0402 via in pad

Hi,

I need help to understand further on the via in pad for 0402 requirement. If I were to do the DFM over the brd design which consist of 0402 with via on pad, what is the criteria that I should look for ? I learned that the via in pad does not work well on ENTEK finished, and the pad design need to be a little bit bigger. IS it right ? Our current pad side is 21X 21, with the gap of 16 mil. What would be the best pad size for 0402 via in pad ?

thx.

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