Ⅰ. The role of PCB in the field of electronics
Ⅱ. Manufacturing PCB
Ⅲ.Characteristics of PCB
Ⅳ.PCB design
Ⅴ.PCB Design Principles
Ⅵ.The development history of PCB
Ⅶ. What are the advantages of PCB application in industry?
A PCB is a basic device used to support and connect electronic components. It is usually made of insulating material and covered with metal wires or copper foil, and is used to transmit signals and power in electronic equipment. PCB plays a key role in modern electronics because it provides stable mechanical support and electrical connections for electronic components such as integrated circuits, capacitors, resistors, etc.
PCB is one of the important parts of electronics industry. Almost every kind of electronic equipment, ranging from electronic watches and calculators to computers, communication electronic equipment, and military weapon systems, as long as there are electronic components such as integrated circuits, in order to make the electrical interconnection between various components, printed circuit boards must be used. plate.
A PCB mechanically supports and electrically connects electrical or electronic components using conductive tracks, other features etched from one or more sheets of copper laminated to and/or a non-conductive substrate between sheet layers. Components are usually soldered to the PCB to electrically connect and mechanically secure them to the printed circuit board.
PCBs can be single-sided (one copper layer), double-sided (two copper layers on both sides of one base layer), or multi-layered (outer and inner layers of copper, alternating with base layers). Multilayer PCBs allow for higher component densities, since circuit traces on inner layers would otherwise take up surface space between components. The proliferation of multi-layer PCBs with more than two, and especially more than four, copper planes has gone hand in hand with the adoption of surface mount technology.
The traditional PCB uses the method of printing etch resist to make circuit lines and graphics, so it is called printed circuit board or printed circuit board. Due to the continuous miniaturization and refinement of electronic products, most of the current circuit boards are made by attaching etch resist (lamination or coating), after exposure and development, and then etching to make circuit boards.
PCB has good product consistency, and it can adopt a standardized design, which is conducive to the realization of mechanization and automation in the production process. At the same time, the entire printed circuit board that has been assembled and debugged can be used as an independent spare part, which is convenient for the exchange and maintenance of the whole machine. At present, printed circuit boards have been widely used in the production and manufacture of electronic products.
Alternatives to CPB include wire-wound and point-to-point structures, which were once popular but are now rarely used. CPBs require additional design work to lay out the circuitry, but fabrication and assembly can be automated. Electronic computer-aided design software can be used to do most of the layout work. Mass-produced circuits with PCBs are cheaper and faster than other wiring methods because components are mounted and routed in one operation.PCB way
Ⅰ. The role of PCB in the field of electronics
1. PCB provides a stable platform to install electronic components (such as chips, resistors, capacitors, transistors, etc.) on its surface or at different levels inside, and connect these components through wires to form a circuit. This connection is necessary because electronic components are often too small or too fragile to be connected directly together.
2. PCB provides mechanical support for the fixing and assembly of various electronic components such as integrated circuits, realizes the wiring and electrical connection or electrical insulation between various electronic components such as integrated circuits, and provides the required electrical characteristics.
3. In the large-scale and ultra-large-scale electronic packaging components, it provides an effective chip carrier for the miniaturized chip packaging of electronic components.
4. The layout and wiring of the PCB determine the function of the electronic device. With reasonable design, PCB can support various circuit functions, from simple switching circuits to complex signal processing and control circuits.
5. After electronic equipment adopts PCB, due to the consistency of similar printed boards, manual wiring errors are avoided, and automatic insertion or placement of electronic components, automatic soldering, and automatic detection can be realized to ensure the quality of electronic products. Improve labor productivity, reduce costs, and facilitate maintenance.
6. The wires and copper foil on the PCB are used to transmit signals inside the electronic device. These signals can be data, control signals, power signals, etc., and they are connected together by circuits to enable the device to function properly.
7. PCB can speed up the manufacturing process of electronic equipment through mass production. Using standardized PCB design and manufacturing processes, electronic products can be mass-produced in a relatively short period of time.
8. The PCB embedded with passive components inside provides certain electrical functions, simplifies the electronic installation procedure, and improves the reliability of the product.
9. Provide solder resist graphics for automatic welding, and provide identification characters and graphics for component insertion, inspection and maintenance.
Ⅱ. Manufacturing PCB
1. Metal coating
In addition to the wiring on the substrate, the metal coating can also be where the substrate circuit and electronic components are soldered. In addition, since different metals have different prices, it directly affects the cost of production. In addition, each metal has different solderability, contactability, resistance value, etc., which will directly affect the performance of the component.
Commonly used metal materials are tin and copper, with a thickness of 5 to 15 μm; lead-tin alloy, that is, solder, with a thickness of 5 to 25 μm and a tin content of about 63%; gold, which is generally only plated on the interface; silver, which is generally only It will be plated on the interface, or in an alloy that is also silver as a whole.
