*Solder Selection*
By: Rubicon Board Posts
29 June 2021

Note: This is a compilation of posts from a recent Rubicon "Crafts And Hobbies" board thread. Rubie IDs have been omitted and posts slightly edited for member's privacy.

Subject: Solder

Since late last year I've taken an interest in Home Autmation/Home Assistant along with ESP32 and relays.

I've been trying to do some basic soldering and the results are lest than stellar.

Looking for a recommendation of good solder for these types of small electronics projects and a soldering iron. I'm currently using a Weller WLC100 kit and I'm not sure if it is the iron, the solder or me (I'm leaning towards not totally me and even tinning wires seems like a chore and that was the first skill I learned.)

A Weller will do the job bro....

Are you using the infamous "Chinese 'Copper' wiring"?

You may find that the problem isn't you at all... You're probably running into the same problem soldering the wiring that Welders run into while welding...

See, ya can't weld Aluminum with a standard welder, because Aluminum INSTANTLY oxidizes when it's heated in the presence of Oxygen... You have to bathe the area with Nitrogen as you weld aluminum.. The cheaper the Aluminum, the harder it is to do ANYTHING with.

And Aluminum wiring in general is a No-No in the United States for many applications...

So what the sneaky guys in CHY-NAH did was put a VERY VERY thin coating of Copper over their Aluminum wires that they sell, and started advertising it as "PURE COPPER" wiring. I ran MILES of the stuff when they first started that scam, and have had to pull ALL of it back out of Buried Conduits, because it's just GOING to fail. Several people commented that they ran it inside walls at data centers and now they're having to pull it ALL back out at HUGE expense... This applies to their "'Copper' Cat-5 Cabling", All guages of Speaker Wire, Security System cables and wiring, etc...

Anyway.. Yeah... the Copper Coated Aluminum Wiring is NOT for the faint of heart.. you get ONE shot at getting it to solder, and you just have to kinda KNOW how hot you can get the wires to GET that "One Shot".. after that, solder just WILL NOT stick to it...

Your Weller WLC100 is a fine piece of kit and will make good solder connections.

As to your problem, it could be several issues but since you asked specifically about solder and it seems like you've had at least some basic training, here's the scoop on basic electronic solder.

For tinning wires and general electronic soldering, you need solder with either a Sn60Pb40 alloy or a SN63Pb37 alloy with a Rosin flux core. The 60/40 alloy is an excellent all purpose electronics solder with a relatively wide plastic range (stays molten for several seconds after you remove the soldering iron). 63/37 is what's know as a Eutectic alloy, meaning it has a very narrow plastic range, going from liquid to solid almost as soon as you remove the soldering iron from the joint. It's good if your hands shake, you have a drafty work area or you're soldering dozens of connections and don't have all day to wait for the solder to cool off.

The internal flux should be Rosin based. As a beginner, stay away from no-clean, low-clean and anything else that isn't Rosin based, they require tighter process control to get good joints.

Good brands are Kester, Alpha Metals and MG Chemicals. As was pointed out with the crap Chinese wire, Chinese solder is also a poor choice.

Now you have a good brand name with Rosin flux so you need to pick the solder diameter. There's a fair amount of personal preference here. I trained a lady once who loved tiny solder not much thicker than a human hair. She had to push it into the solder connection at a rather high rate of speed in order to get enough in the joint but she could do it and it worked well for her. As a general rule of thumb, chose a solder diameter that's 1/3 to 1/2 of the smallest diameter conductor you're soldering; that will give you a good starting point.

If you've got good wire and good solder and still have trouble feel free to post and we can work through it.

I prefer SN63Pb37. It's what was required for work, and works great. The radio suites I made for Blackhawk helicopters are still in use after 25 years, zero solder failure even in the high vibration environment.

For resin, I use RMA. Rosin Mildly Activated. Kester is my preferred brand. I put mine in a smaller applicator bottle with a metal tip. We bought our resin by the gallon, and refilled the applicator bottles as needed. Now Kester sells one ready to go:
I apply a little flux to ALL my solder joints. If the joint doesn't look like money, add a little more flux, have another go.

My optimal tip temperature is 650F. This allows me to apply heat quickly, get the solder to flow, and remove the heat before damaging components or lifting traces from PCBs. Anything hotter tends to cause the tip to overheat, and the solder to quickly oxidize.

I finish up with an acid brush, with the bristles cut down 1/2 way, and some alcohol. Scrub the soldered joints to remove any residual resin. Not required for RMA flux, but does allow for a proper inspection of the work.

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