I have soldered two wires onto this Cree XHP 70.2 LED, tested it in a circuit, and everything works fine. I intend to wire four of these LEDs in series and drive them together at about 48V and 2.4A (12V each). My only concern is how close the solder is to the copper LED backplate (see images below).

Image of LED with two wires Image of LED with solder gap, closeup Image of LED with solder gap

I'm worried that it might arc to the backplate and create a short circuit, bypassing the LED. Is this a legitimate concern?

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    \$\begingroup\$ For goofing around this is fine. If you build a lot of these eventually you will have a stray wire or something and get a dead short. Arcing is not a problem. But soldering like that repeatedly will eventually lead to a failure. \$\endgroup\$
    – user57037
    Jan 18, 2020 at 3:16
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    \$\begingroup\$ When I searched for the Cree XHP I only get the actual LED. Who made the PCB? What's the datasheet for that? \$\endgroup\$
    – pipe
    Jan 18, 2020 at 10:22
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    \$\begingroup\$ @pipe The backplate actually has "CREE" etched into it. I got it at Amazon. I couldn't find a datasheet, but it is a 12V 20mm DTP copper MCPCB. You can also get them from Kaidomain or AliExpress. \$\endgroup\$ Jan 18, 2020 at 18:45

4 Answers 4


Even a very small gap is sufficient to stop quite a bit of voltage. IPC-2221B would specify 0.6mm for 48V for an exposed gap on a PCB.

Breakdown voltage of an air gap is much higher than that-- 48V will hardly start an arc over any non-microscopic gap.

Of course if you get conductive dirt or liquid on it, all bets are off. For example, by using plumber's solder with acid flux.


No problem, Air gap is >1kV/mm with humidity and a bit less with dust which would just burn if you had an inductive transient exceed this level. But then you need reverse LED protection if you had inductive switching.

The wire looks well tinned and bonded. You can always add a 1cm stretch of Polyurethane rigid plastic (subfloor adhesive) for wire strain relief as well for the solder pad protection. This also acts as short circuit protection.

The copper bottom surface should be greased & screw clamped to a heatsink.


It won't be a problem but just for the safety I would use some shrink tubing/electrical tape. You never know what's gonna happen.


If you're worried, you could shallac your worry spot. But with that voltage and amps it's as someone answered and won't arc that air gap.

  • \$\begingroup\$ Do you mean "conformal coating" once permanently installed ? \$\endgroup\$
    – Criggie
    Jan 19, 2020 at 0:33
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    \$\begingroup\$ Conformal coating would be optimal to use. \$\endgroup\$ Jan 27, 2020 at 18:06

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