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Hardware & Electronics

Through Hole Soldering – learn how to do it once and for all

23 Aug , 2016  

Ever had troubles with soldering your components? Solder wire dripping? Components getting burned? Well, worry not, because in this article we will teach you whatever there is to know about how soldering works, and to master the art of soldering! Today we will go over Through-hole soldering (TH Soldering).

For starters, let’s get to know all the required equipment.

Soldering Iron

The first step is to choose a soldering iron and a suitable tip. You want a tip with just the right dimensions for the job. Take a look at the different tips displayed in the image underneath (these were taken through a microscope so excuse the slight blur)


The first one is very thin and is meant for finer soldering. With this tip we would only get the desired soldering spot heated, but we would not be able to actually solder an electronic component.

The second tip is too big for this job. With it, we would heat the soldering spot and melt the soldering wire, but we would also risk damaging the solder mask, or overheating and damaging the component.

The third picture shows a tip which has the right dimensions. It doesn’t go over the surface of the varnish of the board but is big enough to heat the soldering spot.


Solder wire

Soldering wire

Soldering wire

The wire is made out of several different metal alloys that create a soldering joint when melted. There are different types of solder wires, but overall they fall into two categories: Lead and lead-freeLead-free wire is more popular today because it causes less pollution. It is more expensive but not necessarily better. Lead, however, is prohibited by the European Restriction of Hazardous Substances Directive (RoHS) so the use of lead wire is not an option for manufacturing electronic equipment. You can only use it for your own electronics.

If your soldering unit has temperature control, the temperature should be set at between 370 and 380 degrees Celsius for lead wire. For lead-free solder wire, this temperature is usually around 20 degrees higher. That is because lead-free wire contains additional metal alloys with higher melting points.

The most suitable diameter of a soldering wire for TH soldering is between 0,7 and 0,8 millimeters. Choose a wire with flux in its core. It’s simpler to use because you won’t have to add additional flux after soldering.

Here we need to note one more thing: burning flux leaves dark marks on the soldering spot and on the tip of the soldering iron. You will need to clean the tip to remove these stains. This used to be done with a moist sponge, but these days a brass wire is preferred (we use brass because it’s non-abrasive). The reason we don’t use a sponge anymore is simple, yet important: it cools off the iron too fast. Repeated exposure to this kind of temperature shock will wear out the iron tip more quickly.

Brass wire used for cleaning the tip

Brass wire used for cleaning the tip

Now let’s get to the practical part

The secret to successful soldering is to heat up everything simultaneously: the solder wire, the soldering spot, and the component.

First, we put the tip of the iron so that it touches both the soldering spot and the component. Then we add the solder wire, which will start to melt over the soldering spot. We then remove the wire first, followed immediately by the tip of the iron. This whole process usually takes between one and two seconds. To see an animated gif of how it should look like, click here

The iron tip should just touch the soldering points. There is no need to add any pressure because that can only damage the board. If the soldering spot takes too long to heat up, usually it’s because you need to increase the temperature at the soldering unit or choose a different iron tip.

A better view of how the tip should be placed

A better view of how the tip should be placed

How to know if the correct amount of solder is melted? The soldering spot should have a cone-like shape.

Insufficient solder is not acceptable, more solder needs to be applied (the whole process has to be done again).
Too much solder looks messy, but it’s acceptable.

If the solder hasn’t spread out on the board, that means it wasn’t heated up enough, and all the metal has stuck on the pin of the componentThe soldering process has to be repeated.
Here’s an example where additional flux was added although it wasn’t necessary. The flux has spread out over the TFT display of a mikromedia Plus for PIC32MX7.

Run out flux on the board

Run out flux on the board

Run out flux on the TFT display

Run out flux on the TFT display


Soldering your components right can sometimes make a big difference. Devices often malfunction or fail to work at all because of poor soldering. We have covered the basics of TH soldering in this article. However, if you want to learn more, stay tuned! More articles on soldering are already on the way!

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Dragan is a professional solder samurai. Soldering iron is his sword. He works as a reworker, resoldering components which didn't get soldered properly. He also is the person you want to talk to if something needs precise hand soldering, whether it's SMD or through-hole.