave. In the electrovert the chip heats the board, burns up much of the flux for the 1 to 1.5 seconds, then cools. Some of the 5-6 seconds in the contour wave is lost in remelting the solder then wets with whatever flux is left depending on the flux used. We also ran the boards over the Vitronic Delta-max with the smartwave for a continuous contact time which allows the flux and solder to work together. The angle of the smart wave pushes the solder up the holes very well. The main wave continues the process and could solder the same boards at !
a faste
r conveyor speed. Electrovert now makes a new setup where the chip wave is closer to the contour wave. In both cases we used nitrogen inserted wave to increase wetting and have a shiny solder joint.These non-functional engineering boards were about .085" thick.
The result was similar to your findings that a standard hole size with .005" clearance between the lead and the PTH wall or greater worked well. You can compensate for standard designs by slowing the conveyor to add more contact time. Larger hole to lead clearances helps to overcome the sluggish wetting of Pb-free solder and increase the conveyor speeds. The leads with the wagon wheel design tied to ground were the big indicators of what works and what doesn't relative to flux and wetting angles/pressure and continuous wetting of some systems.
We had similar results with the required contact time, temperature and flux on the robotic selective solder tests.
I hope these extra points and observations are helpful.

-------------- Original message -------------- 
From: Pete Houwen <[log in to unmask]> 

> Michael, 
> 
> The testing we did was undertaken to see what we might need to change in 
> our existing designs, after we had made a decision on laminates and finish that 
> would be suitable for our particular needs. So the only finishes we tested 
> were ImAg and ENiG, using no-clean, and .062 boards. We assembled boards 
> using our existing lead/hole/pad ratios, and then ratios on either side of 
> those. What we found was that there was not a large difference, but the 
> ratios in that chart worked well, and fortunately (with no intended bias) were 
> our existing design standards. The hole sizes are slightly larger than what had 
> been normally used in the industry for SnPb solder, it turned out that while 
> they weren't optimal for our old SnPb wave, they are for SAC. We did note 
> that in all ratios, the ImAg seemed to fill a bit better, though both finishes 
> passed the 75% requirement. 
> 
> This hasn't been a cure all, we have found assemblies failing the 75% 
> requirement on occasion, but only when our manufacturinjg process was not 
> properly controlled. So there isn't a lot of room for error, but that's 
> lead-free. 
> 
> Pete 
> 
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