Connect panel mount switch to PCB

Question

I'm looking for more information on how to connect a panel mount switch to a PCB.

Switch Diagram:

I've read that it's generally bad to connect this kind of mechanical device directly to the PCB (since it's a more likely part to fail).

Since there won't be a panel for the device I'm trying to make, how can I attach it to the PCB in a sane way? This is just a hobby project that I want to have some switches for easier testing. It's not a critical component.

I've tried searching but I can't find something that fits this. Perhaps I'm using the wrong terminology.

Specific questions:

1. Should I use a "terminal block" for this purpose?
2. If so, what specifications should I look for? I think it's 3 pin, 7.1mm pitch, but I don't know what to do with the tab width of 4.8mm.
3. Am I just missing some alternative method that would be better for my purpose?

Answer 1

The design of your switch suggests that it is not for direct mounting onto the PCB, but to be contacted through "Fast-on" connectors or direct soldering of wires to the tabs.

If you don't need this specific component, but just a switch functionality, there are switches designed to be soldered directly onto the PCB. Personally, I would choose another one, because these are kinda bulky and there are more compact solutions depending on the application. RS Components, Mouser, Farnell are some good websites to look for electronic components.

If you want to solder this specific switch to the PCB, you can design three holes with a 7.1mm pitch. I'd make the holes 4.9mm in diameter if circular or 4.9mm x 0.9mm if rectangular.

Terminal blocks are normally used to connect wires to a PCB: the component is soldered with through-hole pins on PCB and then the wires are pinched in the case with some screws. I would not use this kind of component as an improvised adapter for your switch.

Answer 2

1. I don't think you need to use a terminal block, if you don't need to be able to rapidly remove and replace the switch.

2. If you are having the PCB made by a PCB manufacturer that will provide plated through holes, then three of those spaced 7.1 mm apart will provide good mechanical strength attachments to the tabs on the connector. Just specify round holes that are large enough for the pins to go through. So, the finished diameter of each mounting hole will have to be at least...

$$d = \sqrt{0.2^2 + 4.8^2} = 4.804 mm $$

Plus add a little bit extra for manufacturing variance. Also note that the through-hole plating reduces the inner diameter of the hole a little bit, by perhaps 0.125 mm, although many PCB manufacturers will take this into account so that you don't have to when you specify a hole size.

3. There are of course switches designed for mounting right on a PCB, but if you want to use this one, then big through holes for the tabs to go through is probably the best way for a cheap hobby board. A plated through hole rectangular slot would match the shape of the tabs more closely for perhaps better mechanical location of the switch, but for a hobby board, round holes are probably good enough for what you want.

Answer 3

Don't directly solder the terminals to your PCB - that's good advice. You stand the chance of damaging the switch internally. This type of switch is generally meant to be used with "Fast-On" contacts. These crimp on to single conductor wire and are available at so-called "home improvement" stores like HD & Lowe's, and also auto parts supply stores. They come in several widths. Your 4.8 mm terminal will probably take a 1/4" size, you need the female type.

You crimp the contact onto the wire. You probably don't have a crimp tool, so you can use a pair of hefty pliers, or press it in a bench vise. Cut the wire to the desire length, solder the other end into your PCB. Then push the Fast-On onto the switch terminal. You obviously need 2 or three of these wire assemblies depending on how you intend to use the switch ( i.e. single throw or double throw).