Do You Make These 7 Common PCB Soldering Mistakes?

When hand soldering your PCB, the chances of making mistakes is high. And sometimes those mistakes could be very costly, you would want to avoid them while soldering your PCB.

You can never be too careful when it comes to soldering a PCB. Being a process of joining two or more metal parts by the method of melting solder (filler material) and connecting them together for a good and permanent electrical bond. 

Therefore a lot can go wrong when creating these bonds, and mistakes happen frequently. The ability to identify and quickly resolve them is vital to ensure a perfectly soldered PCB.

However, there are some PCB soldering mistakes that are common that you should prevent yourself from making.

Here are 7 common PCB soldering mistakes, how to prevent them and how to fix them when made.

1. Overheating the solder joint

When the hot iron is applied to the solder before it is ready to flow, the soldering wire fails to melt despite heating. And this leads to a burned flux, which is no kidding a pretty huge mess on your PCB.

The burned flux residue makes fixing this joint extremely difficult. So, obviously, this is one mistake you want to be ultra-careful about.

An overheated joint can be fixed by carefully scraping the joint with the tip of a knife or using isopropyl alcohol with a toothbrush to remove the burnt flux. 

To prevent this disaster, keep your soldering iron hot and clean to avoid overheating solder joints. Been properly prepared will also help a long way.

2. Not letting the solder melt completely

This is a more moderate situation compared to the one explained above. This time, the solder did not melt completely due to insufficient heat and this is referred to as a "Cold Joint". 

When there's a cold joint on your PCB, the surface becomes roughened and rocky. It results in a weak solder bond, making cracks develop in the joint over time which makes it an unreliable joint.

To prevent a "Cold Joint" on your PCB, properly preheat your soldering iron with sufficient operating power. Like the disturbed joints, cold joints can usually be fixed by re-heating the joint with a hot iron until the solder flows. 

Note: Sometimes, cold joints suffer from excessive solder. The excess can be drawn-off with the tip of the iron.

3. Movement during the alloy solidification

When there's any form of movement be it from human interruption or mechanically such as vibration, it can result in a "disturbed joint." 

The surface of a disturbed joint appears frosted, crystalline or rough. Note, this is often misunderstood as a 'Cold Joint' but it's not, because the causes are different. 

This can be prevented by immobilizing the joint and stabilizing the work in a vise. It can also be repaired by reheating and allowing it to cool off undisturbed.

4. Starving the solder joint

Exactly what it is: not applying the needed amount of solder to the solder joint, which leads to a weak solder joint. If this happens, it makes it prone to failure as it will develop stress cracks over time because of the weakened joint.

This can be fixed by re-heating the joint and adding more solder to make a good strong joint. To prevent it, make sure you put the right amount, not too little or too much, which brings us to our next point.

5. Applying Too Much Solder

Just the way you shouldn't apply less solder, you should also not administer excessive solder to the solder joint. Excess solder often results in rounded globs over the tip and pad, which then leads to a lack of proper connection.

An excessive filled solder joint can be fixed by drawing off some of the excess solder with the tip of a hot iron. If it is really over the top, a solder-sucker or some solder wick can be helpful as well.

6. Creating a solder bridge

This also happens as a result of excessive solder, but this time between two separate joints melting together and it is called a "solder bridge".

Since it's between two separate joints, it creates an unplanned connection, which can lead to short circuits on your PCB ultimately affecting the overall functionality of the PCB.

One of the causes of a solder bridge is designing your PCB with poor weight distribution and large components all on one side.

A solder bridge can be prevented by leaving enough space between your pads and the solder mask layer. Also, orientating components of the same type in the same direction will reduce the risk of an abnormal connection.

A solder bridge can be fixed by dragging the tip of hot iron between the two solder joints. As mentioned above, a solder sucker or solder wick can come in handy if it's too much.

As always, not less, not more but just enough solder.

7. Untrimmed leads

When the length of your leads isn't trimmed appropriately/accurately, they run the risk of coming into contact with other leads which is very dangerous because they become unwanted short circuits.

Untrimmed leads have high chances of bending and making contact with adjacent traces. Therefore, these lengthy leads should be trimmed at the solder joint tops.

To prevent this, trim all leads to their necessary and appropriate lengths.

These are simply some common soldering PCB mistakes. There are a lot of errors that can happen while soldering your PCB but being adequately prepared and taking extra care will lessen the possibilities of making these errors.

Finally, you have to be realistic about your expectations while soldering and not panic when a couple of things go wrong. Rather, be patient and ready to make some fixes in the process.