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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