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Apologies in advance if this is a duplicate, FWIW I searched the site for a while but never found what I was looking for.

I'm putting together a random kit from AliExpress for the sake of practicing soldering, and I'm not sure which way to put in my electrolytic capacitor. Here's the symbol:

enter image description here

I know how to identify the polarity on the capacitor itself, but I'm not sure about the PCB. My guess would be the shaded part is negative? But I have no idea. Thanks in advance!

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  • \$\begingroup\$ No need to apologize. It’s a good question. \$\endgroup\$
    – Ste Kulov
    Commented Aug 15 at 2:29

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It is definitely the '-' side (the side with the stripe on aluminum electrolytic cans). Check out this photo from here with some light behind it.

The capacitor has the (+) terminal connected to the NE555 output and the (-) terminal goes to one side of the speaker. The other side of the speaker goes to ground. It is there to block DC from the speaker.

enter image description here

schematic

simulate this circuit – Schematic created using CircuitLab

enter image description here

Incidentally, though this is a common practice it is not the only one. For example, my layouts for hand assembly of electrolytic caps typically have a thick silk screen circle around the (+) lead. That's because that lead is longer on polarized caps so the assembler is targeting that hole first.

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  • \$\begingroup\$ Not that for axial caps you won't have the longer leg but a "dent" towards +. But usually they mark the + with + on the component print too, if they are being clever. \$\endgroup\$
    – Lundin
    Commented Aug 14 at 14:49
  • \$\begingroup\$ @Lundin good point. I've been prone to using radial caps on their side for some relatively low-profile applications since they seem more available/cheaper and can be used in either orientation. That mounting needs a bit more attention to vibration though. \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Aug 14 at 14:53
  • \$\begingroup\$ Of course, it is not impossible for the silk screen to be wrong. Always try to see if the capacitor and silkscreen markings match when replacing a capacitor. \$\endgroup\$
    – Andrew Morton
    Commented Aug 15 at 18:45
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Important: It depends on the component type!

In case of capacitors then the marking on aluminium electrolyte capacitors specifically is for negative. Meaning that the marked side should be matched against the black stripe on the capacitor. In this case you very likely have an aluminium electrolyte.

Note however that in case of tantalum capacitors, the marking indicates the positive side! Tantalum caps don't usually come in can-shaped packages however, but in case of through-hole, blob-shaped packages.

In case of ceramic or film capacitors, they do not have polarity and should therefore (pedantically following IPC requirements) instead be soldered so that the component text can be read when holding the board as in your picture.

In case of diodes, the marking is always the negative (cathode).

In case of connectors, there are as many options as there are types of components.

And so on. Although, if the PCB was made by a sane designer (not necessarily the case) then the PCB markings in silk screen should follow the component markings, no matter the component.

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    \$\begingroup\$ Non-polarized capacitors often have an "outside" electrode which is more strongly capacitively coupled to the environment than the inside one, though manufacturers aren't always consistent about marking that; some kinds of circuits may be less susceptible to noise if the outer electrode is grounded. \$\endgroup\$
    – supercat
    Commented Aug 14 at 23:28
  • \$\begingroup\$ The question is not about identifying the polarity of a capacitor. \$\endgroup\$
    – pabouk - Ukraine stay strong
    Commented Aug 15 at 8:16
  • \$\begingroup\$ @pabouk-Ukrainestaystrong If you know which side that's supposed to be ground then you can find out how to mount the component regardless of silk screen, by using a multimeter. \$\endgroup\$
    – Lundin
    Commented Aug 19 at 6:15

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