PHIL
In a past life did high voltage design. The tracking usually follows the
weave of the material as you said. We used a material that was a blown glass
in plastic this produced a random weave the material was called Milacron.
Don't know the cost. I posted the information for this material awhile back.
I don't even know if the material is made anymore.



      Thankyou
      Joe Keary

-----Original Message-----
From: Phil Nutting [mailto:[log in to unmask]]
Sent: Wednesday, May 15, 2002 2:03 PM
To: [log in to unmask]
Subject: [TN] High Voltage tracking on pbc surface


Hi folks,

Today I have a question about high voltage tracking.  The actual set of
materials and applications are as follows.

FR4 material, 0.090" thick, two layer, plated through hole, LPI solder mask,
submerged in Shell Diala AX dielectric oil, operating at 100kV.  We are
seeing hv tracking marks that run with the grain (fiber directions) of the
FR4 material.  This burn marking is in the LPI, but also in the FR4 material
as can be seen in the photo where the LPI has been scrapped off.  The
measling is from removing the copper from the board.

Here is the photo http://www.stevezeva.homestead.com/files/HVTracking.jpg.
It is the top left hand photo entitled High Voltage Tracking.  Thanks, Steve
Gregory for posting this on your page www.stevezeva.homstead.com.

We have seen this tracking on other boards which do not have the LPI solder
mask, they are bare boards, so that eliminates the LPI as the cause.

One of our engineers had seen this in a former life and it was attributed to
the small air bubbles in the substrate where the fibers were.

Is there a different type of material that will not exhibit this tracking?

Thanks, Phil Nutting

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