PCB is more and more widely used, because it has a lot of unique advantages, trichosanthes as follows.
can be high-density. For decades, the high density of PCB has been developed with the improvement of integrated circuit integration and installation technology.
High reliability. Through a series of inspection, PCB testing and aging tests can ensure that the PCB long-term (use, generally for 20) and reliable work.
can be designed. PCB Performance (electrical, physical, chemical, mechanical, etc.) requirements, can be designed through standardization, standardization, etc. to achieve PCB design, short time, high efficiency.
Production. The use of modern management, can be standardized, scale (volume), PCB automation and other production, to ensure consistency of product quality.
Testability. Set up a relatively complete test methods, testing standards, PCB a variety of testing equipment and instruments to detect and identify the PCB product eligibility and service life.
can be assembled. PCB products are not only convenient for a variety of components standardized assembly, and can be automated, large-scale production. At the same time, PCB and various components assembly parts can also be assembled to form larger parts, systems, until the machine.
Maintainability。 As PCB products and components are assembled in a standardized design and large-scale production, and therefore, these components are also standardized. Therefore, PCB once the system fails, can quickly, easily, flexibly to replace, quickly restore service system work. Of course, you can say more about it. such as the miniaturization of the system, lightweight, high-speed signal transmission and so on.
What should be paid attention to the PCB walking line?
1. General rules
1.1 PCB board on the pre-division digital, Analog, DAA signal wiring area.
1.2 Digital, analog components and corresponding walking line as far as possible separate and placed in the respective wiring area.
1.3 High-speed digital signal line as short as possible.
1.4 Sensitive analog signal lines as short as possible.
1.5 Reasonable distribution of power and ground.
1.6 Dgnd, Agnd, field separation.
1.7 power supply and critical signal line use wide line.
The 1.8 digital circuit is placed near the parallel bus/serial DTE interface, PCB and the DAA circuit is placed near the telephone line interface.
2. Component Placement
2.1 In the schematic diagram of the system circuit:
A digital, analog, DAA circuit and related circuits are divided;
b in each circuit to divide digital, analog, mixed digital/analog components;
c) attention to the IC chip power supply and signal pin positioning.
2.2 The initial division of digital, Analog, DAA circuit on the PCB board of the wiring area (the general ratio of 2/1/1), digital, analog components and their corresponding walking line as far away and limited in their respective wiring area.
Note: When the DAA circuit accounted for a larger proportion, there will be more control/status signal line through its wiring area, can be adjusted according to local rules, PCB such as component spacing, high pressure suppression, current restrictions.
2.3 After the initial division, from connector and Jack began to place components:
A the location of the plugin around connector and Jack;
b The space around the components to leave the power supply and the ground line;
c the position of the corresponding plug-in around the socket.
2.4 First placed mixed-type components (such as modem devices, A/D, d/a conversion chip, etc.):
(a) to determine the direction of the placement of components, PCB as far as possible digital signals and analog signal pins toward their respective wiring area;
B Place the components at the junction of the digital and analog signal wiring area.
2.5 Place all Analog Devices:
(a) Placing analog circuit components, including DAA circuits;
b) The analog devices are close to each other and placed on the PCB containing TXA1, TXA2, Rin, VC, Vref signal line;
c) TXA1, TXA2, Rin, VC, Vref signal line around to avoid placing high noise components;
D for serial DTE module, DTE EIA/TIA-232-E
Serial interface signals receive/drive as close to the connector and away from the high-frequency clock signal line to reduce/avoid the increased noise suppression devices on each line, PCB such as a choke coil and capacitance.
2.6 Put digital components and decoupling capacitor:
(a) centralized placement of digital components to reduce line length;
b in the IC Power/ground to place 0.1uF decoupling capacitor, connecting the line to minimize EMI;
c) on the parallel bus module, the components close to
Connector edge placement to conform to application bus interface standards, PCB such as ISA bus line length limited to 2.5in;
d) on the serial DTE module, the interface circuit is close to the connector;
e) The crystal oscillator circuit as close to its drive parts as possible.
2.7 ground wires of each region, PCB usually with 0 ohm resistors or bead connected at one or more points.