How to use panel-mount connectors where the nut goes on the inside of the panel

Question

Some panel-mount controls have the nut on the outside of the panel, like this:

Other panel-mount controls have the nut on the inside of the panel, like this:

With the nut on the outside, I first solder everything while it is outside of the project box. That gives me plenty of working room. Then I insert the PCB into the box and mount the controls into the project box, then tighten the nuts on the outside of the panel.

But when the nut is on the inside, the panel-mount control must enter from the outside, so I cannot solder it to the PCB. I am stuck soldering while the parts are inside of the project box. Either that, or any connector I solder to it must be smaller than the control itself so it can fit through the hole.

Is there something I am missing here? It seems to me that the only realistic way to use these is to solder something small like a JST connector to the control, and pass that through. This adds clutter and work. Is there a better way?

Answer 1

The second jack shown can be furnished with a ‘pigtail’ connector with a wire-to-board plug, which then plugs into the board. You may not like it, but this approach is very common.

What’s inconvenient is soldering wires directly to a board. Bad idea for a couple of reasons. First, wires in board makes wave solder assembly much more difficult than a board using connectors; they will likely need hand soldering. Second, soldered wires in a rigid PCB are a weak point for vibration / flex: the solder wicks into the wire, forming a ‘stiff’ section that can fracture under repeated stress. And of course it’s a possible assembly error waiting to happen.

This isn’t a problem when solderless crimp connections (e.g., those JST connectors you consider to be ‘clutter and work’) used for plugs: the crimped wire is free to flex, and its mating header is compatible with wave soldering.

Look at a typical PC motherboard for example. They don’t have wires hanging off of them. Instead they use wire-to-board receptacle connectors for everything. The first two reasons given above - soldering and flex - is why.

On the other hand, if ultimate low cost and assembly simplicity are your goals, mounting the jack directly to the board is the way to go. This is possible with the first connector you show; it has standoffs for board mounting. This of course constrains your enclosure.

If you’re not ready to make that commitment, then you can provide sites on your board for either the barrel connector or a plug header.

Answer 2

For this application, where you don't have a lot of room to attach a connector (or want to drop $300 on a crimper), there's a category of connectors called wire-to-board, which is exactly what it sounds like (image from Digikey):

You strip your wires coming from the connector, add a ferrule if you want, put them into the rectangular holes, and tighten the screws. There are lots of different configurations like spring loaded or lever locks.