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I have a substrate with multiple conductor traces (0.5mm gap from each other) with aluminum plate on top used as electrode. The aluminum plate is connected to the hipot "line" and the substrate ground is connected to the hipot "ground". While testing at 1.2 KV (both AC and DC) I noticed that AC produced arcing between traces, the DC did not produce any arcing.

What's going on?

Please see attached photo and thank you.enter image description here

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1 Answer 1

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The AC can go through the insulation (what looks to be silkscreen) easier because of the additional capacitance through the air, the DC dosen't get the extra impedance reduction from the capacitance in parallel. The lower impedance apparently is also enough to overcome the insulation barrier.

According to IPC specs you need at least ~1mm (depending on the assembly spec) to prevent arcing

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  • \$\begingroup\$ If the insulation is indeed just soldermask/silkscreen, notice it doesn't count as insulation at all, and the plate is certainly arcing to some traces. \$\endgroup\$
    – Tim Williams
    Commented Nov 9, 2023 at 17:12
  • \$\begingroup\$ It doesn't count as insulation, but it is insulation and not for high voltage. \$\endgroup\$
    – Voltage Spike ♦
    Commented Nov 9, 2023 at 17:22
  • \$\begingroup\$ The insulation is a ceramic material, therefore it can withstand high voltage. \$\endgroup\$
    – Ybx Nop
    Commented Nov 9, 2023 at 19:21
  • \$\begingroup\$ @YbxNop It can at DC, AC current can go through any high voltage material, especially at small distances, at small distances you've built a capacitor. \$\endgroup\$
    – Voltage Spike ♦
    Commented Nov 9, 2023 at 20:20
  • \$\begingroup\$ @Voltage Spike. I like your answer, thanks. Could you please explain further "at small distances you've built a capacitor" so that means in AC, if you're building a capacitor you will see a leakage current. In DC you are not building a capacitor therefore there is no leakage current. Is my understanding correct or do you have a better explanation. Sorry my electrical knowledge is not that great! \$\endgroup\$
    – Ybx Nop
    Commented Nov 14, 2023 at 17:55

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