Hi All,

I have a question concerning the layer stack-up of a board that I am
designing for an engineer who is concerned about the voltage isolation
provided by the pre-preg material between the layers. The design is for a
power supply board that will be 4 layers/0.094" thick with 2 oz. copper
on all layers and will contain max voltages of 240 VAC. It also must meet
certain CE agency guidelines. He feels that the pre-preg material doesn't
provide the voltage isolation needed that FR-4 provides. So to maintain
certain high voltage clearances, he wants to fabricate the board with 2
double-sided copper clad laminates and use pre-preg between layers 2 & 3.
Some other sources tell me that pre-preg contains the same
characteristics of FR-4 when cured and thus the cost of the board would
be less if 1 double-sided copper clad laminate was used with foil on each
of the outside layers and pre-preg being used between layers 1 & 2 and 3
& 4. Is this true and can anyone supply me with technical info comparing
FR-4 to pre-preg materials and also help me in understanding the most
cost effective way to fabricate this board. He would also like to use
more than 2 oz. copper, but I'm told that 2 oz. is more common than 3
oz., so we are making every effort to use 2 oz. unless someone can tell
me of a process that is available that will not add too much cost to the
board and provide a higher copper content. Any help would be greatly
apprreciated.

Regards,
Bob Walker

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