Introduction: PCB Concepts and Materials

About: My name is Randy and I am a Community Manager in these here parts. In a previous life I had founded and run the Instructables Design Studio (RIP) @ Autodesk's Pier 9 Technology Center. I'm also the author of t…

In this class we are going to learn how to convert a circuit from a mess of wires on a breadboard into a custom printed circuit board. This class is intended for hobbyists who want to take their projects to the next level and produce an end-product which is more finished. The benefit of designing a circuit board for printing is that it is cleaner and more reliable than a circuit built on a breadboard or perf-board. The other main benefit is that it is repeatable. If you need to make ten boards, it will save you a lot of time to have a custom board printed.

This is an introductory level class and we will not be going over more advanced topics in design and testing that would help you make your board ready for consumer manufacturing, but the skills covered here are a stepping stone to making professional-quality circuit boards.

Step 1: What Is a PCB?

PCB stands for "Printed Circuit Board." This is the standard circuit board you will find inside of most electronic consumer products.

A PCB consists of a fiberglass board with conductive copper pathways or traces that connect together electronic components that are soldered to them. The totality of connections between components is what constitutes the circuit.

A standard circuit board has 4 layers that we need to concern ourselves with. This includes the base, copper layer, soldermask and silkscreen layer.

The circuit board's base is typically made out of a type of fiberglass called FR4. This material provides rigidity, and has good heat resistance properties. Thicknesses vary from board to board, but 1.6mm is fairly common.

The copper layer is laid atop the fiberglass base (making the base "copper clad"). This is the layer that conducts electricity and the circuit's components are soldered to. All of the circuit's connections occur on the copper layer.

The soldermask is a layer of colored resin strategically laid over the copper layer to insulate the parts of the circuit that do not get soldered to. Typically the soldermask is green, but it can be all kinds of different colors.

The silkscreen layer is printed atop the soldermask and serves as a guide for assembling the board.

Typically, a circuit board will have two sides, which means there will be a top side and bottom side. Each side can have all four of these layers, but the bottom often excludes a silkscreen layer since it is often unnecessary (which also reduces manufacturing cost). This 2-sided arrangement is fairly standard and the board we will design in this class will be like this.

More advanced circuit boards, such as you might find in a laptop or smartphone can have many conductive layers or "sides" sandwiched together. However, we won't be covering anything that complicated in this course.

The type of components we will be using to build circuits in this class use through holes. These are round metal plated holes that serve to both connect the top and bottom copper layers together, and give you a surface to solder the component to the board. In this class, I will be dealing exclusively with through-hole parts.

The other common type of component you might attach to a PCB are surface mount. These are small parts with metal tabs that get soldered directly to the surface of the board.

Step 2:

When designing the board we will refer to the parts of the circuit in different ways. Let's take a moment to clarify the ways that we can talk about a part.

A component refers to any part used in a circuit. This is always referring to the part itself, and always has the same symbol. It can and often does have a different package and footprint.

A symbol is used when drawing a schematic as a stand-in representation of a component. It has all of the necessary pin connections required by the component.

A package is the 3-dimensional shape of the component, and also indicates how it mounts to the circuit board (through hole, surface mount, or otherwise). This specification is typically provided by the manufacturer or retailer and is used for selecting the appropriate footprint when designing the board.

A footprint is the 2-dimensional layout of the package atop the surface of the board. It consists of a silkscreen layout, name label, plated through holes or pads, and any other necessary layout information.

There is, of course, much more terminology related to designing circuit boards, but this will be introduced as we need it.

Step 3: Download Software

To design a PCB we will be using Autodesk Eagle software, which is a CAD program specifically designed for making circuit boards. This software is free for 2-sided boards up to 80cm². This should be more than enough area for any hobby project.

You can download Eagle from Autodesk's website, and you will also need to sign up for a free Autodesk account.

Step 4: Gather Supplies

Since most of the design will be done on a computer, and the board will be sent out for manufacturing, there are not really many things you will need.

In fact, the only things you will need for this class are:

  • A circuit (of your choosing) on a breadboard that you want to create a PCB for
  • Paper and a pencil
  • A fine tip marker (optional)
  • Digital calipers (optional, but recommended)

Once you have rounded up these things, it's time to get psyched for the next lesson.