Soldering Basics: 1
Soldering Basics: Through-hole Components
This is a quick tutorial for people who want to make kits but have never soldered before. Soldering is really straightforward with the right equipment and a little bit of practice. I'm going to assume you have at least some of the equipment, so let's get some practice!
For this tutorial, we'll be soldering wires to component terminals to get some soldering practice. You'll need to do this any time you want, say, switches in a project box to connect to your circuit board, or breakout wires from some connector into a breadboard. Let's say we're interested in getting USB into a breadboard. We'll need a cable assembly consisting of a USB type B receptacle on one end, and a 4-pin header on the other.
Although we'll only work through soldering to the receptacle and header, the same approach could be used to attach wires to switches, encoders, or anything else with solderable terminals.
The most important thing to keep in mind when soldering is to get the entire joint heated to the proper temperature quickly, so that solder applied to the joint (not to the iron!) will flow evenly throughout. If the joint is heated too slowly, the component could be damaged from overheating. As a rough rule of thumb, try not to leave the iron on a joint for more than 3 seconds.
What You'll Need
As part of this tutorial, I'll be removing a component from a circuit board. If you want to follow along with this part, you'll also need:
Let's Get Started
It’s a good idea to have everything prepared before turning on the iron, so let's start by cutting 4 pieces of hook-up wire, approx. 6" length each, and stripping 1/4" of insulation from the ends. Next, cut two pieces of heat-shrink tubing, 1/2" or so each, for every wire (8 pieces total). The length of tubing should always extend a little beyond the joint itself.
Now that the wire is ready, we’ll need a USB receptacle. If you've already got one, great. I don’t have any floating around free in my parts bin, but I found one on a scrap pcb, so before continuing, I’ll show how to remove it (feel free to skip ahead to the next section if you’re not interested in seeing this).
I have already removed a receptacle from this board, but there is one more left. There is also a barrel jack, a few type A receptacles, some capacitors, and a 7 pin header. Not too bad for a board that I found in the trash! Let’s have a look at the underside.
There are a total of six joints I need to remove, two of which are fairly large. I'll use the solder wick on all joints, but the solder sucker will be most useful for the two large joints. I could remove all the joints without a solder sucker, but this would use up more (expensive) solder wick.
First, I’ll turn on my iron and check the temperature setting (it should be around 700° F for this joint, assuming it's leaded solder). Next, I’ll arm the solder sucker by pushing down on the spring-loaded plunger until it locks into place. Finally, with the iron in one hand and the solder sucker in the other, I’ll clean the tip with a damp sponge, heat the joint until it’s fully liquefied, put the solder sucker as close as possible to the liquefied solder, and trigger the solder sucker. Slurp!
I’ll repeat this for the other large joint. When I push the plunger down again, flattened bits of solder should be expelled from the solder sucker nozzle. Note that the solder sucker may not remove all of the solder from the joint, and that’s ok.
Now that the big blobs of solder have been removed, I’ll use solder wick to remove the rest. Solder wick pulls solder from the joint via capillary action in the wick. To be effective, the braided copper must be heated thoroughly and pressed firmly on the joint.
To get the necessary heat transfer, I’ll put a little extra solder on the tip of the iron when wetting the tip. Now I’ll place the braid over the joint, and then press it firmly against the joint with the tip of the iron. Again, the success of this process depends heavily on good heat transfer, so at least a little solder should be sandwiched between the tip and the braid during the wicking process. All of the solder from the joint should eventually be soaked into the wick.
After repeating these steps for the other five joints, I’ll gently wiggle the receptacle until it comes free of the board.
Back to the Cable Assembly
After that little digression, I now have my USB receptacle, and we're ready to attach the hook-up wire. First though, you'll need to tin the wire ends. This prepares the wire by coating it thoroughly with a thin layer of solder. Place the wires in the vise so that you can quickly tin each one, taking care to heat the underside of the wire with the iron while applying solder to the top surface. As the rosin boils over the wire, it removes any oxidation from the copper, so that the solder will make a nice bond. After tinning both ends of all four wires, go ahead and tin the terminals on the receptacle as well.
A word about terminals with the little holes in them. You may be tempted to insert the wire into the terminal hole, and wrap the wire around the terminal a few times for a really sturdy joint. I don't do this for two reasons.
First, it makes (in my opinion) an uneven looking joint that is difficult to heat-shrink in a professional way, and second, it's quite difficult to remove the wire from the joint if you make a mistake (and yes, I goofed on my first attempt, swapping the power and data lines because I was reading the USB diagram incorrectly, but it was no problem since the wire just lifts off of the terminal when heated).
So, I just ignore the holes and lay the tinned wire down parallel to the tinned terminal.
So now you're ready to attach the wires to the terminals. With the receptacle still held firmly in the vise, rest the wire on the terminal with one hand while you heat the underside of the terminal with the other. Within a second or two the tinned wire should melt into the terminal.
When the joint forms, remove the iron while keeping the wire as still as possible until the joint cools. If the wire is moved too much before it cools, a “cold joint” will result, and the process will need to be repeated.
After attaching the remaining three wires, thread the heat shrink tubing onto the wires from the other end, two pieces per wire, and push them down toward the ends you’ve just soldered.
It's important to do this before the other ends of the wires are attached to the header; otherwise, there will be no way to get the heat shrink on and you'll have to remove the wires at one of the ends. It's also a good idea to twist the data lines (the green and white wires), to increase noise immunity when the assembly is in use.
Next, break off a 4-pin section of 0.1 inch header and clamp it in the vise. After giving your soldering iron tip a few swipes on the sponge, wet the tip with a little solder, tin the header pins, and attach the wires, using the same technique as before.
The solder shouldn’t touch the iron directly at any point in the process. It’s no big deal if they touch briefly, but you’ll know you’re doing it properly if you can avoid it, because the solder only melts on a joint heated to the proper temperature.
Now cover the joints with the tubing that you threaded onto the wires, and shrink the tubing on both ends with a heat gun or a hair dryer. Always keep the heater (or the wire) moving so that you don’t melt the heat shrink.
That’s it! The cable assembly is now ready for use.
I hope you were able to pick up some soldering basics from this tutorial. I'll end the tutorial with two of my favorite videos demonstrating soldering in action.
If you practice soldering on a real pcb (even if it's scrap), and watch the above videos a few times, you can actually get pretty good at soldering in a few hours. Now quick! Go practice, before you forget everything!