Printed circuit boards (PCBs) appear in almost every electronic device. If there are electronic parts in a device, they are all mounted on PCBs of various sizes. In addition to fixing various small parts, the main function of the PCB is to provide the mutual electrical connection of the various parts above. As electronic devices become more and more complex, more and more parts are required, and the lines and parts on the PCB are also more and more dense. A standard PCB looks like this. A bare board (with no parts on it) is also often referred to as a “Printed Wiring Board (PWB).”
The base plate of the board itself is made of insulating material that is not easily bendable. The thin circuit material that can be seen on the surface is copper foil. Originally, the copper foil covered the entire board, but part of it was etched away during the manufacturing process, and the remaining part became a mesh-like thin circuit. . These lines are called conductor patterns or wiring, and are used to provide electrical connections to components on the PCB.
To attach the parts to the PCB, we solder their pins directly to the wiring. On the most basic PCB (single-sided), the parts are concentrated on one side and the wires are concentrated on the other side. As a result, we need to make holes in the board so that the pins can pass through the board to the other side, so the pins of the part are soldered on the other side. Because of this, the front and back sides of the PCB are called the Component Side and the Solder Side, respectively.
If there are some parts on the PCB that need to be removed or put back after the production is completed, the sockets will be used when the parts are installed. Since the socket is directly welded to the board, the parts can be disassembled and assembled arbitrarily. Seen below is the ZIF (Zero Insertion Force) socket, which allows parts (in this case, the CPU) to be easily inserted into the socket and removed. A retaining bar next to the socket to hold the part in place after you insert it.
If two PCBs are to be connected to each other, we generally use edge connectors commonly known as “gold fingers”. The gold fingers contain many exposed copper pads, which are actually part of the PCB layout. Usually, when connecting, we insert the gold fingers on one of the PCBs into the appropriate slots on the other PCB (usually called expansion slots). In the computer, such as graphics card, sound card or other similar interface cards, are connected to the motherboard by gold fingers.
Green or brown on the PCB is the color of the solder mask. This layer is an insulating shield that protects the copper wires and also prevents parts from being soldered to the wrong place. An additional layer of silk screen is printed on the solder mask. Usually, text and symbols (mostly white) are printed on this to indicate the position of each part on the board. The screen printing side is also called the legend side.
Single-Sided Boards
We just mentioned that on the most basic PCB, the parts are concentrated on one side and the wires are concentrated on the other side. Because the wires only appear on one side, we call this kind of PCB a single-sided (Single-sided). Because the single board has many strict restrictions on the design of the circuit (because there is only one side, the wiring cannot cross and must go around a separate path), so only early circuits used this type of board.
Double-Sided Boards
This board has wiring on both sides. However, to use two sides of the wire, there must be a proper circuit connection between the two sides. Such “bridges” between circuits are called vias. Vias are small holes on a PCB, filled or painted with metal, that can be connected to wires on both sides. Because the area of the double-sided board is twice as large as that of the single-sided board, and because the wiring can be interleaved (can be wound to the other side), it is more suitable for use on more complex circuits than single-sided boards.
Multi-Layer Boards
In order to increase the area that can be wired, more single or double-sided wiring boards are used for multilayer boards. Multi-layer boards use several double-sided boards, and put an insulating layer between each board and then glue (press-fit). The number of layers of the board represents several independent wiring layers, usually the number of layers is even, and includes the outermost two layers. Most motherboards are 4 to 8-layer structures, but technically, nearly 100-layer PCB boards can be achieved. Most large supercomputers use fairly multi-layer motherboards, but because such computers can be replaced by clusters of many ordinary computers, ultra-multi-layer boards have gradually fallen out of use. Because the layers in a PCB are so tightly bound, it’s generally not easy to see the actual number, but if you look closely at the motherboard, you might be able to.
The vias we just mentioned, if applied to a double-sided board, must be pierced through the entire board. However, in a multilayer board, if you only want to connect some of these traces, then vias may waste some trace space on other layers. Buried vias and blind vias technology can avoid this problem because they penetrate only a few of the layers. Blind vias connect several layers of internal PCBs to surface PCBs without penetrating the entire board. Buried vias are only connected to the inner PCB, so they cannot be seen from the surface.
In a multi-layer PCB, the entire layer is directly connected to the ground wire and the power supply. So we classify each layer as signal layer (Signal), power layer (Power) or ground layer (Ground). If the parts on the PCB require different power supplies, usually such PCBs will have more than two layers of power and wires
Post time: Aug-25-2022