SMT Soldering Tools

Last edit on 2014-03-02: added a glue gun section.

A year ago, I had to solder a serial console output to the Ben Nanonote in order to hack its Linux kernel.

Went the cheap way back then, and bought a soldering kit off eBay that got the job done, albeit painfully. I remember the guys at Qi-Hardware making fun of me, for it took me ages to solder 3 wires on the device: "Were you using candles to melt the tin ?" :-).

I'm now planning to hack the GCW Zero, and thought it may be time to invest in proper soldering tools for surface-mount technology (SMT). For the record, here is a breakdown of the gear I will be using from now on.

Soldering station

Out is the cheapo 30W soldering iron, welcome the Xytronic LF-389D soldering station.

Xytronic LF-389D soldering station

It's affordable, quite small and feels sturdy.

Having more power (it's a 60W unit) means it can heat up quicker, recover from a heat loss more rapidly, maintain higher temperatures and heat larger areas. And the iron temperature can be set as needed.

Bought it from Elfa Distrelec since I needed a European plug and 220-240V power supply.

Additional iron tips

SMT means small electronic components to work with. Along the soldering station, I also bought 2 additional soldering tips.

Xytronic LF-389D soldering tips

From left to right:

  • Soldering tip Chisel shaped 1.2mm (ref. XYB06),
  • Soldering tip Conical 0.4mm (ref. XYB03),
  • Soldering tip Conical 0.8mm (ref. XYB01, sold with Xytronic LF-389D).

Soldering wire

Lo and behold, all solder formulae are not made equal either.

Stannol Sn62Pb36Ag2 solder

This one is a manufactured by Stannol and has an Sn62Pb36Ag2 chemical formula, which reads 62% Sn, 36% Pb and 2% Ag.

Having lead in the solder means a lower melting temperature to work at, decreasing the risk of damaging components. This specific formula is designed by the manufacturer to be used with surface-mount devices (SMD), so it seems to be a perfect match for SMT work. Regarding health and RoHS directive in the European Union, this should be ok since the solder will be used in small amounts for personal hardware modifications, nothing industrial or to be sold (in which case it's recommended to use lead-free solder).

Thickness of the solder wire is another important parameter. For SMT, thin (< 0.7mm) is preferable since it makes it easier to drop small amounts of solder at once. 250g of 0.5mm solder wire should be aplenty.

Bought it from pkelektronik.com, I couldn't find it elsewhere.

Flux

"And don't forget the flux: it's the SMT-solderer's best friend" I was told :-).

Stannol flux pen

In order of convenience: marker pen > ballpoint pen > syringe > paste > powder. Of course, this also depends on what you're working on.

Flux is an acid that helps removing oxides and reducing the surface tension of the tin in the solder (the Sn component), preventing it to form little balls that do not stick to the metal you're working on.

There is 3 basic types of flux: RA/RMA, water-soluble and no-clean:

  • Rosin Activated (RA) is the most vigorous type, but it's very sticky and a pain to remove from PCB (and it must be removed since acid attacks metals). Rosin Midly Activated (RMA) is less strong than RA but still in the same ballpark,
  • Water-soluble means "hot demineralized water under high pressure". Not quite as easy to get rid of at it may sound, but it's feasible. Use a cheap ultrasonic cleaner for that,
  • No-clean promises that you don't need to clean up but you should be careful with such statements. It's the weakest of the three though.

When it comes to flux formulae (yeah, flux is a field of its own), better use F-SW33 or F-SW34 types (better the latter). Stay away from all F-SW1x and F-SW2x and avoid F-SW31/32 Rosin flux if possible. This does not tell all the truth about flux though: you should get a non-activated no-clean no-rosin flux, but it still needs explicit classification "for SMT" by manufacturer. Trial and error, and collecting different types of flux for different purposes seems the only way to go here.

Stannol X32-10i is an F-SW33 no-clean type, but I will be using alcohol to clean the PCB after I'm done.

Wire-wrapping wire

Not much to say about that one.

30AWG Olympic wire rings

Thinness is the key factor here, so I went for 30AWG Kynar wires. Also bought different colours to make it easier to tell which is connected to what.

Bought it from eBay (love that place).

Glue gun

A useful, affordable tool for finishing touches.

Steinel Gluematic 3002 glue gun

Not directly related to soldering, using a glue gun can be useful to glue wires in place once the job is done. Nothing moves beyond the glue point, preventing wires and joints from being stressed.

Many thanks to Werner Almesberger and Joerg Reisenweber for the invaluable insight and the funny talk.