Printed circuit board, PCB will appear in almost every electronic device. If there are electronic parts in a device, they are all mounted on PCBs of various sizes.
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 (no parts on it) is also often referred to as a “Printed Wiring Board (PWB)”, the board itself The base plate is made of a material that is insulating and heat-insulating and is not easy to bend. The small 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. The part that comes down becomes a mesh of small lines. These lines are called conductor patterns or wiring, and are used to provide electrical connections to components on the PCB.
To hold the parts on 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. It is necessary to punch 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 respectively called the component side (Component side).
If there are some parts on the PCB that need to be removed or put back after the production is completed, then the parts will be installed using the plug Socket. 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, zero-pull 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 we want to connect two PCBs to each other, we usually 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 other.
On the appropriate slot on the PCB (generally called the expansion slot Slot). In the computer, such as graphics card, sound card or other similar interface cards, are connected to the motherboard by gold fingers.
PCB The green or brown on the top is solder mask (solder mask) color. 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 screen printing surface will be printed on the solder mask layer (silk screen). 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.
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 type of PCB single-sided. Because the single-sided 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 the early circuits were used this type of board.
This board has wiring on both sides. However, to use two-sided wires, it must be between the two sides.
Proper electrical connections are required. 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 of the double-sided area
It is double the size of a single-sided board, and because the wiring can be interleaved (can be wrapped around to the other side), it is more suitable for use on more complex circuits than single-sided boards.
Multi-Layer Printed circuit boards
For In order to increase the area that can be wired, multilayer boards use more single or double-sided wiring 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 how many layers there are.
Independent wiring layers, usually with an even number of layers, and including the outermost two layers. Most motherboards are 4 to 8-layer structures, but technically, nearly 100-layer PCB boards can be achieved. large supercomputer.
Most 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 the PCB are tightly combined. It’s not easy to see the actual number, but if you look closely at the motherboard you might.
The vias we just mentioned, if applied to double-sided boards, must be is to pierce 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 vias) and blind vias (Blind vias) techniques 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 only connect the internal PCB, You can’t see it just 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.