Sid Tryzbiak wrote:
>
> I have a board running 250 volts and would like to know what the
> minimum spacing from copper to copper should be on internal layers as
> well as outer layers.
>
> Thanks,
>
> Sid Tryzbiak
> MicroVia, Inc.

Sid, you don't indicate if it's dc or ac peak or rms

You may also have regulatory requirements like UL

In general, the IPC's design standard has a table of electrical spacing
requirements in IPC-D-275, page 11, Table 3-1 "Electrical Spacing"

For inner layers (fully encapsulated) for 101-300 Vdc or Vac(peak), the
minimum electrical spacing is 0.2 mm (0.008 inch).

Personally ---- if you are concerned about long-term reliability, don't
do it, use an electrical spacing use an electrical spacing of 800 V/mm
(20 V/millinch) for a good 10-20 year life and 400 V/mm (10 V/millinch)
for 20+ years of reliable service.

For external conductors the Table has three levels of electrical spacing
depending on the design of the PB.

For "Uncoated" use < 3 km (10 kft) altitude, 151-300 Vdc or Vac(peak)
it's 1.27 mm (0.05 inch)

For "Uncoated" use > 3 km (10 kft) altitude, 171-250 Vdc or Vac it's 6.4
mm (0.25 inch), for 251-300 it's 12.7 mm (0.5 inch)

For "Coated" (with permanent polymeric coating, any altitude) 101-300
Vdc or Vac(peak) it's 0.38 mm (0.015 inch) and here again, I'd suggest
going to the above recommended long-term deratings or 800 or 400 V/mm
(20 or 10 V/millinch) if you can.

These electrical spacings apply to anything that could be a leakage
path, which means any component body, mounting hardware, etc.  If you
have ac (alternating current/voltage) you will need to take the Dk
(dielectric constant) of all insulative materials into account for
analysis as the greater voltage stress will be across the dielectric
with the lowest Dk.

If you need further information, please feel free to contact me
(directly or indirectly)

Ralph

--
Ralph Hersey

Ralph Hersey & Associates
3885 Mills Way
Livermore, CA 94550-3319
PHN: 510.454.9805
FAX: 510.454.9805
e-mail: [log in to unmask]

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