Hello All

Soldermask formulations today adhere fairly well to almost any PWB
surface. This is debatable. However I believe no-one would argue that
soldermask adheres best to laminate.

Adhesion issues aside, If your boards require UL recognition, one item
to be concerned with regarding whether or not to cross hatch the board
surfaces is the UL 796 "maximum unpierced  diameter" design parameter.
If this PWB parameter is still in effect per UL796, then your PWB
supplier could have an issue if your unhatched area exceeds their
recognition limits. UL is/was sensitive to this parameter with regard to
delamination and blistering of large surface planes and subsequent
safety hazards. They test for this when the board shops submits it's PWB
samples for a change in recognized design  parameters.

I could be mistaken today, but when we made boards internally, all our
shops were recognized for a maximum unpierced diameter of 2.0 inches
which meant our designers either put in clearance pads or cross hatched
the surface planes to keep us within this UL parameter.

I'm sure most board shops today have recognition limits which would
cover many unhatched situations, but if you have a very large board with
surface planes that is not particularly dense with components...who
knows.

Regards

Gerry

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