PCB Fabrication

PCB design basis and design guidelines

by:A-TECH      2021-04-07
There will be many problems in PCB design. I won't talk about them one by one here. Now I will summarize a PCB design guideline, I hope it will be helpful for beginners.  1. Purpose and function  1.1 Standardize design operations, improve production efficiency and improve product quality.  2. Scope of application  1.1 VCD super VCDDVD audio and other products of the company’s development department.  3. Responsibilities   3.1 Electronic engineers, technicians and computer drafters in the development department. 4. Qualifications and training 4.1 Have a foundation in electronic technology;   4.2 Have basic computer operating knowledge;   4.3 Familiar with computer PCB drawing software.  5. Work instruction (the length unit is MM)   5.1 Minimum line width of copper foil: panel 0.3MM, panel 0.2MM The minimum distance between the edge copper foil is 1.0MM  5.2 The minimum gap between the copper foil: panel: 0.3MM, panel: 0.2MM.  5.3 The minimum distance between the copper foil and the edge of the board is 0.55MM, the minimum distance between the component and the board edge is 5.0MM, and the minimum distance between the disk and the board edge The distance is 4.0MM  5.4 The size (diameter) of the pad of the through-hole mounting component is twice the diameter of the hole. The minimum double-sided board is 1..5MM, and the minimum single-sided board is 2.0MM. Circular pads cannot be used (2.5MM). Waist round pad,   5.5 Electrolytic capacitors cannot touch heating elements, high-power resistors, sensitive resistors, voltages, heaters, etc. The minimum distance between the decapacitor and the radiator is 10.0MM, and the minimum distance between the component and the radiator is 2.0 MM.  5.6 Large-scale components (such as transformers, electrolytic capacitors with a diameter of 15.0MM, high-current sockets, etc.)   5.7 Screw hole radius 5.0MM There must be no copper foil (external grounding) components. (According to the requirements of the structure drawing).  5.8 There should be no silk screen oil on the upper tin position.   5.9 The center distance of the pads is less than 2.5MM, the adjacent pads should be wrapped with silk screen oil, and the width of the ink should be 0.2MM (0.5MM is recommended).    5.10 Do not place jumpers under the IC or Motors and potentiometers are under the components of its large-volume metal shell.   5.11 In the large-area PCB design (approximately more than 500CM2), to prevent the PCB board from bending when passing through the tin furnace, leave a 5 to 10mm wide gap on the PCB board without placing the element Device (wiring), used to add layering strips to prevent the PCB board from bending when passing through the soldering furnace,   5.12 Each transistor is marked with e, c, b pins on the silk screen.   5.13 Components that are soldered after the soldering furnace, plate To drive away the tin position, facing the opposite of the tin passing direction, the size of the viewing hole is 0.5MM to 1.0MM   5.14 When designing double panels, pay attention to the metal shell components, when the shell is in contact with the printed board when plug-in, the top layer is soldered. The disk cannot be opened, and should be covered with green oil or silk screen oil (for example, two-pin crystal oscillator).  5.15 In order to reduce the short circuit of the solder joints, the double-sided printed circuit board does not open the green oil window through the holes. 5.16 On each PCB, a solid arrow is used to mark the direction of the soldering furnace:   5.17 The minimum distance between the holes is 1.25MM (double-sided invalid)    5.18 When the layout, the direction of the DIP packaged IC is perpendicular to the direction of the soldering furnace , Not parallel, as shown in the figure below; if there are difficulties in the layout, it is allowed to place the IC horizontally (the OP packaged IC is placed in the opposite direction to the DIP). 》  5.19 The wiring direction is horizontal or vertical, and it takes 45 degrees to enter from vertical to horizontal.   5.20 The placement of components is horizontal or vertical.  5.21 The silk screen characters are placed horizontally or rotated 90 degrees to the right.  5.22 If the width of the copper foil into the round pad is smaller than the diameter of the round pad, then teardrops should be added.  5.23 The material code and design number should be placed on the empty space of the board.  5.24 Reasonably use the place without wiring as grounding or power supply.   5.25 The wiring should be as short as possible, especially the clock line, low-level signal line and high-frequency loop wiring should be shorter.   5.26 The ground wire and power supply system of analog circuit and digital circuit should be separated.   5.27 There is a large area of u200bu200bground wire and power wire area on the printed board (the area exceeds 500 square millimeters), and the window should be partially opened. , 5.28 The positioning holes of the electrical plug-in printed board are specified as follows. The shaded parts cannot be used to place components, except for hand-plugged components. The range of L is 50 to 330mm, and the range of H is 50 to 250mm. If it is less than 50X50, the board must be opened and the mold can be opened. If it is more than 330X250, it will be changed to a manual board. The positioning hole must be on the long side.
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