Computing stuff tied to the physical world

TK – Soldering Iron

In Hardware on Mar 15, 2012 at 00:01

Welcome to the Thursday Toolkit series, about tools for building Physical Computing projects.

The very first tool you’ll need – inevitably – when going beyond breadboards and wire jumpers to hook stuff together, i.e. when building things which need to become more or less permanent, is a soldering iron.

A soldering iron is just a heater which gets hot enough to melt solder. For the solder used in electronics, the iron’s tip is usually kept at between 275°C and 375°C. That’s more than hot enough to give you a serious burn when touched. So the whole idea of a soldering iron is really to get that heat in the right place, while giving you a way to hold the thing and manipulate it fairly precisely.

There are tons of different models, costing from €10 to €1000. The idea here is to pick one which doesn’t burn a hole in your pocket (heh, turned off, I mean :) – The target I’ve set myself for this initial Thursday Toolkit series is to be able to get all the tools you need for having oodles of fun with various Physical Computing projects for a total of under €150.

That rules out a lot of soldering irons, and forces use to focus on two essential features, i.e. that the soldering iron has enough heat to work well, and also has some sort of basic temperature control. A soldering iron which is too cold will be an awful time-consuming hassle, but one which is too hot will burn and damage electrical components, and will oxidize the solder much too quickly. The big fat uncontrolled “after-burners” used by electricians and plumbers are not suitable here.

As mentioned in the initial post, I decided to buy all the tools at Conrad, item 588417 in this case:

DSC 2940

(just the iron and the two tubes at the left are included – the rest was ordered separately)

What I like about this 45W unit is that it has a solid base and sort of a temperature control, letting you regulate how much heat gets generated. This is definitely a low-end unit. Another option, with a better (smaller!) soldering iron, is the Aoyue 936 (here’s a link to a Dutch shop carrying this particular model).

The Conrad unit is a soldering iron heated at 230 VAC. Let’s have a look in close up:

DSC 2942

It’s all about heat, and keeping it away from your hand. You hold it like a big pencil or marker, and after an hour or so of use, you’ll note that the middle of that thing gets warm, but not too hot – which is the whole idea. The metal part is the hot end, as you’ll quickly find out once you touch it and get a nasty burn. Trust me, you will get burned at least once – it comes with the hobby…

As I said, this is a low-end unit. One of the compromises is that the hot end is fairly large – so holding this thing steady and accurately placing the tip where you want it takes some practice. But no worries – everyone starts out this way, and many of us keep on working with such a unit for years. It works fine.

The other compromise is that this unit isn’t really controlled by a thermostat, it’s really just trying to keep the tip at a somewhat constant temperature, based on thermal flow in free air. Let’s take it apart:

DSC 2945

The shiny metal barrel is the heater. Some nichrome wire, wound inside an isolated jacket no doubt. Much like toasters, hair driers, etc – but only 45W. In the middle sits a big metal core, with the pointy tip we’ll be soldering with. Its main task is to conduct the heat to the tip, and being such a large piece of metal, it’ll keep a reasonably constant temperature, even when the tip touches the copper and wires of the circuit being soldered.

There are two heat-insulated wires to the heater, powered from AC mains. The third wire is ground, and is attached directly to the barrel. This provides three types of safety: 1) if the heater breaks down, it’ll cause a short to ground and blow your AC mains fuse instead of electrocuting you, 2) if you accidentally burn through a wire carrying AC mains current (such as the soldering iron’s own!) it’ll also blow a fuse, and 3) the tip of the soldering iron is at ground potential, so any static electricity around your circuit will be conducted safely away from the sensitive electronic parts.

Then there’s the base, where the hot soldering iron is kept between your soldering work. Note the metal spring / holder, which keeps soldering iron itself hot, but tries to stay reasonably cool to the the touch on the outside. You’re not going to get burned touching it – just a quick reminder that there’s something very hot inside!

And then there’s this thing:

DSC 2943

That’s actually a synthetic sponge. It’ll probably make more sense once you soak it in water:

DSC 2944

Part of the skill needed to solder stuff together, is to keep a good clean soldering tip. Solder tends to oxidize, so over time you’ll get in the habit if wiping that scorching hot tip clean and applying fresh solder. The wet sponge is one way to clean that tip – it’ll sizzle and scorch a bit, but it works fine.

So much for the venerable soldering iron. Get one, don’t go overboard on features (a small size is great, but it’ll cost ya’). Far more important is to get a decent one and practice, practice, practice! – I won’t go into the actual soldering skills here, there are plenty of articles, books, and weblogs on internet, so my suggestion would be to just google around a bit. And then: practice – there’s no magic pill around that.

Next week, I’ll go into one of the best other investments you can make – apart from the soldering iron.

  1. I have that exact soldering station on site where I’m installing my µC based controllers. I bought it ’cause I needed one badly since I forgot to bring my own digital station. Now my digital Stations stays at home and I continue to use this for soldering everything. I don’t do surface mount, though. After hours of use the rubber part of the grip gets warm, however, it was on all day.

  2. Nice article.

    My usual weapon of choice this, the Antex 18watt

    I do have an optional extra tip for it, 0.5mm

    It doesn’t have the power of your 45watt, so I couldn’t solder 4mm earth cable with it, but it has built every JeeNode I’ve bought, including the SMD Kit.

    And yes, a cleaning sponge is essential if you are soldering more than a couple of joints.

    One thing I just can’t get on with is skinny solder! Good old 1.2mm flux cored 60/40 for me :-)

  3. Spent some time yesterday soldering 34 gauge wire leads onto some 0402 size thermistors (not a typical need, but for this experiment I needed a tiny thermal mass). Trust me, you want skinny solder for that (+ microscope). I usually use a metal-mesh pad for tip cleaning instead of a sponge. People argue about what’s better; not sure myself.

  4. The metal mesh pad surely seems more convenient, since it doesn’t require a run to next faucet to soak the sponge.

  5. I have a similar vellmann unit. Gets hot fast, had a place to put the soldering iron. Thats all I really ask of a solder melter. Controling the temp is also nice, but I have dealt with far older, far worse soldering irons for long enough to appreciate my one and only good one.

  6. I just got one of these , it’s in the mail

    After reading here

    It’s going to be my first induction iron.


  7. Temperature controller isn’t really needed: once you have enough experience you can tell if the iron is at the right temp with your wet finger (and w/o getting burns! — that’s where most experience is needed :) ).


    Quite old-school but it works.

    • Well yes, but it’s not just for soldering – it’s also to prevent the iron from getting too hot or cold while waiting. Ideally, it should be ready for use every time to need it – sometimes many hours on end.

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