We often say that circuit boards are the backbone of electronic devices. Without their invention, we wouldn’t have the advanced society we enjoy today. Some people who are unfamiliar with them might think this is an exaggerated statement, but in fact, it isn’t. Once you understand how they work, you’ll agree with this view.
What is a Circuit Board
Some people’s understanding of circuit boards may only go as far as the term itself. However, if you disassemble any electronic device around you, you’ll certainly find an electronic board filled with numerous electronic components—that’s an assembled circuit board. When your electronic device is powered on, the current flows along the circuit paths on the board, reaching each component and activating them to perform their functions.
Significance of Circuit Boards
Early electronic devices were not as compact and flexible as they are today; they were large objects. This was because a large number of components were needed inside to make the device work. Clearly, these components couldn’t just be thrown into a shell but had to be connected by wires. If there were only one or two components, it would be simple to connect them. However, as demand evolved, people needed electronic devices to perform more functions, which meant integrating more components inside the device—perhaps hundreds, thousands, or even tens of thousands. While it would be possible to use wires to connect these components in the old way, the massive amount of wiring would naturally cause the device to expand indefinitely. More critically, if the device malfunctioned, it would be impossible to pinpoint the fault in such a complex web of wires. The circuit board was born to solve this problem.
How Circuit Boards Work
When you look at a circuit board in your hand, you might think it’s a simple object, but that’s far from the truth; there’s a lot going on inside. To give you a simple example, your phone might be only six inches in size and as thin as two coins stacked together, but the circuit board inside the phone could have circuits that are 300 feet long. That’s a staggering length, considering that a standard football field’s inner track is only 1,300 feet long. Now, these circuits are integrated into a palm-sized area and are used to connect dozens of components such as the phone’s WiFi, GPS, speakers, and so on, forming a complete PCBA board to achieve specific functions.
You might wonder, why can’t I see these so-called circuits?
The answer lies within. These circuit boards might be made up of simple single-layer structures or complex multi-layer structures. What you’re actually seeing is the top and bottom layers of the circuit board, known as the solder mask layers, which isolate the air and protect the internal copper layers from oxidation. Beneath that is the copper layer, responsible for the actual circuit connections. When we talk about the number of layers on a circuit board, we’re actually referring to the number of internal copper layers. The following image shows the structure of a 10-layer PCB, with the yellow parts representing the copper layers:
As you can see, there is an orange part between every two copper layers. This is an insulating material used to isolate different copper layers. The purpose is obvious: if each copper layer were connected, there would be no need to separate them into different layers.
Some readers might wonder how signals are transmitted between different circuit layers in this separated structure. The answer is quite simple: through vias, which are holes on the surface or inside the circuit board. The walls of these holes are plated with a layer of copper, which conducts electricity, thus allowing signals to pass between different circuit layers. If you want to ensure that certain layers aren’t connected, you can simply remove the copper around the vias.
At this point, the components and the circuit board are still separate. To connect them, the component’s pins need to be inserted into the reserved holes on the circuit board and then soldered. Once this is done and the circuit is connected, the current will flow along the traces on the circuit board to the specified component pins, activating the components to perform their functions.
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