# Connect panel mount switch to PCB

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?
• Do you want it soldered or socketed? – Wesley Lee Apr 3 '17 at 19:29
• I'm new to this so I'm not 100% sure. I thought direct soldering this kind of switch onto the PCB was bad. That's why I thought a terminal block could act as the socket to allow for removal. Any input is appreciated. – jakekarnes42 Apr 3 '17 at 19:31
• Do you need this particular switch or you are just looking for a toggle switch component? – FlyerDragon Apr 3 '17 at 20:04
• somewhat related question: How to best attach a wire to a switch without soldering? – Nick Alexeev Apr 3 '17 at 20:19
• @FlyerDragon. Not committed this particular switch. I like this one because it's cheap and can handle 12VDC with lots of current. – jakekarnes42 Apr 3 '17 at 20:34

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.

• Thanks for all your help with this answer and your other comments. It seems like I might be thinking about this the wrong way. I might be trying to force this into a PCB mounted switch where it really doesn't want to be. This is very good information. – jakekarnes42 Apr 3 '17 at 20:57
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.

1. 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.
• Thanks for the input. Is there an advantage to ordering a PCB with a round hole when I know the rectangular tab size? – jakekarnes42 Apr 3 '17 at 20:35
• Depending on the PCB manufacturer, making a non-round hole might be considered a premium service and cost extra. Especially if it's plated inside of it. – alexwarrior Apr 3 '17 at 21:09

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).

• ADDITION: Or use a simple/cheap header connector at the board end. – Trevor_G Apr 3 '17 at 19:51
• Thanks for the answer. If I understand you correctly, then the connections will be Switch terminal → Fast-On contact → Wire → 3 pin Terminal → PCB. I'm not fully understanding/visualizing how these are connected. If the switch is effectively attached to the PCB through a few wires, will it just be dangling off the board? I'd like to avoid that. – jakekarnes42 Apr 3 '17 at 19:56
• @jakekarnes42 Yes it would be dangling off the board. Usually the switch is mounted on a front panel and you use wires to reach the PCB. Fast-on contacts help to reduce the soldering required. – FlyerDragon Apr 3 '17 at 20:10
• Got it. Thank you. Is there some solution between dangling off the board and soldered directly onto the board? I know there are specific surface mount switches, but none of them handle the 12VDC with 5A. Maybe PCB just isn't the right way to go and I should wire everything up individually... – jakekarnes42 Apr 3 '17 at 20:36
• @jakekarnes42 usually this is all done with a nice harness that has crimps and connector at the appropriate locations. The board connectors are usually high friction connectors that wont come loose without applying some force or have a latching mechanism built into the plastic. – Trevor_G Apr 3 '17 at 20:40