Ask Hackaday: What’s Your Worst Soldering Job?

Dec 20, 2023

Soldering! It's the primary method for attaching one component to another in the world of electronics. Whether you’re free-forming a circuit, attaching connectors to cables, or populating a PCB, you’ll eventually find yourself doing some soldering, whether by hand, reflow, or maybe even a fancy wave soldering machine.

It's a fundamental skill that nevertheless remains one of the biggest hurdles for newcomers to overcome when diving into the electronics hobby. Difficult jobs with tiny components or with large heat sinks can up the challenge for even well-practiced hands. Thus, today we ask the question: What's your worst soldering job?

One of the most common causes of a bad solder joint is not getting everything hot enough. If you don't get the temperature high enough, the solder will simply fail to stick. This doesn't just apply to the soldering iron, or the solder itself. You have to get the component leads, PCB pads, or wire you’re soldering up to high temperature as well.

If you’ve ever had a molten blob of solder that simply won't grab on to, or wet, the part you’re soldering, you probably haven't gotten things hot enough. The principle is easy to see in action. Bring a soldering iron tip with plenty of solder on it up to a stripped piece of copper wire. The solder will blob ineffectually next to the wire until the copper itself reaches a suitable temperature. Then, you’ll readily see the solder wick on to the wire itself.

Of course, in some situations, it can be difficult to get things hot enough. Trying to solder a component on to a PCB pad that's part of a large ground plane can be incredibly difficult, as the ground plane acts as a heat sink. Similarly, soldering large-diameter battery cables or big high-current connectors can be similarly difficult. Where a little 20 W soldering iron might be perfect for soldering small chips and resistors, you may find you want a 80 W iron – or more – when soldering things like connectors for high-current LiPo batteries in hobby applications. Alternatively, design changes can help – many PCBs use thermal reliefs around ground pads to reduce the outflow of heat from the pad while soldering.

Without plenty of heat, a solder joint will look frosty and have very poor adhesion. It’ll probably fail under even the slightest physical disturbance, flex, or vibration.

Other times, you might find a soldering job difficult because of the materials involved. Metals like aluminium are incredibly difficult to solder, as the metal forms a oxide skin that prevents solder sticking. Plus, it's a great heatsink as well, only making things more difficult. In situations like these, specialist fluxes are often essential to making a bond without a lot of hassle.

Alternatively, homespun DIY techniques can also help. When it comes to aluminium, some see success by pouring an oil layer over the metal and scraping away with the soldering iron tip or a sharp object. This penetrates the oxide layer while the oil protects it from reforming.

But beware: often, a failed solder joint under these conditions will look like a smooth, well-rounded blob on a wire or component lead, but be completely unattached to the metal below.

In these situations, mistakes are common, and injuries and light burns are often more likely. However, it's these tough fixes that often bring the most pride and joy. Whipping up a crucial audio cable backstage might just save a gig, and some hasty jumper wiring might just get your company's product up and running for the big annual convention.

The fact is, we’re all learning every day, with every solder joint we make. Along the way, it's often the tough jobs and the bad joints that teach us how to become better at soldering, whether it's through-hole, SMD, BGA, or for a production run of millions.

We’d love to hear your stories, and see your pictures, so hit us up in the comments. What are your worst solder joints, with the worst tools, or with the worst outcome? What have you gained or lost in the process? Let us know!