I have a switch mode power supply (flyback) LED driver. I just wanted to extract its schematic but some straight parallel lines of soldering made me confused. Both layers of this pcb is presented in following pictures. What are these strange lines? enter image description here enter image description here

  • \$\begingroup\$ The soldering overall looks really strange with all those shorts and strange exposed pads with no wetting. Almost as if they ran it through wave soldering... \$\endgroup\$
    – Lundin
    Commented Jun 7, 2021 at 6:56
  • \$\begingroup\$ @Lundin I think it's pretty definitely a wave-soldered board. It looks like there's a lot of through-hole components on the other side, so it makes sense. Would explain the amount of adhesive you can see under some of the components too. \$\endgroup\$
    – Hearth
    Commented Jun 7, 2021 at 14:09

1 Answer 1


That is simply solder that is put on the copper layer. It is there to allow the copper tracks to pass more current than without solder.

  • \$\begingroup\$ The slit in that area however, tells another story. Two high current areas are isolated from each other except at one point : which happens to be one terminal of the decoupling capacitor. This helps isolate noise (or heavy current pulses) in one side from the other side \$\endgroup\$
    – user16324
    Commented Jun 6, 2021 at 20:29
  • \$\begingroup\$ @user_1818839 That still does not change the answer. Even with the slit that forces all the current to pass via the capacitor terminal, still the tracks with solder stripes can carry more current with less voltage drop and less heating than without solder stripes. \$\endgroup\$
    – Justme
    Commented Jun 6, 2021 at 20:40
  • \$\begingroup\$ So why stripes? Wouldn't the tracks be able to pass even more current if the entire area was covered in solder? \$\endgroup\$ Commented Jun 6, 2021 at 21:48
  • \$\begingroup\$ @BruceAbbott I believe such a large area with no soldermask at all might become prone to peeling of the soldermask at the edges when wave soldered, but I don't have a good source for that--it's just a gut feeling. \$\endgroup\$
    – Hearth
    Commented Jun 6, 2021 at 22:19

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