Physical computing hackers need to solder things. It’s a required skill.
Wires need to be fastened to connectors. You’ll need to place a component on a printed circuit board. I create the brass and copper frames for my conference badges and Steampunk-themed wearables using this method of joinery.
What Is Soldering?
Soldering is a method of joining two metals with a low-temperature, conductive filler material. Base metals, to be soldered, include steel, copper (or copper coated), galvanized parts and brass but not aluminum or plastics. The filler alloy has a lower melting temperature (around 470 degrees F) than the base metals and is typically made up of tin and lead, usually in a 60/40 mix. Soldering differs from welding in that the base metal is not heated to the melting point, instead just up to the point where the filler alloy flows easily into the joint. A flux is used to chemically clean the metal surfaces, so the filler smoothly adheres to the base metals, creating a strong bond. Soldering ensures an electrically solid joint, as well.
The low melting point of typical tin-lead solder makes it practical to join connections with a hand-held, plug-in soldering iron. These tools are available at electronics shops, big-box home improvement stores and on the Internet. A 15 to 30-watt model is fine for soldering wires to small connectors and printed circuit board work. A soldering gun works well for larger electrical connections and parts requiring more heat, like my brass Steampunk project frames.
I’ve used the same Weller gun for about 30 years and they are practically bullet-proof. There’s no need to spend a lot of cash on these tools, so just get the basics.
You’ll also need some solder. I like the 0.032-inch, 2.5-ounce, 60/40, rosin-core spool available from your local electronics store. This small roll will last you quite a while. Steer clear of acid-core solder because it’s used for joining copper plumbing and is corrosive to electrical components. Likewise, there’s no need for silver or high-temperature alloys. The rosin is built right into the middle of the solder and is a very effective and inert flux. Keep it simple and don’t get exotic is this area.
It’s helpful to have a brass Brillo pad handy for periodically cleaning the iron tip. The flux tends to erode the iron or gun tip, so you can also use a file every once in a while to expose clean copper and keep it crater free. Some fine sandpaper is also suitable for this task. Be sure to re-coat the tip with solder after filing.
A good solder joint is smooth and adheres well to the base metals. A cold joint looks blobby and gives a poor or non-existent electrical connection. Too much heat melts surrounding parts and damages delicate electrical components, particularly transistors, integrated circuits and the copper traces on printed circuit boards. It’s always best to use just enough heat to get the job done, without overheating.
Joint prep is also an extremely important part of making a good connection. Lightly scrape or sand the metal surfaces to be joined, especially if there is any corrosion or oxidation. All wax, oils and plastic coatings need to be removed to ensure high-quality adhesion. Even the oil on your fingers will make it hard to get a good joint, so be sure everything to be soldered is bright and contaminant free.
We’ve finally come to the actual act of soldering.
It’s pretty straightforward. Say you are adding a wire to a small connector. Clean the surfaces and solidly wrap the wire around the connector, if practical. You might also use a so-called helping or third hand to hold the wire against the connector. There shouldn’t be any movement between the parts, during the soldering process, otherwise you’ll end up with a bad joint.
Next, evenly heat both parts while holding the end of the solder against the joint. As the filler melts feed it into the joint, so a smooth flow is created around the base metals. There shouldn’t be any holes or voids in the liquid filler. Remove the iron or gun as soon as the joint is thoroughly coated. You might need to move the iron around to evenly heat both parts of the joint, so the solder flows smoothly. Try not to leave the iron on the joint any longer than needed to get good flow, otherwise you will probably damage other parts. For small connectors, it helps to “pre-solder” each part separately, before bringing them together to make a joint. You then just need to position the parts together and “touch” the iron to the joint to get good flow. You can also touch the end of the solder, to the joint, to add a tiny bit of flux. This helps the filler flow around the parts.
The larger the joint the more heat is required. So, soldering wire lugs or 3/16-inch brass tubing needs a bigger iron or gun. I usually use the Weller gun, on high (140-watts) for such jobs. For small connectors or working with tiny components on boards, a 15 to 20-watt iron is safe and effective, without causing excessive component-destroying heat.
I always keep a slightly dampened paper towel handy to wipe the tip, while I make my joints. You’ll quickly learn an effective technique so you don’t burn your fingers.
Lastly, you’ll need to practice. You’ll likely damage a few components in the very beginning. Don’t be discouraged. Perhaps do a series of trial joints on larger parts to start. Naturally, I think working on real projects is the best way to learn and not melting your parts, is certainly an incentive to pick up the skill quickly.
Soldering is a critical skill for the off-the-shelf physical computing hacker.
Remember to clean the parts, use the right iron, don’t move the joint and don’t heat the things any longer than necessary. You’ll also get better with practice.