How to Solder a Printed Circuit Board (PCB)

How to solder

This is part of our How to Solder Guide

For a hobbyist, soldering a PCB is usually the most common form of soldering. The basic techniques are pretty easy to understand but there is still an amount of skill involved that can be mastered with practice. The best way to practice this is to buy a simple electronics kit or assemble a simple circuit on a perfboard.

The first step is to clean the surface to ensure a low resistance solder joint. Use a cleaning pad or a fine grade of steel wool to clean a surface that has tough deposits board. Take care with boards that have tight tolerances because the fine steel wool shavings can get caught between pads and in holes.

After the board has been cleaned thoroughly, you are ready to add the components to the board. Unless you have a simple circuit and only have a few components to solder, you won’t be placing all the components on the board and soldering them all at once. It is more likely you will be soldering a few components at a time before turning the board over and placing more on it.

It is usually best to start with the smallest and flattest components (resistors, ICs, signal diodes, etc.), which makes it more stable during soldering. It is also a good idea to save your sensitive components until the end so there isn’t a greater chance of damaging them during the assembly of the rest of the circuit.

Bend the leads as necessary and insert the component through the proper holes on the board. You may want to bend the leads on the bottom of the board at a 45 degree angle to hold the part in place while soldering. This keeps the broad relatively flat, which makes it more stable during the assembly of the rest of the circuit.

Apply a very small amount of solder to the tip of the iron. This will help conduct the heat to the component and board, however, this isn’t the solder that will make up the joint. To heat the joint lay the tip of the iron so that it rests against both the component lead and the board. It is crucial that you heat the lead and the board, otherwise the solder will only pool and not stick to the unheated item.

The small amount of solder you applied to the tip before heating the joint will help make contact between the board and the lead. It usually takes a second or two to get the joint hot enough to solder. However, larger components and thicker pads/traces will absorb more heat and can increase this time. If you find an area under the pad that is starting to bubble, stop heating and remove the soldering iron because you are overheating the pad and it is in danger of lifting. If this happens, let it cool then carefully heat it again for a shorter amount of time.

When the component lead and solder pad has heated up, you are ready to apply the solder. Touch the tip of the strand to the component lead and solder pad, but not the tip of the iron. The solder should flow freely around the lead and pad if everything is hot enough. Continue adding solder to the joint until the pad is completely coated and the solder forms a small mound with slightly concave sides. If it starts to ball up, you have used too much solder or the pad on the board is not hot enough.

Image cc Flickr via AMagill