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What is a PCB (Printed Circuit Board) and its manufacturing methods
Like solder resist, silkscreen can be any color. White is common, but a color that contrasts with the solder resist is usually chosen. Black silkscreen is used for white or yellow boards. Multiple colors are rarely seen on PCBs.
Printed Circuit Boards (PCBs) are the internal components of every modern electronic device. Almost every small gadget you use would be unimaginable without a PCB. We've become so used to it that we don't even think about it. But what exactly is it? Let's talk about that.
Introduction to PCBs
Early electronic components and devices were manufactured and connected using a point-to-point structure. It was essentially a set of wires and components directly connected to each other. This easily became a mess, with everything overlapping. This led to many difficulties in scaling production and repairing damaged devices. You can see an example of a point-to-point structure below. Imagine making electronic projects like this today. A nightmare!
A printed circuit board, sometimes also called a printed wiring board (PWB), is a layered structure made of conductive and insulating materials. It serves two functions. One, it connects electronic components to different locations on the board via soldering. Since solder is metal, it acts as both an electrical connection and a strong mechanical bond. Two, it provides connections between component terminals. Each conductive layer has a pattern that provides electrical connections. This is why you should avoid drilling holes in a PCB to make room for other components. It may seem fine at first glance, but you can easily go through connections that are not visible from the outside. Internet forums are full of people who realized this when trying to make more space on their computer motherboards.
Number of PCB Layers
As mentioned above, PCBs are made up of multiple layers. These layers are made of different materials and combined to form a single unit. This is why we say it has a sandwich structure. Let's start with the "meat" of the sandwich, the middle of the PCB, and then move to the outside.
Substrate (FR4)
The substrate is the base material of the PCB. It is usually made of fiberglass. This makes the circuit board thick and strong. It maintains its strength and electrical insulation properties in both humid and dry environments.
The commonly used type of fiberglass in PCB design is FR4. "FR" stands for "flame retardant," a chemical applied to materials to prevent or slow down fires. FR4 is made of woven fiberglass cloth and an epoxy resin binder.
Copper Foil
The next layer in the sandwich is a very thin layer of copper foil. It is applied to the PCB using heat. When we talk about the number of layers in a PCB, we are referring to how many layers of copper foil it has.
Circuit boards can be single-sided, meaning they only have conductive material on one side, or double-sided, meaning they have conductive material on both sides. PCBs typically have 4 to 8 layers, but can be made with close to 100 layers. This is achieved by laminating (bonding) multiple double-sided circuit boards together and placing insulating layers between them. This increases the area available for wiring, as there are more conductor patterns inside the board that we cannot see with the naked eye. At this point, we need to refer to the circuit board's datasheet to ensure we have connected everything correctly.
The higher the power a PCB needs to handle, the thicker the copper foil layers. PCBs handling low power typically have thinner copper foil layers. Therefore, the copper foil layers of PCBs handling very high power throughput will be much thicker. This value is called copper weight and is expressed in ounces of copper per square foot (oz/ft2).
Solder Mask
The layer above the copper foil is the solder mask. The color of the PCB comes from this layer. The usual color is green, but PCBs can come in a variety of different colors.
The solder mask plays a very important role; it's not just there to make your circuit board look cool. It also protects the copper traces, preventing accidental contact with other metals or conductive parts. This insulation prevents short circuits that can cause the board to burn out, as well as soldering errors.
Silkscreen
The silkscreen layer is located on top of the solder mask. Its purpose is to help us better understand the circuit board by adding symbols, letters, and numbers. The function of each pin and LED is usually indicated.
Like the solder mask, the silkscreen layer can be any color. White is commonly used, but a color that contrasts sharply with the solder mask color is usually chosen. A black silkscreen layer is used for white or yellow circuit boards. Multiple colors are rarely seen on PCBs.
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