Hi Allen:
> Does anyone know how to calculate minimum distances between traces on
> a printed circuit board that would allow one to pass the dielectric test
> at a given voltage? Or has anyone taken any empirical data that would
> shed light on this topic? Also, would trace width have an impact on the
> dielectric test results?
Both air and solid insulation, in parallel, comprise the insulation
between conductors of a printed circuit board. (The interface between
the air and solid insulations is called "creepage distance.")
Air has the lower electric strength. Therefore, the electric strength
of air sets the minimum distance between conductors.
The electric strength (and conversely, the dielectric breakdown) of a
gas (e.g., air) "in a uniform electric field depends on the product of
the gas pressure and the electrode spacing (Paschen's law) for a given
gas mixture, electrode shape and material." (IEC 664, First Edition,
A.2)
The electric strength of air as a function of voltage, waveshape,
distance, pressure, and electrode shape is published in IEC 664.
Air does not break down at less than 327 volts peak, regardless of
distance and shape of electrodes.
If you are considering low-voltage secondary circuits less than 42.4
volts peak or 60 volts dc, then the operational insulations must be
able to pass/withstand a 500-volt rms electric strength test. (UL
1950, Sub- clause 5.3.)
According to IEC 664, Table AI, 0.1 mm in air will always, regardless
of electrode shape, withstand 500 V rms at an altitude of 2000 meters!
Best regards,
Rich
ps: Trace width has no effect on the electric strength of air. The
only parameters that affect electric strength are the distance
between conductors, the air pressure, and the shape of the
conductors at and near their minimum distance.
-------------------------------------------------------------
Richard Nute Product Safety Engineer
Hewlett-Packard Company Product Regulations Group
AiO Division Tel : +1 619 655 3329
16399 West Bernardo Drive FAX : +1 619 655 4979
San Diego, California 92127 e-mail: [email protected]
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