Does perfboard/prototype board/donut board made of paper or something (at least it's not fiberglass, that much I know) become conductive when heated to the point of becoming black? I'm assuming these are carbons which would be conductive.

I had a circuit that was unstable after being soldered on the board. The surfaces around the copper plates are black (in places which I de-soldered and re-soldered a lot, since I kept making changes to the design.) After much repeated soldering, I arrived at the final design where I was sure there shouldn't be any obvious problems with my circuit and that it should work, which it did, only then to become unstable again, except this time I was hearing a sizzling sound.

I waited to see which component was causing this, I sure didn't expect the board to burn itself, and also blow up the capacitor on top of it while melting all the solder under.

I did some experimentd to find the cause.

I have concluded that the fully burnt places are completely conductive.

Somewhat burnt places have some resistance or they even act like capacitor, I don't really know since my multimeter flashed some numbers before becoming unreadable when I probe the places.

Soldering paste helped the board to burn, without them, it doesn't seem to be able to burn a hole, mostly some tiny glowing carbon paths are all I see, so perhaps the soldering paste is also conductive.

I had the black area around transistors which is what I think are causing all these instabilities, since the board itself is already acting like a resistor or capacitor and letting current from the collector to flow to the emitter without the control of the base or gate, the final design, I changed the transistor on top to a voltage regulator (because I figured since the transistor wasn't working, might as well change it, at that time I didn't know it was the board) which put the power railsb(32V) right next to each other and made a spectacular boom.

All these instabilities also started small and eventually grew bigger, can I assume that as I continued to power the board, the black areas became more and more conductive?

Now I have my worries of soldering pastes, how conductive or how much resistances they have. Because my circuit is big, rubbing each tiny nook with alcohol would take too much time, not to mention the paste flows down to the other side too, they don't exactly dissolve when I submerge them in some liquids either.

Had I known all this earlier I sure wouldn't have wasted all that time to solder an important circuit on this cheap board when I didn't know there was such a problem and innocently broke more than 5 transistors.

Any suggestions? For now I have completely given up on that board and de-soldered all the important components. Do fiberglass boards becomes black/carbonize too? It seems for now the best and most expensive board I can get around here are the fiberglass ones that looks like this:

Fiberglass board

Can a fiberglass board possibly fix all of my problems and end my month long suffering?

  • \$\begingroup\$ Fibre glass boards will be fine. \$\endgroup\$
    – Andy aka
    Sep 22, 2021 at 18:05
  • \$\begingroup\$ @Shirotae: What do you mean by "soldering paste?" You shouldn't need anything besides the solder. Any decent solder for electronics will have flux in it. If you used solder paste made for soldering copper pipes then that is what ruined your circuit. That stuff "eats" copper, and is conductive. \$\endgroup\$
    – JRE
    Sep 22, 2021 at 18:14
  • \$\begingroup\$ @JRE it makes bridges easier, otherwise I would have to add more solder to add more flux, and too much solder means I have to suck it up, and means more soldering iron time to the board which is more heat, I like myself healthy solder bridges that doesn't look crap. What do you mean copper pipes? I use normal soldering paste for normal people mybotic.com.my/image/mybotic/image/cache/data/… \$\endgroup\$
    – user277524
    Sep 22, 2021 at 18:39
  • \$\begingroup\$ No. Just, no. Use something like this. That's a standard 60/40 percent tin/lead solder with a flux core. \$\endgroup\$
    – JRE
    Sep 22, 2021 at 18:47
  • \$\begingroup\$ @Shirotae there is no such thing as normal people \$\endgroup\$
    – jsotola
    Sep 22, 2021 at 19:02

1 Answer 1


You should not have burned black places on your board just from soldering, even if you have soldered and removed parts multiple times. Your problem isn't caused by using an inexpensive phenolic perf board.

You mention solder paste, and how it flows all over the board and through the holes. I expect that is the source of your trouble.

Solder made for electronics includes flux in it. You should not need to add flux or solder paste of any kind when soldering on a simple perf board.

  • Put the soldering paste away and get some solder intended for electronics.
  • Use a soldering iron with a temperature control.
  • Set the temperature to about 270 degrees celsius.

Practice soldering and making good joints with scraps before you start assembling your circuit. Just solder small pieces of wire to the holes in the board. Practice making the joints quickly and cleanly.

This is an example of soldering on a cheap perf board:

enter image description here

That was made using a really cheap soldering iron and lead free solder with a flux core.

You can easily make solder bridges between pins using standard solder and a soldering iron. You do not need extra flux or solder paste.

This is a solder bridge between two pins made with lead free solder, my cheap soldering iron, and no extra flux or paste:

enter image description here

Check here for more examples of how to use a soldering iron.

The solder paste you linked to contains zinc chloride.

Zinc chloride is normally is in the flux used used to solder copper pipes or rain gutters. It is not appropriate for electronics.

  • \$\begingroup\$ If your chemistry can prove that the solder paste actually reacts with the board by some magic and make carbon out of no where then I might believe you. But your second statement is still wrong, I do solder without it first, I use it when solder doesn't bridge, by that I mean I have seen the board turn black without the paste because I don't use it all the time, with enough heat, now imagine me de-soldering and pulling out long pins transistors with big heatsink more than 4 times. \$\endgroup\$
    – user277524
    Sep 22, 2021 at 19:50
  • \$\begingroup\$ I'm sorry what now? Do you realize those are made specifically for electronics? There's even a tag in this StackExchange that explains just that. That aside, are you just hating on soldering paste because you have never used or seen the electronics used ones, especially in SMD. Low concentration of zinc chloride isn't supposed to eat but instead helps remove corrosion or oxidation, but you do need to clean it or it will eat overtime, your last statement is plain wrong and shows ignorance of soldering paste in electronics. This specific paste said to clean and was also purposed for electronics. \$\endgroup\$
    – user277524
    Sep 22, 2021 at 19:50
  • \$\begingroup\$ Temperature control? If I were that rich I'd probably just order a PCB online, I soldered without paste for 3 years, good and bad solders, true that good solders don't need them, but I have had my hell with solders that has high melting point and barely any flux in them. \$\endgroup\$
    – user277524
    Sep 22, 2021 at 19:50
  • \$\begingroup\$ I used unregulated soldering irons when I was a kid. I never managed to burn the board to the extent that it became conductive. All I had was a crummy iron and cheap solder. You do not need anything more to solder on a perf board. Your solder paste is causing problems. Stop using it. Even with a crummy iron, you should not be burning the board - even if the board is crummy. \$\endgroup\$
    – JRE
    Sep 22, 2021 at 19:57
  • \$\begingroup\$ @Shirotae: This is the iron I learned to solder with. It cost about 3 dollars when I bought mine forty years ago. I used electronic solder on cheap perf board. I never managed to burn to board to the point that it carbonized. I managed to burn the solder pads off the board quite often, but never destroyed a board to the extent you describe. Probably because I used (cheap) rosin core electronic solder and not zinc chloride containing plumber's flux. \$\endgroup\$
    – JRE
    Sep 22, 2021 at 20:06

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