2. Substrate
Substrates are generally classified by the insulating and strengthening parts of the substrate. Common raw materials are bakelite boards, glass fiber boards, and various plastic boards. PCB manufacturers generally use an insulating pre-impregnated material composed of glass fiber non-woven material and epoxy resin, and then press it with copper foil to form a copper foil substrate for use.
3. Circuit design
The design of the PCB is based on the circuit schematic diagram to realize the functions required by the circuit user. PCB design mainly refers to layout design, which requires various factors such as internal electronic components, metal connections, layout of through holes and external links, electromagnetic protection, heat dissipation, and crosstalk.
Excellent circuit design can save production cost and achieve good circuit performance and heat dissipation performance. Simple layout design can be realized by hand, but complex circuit design generally also needs to be realized with the help of computer-aided design (CAD).
Ⅲ.Characteristics of PCB
1. Surface mount technology
Surface mount technology emerged in the 1960s, developed in the early 1980s, and became widely used in the mid-1990s. Mechanically redesigned the assembly to have smaller metal lugs or end caps that can be soldered directly to the PCB surface instead of running wires through holes.
Components have become smaller compared to through-hole mounting, and placement of components on both sides of the board has also become more common, allowing smaller sized PCB assemblies with higher circuit density. Compared with through-hole circuit boards, surface mount is ideal for a high degree of automation, which reduces labor costs and greatly increases productivity. Components can be mounted on carrier tape.
Surface mount components are about one-fourth to one-tenth the size and weight of through-hole components, and passive components are much less expensive. However, semiconductor prices for surface mount devices (SMDs) are determined by the die itself, not the package itself, offering little price advantage over larger packages, and some end-of-line components (such as 1N4148 small-signal switching diodes) Much cheaper than SMD equivalent components actually.
2. Through hole technology
The earliest PCBs used through-hole technology to mount electronic components by inserting leads through holes on one side of the board and soldering to copper traces on the other side. Boards can be single-sided with no coating on the component side, or more compact double-sided boards with components soldered on both sides. Through-holes with two axial leads (such as resistors, capacitors, and diodes) can be mounted horizontally by bending the leads 90 degrees in the same direction and inserting them into the board (usually with the bent leads on the backside of the board) Component.
Make the connections in the opposite direction to increase the mechanical strength of the part), solder the leads and trim the ends. The leads can be soldered manually or by a wave soldering machine.
Via fabrication requires precise drilling of many holes, adding to board cost and limiting the available routing area for signal traces on layers just below the top layer of a multilayer board, as the holes must pass through all layers to the opposite side.
Once you start using surface mount, small SMD components will be used where possible, only through-hole mounting is not suitable for large components that are surface mounted due to power requirements or mechanical limitations or exposure to mechanical stress that could damage the PCB (eg, lift the copper off the board surface).
3. Circuit characteristics of PCB
Each trace consists of a flat, narrow portion of the copper foil that remains after etching. Its resistance, determined by its width, thickness and length, must be low enough that the conductor will carry current. Power and ground traces may need to be wider than signal traces.
On a multilayer board, the entire layer may be mostly solid copper to serve as a ground plane for shielding and power return. For microwave circuits, transmission lines can be laid out in a planar form such as stripline or microstrip, with dimensions carefully controlled to ensure consistent impedance.
In radio frequency and fast switching circuits, the inductance and capacitance of printed circuit board conductors become important circuit elements and are generally undesirable. Instead, they can be used as an intentional part of circuit design, such as in distributed element filters, antennas, and fuses, eliminating the need for additional discrete components.
Ⅳ.PCB design
PCBs are designed manually by creating a photomask (usually double or quadruple the real size) on a clear mylar sheet. Starting with the schematic, lay out the component pin pads on the mylar, and trace traces to connect the pads. Friction-based dry transfer of common component footprints improves efficiency. Make marks with self-adhesive tape. A pre-printed non-replicating grid on mylar helps with layout. Photolithographically replicate the completed photomask onto the photoresist coating on the blank CCL.
Modern PCB design has dedicated layout software, usually follow the steps below:
1. Schematic capture via electronic design automation (EDA) tools.
2. The size and template of the card depends on the required circuit and the enclosure of the PCB.
3. Determine the location of components and heat sinks.
4. Determine the layer stack of the printed circuit board, depending on the complexity, one layer to dozens of layers. Identify ground and power planes. The power plane is the opposite side of the ground plane, and it also acts as an AC signal ground while providing DC power to the circuits mounted on the PCB. Signal interconnects are located on signal planes. Signal planes can be on outer and inner layers. For best EMI performance, high frequency signals are routed in internal layers between power or ground planes.
5. Line impedance is determined by dielectric layer thickness, wiring copper thickness and trace width. In the case of differential signaling, trace separation should also be considered. Microstrip, stripline, or dual stripline can be used to route signals.
