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Dielectric strength of PCB perpendicular vs parallel
1371 1 Mar 11.2020, 21:24:53

Laminate suppliers only list one "Dielectric Strength" so I assumed that orientation didn't matter.
Then I discovered that there are two voltage breakdown tests.  Test method IPC TM-650 2.5.6.2 is used for testing perpendicular to the plane and 2.5.6 parallel to the plane. 
The 2.5.6 test appears to have a much lower passing threshold.  So much so that IPC2221B guidelines for internal clearances come into question. 
Does the claimed "Dielectric Strength" value of a PCB laminate really only apply to voltages perpendicular to the plane (2.5.6.2)? 
Is there another name for the test results of 2.5.6?
Thank you.

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A****min

Mar 17.2020, 10:38:20

The difference between the two is related to a phenomenon usually called "surface flashover". You can look that up - not an extremely simple thing - but basically, voltage breakdown between conductors on the surface of an insulator occurs at much lower voltages/lower distances than through the material (perpendicular).

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