[SI-LIST] : Traces isolation vs FCC68

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From: Michel Bazinet (m.bazinet@nhc.com)
Date: Fri Nov 12 1999 - 09:26:03 PST


To whom it may concern,

        I would like to know what you think about one of the assertions of Mr
Lee Ritchey who said that the dielectric breakdown voltage for a
standard
FR-4 Epoxy Glass is about 1100Volts/mils. On one of our projects, to
pass the FCC68 test, we needed 1500 Volts of isolation on some traces.
At
this
time when I made the PCB I checked in the IPC-D-275 table (table 3-1,
P11,
september 91 edition) to find some very huge results (1500V ->
150mils). In
reality yon cannot design a project and keep this clearance between 130
different nets. So in this specific project I kept an isolation of
30mils
between each of the concerned traces. And in the Z axis I increased the
thickness of the PCB to 115mils (just to be able to solder every part
on
the pcb) on an 8 layer board. The problem with the tickness of this
board
is that we have a lot of trouble with the fabrication and the assembly.
Furthermore, it is more expensive.

        When I spoke with Mr. Ritchey at the PCB Design Conference he assured
me
that the table he gave me is correct. I would like to know your opinion
on
this
topic, because I don't have any sources other than IPC. If it's
correct, we
can
go down to a 0.062" pcb thickness and reduce the size of the pcb.

        We are currently working on a new version of this board so I hope you
will
have some good news for us.

Michel.

__________________________________________________
Michel Bazinet m.bazinet@nhc.com
PCB Designer http://www.nhc.com

NHC Communications Inc. (514) 735-2741 ext.: 262
5450 Cote de Liesse 1-800-361-1965
Mont-Royal, Quebec, H4P 1A5 Fax: (514) 735-8057

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