The Printed Circuit Board (PCB) is one of the main parts of all electronic products. The application fields of PCB are quite extensive. Wherever electronic components are used, PCBs are almost always used. Currently, they are mainly used in the fields of information, communication, consumer products, automobiles, aerospace and military, precision instruments and industrial products. It is an indispensable basic part of all electronic products. This article will be divided into several aspects to discuss PCB, namely type, material, process, installation and welding. Let us have a good understanding of the "mother of the electronics industry" - PCB.
The Printed Circuit Board (PCB) is one of the main parts of all electronic products.
PCB is a complex circuit copper wire between parts. After careful planning, it is etched on a board. As the main support body for providing electronic components during installation and interconnection, it is responsible for fixing electronic components and providing component currents, is an indispensable basic part of all electronic products, and because of this, the PCB is known as the "mother of the electronic industry".
* Upstream is glass fiber, copper foil and resin and other materials
* Midstream is copper foil substrate (CCL) and printed circuit board
* Downstream is all kinds of electronic products
Without PCB, there are electronic parts, and the efficacy of electronic products cannot be displayed. Although PCB is a mature industry, it is as inconspicuous as a soldier, but it continues to play an important basic role in the electronic technology industry.
The application fields of PCB are quite extensive. Wherever electronic components are used, PCBs are almost always used. Currently, they are mainly used in the fields of information, communication, consumer products, automobiles, aerospace and military, precision instruments and industrial products. According to the application fields, PCB can be divided into single-sided, double-sided, four-layer and more multi-layer boards and flexible boards. Generally speaking, the more complex the functions of electronic products, the longer the circuit distance, the more contact pins, and the more layers required for the PCB, such as high-end consumer electronics, information and communication products, etc. In curved products: such as notebook computers, cameras, car meters, etc.
At present, the mobile phone industry that uses PCBs in bulk is experiencing a slowdown in growth, but with the continuous improvement of specifications, 5G commercial transfer, servers, a large number of small base stations, storage devices, etc., are the next terminal products that use PCBs. , the requirements for materials have also begun to move towards high-speed, high-frequency and high-density packaging; electric vehicles are also another new engine for PCB growth, driving the average selling price of PCBs to continue to rise in recent years.
What is Printed Circuit Board, PCB?
All electronic products must use "Printed Circuit Board (PCB: Printed Circuit Board)" to fix integrated circuits (ICs) and other electronic components (such as resistors, capacitors, inductors), and to integrate all functionally different integrated circuits and electronic components are connected by thin copper wires to provide a stable working environment, so that electronic signals can flow between different electronic components.
Types of Printed Circuit Boards
➤Single sided board: a single plastic board is used as the bottom plate, integrated circuits (IC) and other electronic components are concentrated on one side, and copper wires are concentrated on the other side. The number of copper conductors that can be made on a single panel is small, and only early circuit boards will be used.
➤Double sided board: Using a single piece of plastic board as the bottom plate, copper wires are made on the front and back surfaces of the bottom plate, and "vias" are drilled to allow the copper wires to pass through the plastic board from the front to the back, to connect the copper wires on the front and back surfaces to each other, which is used in more complicated circuits.
➤Multilayer board: Make the required circuits on the front and back surfaces of multiple double-sided boards, and sandwich an insulating layer (plastic material) between the two double-sided boards and bond them to form several layers of copper. The number of copper wires that can be made by multi-layer boards is the largest, and it is used in more complex circuits. At present, the motherboards used in computers mostly use eight-layer boards because of too many components.
Generally, small electronic products, such as mobile phones, tablet computers, etc. Due to the requirement of small size, at least eight layers of boards are required. The more electronic components, the smaller the product size, and usually more layers of circuit boards are required.
"Via" is generally used in double-sided boards to drill holes through the plastic board, but in multi-layer boards, if you only want to connect some internal circuits, it is not necessary to penetrate the entire plastic board, so you can use "via”, “buried via hole" or "blind via hole", it is enough to penetrate only a few layers of the plastic board.
Materials of Printed Circuit Board
➤ Rigid circuit board (RPCB): generally made of glass epoxy resin (glass epoxy), which is a hard plastic board, and then copper wires are made on the circuit board. The biggest feature of the rigid circuit board is that it is "inactive". Because it is hard, it can only be fixed in the casing after it is made. It is a circuit board that all electronic products must use at present.
