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June 1999

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Subject:
From:
Wanner Bernhard <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 22 Jun 1999 21:45:58 +0200
Content-Type:
text/plain
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Dear Technetter,

I'm not sure there is a conflict between IPC-2221 voltage spacing and
SIR test acc. to IPC-TM-650, § 2.6.3.3. The voltage gradient of the SIR
test isn't nessecary the same as the maximal allowed voltage gradient.
Otherwise a voltage gradient for electrochemical migration test (see
IPC-TM-650, § 2.6.14, addressed by IPC-SM-840, § 3.9.2; and most
in-house-standards uses also low voltage gradients for
el.chem.migration) would limit the the voltage gradient of the design to
10V / 0.635mm. So it seems the design isn't limited by the qualification
voltage gradient of SIR or el.chem.migration qualification.
However, may be there resists a conflict or risk, because I can't see a
overall qualification which tests SIR, dielectric breakdown etc. after a
comprehensive test containing thermal aging AND thermal cycling AND
moisture. And this is a question because a current field experience with
dielectric breakdown between different layers as well into the same
layer of a 14-layer multilayer used as transformer winding. Can anyone
tell me:

1.      Are the voltage spacings availabe without restrictions? This
means particular: are the voltage spacings acc. IPC-2221 table 6.1
availabe/safe also after a long time (some years) application at 120°C
resp. 130°C (for FR-4 according to IPC-2222, §4.3, and table 4-1)?
2.      May be such overall qualifications are defind in IPC-6011 or
IPC-6012?

Craig, for reduced voltage spacing see also
"www.fed.de/0x3e906990_0x00028ade" (in german). Thereafter the IEC
document "Insulation Co-Cordination for Low-Voltage Equipment"
(Committee Draft, Reg.No. 28A/127/CD, by SC 28A, issue date 5.6.1998)
defines voltage spacings  smaller as IPC-2221.

Bernhard

        ----------
        Von:  KK Chin[SMTP:[log in to unmask]]
        Gesendet: Montag, 21. Juni 1999 18:57
        An:  [log in to unmask]
        Betreff:   Re: [TN] IPC-2221 Conductor Spacing - More Questions
- Further Questions

        Dear Technetter,

        Graig asked a very good question. I actually experienced problem
following the
        IPC-2221 table 6.1. Analytically, 0.6mm spacing in column B2 for
100 volt seems
        too aggressive when the SIR test (IPC-TM-650 para 2.6.3.3 with
coupon IPC-B-24)
        guarantees up to only 50V for 0.5mm. Practically we also saw
problem with the
        100V/0.6mm voltage gradient but our present findings have not
been conclusive
        yet.

        My question is, is the IPC-2221 voltage spacing really in
conflict with the SIR
        test?

        Graig, my apology for opening another can of worms without
answering your
        question.

        K.K. Chin
        Artesyn Technologies
        Fremont, CA




        Craig Hillman <[log in to unmask]> on 06/18/99 03:00:00 AM

        Please respond to "TechNet E-Mail Forum." <[log in to unmask]>;
Please respond to
              Craig Hillman <[log in to unmask]>

        To:   [log in to unmask]
        cc:    (bcc: KK Chin)

        Subject:  [TN] IPC-2221 Table 6.1 Conductor Spacing




        I was wondering if anyone could provide me with information on
the
        research used to determine the conductor spacing requirements of
        IPC-2221. More specifically, why is it not material dependent
and
        is there a safety factor provided in the spacing determination?

        Any help would be greatly appreciated.

        Thanks in advance,
        Craig Hillman
        University of Maryland





        Dr. Craig Hillman
        CALCE Electronic Products and Systems Consortium
        University of Maryland
        College Park, MD  20742
        (301)-405-5316
        [log in to unmask]

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