Experimenting with hand-soldering SMT components.
Now and again I have looked at SMT (surface-mount technology) components and thought to myself “I should try that one day”. But not wanting to fork out for a toaster oven and a bunch of special tools I did it on the cheap – so in this article you can follow along and see the results. Recently I ordered some ElecFreaks SOIC Arduino Mega-style protoshields which apart from being a normal double-sided protoshield, also have a SOIC SMT pad as shown below:
First up I soldered in two SOIC format ICs – a 555 and a 4017:
These were not that difficult – you need a steady hand, a clean soldering iron tip and some blu-tac. To start, stick down the IC as such:
… then you can … very carefully … hand-solder in a few legs, remove the blu tac and take care of the rest …
The 4017 went in easily as well…
…however it can be easier to flood the pins with solder, then use solder-wick to soak up the excess – which in theory will remove the bridges between pins caused by the excess solder. And some PCB cleaner to get rid of the excess flux is a good idea as well.
Now to some smaller components – some LEDs and a resistor. These were 0805 package types, which measure 2.0 × 1.3 mm – for example a resistor:
The LEDs were also the same size. Unlike normal LEDs, determining the anode and cathode can be difficult – however my examples had a small arrow determining current flow (anode to cathode) on the bottom:
Another way is to use the continuity function of a multimeter – if their output voltage is less than the rating of the LED, you can probe it to determine the pins. When it glows, the positive lead is the anode. Handling such small components requires the use of anti-magnetic tweezers – highly recommended…
… and make holding down the components with one hand whilst soldering with the other much, much easier. Unlike normal veroboard, protoshield or other prototyping PCBs the protoshield’s holes are surrounded with a “clover” style of solder pad, for example:
These solder pads can make hand-soldering SMT parts a little easier. After some experimenting, I found the easiest way was to first flood the hold with solder:
… then hold down the component with the tweezers with one hand while heating the solder with the other – then moving and holding one end of the component into the molten solder:
The first time (above) was a little messy, but one improves with practice. The clover-style of the solder pads makes it easy to connect two components, for example:
With some practice the procedure can become quite manageable:
As the protoshields are double-sided you can make connections between components on the other side to keep things neat for observers. To complete the experiment the six LEDs were wired underneath (except for one) to matching Arduino Mega digital output pins, and a simple demonstration sketch used to illuminate the LEDs, as shown below:
For one-off or very low-volume SMD work these shields from elecfreaks are quite useful. You will need a steady hand and quite a lot of patience, but if the need calls it would be handy to have some of these boards around just in case. For a more involved and professional method of working with SMT, check out this guide by Jon Oxer.
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