How to solder a stranded wire to a THT hole of a PCB as shock-resistant as possible

Question

I'd like to solder several stranded wires of a cable (maximum 18 VDC) to a PCB. I've got corresponding THT holes (⌀ 0.8 mm; it's the eight holes underneath the yellow wire,) but the wire is thicker (⌀ 1.1 mm.) What makes my issue more complicated is that the board is to be part of an automotive electronics solution which must withstand slight shocks. See the picture below:

What is a good method to solder these wires durably to the PCB?

UPDATE: Here is a close-up of the eight soldering holes (J9) in question. The PCB is very cramped as J9 is situated between the amplifier in front and the resistors and caps behind it:

Answer 1

Mount an appropriate connector block to the same substrate the PCB is mounted to. Use this to transition from the oversized wires to smaller wires suitable for connection to the PCB and to provide strain relief.

Answer 2

If the pcb is an automotive electronics solution, it should not only withstand slight shocks, it should also withstand vibrations and some harder shocks.

So you should use only those connectors designed for such cables and don't solder the cable at all. There are additional strain-relief parts for those connectors and cables.

Answer 3

A good way (but a bit late now...) is to have two holes for each wire, perhaps a half-inch apart - one large enough to pass the insulated wire, and the second of suitable size to pass the actual conductor and provide the electrical connection.

The larger hole for the insulated wire provides a strain relief and prevents or reduces movement of the actual wire connection.

Answer 4

Soldering a stranded wire makes the soldered part much less flexible and so bending tends to concentrate on the part of the wire immediately at the end of the solder, causing fatigue and failure. For this reason, crimp or screw terminals are preferred where vibration is likely to be a problem. If you have to solder the wires then it would be wise to immobilise them a short distance from the end, perhaps with a cable tie or clamp. If you’re going to use an adhesive or potting compound then it needs to be stiffer than the wire in order to be effective, so epoxy is better than silicone.

Answer 5

You can leverage unused through holes for lacing wire/string. You can lace wire through the holes and pull the cables down against the board for strain relief. Then the cable/lacing combo should be potted against the PCB with epoxy. I have personally used this method in applications tested to 26G.

If you cannot use epoxy, you can try just the lacing itself.

These are all sub-optimal solutions, but if you're in a pinch they are viable temporary workarounds.

Answer 6

Wire to board solder connections are not ideal for a high vibration environment. Even with good strain relief the solder joint may eventually fail due to cyclical stress. As others have said it would be best to add a connector or terminals of some kind.

However, soldering the wire might work ok ..but make sure they have excellent strain relief. The solder joint needs to be put under as little stress as possible. Be especially careful about repetitive stress, as even a small amount will cause a failure after some time.

If there's too much slack in the wires between the strain relief and the solder connections, the vibration of the wires will cause stress. If there's too little slack the assembly process or flexture of the enclosure and mounting points may tug on the wires, which would also be very bad. You can see how this arrangement is touchy.

Answer 7

If the wires are stranded, you can strip and remove some of the strands to make it fit within the PTH. If it is solid core wire or you dont want to reduce the capacity, find a pin that fits in the PTH (plated through hole) then wrap and solder your wire onto it. To make it shock resistant the wires need to be staked (glued down to the board for strain relief) that way there is no stress on your solder joint.