I have 2 wireless passive infrared (PIR) sensors (Paradox PMD85) that failed after an intense electrical storm with nearby strikes. The PCBs in both show spidery tracks of solder in arc-shaped patterns of small dots. See image.

Can this be a result of the lightning?PCB image

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    \$\begingroup\$ Can you find another that wasn't involved for comparison ? I can't think of anything that would make marks like that all over the board. In some cases in a group you might explain it by liquid running off or something but it's in different places at different angles. Lightning can do some extremely strange things. \$\endgroup\$
    – Russell McMahon
    Feb 25 at 12:38
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    \$\begingroup\$ Are you sure all of that is solder? To me it looks a lot like residue from being exposed to moisture. \$\endgroup\$
    – Klas-Kenny
    Feb 25 at 12:56
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    \$\begingroup\$ If it was lightning there would be burn marks. You don't vapourize things without a lot of residual heat. \$\endgroup\$
    – DKNguyen
    Feb 25 at 21:14

5 Answers 5


What you see is a rather common no-clean flux residue left over from selective soldering of through hole components.

If you look closely you will see the outline of the selective solder mask that was used to prevent solder from getting into mounting holes, around the board edges, etc. It is a very characteristic look and that’s what we’re seeing here.

I’ve had brand new boards from manufacturing look like that. Having it removed cost extra and wasn’t necessary in my case.

This residue is a bit moisture-sensitive and will look worse (“bloom”) if it was exposed to water condensation/liquid water at some point.

spidery tracks of solder

That’s not solder. It’s very recognizable soldering flux though. It’s not conductive or may be very mildly conductive if you have a sensitive enough meter. You can wash it off with 50-50 alcohol and acetone mixture.

The look of those sensors is probably a red herring. I bet you they looked like that from the day they were installed. You haven’t checked after all.

Can solder on wireless device PCB be vaporized during electrical storm?

Yes, in case of a very close lightning strike (direct to the building). But that is not at all what you’re showing us. Absent other information the photo you took is of a healthy board.

failed after an intense electrical storm with nearby strikes

If the sensors are connected with cables to the alarm “brain”, the voltages induced in the cables could have damaged the sensors and/or the brain. Are you sure specifically the sensors are damaged and not their power source etc?

If the sensors are wireless, can they be tested without connection to the “brain”? If they can, then of course they could have got damage from induced currents from a lightning strike. But to assess that we’d need to see the other side of the board. That’s where the damage is - whether visible to naked eye or not.

Can this be a result of the lightning?

The look? Definitely not. Nothing looks damaged on that photo.

The invisible damage, or at least damage to components on the other side of the board (and/or the alarm “brains”)? Sure.


Looks more like it got wet, which could also cause failure, particularly if it was powered while it was wet. It could also just be sloppy manufacturing, in which case the white deposits mean nothing.

In either failure case there will most likely be more obvious sequelae such as traces corroded (or vaporized). Narrow PCB traces are only a few 10’s of microns thick and are easily damaged, relative to a blob of solder. On the other hand, I have seen nearby lightning strikes merely open up a film resistor (attached to a long sensor wire) with no visible changes other than that (and only visible under a magnifier).

Bottom line is that there is no evidence I can see in the photo of lightning damage, and only indirect evidence of water damage (the lower right corner may show some electrolytic corrosion.


If enough energy had been supplied to the board to do that to the solder I would expect to see other damage to the PCB, for example burnt out tracks and burnt components.

This is more likely to be poor manufacturing either a problem in the wave soldering process or residue left on the board.


When you see amps of current, you will see the traces heat up and carbonize things. Lightning can do much more than that, even secondary EMI can be hundreds of amps. Also, lightning dissipates a lot of energy, and you would see something black or something exploded on the PCB. Looks like it was bad soldering.


Its from high current discharged, higher temps melt the already easy to solder metal. My ups web soldering at battery terminal melted into a couple of spots disrupting the circuit and failing to recharge. Took me a lot of soldering above 400 degrees C to fix that dissipating heat web terminal connection. Think amps, I'm surprised it did not caught on fire, only loud buzzing happened while thunder was miles away.Check for cracks in circuit while dust cleaning


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