The basic concept of printed circuits has been proposed in patents at the beginning of this century. In 1947, NASA and the American Bureau of Standards launched the first technical seminar on printed circuits. At that time, 26 different printed circuit manufacturing methods were listed. And summarized into six categories: coating method, spray method, chemical deposition method, vacuum evaporation method, molding method and powder pressing method. At that time, these methods failed to achieve large-scale industrial production. Until the early 1950s, the adhesion problem of the platen between copper foil and layer has been solved, the performance of the copper-clad laminate is stable and reliable, and large-scale industrial production has been realized. The copper foil etching method has become the mainstream of the printed board manufacturing technology, and has been developed until now. Surface printing and multi-layer printed boards achieved mass production. In the 1970s, due to the rapid development of large-scale integrated circuits and electronic calculators, the rapid development of surface mount technology in the 1980s and the rapid development of multi-chip assembly technology in the 1990s promoted printing. With the continuous advancement of circuit board production technology, a number of new materials, new equipment, and new testing instruments have emerged one after another, and printed circuit production technology has further developed in the direction of high-density, thin wire, multi-layer, high reliability, low cost and automated continuous production.
1. The Design Process of The Schematic Diagram
The generation of the schematic diagram is generally regarded as the first step in the PCB production process. It is also the specific realization of the product vision by electronic engineering technicians. It is composed of many logic components (such as various IC gate circuits, resistors, capacitors, etc.). ) through different logical connections. To make a schematic diagram, the source of its logical components is that some CAD software contains a huge logical component library (such as TANGO PADS, etc.) , and new logic components (such as Cadence, Mentor, Zuken, etc.) can be added and established by the user, and the user can use these logic components to realize the logic function of the product to be designed.
1.1. Create Logical Components
A logic component is a component that provides a logic function (such as an LSOO gate, a flip-flop or an ASIC circuit).
1) Definition of logical component model (or component name)
2) Package form of logic component pins
3) Description of logic component pins
4) Definition of the shape and symbol size of logic components
1.2. Description of Functional Characteristics of Logic Components
To simulate the logic circuit, it is necessary to describe the functional characteristics of each logic component, such as the timing relationship of the logic component, the initial state rising edge (RISE), falling edge (FALL), delay time, and drive attenuation, decay time, etc.
1.3. Description of the Logic Component Library
Since there are many logic components, all of them are built under one library, which is easy to cause confusion and difficult to manage. Therefore, logic components with similar functional characteristics are generally placed in a library and managed according to their functional characteristics, such as A/D, D/A conversion devices, CMOS devices, storage devices, TTL devices, linear devices, operational amplifier devices, comparison devices, etc., are all placed under the same library. It can also be classified by company manufacturers such as: MOTOROLA, NEC, INTEL, etc.
2. The Function of Printed Circuits In Electronic Equipment
(1) Provide mechanical support for fixing and assembling various electronic components such as integrated circuits.
(2) Realize the wiring and electrical connection or electrical insulation between various electronic components such as integrated circuits.
(3) Provide the required electrical characteristics, such as characteristic impedance, etc.
(4) Provide solder mask graphics for automatic soldering, and provide identifiers and graphics for component insertion, inspection, and maintenance.
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