A local Makerspace question reminded me of an article I had planned to write ‘any day now’ – how to solder. Not because I am a soldering virtuoso eager to impart my vast knowledge – but because I am a real neophyte, and if I can do it, so can you.
Although I had soldered for some time (and even somehow justified going from a nice temperature controlled wand soldering iron to a fancy ) I was generally soldering wires together, and the occasional resistor.
However, for my Speaking Multimeter Project, I needed to add audio to the Arduino, using the Adafruit Wave Shield. Which ships unassembled. And with a lot (to me) of parts. Tiny, little, sensitive, solder it carefully once ‘cuz you’ll never get a second chance parts. And I realized I was in deep waters.
So I researched like mad, scoured the net for videos and articles, and ended up soldering not just one, but three audio boards. And most surprisingly, they all worked first time. But they didn’t go smooth at first, so here’s the summary so you don’t have to struggle:
Firstly, get your tools together. And get them ahead of time. Here’s a list of parts I used for my job (including a few I wished I had at the time). The links point to eBay where I got most of my items.
- A to hold the board. Imagine: You’ve got solder in one hand, the iron in the other – so something to grip the circuit board is very useful! In fact, they are sometimes called a third hand – I got an inexpensive one at a local Automotive store (Princess Auto).
- Magnifier. The third hand jig I got had one built in, but you’ll likely need something more portable. Buy cheap reading glasses in high power, and hang them low on your nose for instance. Another option is a , especially one with a light, flip up magnifier, and frames so they can stay on your face. eBay has a variety of these types of .
- Fan. Some form of to keep the fumes away from you. Fancy ones can include an activated charcoal filter to keep smells down. I used a household fan on low pointed nearly at me but not quite (direct fan would have cooled the solder, whereas indirect was enough to push the fumes away).
- . As much as we all want to save the world and avoid toxins, lead solder is much easier to work with than lead-free. Get thin solder with a rosin core.
- . I’ll discuss this in detail further down, but rosin (flux) paste is vital – get a few extra containers since they are so cheap.
- Soldering braid. Also called a , it’s a woven wire mesh that helps ‘mop up’ solder. Handy for when the solder goes in the wrong hole!
- . Great for trimming soldered leads sticking up afterwards.
- . The audio board needed jumper wires, so I found some wire and soldered it in. However, I hadn’t planned for it, so ended making some really large wire joints in a tight space on the board. It works, but I’m not proud of it, and wished I had more wire size selection before I started.
- or at least a heat sink. Handy for cleaning and scraping, the non-metallic ones will be safest overall. A heat sink lets you heat a part and divert some of that heat away from the part’s delicate internals.
- . A simple pump that will suck up molten solder. Like the solder braid, useful when the solder goes in the wrong place.
- A good soldering iron. At a minimum, you’ll get better results with a iron that can have its temperature adjusted. Lead and lead free solder have different melting points, so finding the sweet spot for each is key. I’ve found inexpensive on eBay for ten bucks or so that I’ve liked, which is an inexpensive way to start.
This isn’t a comprehensive list. Different projects require different things. For instance, a large board may require a larger jig to hold it. Also, I live on the (damp) coast and so static electricity is rarely an issue. If you live in a dry area (say, the prairies during winter), consider an and frequently ground yourself with it so you don’t zap any components.
So that’s the parts – now the techniques:
- Build one, but get parts for two. At the beginning, I didn’t know how successful I’d be soldering the board, and I had promised to make two devices, so buying a third one was a no-brainer: I had replacement parts if something didn’t work or was damaged by the heat. Much less stress – and as it turned out, all three worked, an unexpected bonus!
- Keep the instructions handy. Adafruit is phenomenal in this way – all their projects are detailed online, and by wandering through it very slowly I had few problems. I had their audio shield web page open next to me as I worked, where I pinched, zoomed, scrolled and soldered away.
- Check twice, solder once. I cannot emphasize enough to go slow and check again and again (and again). For example, transistors fit only one way, as do electrolytic capacitors, but disc capacitors and resistors are position agnostic. To give you an idea of how cautiously I approached this project, the ICs were marked for orientation with either a dot near pin 0 or a half circle notch. One IC had both of these, but on opposites ends! So rather than guess the correct orientation, I soldered in a DIP socket for the chip, and then press fit the IC in later – I figured if it didn’t work, I’d just reverse the chip without soldering (and hopefully no blown parts). I ended up with the right orientation, but was still happy using the socket – soldering it in directly could have been really bad…
- Flux is your friend – so show the love. One thing I learned online is how flux is actually a descaler/cleaner for the metal you are bonding – without it, you are trying to join two metals that have an oxidized coating on them. Oxidation equals no conduction, so flux and heat cleans the metal for the bonding. Now I’m a fluxing fool; my boards may be a tad sticky from too much rosin applied before soldering, but the joints are oxidation-free where it counts.
- The ‘Two Mississippi Rule’ is all you need. Another technique I found is to apply the soldering iron to the joint, and count to two seconds (three if necessary.) If the joint isn’t right by then, stop. Let everything cool down, then try again. Getting in that habit prevents you from trying to melt solder ‘just a little bit longer’ and risk heating/damaging the part.
- Hot is good, not bad. Everyone has a different idea online of the temperature to set the soldering iron. One thing is for sure though – too cold is useless. I thought keeping the soldering iron’s temperature a little low would give me more time for each joint, but the solder flowed poorly, and I wasted time. Instead, keep it the right temperature (and maybe a teeny bit more), never keep it on too long (the two second rule) and the result is better. Also remember there are two popular types of solder, and each needs a different temperature to melt. I recommend lead solder, but no matter what you use, make sure the soldering iron’s temperature is appropriate for it.
- Heat the part, not the solder. I admit, I’m a fan of touching solder to iron and flowing it into the joint. Really bad idea – the connection between the solder and the part may never get hot enough to really join. Always heat the part directly, while the solder is touching it, and then you’ll have your good connection.
- Learn what good solder joints looks like. This page is excellent. Shiny, concave, and no gaps. Making all your joints like that is the gold standard – and knowing what a good joint looks like first is the key.
- Naughty tip: Reheat everything. I’ve seen this tip nowhere else, and I suspect real soldering people will want to lynch me for it; however, I find reviewing all the solder joints and getting them to flow one more time makes me feel better. If I wait long enough, the part starts cold so I don’t risk overheating (which can happen if I try to melt the solder too long), and I can try and retry until I get the solder joint looks just right.
- Check after as well. Imagine you have a short somewhere when you’re done. You’re optimistic, so you power it up – and blow a few parts in the process. Now measure the annoyance of tearing apart a board you just finished, versus checking and rechecking everything BEFORE power goes on. It’s really tempting to see something in action immediately after all that work, but checking first is well worth it.
- Be prepared to test. Fortunately, I didn’t have this issue, but make sure you have a meter nearby. It might also help to have the company’s forum open on your browser and pointing to pages where people have needed troubleshooting help. This may be overkill, but knowing what often goes wrong before you start can keep you aware of the problem areas as they happen.
And remember to practice – because if you know the fundamentals and practice, you will get better!