Using large plane areas of solid copper under soldermask at one time presented
a problem because the copper was tin/lead coated before soldermask and when
heated during the assembly process might reflow and cause chipping , flaking,
bubbling, etc. of the soldermask.

Using soldermask over bare copper (SMOBC) prevents this from being an issue
and should not present a  problem for you to use large solid ground areas on
the outer layers if that is what is preferred.

Tim Easterling
SCI Systems Inc.
(205) 882 4426

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