Many factors play a role in the overall outcome of PCB assembly, especially when very small components are involved. Broadly speaking, tombstoning is a problem with very small 2-pin components (0201 caps and such) and we've filtered out the following challenges:
- proper paste application
- component placement
- designing for "good" thermal properties of the PCB with regard to tombstoning
- moon phase
It seems that the effect of moon phase is least understood and researched, so I'm now designing a small PCB that is cheap, not useless (if the assembly process was successful), and - most importantly - contains some 0201 components.