Soldermask under QFN

[buenos]

Have you seen a QFN footprint with absolutely zero soldermask under the qfn package? The package body is a massive rectangle opening on the soldermask layer.
Someone was showing me this, and the purpose was to allow flux to exit from under the center pad.
But with no soldermask coverage, adjacent pins that are on the same net (like many dcdc converters), would short, so to solve this artificial problem they only connect the pins to a common power shape outside of the package (no flooding), that creates a third problem with power integrity.

 

[KlausST]

Hi,

Show pictures of the footprint and the soldermask.
What's the exact part name?

Klaus

 

[FvM]

I don't see indications that the industry standard QFN footprints, as specified by IC and package manufacturers (e.g. amkor.com) don't work. There may be special cases where you want to depart from recommendations.

But with no soldermask coverage, adjacent pins that are on the same net (like many dcdc converters), would short, so to solve this artificial problem they only connect the pins to a common power shape outside of the package (no flooding), that creates a third problem with power integrity.

I can't follow the considerations. Perhaps a picture can explain what you mean.