6. The component is placed. Thermal considerations and geometry are considered. Mark vias and land.
7. Signal traces are routed. Electronic design automation tools often automatically create gaps and connections in the power and ground planes.
8. Generate Gerber files for manufacturing.
Ⅴ.PCB Design Principles
1. Layout
First, consider the size of the PCB. If the PCB size is too large, the printed lines will be long, the impedance will increase, the anti-noise ability will decrease, and the cost will also increase; if it is too small, the heat dissipation will not be good, and the adjacent lines will be easily disturbed. After determining the PCB size, determine the location of special components. Finally, according to the functional unit of the circuit, all the components of the circuit are laid out.
When laying out, shorten the wiring between high-frequency components as much as possible, and try to reduce their distribution parameters and mutual electromagnetic interference. Components that are susceptible to interference cannot be too close to each other, and input and output components should be kept as far away as possible.
For the layout of adjustable components such as potentiometers, adjustable inductance coils, variable capacitors, and micro switches, the structural requirements of the whole machine should be considered. If it is adjusted inside the machine, it should be placed on the printed board where it is convenient for adjustment; if it is adjusted outside the machine, its position should be adapted to the position of the adjustment knob on the chassis panel.
There may be a high potential difference between some components or wires, and the distance between them should be increased to avoid accidental short circuit caused by discharge. Components with high voltage should be arranged in places that are not easily accessible by hand during debugging.
Arrange the position of each functional circuit unit according to the flow of the circuit, so that the layout is convenient for signal circulation, and the direction of the signal is kept as consistent as possible.
The core components of each functional circuit are centered, and the layout is carried out around it. Components should be evenly, neatly and compactly drawn on the PCB, minimizing and shortening the leads and connections between components.
2. Wiring
The wires used for the input and output terminals should avoid being adjacent to each other in parallel as much as possible. It is best to add a ground wire between lines to avoid feedback coupling.
The minimum width of printed circuit board wires is mainly determined by the adhesion strength between the wires and the insulating substrate and the current value flowing through them.
The minimum spacing of the conductors is mainly determined by the worst-case insulation resistance between the lines and the breakdown voltage. For integrated circuits, especially digital circuits, as long as the process allows, the pitch can be as small as 5-8 um.
The corners of printed wires are generally arc-shaped, while right angles or included angles will affect electrical performance in high-frequency circuits. In addition, try to avoid using a large area of copper foil, otherwise, when heated for a long time, it is easy to cause copper foil to expand and fall off. When a large area of copper foil must be used, it is best to use a grid shape, which is beneficial to eliminate the volatile gas generated by the adhesive between the copper foil and the substrate when heated.
3. Pad
The center hole of the pad is slightly larger than the diameter of the device lead. If the pad is too large, it is easy to form a virtual solder joint. The outer diameter D of the pad is generally not less than d+1.2 mm, where d is the lead hole diameter.
Ⅵ.The development history of PCB
In the early 20th century, researchers in the field of electronics began to try to use wires on circuit boards to connect electronic components. The earliest experiments used hand-drawn circuits, connecting components with pins and wires.
In the 1940s, during World War II, the development of PCBs was boosted by military and communications needs. During this period, circuits were made using copper foil on paper or phenolic resin based substrates.
Manufacturing of PCBs improved in the 1950s with the introduction of plastic substrates and lamination techniques. Lamination technology allows multiple thin boards to be laminated together to form a multi-layer PCB, which increases the connection density.
In the 1960s, electronic equipment became more and more complex, and the design and manufacture of PCBs were gradually automated. Computer-aided design (CAD) began to be applied to PCB design.
In the 1970s, surface mount technology (SMT) began to be applied to PCB manufacturing, allowing components to be mounted directly on the surface of the board, reducing the need for socket assembly.
In the 1980s, the PCB design and manufacturing process was gradually digitized, and the development of CAD tools enabled designers to perform layout and routing more quickly and accurately.
In the 1990s, the demand for high-speed digital signal transmission and complex circuits increased, and PCB design paid more and more attention to signal integrity and anti-interference.
Ⅶ. What are the advantages of PCB application in industry?
1. High-frequency and high-speed signal transmission: PCB design can optimize signal integrity so that signal quality can be maintained when high-frequency and high-speed signal transmission is required in industrial equipment.
2. Reliability and stability: The manufacture and design of the PCB are under precise process control to ensure the stability and reliability of the circuit. This is critical for the long-term operation of industrial equipment.
3. Adaptability and customization: PCBs can be custom designed according to specific industrial application requirements to meet different functional and performance requirements.
4. Compactness and integration: PCB can integrate multiple electronic components in a relatively small space, so that industrial equipment can be designed more compactly, reducing volume and space occupation.
5. Heat resistance and environmental impact resistance: PCB materials can be selected as materials resistant to high temperature, chemical corrosion or environmental impact, suitable for various industrial environments.
标签：PCB
