I'm working on the second iteration of a board which uses quite a lot of 0402 caps for decoupling around processors. On the first version of the board I had complaints from the subcontractor that there was a lot of tombstoning on these caps, not in any particular pattern, just generally on the 0402 caps. They suggested that the 0402 pads seemed quite large. I'd used the standard 0402 reflow part in the Eagle RCL library which I'd assumed would be correct.
So, I've investigated further. I've looked at the IPC standard :
This land pattern is even bigger than what I was using and seems hard to believe. I've also looked at a selection of manufacturers recommendations on their datasheets for 0402 components :
There doesn't seem to be much consistency here other than they're all smaller than the IPC recommendation.
So, I'm confused. I really need to use 0402 caps as the tracking on this board is tight, but I don't want problems with tombstoning again. I'm particularly confused about this problem as I'd made a lot of effort with tracking on the 0402 caps to make sure the thermal paths to each pad were fairly equal so I'm pretty sure that's not the problem, I'm fairly convinced it's the land pattern that's causing the issue.
Has anyone got any recommendations, or even just an 0402 land pattern that's tried and tested working?