➤ Flexible circuit board (FPCB): generally made of polyethylene terephthalate (PET) or polyimide (Polyimide), and then the copper wire is made on the circuit board. The biggest feature of the flexible circuit board is that it can move, because it is soft, in fact, PET is the material used to make the bottle, it is a bit hard and soft, so it can be bent into various shapes after the production is completed. If two rigid circuit boards are to be connected, but flexible circuit boards are required to be able to move back and forth, they are widely used in consumer electronic products, such as LCD screens of notebook computers, foldable mobile phones, digital Cameras, CD players, hard disk storage devices, etc.
Printed Circuit Board Production Process
The production process of printed circuit boards includes: single-sided production, drilling and electroplating, multi-layer printed circuit board bonding, protection and surface treatment, circuit testing, etc. The details are as follows:
➤Single-sided production: Make the designed circuit into a negative, and then transfer the circuit on the negative to a thin layer of copper foil, and dissolve the unnecessary copper foil with chemicals to get the circuit we need. This process is a bit similar to transferring the pattern on the photomask to the silicon wafer in the fab. If the double-sided board is produced, copper foil will be applied on both sides of the plastic board. If the multi-layer board is produced, it must be many double-sided panels are glued together.
➤Drilling and electroplating: If you want to make double-sided or multi-layer boards, you must first make via, buried via hole, blind via hole, generally you can use "mechanical drill" directly drill with a drill bit, the minimum size of the hole is 8mil (about 0.2mm); you can also use "laser drill" to penetrate the plastic plate with laser light, and the minimum size of the hole can reach 4mil (about 0.2mm). 0.1mm) or less, making the copper wires thinner and denser, we call it "HDI process (High Density Interconnection)", which makes the integrated circuit (IC) and other electronic components denser on the printed circuit board, which can reduce the size of electronic products. Size, after the drilling is completed, a layer of metal is plated into the holes to form vertical copper wires, so "via" is also called "PTH: Plated Through Hole".
➤Multilayer printed circuit board bonding: The fabricated double-sided boards are bonded to form a multi-layer board. When bonding, an insulating layer (plastic material) must be added between the layers. If there are perforations (via) that penetrate several layers, then each layer must be By repeating the above steps, the circuits on the front and back surfaces of the multi-layer board are usually fabricated after the multi-layer board is bonded.
➤Protection and surface treatment: The green or brown on the printed circuit board is the color of the "solder mask". The solder mask is an insulating protective layer, which can protect the copper wires from oxidation. A layer of "silk screen" will be printed on which text and symbols will be printed to indicate the names and positions of various integrated circuits (ICs) and other electronic components. “Legend", if the printed circuit board has gold fingers, then the circuit of the gold fingers is plated at the end.
➤Line test: It is used to test whether there is a short circuit or open circuit on the printed circuit board. Generally, the board can be scanned optically with infrared light to find out the defects of each layer, and whether there is an incorrect gap between the wires. It can also be used electronic testing uses a "flying probe" to check all copper wire connections for shorts or open circuits.
Component Mounting and Soldering Technology
After the printed circuit board is completed, the integrated circuit (IC) and other electronic components must be connected and fixed on the printed circuit board.
➤Through Hole Technology (THT): Electronic components are placed on the front of the circuit board, and the pins are soldered on the back, usually using "wave soldering" technology, first cutting the pins close to the board , and bend it slightly so that the components can be fixed, then move the board to the water wave of the flux, let the bottom contact the flux to remove the oxide on the bottom pins, reheat the board and move it to the melted solder, wait for the solder After cooling, the connection is fixed. This method will take up a lot of space, and a hole needs to be drilled for each pin, so each pin occupies the space on both sides of the circuit board, and the solder joints are relatively large, but the fixing effect is better.
➤Surface Mounted Technology (SMT): Electronic components and pins are placed on the front of the circuit board, usually using "over reflow soldering" technology, the solder paste containing flux and solder is first It is printed on the circuit board where it is to be connected to the pins of the electronic components, and then the electronic components are placed on the circuit board so that the pins are in contact with the solder paste on the circuit board, and then the circuit board is heated to melt the solder paste and bond the pins of the electronic components when it cools down, the electronic component pins will be fixed on the circuit board. The electronic components soldered in this way are relatively small in size, and the electronic components are denser on the circuit board, and the printed circuit board after production is relatively small, so most of the current electronic products use SMT technology instead of THT technology.