RE: [SI-LIST] : Traces isolation vs FCC68

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From: Jack Olson (JackOlson@NVISION1.com)
Date: Fri Nov 12 1999 - 11:39:01 PST


I'm almost sure he meant the breakdown THROUGH the material (in the Z-axis)
It is much different ACROSS the surface of a board!

Jack

                -----Original Message-----
                From: Michel Bazinet [mailto:m.bazinet@nhc.com]
                Sent: Friday, November 12, 1999 9:26 AM
                To: si-list@silab.eng.sun.com
                Subject: [SI-LIST] : Traces isolation vs FCC68

                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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