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June 1998

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Subject:
From:
John Parsons <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 25 Jun 1998 08:15:49 +0000
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Bob,

FR4 prepreg has the same characteristics as FR4 laminate in this
respect.  Contact your board vendor for the exact specs of the
material they use but the Electrical Strength will probably be around
1000-1100 volts/mil.

Regards

John Parsons
Circuit Graphics Ltd.

> 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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