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Basic knowledge of printed circuit boards

Posted:02:36 PM February 13, 2019 writer: G

The substrate of the board itself is made of a material that is insulated and heat-insulating and is not easily bent. The thin circuit material that can be seen on the surface is copper foil. The original copper foil is covered on the whole board, and part of the manufacturing process is etched away, and the remaining part becomes a mesh-like small line. . These lines are called conductor patterns or wires and are used to provide electrical connections to the parts on the PCB.

To secure the parts to the PCB, we soldered their pins directly to the wiring. On the most basic PCB (single panel), the parts are concentrated on one side and the wires are concentrated on the other side. In this case, we need to make holes in the board so that the pins can pass through the board to the other side, so the parts are soldered to the other side. Because of this, the front and back sides of the PCB are called the Component Side and the Solder Side.

If there are some parts on the PCB that need to be removed or replaced after the production is completed, the part will be installed with a socket. Since the socket is directly soldered to the board, the parts can be detached at will. ZIF (Zero Insertion Force) socket, which allows parts (here referred to as CPU) to be easily inserted into the socket or removed. A fixing rod next to the socket that secures the part after you insert it.

If you want to connect two PCBs to each other, we usually use the edge connector called "Golden Finger". The gold finger contains a lot of bare copper pads, which are in fact part of the PCB layout. Usually when connecting, we insert the gold finger on one of the PCBs into a suitable slot on another PCB (generally called the expansion slot Slot). In a computer, such as a display card, a sound card or other similar interface card, it is connected to the motherboard by a gold finger.

The green or brown color on the PCB is the color of the solder mask. This layer is an insulating protective layer that protects the copper wire and prevents the part from being soldered to an incorrect location. A layer of silk screen is additionally printed on the solder mask. Text and symbols (mostly white) are usually printed on this to indicate the position of each part on the board. The screen printing surface is also referred to as the legend.

1. Single-Sided Boards

On the most basic PCB, the parts are concentrated on one side and the wires are concentrated on the other side. Because the wire only appears on one side, we call this PCB a single-sided. Because single-panel has many strict restrictions on the design line (because there is only one side, the wiring can not cross and must be around the path), so only the early circuit used this type of board.

2. Double-Sided Boards

This board has wiring on both sides. However, to use the wires on both sides, it is necessary to have proper circuit connections between the two sides. The "bridge" between such circuits is called a via. The via hole is a small hole filled or coated with metal on the PCB, which can be connected to the wires on both sides. Because the area of the double panel is twice as large as that of the single panel, and because the wiring can be interlaced (can be wound around the other side), it is more suitable for circuits that are more complex than single panels.

3. Multi-Layer Boards

In order to increase the area that can be wired, the multilayer board uses more single or double-sided wiring boards. The multi-layer board uses several double-sided panels and is adhered (pressed) after placing an insulating layer between each layer. The number of layers in the board represents several separate layers of wiring, usually with an even number of layers and containing the outermost two layers. Most of the motherboards are 4 to 8 layers of structure, but technically can achieve nearly 100 layers of PCB. Large supercomputers mostly use quite a few multi-layer motherboards, but because such computers can already be replaced by clusters of many common computers, super-multilayer boards have gradually disappeared. Because the layers in the PCB are tightly coupled, it's not easy to see the actual number, but if you look closely at the motherboard, you might see it.


If applied to a double-sided board, must be worn through the entire board. However, in multi-layer boards, if you only want to connect some of these lines, the vias may waste some of the wiring space of other layers. Buried vias and Blind vias can avoid this problem because they only penetrate several layers. Blind holes connect several layers of internal PCB to the surface PCB without penetrating the entire board. The buried hole is only connected to the internal PCB, so the light is not visible from the surface.

In the multi-layer PCB, the entire layer is directly connected to the ground wire and the power supply. So we classify each layer as a signal layer, a power layer or a ground layer. If the parts on the PCB require different power supplies, this type of PCB typically has more than two layers of power and wiring.

Part packaging technology

1.Through Hole Technology

The part is placed on one side of the board and the pins are soldered on the other side. This technique is called a "Through Hole Technology (THT)" package. Such parts can take up a lot of space and have to drill a hole for each pin. Therefore, their pins actually occupy the space on both sides, and the solder joints are relatively large. On the other hand, THT parts are better than SMT (Surface Mounted Technology) parts. Plugs like cable, and similar interfaces all need to withstand stress, so usually they are all THT packages.

2. Surface Mounted Technology

Using Surface Mounted Technology (SMT) parts, the pins are soldered to the same side as the part. This technique does not require drilling holes in the PCB for each pin.

Surface-adhesive parts can even be soldered on both sides.

SMT is also smaller than THT parts. Compared to PCBs that use THT parts, PCB board components using SMT technology are much denser. SMT package parts are also cheaper than THT. So most of today's PCBs are SMT, which is not surprising.

Because the solder joints and the pins of the parts are very small, it is very difficult to use manual soldering. However, if you consider that the current assembly is fully automatic, this problem will only occur when repairing parts.

Tag: single-sided boards double-sided boards multi-layer boards
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