Adventures in SMD soldering – part 4: conclusions

Over the past three posts I’ve looked at three ways of soldering SMD/SMT components on to a PCB – by hand, reflow soldering with a hot air gun, and reflow soldering with an oven. Now it’s time to draw some conclusions.

The pictures show the three boards I made up using the various methods. The sub-heads link to the main posts.

Soldering by hand

This was surprisingly easy and, ironically, gave me the least grief when it came to the most challenging component – the TXB0104 chip which came in a TSSOP-14 package with 0.3mm pins with a 0.65mm pin pitch. It’s ironic because I decided to invest in the equipment for hot air and reflow soldering specifically to deal with ICs with fine pin pitches.

Hand soldered. Yeah, it’s a bit messy in places, but works fine.

The truth is, I found 1206 capacitors to be more of a struggle than the TSSOP-14 chip. So long as I use the magnifier and a finely pointed soldering iron tip, the chip is relatively easy to handle and I didn’t hit any of the solder bridge problems I had with the two reflow soldering techniques.

So hand soldering is definitely an option – but with some caveats.

It’s labour-intensive and gets tedious beyond, say, 10-12 components. More so than through-hole soldering? Well yes, because of point 2.
It’s easy when it goes right. When it goes wrong, it’s intensely frustrating. You can end up chasing a part around, with it flipping up into a tombstone at the slightest provocation. Sometimes I had to step away and take a deep breath before continuing.
It’s not as neat as reflow soldering. How much that matters depends on your own aesthetic standards.
Personally, I wouldn’t attempt parts smaller than 1206.

Compared to reflow soldering, hand soldering is highly dependent on your skill level. For instance, some people have told me that to tack a component in place they like to hold it in a pair of crossover tweezers. That was actually the first method I tried and, while it worked sometimes, my shaky hands made it a hit-and-miss affair. All too often the hand holding the tweezers would twitch slightly just as I was applying the heat. And there was a tendency for the part not to end up flush with the board surface.

In other words, you’ll have to decide whether this method is for you by trying it. Practice makes perfect, of course,.

Reflow soldering with a hot air gun

With all but the fine-pitched IC, this technique was easy and the results were pleasing. In a way, though, it falls between two stools.

Hot air soldered. Note how the regulator is a bit off-centre. This was the second attempt. The first attempt also had off-centre parts – and solder bridges on the IC.

It has all the setup required for reflow soldering. You have to remember to get the solder paste out of the fridge a few hours before working. And in my setup I have to ensure the air bottle is charged. Yet this technique isn’t as quick and convenient as using the oven. And it did take me two goes to get a working board.

There’s always the danger that parts – especially those close to the one you’re actually working on – will get blown out of position.

This is the technique I’ll probably use least. But the rework station is useful for other things, such as desoldering. And, of course, it’s good for reworking boards. If, say, I want to change a resistor for one of a different value, the hot air rework station makes it easy to remove and replace that one component (can’t use the oven for this). I could also do that with hand soldering, but reflow soldering makes it possible to go for smaller components than I’d be comfortable hand soldering.

Reflow soldering with an oven

I documented my issues with the TSSOP chip in the main post. This is the only component that caused me problems. Everything else soldered beautifully. And this is, without doubt, the fastest and lowest-hassle of all the methods. It’s like pizza: stick on the ingredients, pop it into the oven, take it out when the bell dings. And the results are great – just don’t burn your tongue.

Reflow soldered in the oven. This gave the best result, although I now realise I should have cleaned up that flux residue before taking the picture.

But what about that TSSOP issue? Well, I’m working on that and I think it’s just a matter of refining my solder paste application technique. And maybe getting better paste. I’m confident this is a crackable issue (and I have another post coming that addresses this.)

In the meantime, if I have a board with a TSSOP package, I’m tempted to use reflow for all the other components and then solder on the TSSOP by hand.

Although I haven’t tried it yet, I can see myself using parts smaller than 1206 with this method. This can help reduce board size and offers more choice when it comes to components.