Friday, 11 September 2015

Autumn Soldering Tips (SMD)

In this next post, I am going to explain how we dealt with surface-mount devices (SMD).
From our experience handling them, one advice that we would like to share is that we should not take soldering SMDs lightly as a lot could happen if we do not get it right. However, failure is unavoidable and as they say "the first try is always the hardest". Luckily, it gets easier with practice. Most of the problems surfaced were mainly due to short-circuits. So, we did some research on how to solder such tiny devices on our customized pcbs and found a video by EEVblog on YouTube. It was pretty hard to get our fingers right on target at first but we managed to mount them easily at the end of the day. Of course there are other ways of doing it like using solder paste and an oven but we decided to do it manually and trust us, although it was hard, but it was worth the experience. At that point we asked ourselves this "when will we ever get the chance to do SMD soldering by HAND?".

Below is the link to the video.

Here are the list of items that we used during soldering SMDs ...

1. Variable Temperature Soldering iron station and a Flat/Weller tip soldering iron.

To start with, we tried using a fine tip soldering iron and it was super hard to get the solder to stick. Instead of sticking onto the board, It kept sticking to the side of the tip. A flat tip ensures that it does not (well it worked for us). Make sure to wear safety goggles and be careful on where you are pointing them. Do not risk on getting a scar. Other essentials that comes with this is a damp sponge.

2. A 0.3 mm solder and we also used a 1.0 mm solder for bigger thermal mass (It might not be the best way but it does work for us)

"Not your everage solder size" you wont see these lying around your electronic study rooms as it is rarely seen that schools or even universities for that fact, that teaches SMDs to students. We manage to grab some from our lab assistants. At some point, ended up buying a roll for ourselves for future use. 

3.Solder wick

One might wonder what on earth do we use it for? I know I did :). Turns out, a solder wick work wonders during SMDs. It helped us to remove excess solder from the chips without much hassle. Just by laying a cut out strip onto the desired area and using heat from the soldering iron, excess solder gets sucked onto the strip almost instantly! Say goodbye to solder suckers! :)
but... there are times when it does not really remove excess solder but cause solder bridges. At one time, when we tried to fix it, as a result of putting to much pressure, one of the traces connected to the chip got lifted. We lost a good board that day. RIP. Well, to fix this, we added a bit of flux on the wick and more flux on the target are. With a bit of time we manage to fix it. Patience is the key young grasshopper!

4.Microscope/Magnifying glass

We started out using the big microscope in the workshop but we always find ourselves stuck waiting for the workshop assistant to arrive. Thus, we bought a jeweler's magnifying glass and mount it to one of our phones camera and surprisingly, was much easier than using a huge microscope. We might need a multi-meter for continuity testing to make sure there are no short circuits.

5. Flux pen

This fine pen is no ordinary pen. We used it so ease the soldering process and any kind of solder rework. The flux prevents beading of the solder (clumps) and helps the solder flow cleanly onto the parts we are soldering. However, flux is mildly corrosive over long lengths of time (months). The water soluble flux will cleanly wipe away after wetting the soldered surface. (will be explain later)

6. PCB and Flux cleaner/remover

I mention a bit on some water soluble flux earlier. Well, here it is! Presenting the ever powerful flux remover haha! We bought it from Maplins 'The electronics specialist' =)
Basically, it is an isopropanol base compound which removes flux residues, clears oxidised PCB tracks and evaporates without leaving any residue! MAGIC!

7. Solder tip cleaner

Your basic tip cleaner. A 'tip' (see what just did there :p) is to make sure your soldering iron tip is always clean (a silver tip)

8. Variable Temperature Hot Air Gun

The 8580. This is brand new to us. It is the first time we are using a hot air gun station because some of the SMDs (eg. oscillator) uses mounting pads (no legs basically) which we could not reach using the solder iron. We set up the station at about 360 degrees. As u can imagine, it is HOT AIR! so be careful where you are pointing it. (at one point we triggered the fire alarm haha). One way of doing it is, with a circular motion, heat the components about an inch away. Be cautious not to burnt other components. Test the components after each and every 6 seconds of heating and test if they are still loose before heating it again. This is to make sure the component does not get too hot and damaged.

9. Tweezers

A fine tool in picking and placing tiny components :)

10. Wire cutters

Good ol' wire cutter. 

11. Safety goggles and Fume Extractors

Desmond and I at Bristol Robotics Lab :)

Last but not least safety. Always wear safety goggles and have a fume extractor to avoid inhaling the fumes. (Fun Fact: the fumes could trigger asthma attacks)

Bonus content!
Heres a time lapse of the entire process =)

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