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I want to produce (small scale) a simple device (0.5A stepper motor controlled by atmega and a498 with a potentiometer to regulate speed).

To simplify the whole process I'm using as many ready made modules as possible. A498 and Arduinos are simple - can be connected with "mother" pcb by headers, but I'm not sure about buck converters.

The ones I'm interested in do not have castellated vias, they have regular pads with vias (do they have a proper name?) at each corner of the module. How to connect them properly to other pcb? Can one just solder those IN, OUT pads to "mother" board?

buck converter example

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You're doing it backwards if you're trying to SMD-mount these modules:

You get Wireless and high-speed boards with castellated edges, because it's easier and cheaper to make one small board with many layers, on-board antennas, impedance matching and so forth, instead of directly putting your components on your main board.

These cheap voltage converters do not require any of that. Instead of buying a board with standard components soldered to it and soldering that to your motherboard, simply directly put the voltage controller IC and the other components on your board. The datasheets and design assistants of the voltage regulator IC manufacturers are good, and it's pretty easy to do so.

So, long story short, the thing you want doesn't exist because it bears no advantage.

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  • \$\begingroup\$ Also, honestly, the picture you're showing contains a counterfeit chip – I'd strongly recommend not trying to include modules containing counterfeits in your small production run. Aside from reliability issues (someone had to cut some corner to build that counterfeit), you might get into real legal trouble if you import such modules for commercial reasons. \$\endgroup\$
    – Marcus Müller
    Aug 9, 2020 at 17:42
  • \$\begingroup\$ thx, fair point about counterfeits, it's a pic of very similar module, mine are from big distributor, I assume they're legal. \$\endgroup\$
    – Jannki
    Aug 9, 2020 at 17:49
  • \$\begingroup\$ Regarding your advice to integrate voltage controller on the main pcb - thx, makes sense, maybe avoiding it is not so terrific idea after all \$\endgroup\$
    – Jannki
    Aug 9, 2020 at 17:57
  • \$\begingroup\$ @MarcusMüller - There are such modules from many reputable manufacturers such as TI intended for SMT. The last ones I used had copper pillars at each of the terminal points. It was a useful way to avoid the issues of designing and optimizing the design for the PSU. \$\endgroup\$
    – Kevin White
    Aug 9, 2020 at 22:58
  • \$\begingroup\$ you mean the TI simpleswitcher modules? Yep, those are intended to be put on other PCBs, and they are actually beneficial: high-density, well-tested, high-speed, calibrated. The modules here aren't. \$\endgroup\$
    – Marcus Müller
    Aug 10, 2020 at 7:01
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You can use individual header pins (which would space the board off), bare wire (introduce some spacing somehow to allow traces to be routed under the module safely) or individual male/female pins and sockets (eg. from Mill-Max).

Whatever you do, keep in mind that there are multiple sources of those PSU modules, and the next one you get may not be identical in terms of pin placement, which could be inconvenient if you have a bunch of PCBs fabricated.

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Just grab a single-row .100" header, and cut off some single pins and solder it to your daughterboard. Then stick it into your motherboard and solder the pins.

Unless you are holding the PCB in your hands, do not try and guess if the bottom side has a solder mask and no components so that you can just place it against a motherboard without raising it. The mechanical strength won't be very good anyways without the pins.

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  • \$\begingroup\$ I did that on the prototype, looks and feels terrible, I hope there is a better way. Regarding bottom side - it's flat, solder mask or not I was going to prepare an empty area on the motherboard, that should be enough to separate them electrically, right? \$\endgroup\$
    – Jannki
    Aug 9, 2020 at 17:46

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