Introduction: How to Solder Flashing LED's on a Blank PCB

A PCB is an acronym for " Printed Circuit Board ". On a PCB you will A PCB has holes where you can slip in the component and on the flip side, you can solder the legs of the components in order to keep them in place. Soldering is also a very good way to connect components together. Solder is a good conductor of electricity and it is easy to use.

In this project, we will be using a blank PCB and soldering our own connections. We will use the capacitors, transistors and resistors to make two 5mm green LEDs flash on their own, without any code!


  • Soldering Iron with stand
  • Solder
  • Blank PCB
  • Third-Hand Soldering Stand
  • Jumper wires
  • 2X 10K ohm resistors
  • 2X 560 ohm resistors
  • 2X 2N3904 NPN transistors
  • 2X 5mm Green LEDs
  • 100 μF capacitors
  • Wire strippers and Clippers

Step 1: Learning the Soldering Basics

It is important that you know how to solder before starting this project. To get ready to solder, you need to make sure you the basics of soldering and the parts and equipment needed during the soldering process.

What is Soldering?

Soldering is the process of melting a special metal alloy known as solder using a very heated iron called the soldering iron. Solder is made up of tin and lead, but some lead-free solders are made up of copper and tin.

Parts of a soldering iron

A soldering iron has two main parts; the tip and the wand. The tip is the heated part at the very front of the iron; the part that actually melts the solder. This part can become as hot as 450°C (842°F). It is extremely important that you do not touch the tip with your hands. When putting down the iron, make sure to always put it into the slot on the iron stand. The iron stand should come with a slot to put in a sponge, if not with the sponge. Make sure you wet the sponge before starting. The tip can also easily become rusted so we must tin the tip. Tinning means covering the tip with a little bit of solder. This helps prevent the tip from rusting which can ruin the iron tip.

How to remove solder (desoldering) from a circuit/board

Soldering, by all means, isn't the easiest thing to master and even the best of the best can make mistakes. In order to fix your mistakes and restart, you need to know how to desolder. The best way to do this is by using what is called a solder pump. In order to use a soldering pump, heat up the old solder that you don't need and quickly pump it out before the solder cools down.

Cleaning the tip

Once you have finished soldering, make sure you clean and tip the tip. To do this, wipe you iron tip on the wet sponge at the base of the soldering iron stand. This will help get rid of the excess substances that may be on the tip. Afterwards, make sure you tin the tip. To do this, just hold the solder on the tip and let it cover the iron bit by bit. You may have to repeat the process multiple times before it is fully tinned.

Step 2: Placing the Components in Their Positions

Once you have finished preparing your station, it is now time to gather the components needed for this project. After you gather the materials, start placing them into the PCB using the model breadboard model shown above. An important thing to remember is that breadboards have internal connections (the power and ground rails are all connected and the individual rows are connected. On a PCB though we must solder these connections.

When placing the components together, be sure to check which side is negative and which side is positive for the LEDs and capacitors. This is important as these two components have an anode and a cathode.

Step 3: Making Bridge Connections

One last step before we begin to solder; bridges.

Making bridges helps us connect two (or more) components together without having any excess solder. This helps us to prevent making any unnecessary connections. This may happen when your solder accidentally touches another component (that you don't need to connect to) while it is still hot.

To make bridges, take the legs of two components that are beside it each other and twist them a little to keep it in place. Once you made the twist, we can move onto the next part; soldering.

Step 4: Soldering

Now that we have everything ready to go, all that's left is soldering and actually making the connections. Be sure to clear your work station before starting in order to prevent injuries. Make sure there no wires that someone can trip over.

Soldering the component legs

Clip your PCB board to the helping stand and get your iron. Hold the iron by the wand in wand hand, and the solder in the other hand. Hover the tip of the solder where you want to melt it and gently touch the tip of your iron to the solder. The solder should melt fairly quickly and pool around the leg of the component before cooling down and hardening.

Soldering the bridges

Soldering the connected components can be easy and hard. All you have to is melt a bit of solder and drop it onto the connection and let it cool, but that's not enough to form a strong connection. Melt a few more drops of solder around the connection; enough to hide the connection (the twisted legs).

Soldering the wires

Soldering the wires are a little more tricky than the actual components but here are some tips you can use to help:

  • Make sure you strip off enough of the plastic insulation that you won't melt the plastic instead of the solder
  • Bend the wire at the front to keep the wire in place
  • Get as close to the wire as you can with the iron and then bring the solder in

Ground and Power rails

Since the PCB doesn't have any connections, it means that there is no power or ground. In order to make our own power and ground rail, we must drop solder in every hole on the designated row. Once all the holes have been filled, drop a bit of solder in between them to connect them together. Do this for all the holes on the power rail and repeat for the ground rail.

Attaching the Battery Clip

Attaching the battery clip is simple. Strip the wires enough so that you don't melt the plastic. Then, take the positive wire of the clip (red) and hold it onto the power rail of your board using the clips on the helping stand. Then drop a bit of solder onto the wire. Repeat with the negative wire (black) on the ground rail.

Cleaning up

Once you have soldered a connection, clip off the legs of the components using the clippers. Make sure you are careful as the legs can sometimes fly away.

Step 5: Finished Product

The overall idea of this project is to have the LEDs flashing. This will happen with the help of the capacitors and transistors. And that's how to solder flashing LEDs on a PCB board. While one LED is turned on, the transistor will send current to the capacitor, which will store it for a few seconds until the first LED turns off before letting it out and powering up the second LED. This process repeats for the other LED as well. That was the motive of my project. Hope that you had fun while doing it!