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I make and sell low voltage, mostly digital, retrocomputing expansion boards as a hobby/hustle. I use all through-hole components partly because of the retro aesthetic and partly because I find soldering through-hole relaxing and fun to do.

I'm selling enough boards now that I'm feeling like my assembly and soldering process should be optimized. One of the boards has about 30 components on it and if I'm making 10 of them, it can take up a whole Saturday afternoon.

Currently I place a part, flip the board in my hand while holding the part, tack one of its pins with the iron while making sure the part is fully inserted and aligned if necessary, lay the board down and solder the rest of the pins, then move on to the next part. I am pretty sure this isn't the best way to do this.

Do you have any tips or tool recommendations to help me optimize my board assembly / through-hole soldering process?

Thanks!

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    \$\begingroup\$ When I was soldering a lot of through-hole parts, I would usually insert the part then bend the leads or at least 2 of the pins outward a little to hold the part. Flip back over and repeat for 10 or so parts, then solder and trim leads in a batch. \$\endgroup\$
    – brhans
    Jan 30, 2021 at 16:09
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    \$\begingroup\$ Safety first: if you're doing a lot of this assembly yourself in a residential setting, I dearly hope that you're using a fume hood, a mask and lead-free solder. \$\endgroup\$
    – Reinderien
    Jan 30, 2021 at 16:10
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    \$\begingroup\$ Re "side-hustle", see this. I'm a bit surprised that using it led to confusion. AFAIK, it's not local at all, unless you mean the English-speaking world. \$\endgroup\$ Jan 30, 2021 at 16:27
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    \$\begingroup\$ Some of prototyping services will also do assembly. For basic boards I've seen quotes of a few dollars per board in low volume (~10 boards). If time is a major factor and you want to make tens of them, consider having some or all of the board assembled. \$\endgroup\$ Jan 30, 2021 at 16:36
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    \$\begingroup\$ On the topic of soldering without proper ventilation, if you're going to do it anyway, you can at least use computer fans to build a filter box with hepa and carbon filters and solder right in front of it. \$\endgroup\$
    – K H
    Jan 31, 2021 at 5:04

6 Answers 6

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Insert all the components of the same height. Maybe you have a holder to hold the board steady and off the bench. Put a piece of material (wood, heavy cardboard, foamcore) on the top of the board and flip it. Solder all the parts in and trim the leads. Repeat for taller parts.

If you have a 3D printer or a milling machine you can easily make a jig that will hold all the parts in one go. It helps to have the leads bent so that they don't slop around too much.

For parts that need to be located very accurately for functional or aesthetic reasons (for example, LEDs or terminal blocks), a more precise jig may be beneficial.


If your boards are reasonably small, you can save a lot of work by panelizing them in the design stage. The reduction in handling makes a significant difference. Even having a small number such as 4 in an array helps. Try to keep them together as long as possible, even as far as testing. You will pay more for the boards but everything else is cheaper.

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  • \$\begingroup\$ "a 3D printer or a milling machine" - would a chunk of hard putty or play dough work? \$\endgroup\$ Jan 31, 2021 at 1:03
  • \$\begingroup\$ @AndrisBirkmanis You mean like pressing an assembled PCB into the substance, then cleaning up the depressions and hardening it? Maybe. It might just make a mess. \$\endgroup\$ Jan 31, 2021 at 1:14
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    \$\begingroup\$ You can make a good one, put some cling wrap over the top (to make sure you end up with enough room), turn it upside-down, and make a plaster cast \$\endgroup\$ Jan 31, 2021 at 15:48
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Decades ago there were clamping systems available. Components were mounted on the top side, a sheet of board-backed foam pressed down on the stuffed board and a frame clamped the whole lot together prior to turning upside down.

enter image description here

Figure 1. A solution from Nuts and Volts.

As usual, you'll probably need to do the low-profile components in the first pass and the taller ones in subsequent passes.

Check the linked article where a design is published.

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    \$\begingroup\$ This looks so cool! \$\endgroup\$ Jan 31, 2021 at 4:21
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    \$\begingroup\$ An excellent example of an assembly frame in use is Mr Big Clive at youtube.com/watch?v=qfOardiykPs&t=600s \$\endgroup\$
    – Criggie
    Jan 31, 2021 at 6:41
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    \$\begingroup\$ These are still a thing. \$\endgroup\$
    – Jeroen3
    Jan 31, 2021 at 18:44
  • \$\begingroup\$ @Jeroen3: 300 Euro!! I did it with a scrap bit of foam - no need for the fancy frame. \$\endgroup\$ Feb 1, 2021 at 16:22
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When I built through-hole boards, I'd put all parts of a similar height in the board (starting with the lowest parts), then lay a piece of soft-ish foam over the board, flip the assembly and lay it foam side down on the bench, then solder those parts and trim their leads. Repeat the process for thicker parts. I might do all the bypass capacitors in one step, then all resistors, etc...

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Here is a probably-obvious trick I found to make thru hole prototypes easier on myself:

For axial components (resistors, many caps), pre-bend and pre-trim the leads down to about 10-15mm. That way the bottom of the board is less of a jungle...

I found I could do this efficiently, by doing the bending and trimming while the components are still on the reel-tape. Example: count out 32 resistors on the tape, and cut off that length of tape. Fold it over 1-2 times, so now you are holding tape that is "8-16 resistors" long, with 2-4 resistors at each "location". Now bend all the leads, both sides, to 90 degrees at once, over the edge of a piece of rectangular material that is as thick, as the resistor bodies are long. Now, still without having unfolded it, get some relatively large, sharp snippers, and cut all the leads off to the desired length. With minimal practice, everything in the preceding paragraph takes about 10 seconds, and pays off when soldering.

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  • \$\begingroup\$ This is a great tip, thanks! \$\endgroup\$ Jan 31, 2021 at 4:23
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    \$\begingroup\$ nnh, I think you mean "fold it over 1-2 times". Fold once from 32, get to 16x2; fold twice, get to 8x4, etc. I guess you could continue, but 8 leads at a time sounds a bit too thick a bundle to handle cleanly. \$\endgroup\$
    – ilkkachu
    Jan 31, 2021 at 16:39
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    \$\begingroup\$ @ilkkachu - yes you're right, thanks. fixed it \$\endgroup\$
    – Pete W
    Jan 31, 2021 at 18:13
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  • Place all parts.
  • Bend the leads slightly as you place them so that they won't fall out when you turn the board over.
  • Solder all pins in one go rather one part at a time.
  • Trim the pins.

There are racks made to hold PCBs and flip them over and back as you work on them.

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While all the other answers are covering the issue fine, I'd like to add an additional answer about the sequence of soldering and trimming the leads:

  1. Trim the leads
  2. Solder the joints

Why: Because trimming after soldering has several negative aspects:

  • (Long) leads are in the way which can make soldering unnecessary cumbersome
  • It exercises unnecessary mechanical stress to the joint
  • The cut leaves bare metal that can oxidise and over time can cause the joint to deteriorate/go bad

If the leads are cut before the joint is soldered, none of these issues arise.

The amount of work being equal, I prefer this order.

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