0. Introduction

This is the first article of a series dedicated to SMT PCB development. In this one, I’ll talk about technique, tips and tricks to hand-solder SMT components, like SOIC, SOT-23, … up to smaller ones like SDE06A and RWL0009A.

1. Right tools for the job

The right tools enable us to solder better and wasting less time. Those are the tools I always recommend:

  • a good solderer, better with a thin tip;
  • a good-quality soldering flux;

    Solder flux

  • soldering wire (better if lead-free for safety reasons);
  • copper wick for desoldering;

Optionals:

Antistatic tweezers

  • heat gun for small parts removal;
  • antistatic tweezers (required if using some fragile components);
  • antistatic bracelet (also required for fragile components);

2. Good amount of flux and temperature

The two main points in SMT soldering are the amount of soldering flux and the temperature. An inadequate amount of flux will make the soldering difficult (in some cases impossible) and for this reason it’s a good idea to manually add it instead of using only the flux already inside the soldering wire. In addition to that, a too low temperature will take too much time to solder the components, with the risk of damaging them because of heat, and, on the other side, a too high one will just melt the plastic package as soon as we near the solder tip to the component. For this reason, it’s very important to always check the rated temperature of the component. (EX ADUM1250)

3. Soldering

3.1 Aligning the component

The small LMR62421X IC

The IC correctly placed

One very important step, if not the most important, is the alignment of the component. A bad aligned component will not solder well. You can use a small amount of flux in order to somehow “glue” it to the board.              

   

3.2 Applying the flux

Applying the flux

When the component is correctly aligned, it’s time to apply the flux. You have to apply a good amount along the sides of the component because when soldering, too few amount of flux will not allow the solderer to exchange enough heat that could attach the soldering wire to the component.

   

3.3 Soldering

The soldering stage

The final result

The main part is, obviously, the soldering. Be sure that the tip of the solder is hot enough, then put it on the flux that had been applied around the component and at the same time add some soldering wiring next to the tip. At the end, the result should be something like in the picture on the right. If you want to see more clearly how the soldering had been done, a little

The result after cleaning process

digital microscope like this could be a good option. Here you can see some pictures taken with it. The component is aligned, the soldering is clear (I’ll explain how to do in the next paragraph) and there is the right amount of solder on the pads.



3.4 Cleaning

Cleaning with brush and isopropryl alcohol

I’ve tried several methods to clean PCBs from flux, including strong brushes, flux remover (spray), etc… but I found two methods that work all the times. With small amount of flux to be removed, a good brush and isopropyl alcohol (better wear plastic gloves while working with it) would work just fine. If the area that has to be cleaned is larger, the best option is using isopropyl alcohol and an ultrasonic cleaner like this one.


4. Final consideration

I hope this article would be useful to some of you out there. If you need some explanations, write me a message or a email and I’ll be glad to answer.