Issues with High Strand Count Wire Solder Joints - Page 1
Forum section: electronics / projects

author: ROBOT
author_rank: Contributor
timestamp: March 25, 2016, 07:36:31 pm
content: Right now I have an issue. I am using TPE Teflon insulated high strand count (19x34) silver plated wire for a robot project of mine.The issue I have is it tends to just break off a lot easier at the through hole solder joint compared to your typical 7x30 stranding pvc jacket.I am using a lead free Kester solder with silver.Is there a better lead free alternative for high strand wire?I have seen for example automotive boards use press fit connectors. However a connector is not an option in this case. Is it possible to press fit just a single solid wire? Then the only issue I have is reduced flexibility.What about something like spot welding? I know sometimes the lead free solder likes to wick up the high strand count silver wire which might be why it breaks easier? Maybe spot welding by applying only a small area with heat could help this?Any help would be appreciated.

author: elecman14
author_rank: Unknown
timestamp: March 25, 2016, 07:48:52 pm
content: Could you use something like a crimp on ferrule? You would crimp on the ferrule then insert it into the PCB. Then solder directly to the ferrule. This would prevent solder wicking up the wire. Something like this maybe:http://www.digikey.com/product-detail/en/phoenix-contact/3200221/277-2172-ND/349921<- Not really sure of the solder-ability of this particular one. Just linking to get my idea across.

author: Messtechniker
author_rank: Frequent Contributor
timestamp: March 25, 2016, 08:15:23 pm
content: Yep. Wire end ferrules are a requirement for stranded electrical wiring these days in Germany at least.And they really do make sense especially when looking at stranded wiresscrewed down with or without solder some 30 years ago not knowing better.Most of them are loose. Lesson learnt.Yours - Messtechniker

author: suicidaleggroll
author_rank: Super Contributor
timestamp: March 25, 2016, 08:21:22 pm
content: Any chance you could tie the wire off on something nearby (mounting bracket, etc) or glue it in place? Soldered stranded wire connections need strain relief.

author: ROBOT
author_rank: Contributor
timestamp: March 25, 2016, 08:30:31 pm
content: Quote from: suicidaleggroll on March 25, 2016, 08:21:22 pmUnfortunately not easily.Quote from: elecman14 on March 25, 2016, 07:48:52 pmUnfortunately same goes for this. I am absolutely at my limit on hole size and cannot make the wire any smaller due to the current requirements. The hole in the pcb is 0.8mm and I use 22awg stranded. All the 22awg ferrule are 0.9mm then you need room for solder to flow around it.

author: Richard Crowley
author_rank: Super Contributor
timestamp: March 25, 2016, 08:49:05 pm
content: Quote from: ROBOT on March 25, 2016, 08:30:31 pmThen I would use a crimp-type male pin (like you would find in a male DB connector). The upper part will crimp the conductor strands AND the insulation sheath, and then the narrower "pin end" can fit into your PC board for soldering.The key here is being able to crimp the insulation sheath and not just the conductor strands because that is where it breaks (as you have demonstrated first-hand).And if your hole isn't even big enough for a DB-connector pin, there are even smaller pins and even those kind of male connector pins that are used for Arduino breadboards, etc.

author: IconicPCB
author_rank: Super Contributor
timestamp: March 25, 2016, 09:25:06 pm
content: Ypur other option is spring loaded connectors where You simply insert a wire intothe opening.These connectors come in smd variant as well.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 25, 2016, 09:50:01 pm
content: Ultrasonic welding might be worth a look, but you should still have some strain relief

author: Stray Electron
author_rank: Super Contributor
timestamp: March 25, 2016, 11:46:09 pm
content: Quote from: ROBOT on March 25, 2016, 07:36:31 pmThe problem with fine multi-strand wire such as that is that it wicks the solder up into the wire strands and up under the insulation. That makes the wife stiff and it has a tendency to break just above the joint instead of flexing as it should. The .MIL teaches that when soldering joints like that you're supposed to put a small clamp on the wire that prevents the solder from wicking up the wire. The clamp that they use is a small aluminium spring loaded clamp that looks about like an alligator clip except that they two halves meet edge to edge instead of the broad sides meeting (that part is important and I hope that I described it clearly). There is a small notch in each edge that fit around the wire slightly. It's important that the clamp is made of aluminium since solder won't stick to it. Anyway you're supposed to place the clamp around the bare wire and up against the insulation, then tin the wire if necessary and then place it in the joint and then solder it in place and then remove the clamp. I've never seen clamps like that used anywhere else except in the US military but they work very well.

author: ROBOT
author_rank: Contributor
timestamp: March 26, 2016, 12:12:28 am
content: Quote from: Stray Electron on March 25, 2016, 11:46:09 pmThat is interesting do you have any idea where you can buy these or what they are called?

author: Richard Crowley
author_rank: Super Contributor
timestamp: March 26, 2016, 01:25:40 am
content: Quote from: ROBOT on March 26, 2016, 12:12:28 amAnti-wicking tweezer. For example:http://www.techni-tool.com/250TW014

author: ROBOT
author_rank: Contributor
timestamp: March 26, 2016, 01:31:25 am
content: Quote from: Richard Crowley on March 26, 2016, 01:25:40 amThanks! This looks like just what I need.

author: vk6zgo
author_rank: Super Contributor
timestamp: March 26, 2016, 01:56:01 am
content: Quote from: ROBOT on March 26, 2016, 12:12:28 amTelecom Australia used to use these---they called them "Anti-wicking tools".

author: Stray Electron
author_rank: Super Contributor
timestamp: March 27, 2016, 01:25:43 pm
content: Quote from: Richard Crowley on March 26, 2016, 01:25:40 amThose should work but the ones that we had were much smaller and simpler and like I said, they looked about like an alligator clip. But I've never seen them anywhere else so you'll probably have to use the ones that Richard linked to, unless you want to make your own. Also, unfortunately I don't even recall what they were called at the time.

author: Richard Crowley
author_rank: Super Contributor
timestamp: March 27, 2016, 01:37:17 pm
content: Quote from: Stray Electron on March 27, 2016, 01:25:43 pmhttp://www.robotshop.com/en/elenco-soldering-heatsink.html

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: March 27, 2016, 02:26:41 pm
content: One way to strain relieve such wires is to include a feature on the PCB with through holes (need not be plated) through which the wire is threaded. If you have the room, include two holes, through which the wire is snaked (s-shape). This will ensure that the solder joint (not necessarily on the board - this is the point at which the solder no longer wicks up into the wire) never sees any strain, it is instead transferred to the board.

author: SL4P
author_rank: Super Contributor
timestamp: March 28, 2016, 12:28:48 am
content: ok, a lateral thought.Lay the wire flat to the PCB before/after soldering, and secure the unsuiation to the board - say 10 mm away)The flex occurs at the secure point, not the soldered joint.You could add a small loop on the wire to accommodate any rotational stresses.

author: calexanian
author_rank: Super Contributor
timestamp: March 28, 2016, 02:31:48 am
content: +1 for additional strain relief.

author: ajb
author_rank: Super Contributor
timestamp: March 28, 2016, 03:28:39 am
content: If the solder is in fact wicking up under the insulation and causing a problem, tinning in a solder pot rather than with an iron may help. Done properly, the pot will tin the stripped end quickly enough that the solder doesn't have time to wick up, and you should be able to get a faster fillet when soldering to the board versus soldering an untinned wire.Otherwise, a bit of heatsink over the wire to spread out any bending plus some rtv or hot snot around the solder joint, maybe?