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How to Populate a PCB

4/28/2021 | By Maker.io Staff

Electronic DIY kits are a fantastic way for inexperienced makers to practice their soldering. However, the large number of different components might look overwhelming if you assemble a PCB for the first time. While you usually can’t do a lot wrong when you populate a circuit board, there are a few things to take note of to make the process easier. The tips and tricks presented in this article will also come in handy if you assemble a PCB for a custom project that you want to turn out perfect.

Getting Started

Before I assemble a PCB, I lay out all the components needed in my working area. For that, I organize the components in groups and then put them in piles. For PCBs with a lot of parts, I usually also sort by value. Doing so before you populate a circuit board ensures you won’t lose time searching for the next part, and you’ll also immediately notice if you need to buy some components before you start working.

Take a Look at the PCB

Next, investigate the PCB. Make sure you know where each part goes. If you’re working on a PCB that you’ve designed yourself, you can always refer to your design document to determine which part goes where. If you assemble a DIY kit, make sure to look at the silkscreen markings on the PCB:

How to Populate a PCB

Closely inspect the silkscreen on the PCB to determine the position of the individual components and which way around to put them in.

Also, check whether the silkscreen contains details about the component values. If not, the component name should be next to its symbol on the PCB. If the latter is the case, find the documentation, for example, the assembly instructions that come with your DIY kit.

Once you know where each part goes, you can already start thinking about the order in which you want to populate the PCB.

Finding the Right Order to Populate your PCB

Generally, you want to put in the short components first and then gradually work your way up to the tallest parts. If you follow this procedure, you’ll be able to keep the PCB flat for as long as possible, which makes it easier to balance the board when you have to flip it over to solder in the next components. If you put in the taller parts first, smaller components might fall out or get misaligned when you flip the PCB over. Therefore, always start with flat components such as resistors and diodes. If your design contains surface mount (SMD) components, you can put them in first to make it easier to reach the pins. If you put SMD parts in later in the process, you might find that some through-hole components get in the way of the soldering iron.

How to Populate a PCB

Start populating the PCB with flat components such as resistors, diodes, and small switches.

Once you’re done with the flat components, gradually work your way up. I like to add IC sockets and ICs without a socket next. A good trick when soldering ICs and sockets is to put the IC or socket in place first and then solder in one corner pin of the IC or socket. Next, you flip the board back around and verify that the part sits neatly on the PCB. If it does, solder in the pin opposite of the first one, and then solder in the remaining ones.

How to Populate a PCB

IC sockets and integrated circuits without sockets are also a good way to start. Putting them in early makes it easier to properly align them with the PCB.

After adding all the flat components, I typically insert transistors, small capacitors, flat push-buttons, and LEDs next. These parts are usually smaller than most electrolytic capacitors. There are, however, exceptions to this rule, especially if you have to mount the electrolytic capacitors horizontally instead of vertically. In that case, I usually try to place the parts in a way that allows me to easily balance the PCB on the components when I turn it around so that the board doesn’t move too much.

How to Populate a PCB

Once all the flat components are in place, start adding the taller ones such as LEDs and transistors.

Last, I finish the assembly process by adding all the bulky parts, such as large connectors, displays, big FETs, and wires. If you mounted IC sockets previously, now is the time to put the correct IC in each socket. For that, make sure that the IC pins are straight, and then gently push the IC into place until they fully seat.

How to Populate a PCB

Last, put the ICs in their respective socket. Make sure to pay close attention to the orientation of the chips.

Another thing to pay attention to is the direction of some components. Some parts, such as electrolytic capacitors, transistors, diodes, and ICs, may only be soldered in a specific orientation, as they are polarized. Make sure to pay attention to that before you solder in such components to prevent damaging these components.

When you have soldered a part in place, use side cutters to trim excess leads close to the solder joints. However, make sure not to put too much stress on the solder joint itself. When you’re in doubt about where to cut, it’s better to leave some excess. You can trim the leads whenever you like. I typically cut them off when I’m done with one group of components, for example, after soldering in all resistors.

How to Populate a PCB

Don't forget to cut off excess leads to make it easier to work with the PCB.

Summary

Populating a PCB is no difficult task, even if it might seem like it if you try it for the first time. Start by laying out all the components you’ll need. Then, prepare all the required tools and start to gradually work your way up from the smallest to the tallest components in the design. Make sure to pay close attention to the direction of polarized parts to prevent damaging the components.

In the next article in this series, we’ll take a closer look at a critical part of this process - soldering!