0
\$\begingroup\$

I need to solder some wires into a PCB, im dont really master soldering small pads or pins, so i need some help.

I have a question too, those pads are already tinned, soldered, so can i apply some more tin and solder the wires directly? or do i need to desolder before?

enter image description here

\$\endgroup\$
4
  • \$\begingroup\$ This looks to be a pcb from a printer. What part is it? \$\endgroup\$
    – MiNiMe
    Commented Sep 19, 2023 at 22:35
  • \$\begingroup\$ its a encoder from an hp printer \$\endgroup\$
    – tote46
    Commented Sep 19, 2023 at 23:08
  • 2
    \$\begingroup\$ Are you soldering wires onto the through-hole pins or to the ribbon cable pads? \$\endgroup\$
    – Nedd
    Commented Sep 20, 2023 at 0:54
  • 1
    \$\begingroup\$ @tote46 In general for something like this I'd use #30 gauge wire-wrap wire, strip off a tiny bit of insulation, and form a tiny loop of copper wire at the end using needle-nose pliers. This is then carefully laid onto the already-soldered pad/lead you can see in the picture. Then I hold a short length of 21SWG solder wire and the soldering iron, and press down and at the same moment apply the tip of the solder, too. Not much. Just a little. \$\endgroup\$
    – periblepsis
    Commented Sep 20, 2023 at 1:13

3 Answers 3

Reset to default
3
\$\begingroup\$

There are some problems with old joints. There is oxidation and the original solder may or may not be compatible with what you are using - the main concern would be leaded solder (but this looks like RoHS solder far as I can tell). Mixing different flux is usually not a problem.

It looks like the pads to the left might a good place to attach the wires(?). Otherwise lets assume you are attaching them to the through-hole pins of the connector directly. Then I'd recommend doing the following:

  • Remove as much of the old joints as possible using a wicker braid or desoldering station. Be careful not to heat the parts too much. It's not a problem if some of the old solder remains.
  • Clean up with isopropyl.
  • Apply extra flux manually.
  • A finer chisel tip or a thin pointed tip would both work here. Chisel is generally recommended since these are reasonably large areas still.
  • Use thin, multi-strand cable of AWG28-30 somewhere. Peel in advance and apply solder to the exposed wire in advance. Ensure that you don't peel off too much - only to cover the pad area.
  • Solder the wire to the component pin and the PCB plate both at once. In case the wetting looks questionable because of old solder remains etc, let it cool off, then apply more flux and reheat the joint.
  • As usual make sure wires are pressed down along the PCB surface and that they do not cross any other solder joint.
  • Apply hot glue to fixate the cables along the PCB and to act as strain relief.
\$\endgroup\$
2
  • \$\begingroup\$ Unless it's been reworked, it's definitely lead free solder - there is a big (Pb) with a line through it on the bottom left of the board. \$\endgroup\$
    – Jon
    Commented Sep 20, 2023 at 11:50
  • \$\begingroup\$ @Jon It's also the most likely unless the PCB is older than 2005 somewhere when first RoHS went live. \$\endgroup\$
    – Lundin
    Commented Sep 20, 2023 at 11:52
1
\$\begingroup\$

If everything is just right, soldering should be very quick. Only a couple of seconds per wire. Too long and the board ends up charred, and the pads peel off the board.

So make sure the soldering iron is hot and the tip is clean. The wire must be clean. The board you're soldering to must be clean. Use flux-cored solder.

Ideally, you need four hands. One for the soldering iron, one for the solder, one for the wire and one for the board. If you can't arrange a second person. make sure the board is secure and something is holding the wire where it needs to be.

\$\endgroup\$
0
\$\begingroup\$

Since the board is from 2007, and you can see the solder have oxidized, you need to add some extra solder, and if you have, flux too. Be careful around those SMD components if they are needed for the new application.

\$\endgroup\$
4
  • \$\begingroup\$ By SMD Components you are referring to those R1 (I think its a 220 ohm resistor) and C1 (capacitor)?, they are pretty far away from the pins i dont think im that bad at soldering to make any harm, but you tell me in what do i need to be careful regarding those. \$\endgroup\$
    – tote46
    Commented Sep 19, 2023 at 23:10
  • \$\begingroup\$ Yeah those are the ones. Just don't wander off with the soldering iron, that's it. \$\endgroup\$
    – MiNiMe
    Commented Sep 20, 2023 at 1:08
  • 1
    \$\begingroup\$ If you wander off some 5mm from the intended joint you shouldn't be doing SMD work or maybe you are using some crazy large tip unsuitable for the task. This PCB has enormous areas of free space in comparison to how it might look with lots of components cramped tightly together. \$\endgroup\$
    – Lundin
    Commented Sep 20, 2023 at 9:03
  • \$\begingroup\$ Just saying. Good and comprehensive answer btw! \$\endgroup\$
    – MiNiMe
    Commented Sep 20, 2023 at 9:26

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.