Soldering / wire problems with Arduino pro mini

Hi all,

There may be no magic bullet solution but I could use some soldering advice for my pro mini projects.

What I am trying to achieve is a small footprint (so header + dupont connector that raise 2cm over the board are out); and the wires connected to the pro mini move occasionally (typically connected to a box lid that holds buttons, leds, LCDs etc).

I am soldering stranded 24/26AWG wire directly to the board, being careful that the insulation is cut clean and rests firmly on the board's surface: in that configuration if I pull on the wire sideways I get a nice bend, with the insulation providing stress relief.

That usually works well, however...

The cards I am buying have really narrow pads (I mean the round flat copper that I am trying to transfer the heat to when soldering a wire to one of the pins). As a result about 1 time out of 4 I mess around with the iron tip long enough that the wire insulation on the other side of the board melts on a few mm. When that happens the resulting connection is really fragile - the exposed stranded wire quickly breaks with movement.

The yellow wire below is good, the green one is not:

So I am looking for tips or suggestions: different soldering tip/technique? A way to keep the insulation from melting? Some kind of short crimpable and solderable connector that would provide stress relief?

Any idea is welcome!
Thanks,
Franck

You could get wire with higher temperature insulation or you could get heat shrink to put over the connections after you are done.

If you use 20-18awg wire, it is mechanically stronger. I would avoid using cable from DuPont connectors as the wire in them is like 24-28 awg or worse.

also, if the project isn’t subjected to mechanical forces solid wire might be an alternative.

Running you soldering iron hotter so you have go touch the pad/wire for less time is also a good solution if your soldering iron has a temperature adjustment.

Qdeathstar:
You could get wire with higher temperature insulation or you could get heat shrink to put over the connections after you are done.

If you use 20-18awg wire, it is mechanically stronger. I would avoid using cable from DuPont connectors as the wire in them is like 24-28 awg or worse.

also, if the project isn’t subjected to mechanical forces solid wire might be an alternative.

Running you soldering iron hotter so you have go touch the pad/wire for less time is also a good solution if your soldering iron has a temperature adjustment.

Thanks for the tips! I had seen wires with silicon insulation but I never connected the dots, I'll give that a try.
I have been using AWG24 Dupont cable, but without stress relief I am afraid that going to 20 or 18AWG will only marginally improve the life expectancy of the connection.

Franck

Hi,
To support the soldered wire, you could run a bead of hot glue along the line of soldered joints to cover the exposed wire and make a physical connection between the PCB and the wires insulation.
Basically making a strain relief for you line of wires.

Something like this, but probably thinner and with the wire out of the pcb at right angles the surface.


Tom... :slight_smile:

Yes :slight_smile: I knew there had to be a simple solution, hot glue sounds perfect! I also have silicon sealant that should be easy to apply, I will try both.

Thanks!

Standard silicone sealant contains acetic acid, which is corrosive. You can get silicone without.

One suggestion. The excess heat problem may be caused by insufficient or wrong kind of flux. You should be soldering the wires almost instantaneously.

Paul

Indeed - is that a temperature controlled soldering iron? The non temp controlled ones frequently get too hot.

Are you using leaded solder? The lead free solder is awful to work with.

Do you use flux ("no clean gel flux" is what you search for) when you're not adding more solder? (Most solder is rosin-core which has rosin flux in the middle, so you don't need to add flux when you apply fresh solder)

Hot glue is the normal solution here, though - should do that in addition to checking above.

Are you tinning the wires before soldering to the board? Flux is definitely your friend for this.

pert:
Standard silicone sealant contains acetic acid, which is corrosive. You can get silicone without.

"Neutral Cure Silicon Sealant" use in the plumbing industry on galvanized fittings and sheets.
Tom.. :slight_smile:

Thanks for all the tips.

I am using rosin core solder, so I don’t add flux separately. The iron is temperature controlled, and the solder is quick and clean when I can contact both the pad and the wire... but that’s the difficulty with the pro mini pads, my iron tip is not that thin and if the wire comes straight out from the center of the pcb hole I can’t physically contact both the wire and the pad (and that’s not even taking into account the fumbling/shaking I am prone to :slight_smile: ).
Maybe I’ll look for a thinner tip, that would probably help.

I’ll watch out for acetic acid in my sealant...

Franck

DrAzzy:
Indeed - is that a temperature controlled soldering iron? The non temp controlled ones frequently get too hot.

Are you using leaded solder? The lead free solder is awful to work with.

Proper lead-free solder is fine to work with. It contains tin, copper and silver. The cheap stuff without
the silver is not a eutectic (its nearly pure tin) and is indeed hopeless as it goes hard and pasty on the first solidification and is then unworkable.

The proper lead-free solder is notably superior to leaded solder for mechnical strength, note, and doesn't
poison anyone.

Leadfree solder does need higher temperatures and requires a temperature controlled iron - you need to
switch it off when not in use to prevent the tip oxidixing too, as the oxide is unwettable.

Twist the wires, tin them, place in the hole and solder from the bottom touching the wires with soldering tip not PCB, the wires should stick out from the bottom of the PCB 3-4 mm, you cat them when you finish. Use a lot of soldering paste that is the key to success.

Interesting, the tutorials I have watched instruct you to heat up both the pad and the wire to ensure that the solder adheres well?
I was using a conical tip, a bit of research shows that a bevel tip was more appropriate, I ordered a small set.

Franck

There is a lot of personal preference on tip selection.
And a lot of that is based on the specifics of what you are trying to do.
That said, this is the tip that gets the most use on my soldering station.

But a lot of people said that the curved blade works well for them so I ordered some. Have not tried them yet.

Look at my tip,first touch the wires and then pad and wires.

As an update, I received this AWG22 wire with silicon insulation and the ease of use is night and day compared with the dupond cable I was using before:

https://www.ebay.fr/itm/5-metres-super-flexible-22AWG-Silicone-Wire-RED-BLACK-BLUE-YELLOW-and-WHITE/360880293140

The insulation doesn't melt back when soldering, and besides that the cable is way more flexible so connections are much less stressed when moving things around.

This should be mentioned in all Arduino tutorials IMHO.

Franck