Reflow I never read that anyone saw a need to do CPK on reflow. The CPK 
should be done on the placement machines. A good reflow oven has only a 2 
degree C variation from rail to rail. The reflow usually corrects parts that are 
shifted or rotated a little with a good board and stencil design.
DOE on stencils should be tied to squeege pressure and speed as well as 
cleaning and chemistry used to clean the squeeqee, number of machine clean 
cycles (cleaning after  X number of prints), dry or cleaning fluid in printer.
The DOE beside the obvious stencil thickness, laser cut versus electroform etc 
and aperature required for PB-free versus tin/lead are the following for small 
components and BGAs which are usually the ones with issues. 
In the DOE I would select Small Rnets with concave versus convex ("T" 
shaped lead) to be added to whatever components you have in mind. There is 
a new taller but narrow SMT switch with ony 2 pads, that tilt when they 
reflow. This one is a challange. Another point to test is the shifting of pads 
towards the heel versus the toe to prevent opens. Stencil designers have said 
that opposite of what you may think, adding paste to the rear or heel actually 
corrects opens at the toe. The paste flows toward the toe and up the lead 
during reflow. Shifting the pad or aperture toward the toe to fix an open  may 
not help because the leads pushes the paste away during placement, instead 
of fixing the open you may get a short or still have the open. A DOE board 
should have some pads with uneven etches to test stencil designs that may 
prevent components from shifting by changing the amount of paste via width 
and length reductions. A DOE with kings crown versus home plate pad designs 
or staggered tear drop for IC's may be selected. Some say the kings crown 
may lead to tombstoning but I haven't seen it. I know the  homeplate design 
may be good if you have an automated stencil cleaner but if the operator 
does manual cleaning a stencil with all those sharp points would be risky. I'd 
bet you'd have some damaged stencils if the point is bent up when the steel 
squeegee hits them.  

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