Maybe this will help

http://www.smps.us/pcbtracespacing.html

It still gives 3.25mm. 

Maybe the distance can at an angle within the PCB so the distance is 
sqrt(x^2 + z^2)

Karen Tellefsen - Electrical Testing
Alpha / 109 Corporate Blvd./ S. Plainfield, NJ 07080
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908-791-3069




From:   Jack Olson <[log in to unmask]>
To:     <[log in to unmask]>, 
Date:   06/20/2014 11:38 AM
Subject:        [TN] z-axis voltage separation
Sent by:        TechNet <[log in to unmask]>



maybe I'm having a "not enough coffee yet" morning,
but I was asked how much separation I need between layers for high 
voltage.
I tried to search the TechNet Archives, but it doesn't seem to work as 
well
as it used to!
anyway,

We have a design that may have 1700V in several places.
Since we are looking at a clearance into the board, layer-to-layer
I'm pretty sure I can use the "internal" column B1 of Table 6-1 in 
IPC-2221
(using Table 6-1 for z-axis was discussed in an IPC committee meeting and
no one disagreed)

but the number I get for 1700V is =
(.25 mm for the first 500V) plus (.0025 mm for each of the other 1200V, 3
mm)
equals 3.25 mm

For one thing, it already seems like I'm off-track because .25 for 500V
doesn't correspond very well with 3 mm for 1200V, but if you can't trust
IPC..... well, let's not go there.

My REAL question is that, although I'm safe using 3.25 mm, my board is not
that thick!
Is there a smaller z-axis clearance that can be used for 1700V? across
typical FR4 material?
(we are using a RoHS compatible 170Tg /126)

What's the MINIMUM layer spacing I can use for 1700V?

thanks,
Jack


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