I have encountered two independent cases of ceramic capacitors cracking during PCB assembly. Both cases used pick and place machine and lead free solder.
The first case was using ceramic capacitors size 0402 (metric 1206) on a small PCB. It turned out a major contributing factor was that the PCB was flexed slightly when placed in the test fixture.
The second case was using ceramic capacitors size 1206 (metric 3616) on an average size PCB. The root cause has still not been found and it sometimes shows up as sporadic errors. I believe the assembly method is related because the problem showed up after change to a new assembly company.
Does anyone know if there is a preferred package size to reduce the risk of cracking during assembly of a PCB with ceramic capacitors?