How to connect wires to PCB properly

[Phoxtane]

Now that the semester is over, I have time to turn my attention to some of the projects I've been working on.

I've come to realize that I won't be wanting to crimp every connection for the various devices I'm putting into the rail control network; in fact, for many cases I'll be wanting to avoid connectors altogether since the attached elements won't be removed from the control board! For example, in the break-beam detectors I'll be using to detect if a train is present, I will know the exact length of wire I will need in order to have everything hooked up properly. As such, I won't be wanting to use connectors, but a permanently soldered wire or something similar.

What's a good way to design a PCB to accommodate such a connection? For example, in LiPoly battery pack teardowns it looks like the main power connection to the control board is done with thick cables soldered directly to the PCB, no mechanical constraints or anything. However, that's for things like drills and cameras, and I'll be moving the boards around much more than something sealed inside a nice chunky container. I'm thinking of using the same size of holes and pads that .1 inch pin connectors use, but I don't know if this is a good idea, or even what gauge of wire I should be using. Would screw terminals be a good idea? They're quite large and chunky, and I don't think I need 18 AWG for sensor wires.

TL;DR What's a good, cheap, and easy way to connect plain old stranded wires to PCBs that won't fall apart? Through-hole (and if so, what gauge and hole size), or directly to a pad on a PCB?

[Ian.M]

For manual assembly, threading the wire through a pair of holes sized to accommodate the insulation to provide strain relief, then soldering it to a pad works well enough.   

[KL27x]

TL;DR What's a good, cheap, and easy way to connect plain old stranded wires to PCBs that won't fall apart? Through-hole (and if so, what gauge and hole size), or directly to a pad on a PCB?

For any connection that is fixed in place where the two ends will not move, relative to each other, do not use stranded wire. Stranded wire can handle repeated bending, better. But it is stiffer; anytime you touch the wire, it will flex at the weak point, which (in absence of strain reliefe) is the solder joint. Solid core is way more malleable. Gauge is dependent on current and tolerance to voltage drop. In general, as long as it can handle the task, I go with thinner = better. Kynar insulated wire, in particular, is very thin and will hold shape of where you place/route it. For added reliability, just route the wires where they can't get into trouble, and tack them down with hot snot or a drop of super glue. For pads, even small SMD pads are fine, as long as you keep the wiring tidy.

For connection between two points that are not fixed, stranded wire is good. But only beneficial with crimped connection or adding strain relief. Hot snot will work fine on some wire insulation, like kynar. Silicone, if you need solvent resistance.

All my early protoboard circuits were jumpered with stranded 26 gauge CAT 5 wires. Horrible. Solid core 30AWG kynar can handle most intra PCB signal needs and if care is taken will be much more reliable/robust by way of NOT being in a place where it will be touched/bent. Keep it tidy and tack it down, and it will be one with the PCB.