A while back 0402's were a huge pain in the neck. The primary issue with them was honestly footprint design. Pick and place was more than accurate enough but we still kept running into design issues. Because we saw such an enormous variety of 0402 footprints here, we decided to write an article called "The Perfect 0402 Footprint". It was very well received and ever since we published it, we've seen very few poorly designed 0402 footprints anymore.
Fast forward a few years and the 0201 is the new 0402. We keep seeing a number of head-in-pillow and tombstone defects with these. These images are of an 0402 but the defects are effectively the same.
So, just as we did with the Perfect 0402 Footprint, we're recommending what we consider to be the Perfect 0201 Footprint and are encouraging all of our customers to use it in their designs.
The critical aspect of this design is the gap that remains between the two closest edges of the pads. This gap should be no more than 0.3mm. This is what helps to make sure that the terminals of the chip are definitely making contact with each pad. If the gap between the pads was any larger, even by just 0.1mm, then we begin to run into serious head-in-pillow and tombstoning issues.
We put together an EAGLE library for this part which you can download here.
This page will be linked in our Best Practices page for future reference.
If you ever have any questions, please feel free to reach out to us. We'd love to hear from you. My email is address is firstname.lastname@example.org and our phone number is (413) 624-6879.