Computing stuff tied to the physical world

SMD hand-soldering tools

In Hardware on Jun 8, 2010 at 00:01

I’ve been hand-soldering SMD for some time now. The reflow approach is better suited for batches and recurring work, but sometimes I don’t have solder paste stencils, and sometimes I just need to do one-off builds.

There are tons of instructions on the web. Seach for “curious inventor smd” for example, for some great videos.

First thing to note is that it’s not as hard as it seems. Soldering SMDs by hand is still just that: soldering. The only thing you have to take care of, IMO, is alignment. Once a component is soldered on in two or more places, it’s virtually impossible to adjust it. And pushing too hard, or heating far too long, just gives you lifted solder pads and broken traces, because SMD pads are not as robust as a plated-through hole. Once that little piece of copper comes off the board, you’re hosed…

Ok, here are the tools I use:

  • a soldering iron
  • tweezers
  • a flux pen
  • solder wick
  • solder
  • magnifying lamp

That’s it. I hardly ever use my hot-air soldering station. I don’t have a de-soldering unit (a soldering iron with a hole in it and air suction, basically). For lots of SMD-by-hand work, you don’t need ’em. Although for serious “rework”, you probably do.

Here’s the “Ersa i-CON nano” soldering station I’ve been using for a month or so now:

Dsc 1515

The iron is excellent. Small, and due to its construction it’s also incredible cool (yeah, in both senses):

Dsc 1516

The tip is held on with a spring. It’s clever, because that knob shields even more of the heat, and the tip sits around the heat core, absorbing every bit of heat instead of radiating it out:

Dsc 1517

The warm-up speed of this thing is incredible, it’s ready for use in under 10 seconds. The unit will fall back to 240°C when not used for a few minutes, and drops all the way back to about 45°C when left unused yet longer. It’s configurable, but in an odd way: a Windows program can write a file to a µSD card, which you then insert into the base. It’ll pick up the settings, and use them from then on. I’ve configured the presets as 280°, 320°, and 360°, respectively. For manual work (with leaded solder) I usually set it to 320°. For work on reflowed boards (using unleaded solder), I use the 360° setting.

Should have bought this ages ago. I use the smallest tip available, which is a 0.4 mm round tip. It’s slightly too pointed IMO, so the solder tends to move away from the tip due to adhesive forces. But it works well, and the heat really gets all the way to the tip. On the handle, I hardly feel any heat. I check the display to see if it’s on.

The holder is also clever. It’s some sort of shaped rubber, I think. Heavy, so it won’t slide away, nor get damaged from touching it with the iron, and the way it is shaped means that at rest the handle will cool down all the way back to room temperature.

It’s not cheap (Conrad #588374), but to me it’s worth every penny. Having said that, there are no doubt other units at a fraction of the price which should also work really well. What I’d look for: pencil-like, regulated, and no more than 40 to 60 Watt. I fell for the instant startup, the configurability, and the auto switch-off.

Here’s my previous 15 Watt Weller soldering iron, a few decades old by now (tip replaced only once, I think):

Dsc 1518

Also really nice, but slightly underpowered (ground pins and ground planes are a bit tricky, as are thick copper wires). Another difference is the lenght of the tip – I really like the Ersa’s short pencil-like dimensions.

My daughter still prefers the Weller btw, so we’re both happy now :)

Here are the other tools I use:

Dsc 1519

Not much to say about this, other than that you really should get tweezers wich were designed for this work. They become an extension of your hand. They let you pick up grains of sand, even blind-folded. Well, almost. They may not look like much, but use them gently or you’ll bend them and bring the two opposite sides out of alignment – rendering them useless. Can’t remember where I got these – DigiKey and Farnell have ’em too.

The flux pen is essential for SMD work: apply flux, place component, then solder. When fixing things, I often apply flux again. The enemies are corroded solder and corroded pads – flux takes care of both. This is Farnell #876732.

The wick is equally essential. It took me a while to learn an important lesson: shorted pins are no big deal. Just wick the solder away and everything will be fine again. Can’t get the solder off? Just add more solder first, and then use the solder wick. Snip off each piece after use, as solder wick can only be used once. The type I use is not great – it leaves an ugly brown flux residue.

And last but not least, get a magnifying glass with built in circular lighting:

Dsc 1521

Actually, my daughter prefers broad daylight and nothing between her eyes and her work. To which I can only say: 1) yeah, but she’s 21! and 2) I’m a night owl … starlight + moonlight don’t seem to cut it for me! :)

I think I got that lamp from Conrad, but I can’t find it anymore. It was under € 15, ten times cheaper than another lamp I got with a long arm. The short arm is inconvenient, but it’s more solid. The big benefit of this 3x magnifier is that it has a built in 10x close-up section. Great for very close inspection. The one drawback of this small light is that you can’t look through with both eyes, so you don’t get stereoscopic vision with better depth clues. The cover is useless, btw. I haven’t needed a microscope yet, although there are limits to what you can see with this thing.

Anyway, that’s what I’m using. The rest is patience. And practice.