What is programmable circuit board?
The printed circuit board is used as the mounting substrate, and electronic and electromechanical components, devices or other printed circuit board components are mounted on it, and the printed circuit on the board (also can be made into passive electronic components such as resistors, capacitors, and inductors) ) Components that realize electrical interconnection. In small electronic equipment, such as electronic watches, single-board microprocessors, and small semiconductor radios, all components and devices are mounted on a printed circuit board. And large-scale equipment (such as large-scale computer) is composed of dozens to thousands of printed circuit boards composed of plug-ins and corresponding printed circuit backplanes. Various printed circuit board components. Each printed circuit board component is usually a functional unit.
Early electronic equipment, electronic and electromechanical components, and devices were mounted on a chassis made of thin metal plates and used wires to achieve electrical interconnection. After the Second World War, with the development of printed circuit technology, electronic equipment, especially electronic computers, gradually formed a structural system based on printed circuit board components. Its advantages are good electrical performance, high reliability, small size, low cost, and automatic production.
The printed circuit board components belong to the second and third level assembly, and there are two assembly methods.
①Plane assembly or two-dimensional assembly: Components and devices are mounted on a plane and interconnected with printed circuit boards. In order to increase the assembly density, components and devices can be mounted on both the front and back sides of the printed circuit board, or a metal plate can be sandwiched between the printed circuit board to improve the cooling capacity. ②Modular assembly or three-dimensional assembly: In order to improve assembly density, two printed circuit board components parallel to each other are generally used to form a space, and components and devices are installed in the space, or components are installed on the front and back sides of the printed circuit board. Components and boards are interconnected by cables or connectors; it can also be like a bridge, where the legs of components and devices are respectively mounted on two printed circuit boards, which are called sandwich modules. The structural design of printed circuit board components must consider issues such as circuit division and standardization, assembly types, reasonable layout of components and devices, assembly structure, cooling methods, and mechanical dynamic characteristics.
Circuit division and standardization Make reasonable division on the system block diagram, and stipulate the number of circuits and components and devices to be installed on a printed circuit board. This is the circuit division. Simple electronic equipment does not have this problem, it can be solved with one or several printed circuit boards. However, in complex electronic equipment, such as large computers, the central processing unit alone has more than one hundred thousand components. Although large-scale integrated circuits have been used in the fourth-generation mainframe computers, the number of devices is generally several thousand. Therefore, selecting the optimal zoning scheme is a complicated design work. The design must first meet the requirements for electrical performance, including functionalization and testability, trace length and complexity, electromagnetic compatibility, fault location performance and maintainability. The second is the number of external leads and their optimization. Integrated circuits have developed to large-scale and ultra-large-scale integration, and the number of external leads of printed circuits has increased sharply, which severely limits the increase in assembly density and the full use of the potential of large-scale integrated circuits. Therefore, in the computer field, we should focus on the law of the gate-to-pin ratio (that is, the ratio of the number of circuits in the component or the number of gates to the external leads), and how to improve the gate-to-pin ratio. In addition, issues related to reliability, standardization, number of varieties, and assembly efficiency must also be considered.
Assembly type Select the assembly type according to the function, the number of components and devices, the assembly density, environmental requirements, cooling, the number of external connection leads, and the requirements of technology and materials.
Reasonable layout of components and devices Must meet the electrical performance, process, heat dissipation and mechanical requirements.
Assembly structure Different additional structures are added to the printed circuit components as needed, such as skeletons, stiffeners, various structural parts, panels, handles, plug-in accessories, shields and connectors.
Cooling method Commonly used cooling methods are: natural cooling, forced ventilation cooling, liquid cooling, evaporative cooling and semiconductor refrigeration (see electronic equipment thermal control).
Mechanical dynamic characteristics To adapt to the requirements of work and transportation in motion.
In addition to the above requirements, man-machine connection and reliability issues must also be considered in the design.
The assembly of printed circuit board components, from component and device preparation to component inspection, has been mechanized and automated. The equipment for assembly of printed circuit board components includes components, device aging and automatic detection and classification, components and device lead shaping, cleaning, immersion tin and other equipment, components and device automatic insertion machines, automatic and semi-automatic winding machines and various automatic soldering Equipment, etc. Electronic components and devices are generally plug-in installation. In order to increase the assembly density, directly use the chip or chip carrier to assemble.
