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Steven Xiao

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PCB Layout

- Feb 15, 2018 -

PCB is also called Printed Circuit Board, which can realize the circuit connection and function realization among the electronic components, and is also an important part of the power circuit design. Today will be the article to introduce the basic rules of PCB layout.


First, the basic rules of component layout

    1. According to the layout of the circuit module to achieve the same function of the circuit is called a module, the circuit module components should be based on the principle of concentration, while digital and analog circuits separate;

    2. Positioning holes, standard holes and other non-mounting holes shall not be placed within 1.27mm around the mounting holes 3.5mm (for M2.5), 4mm (for M3) shall not be mounted components;

    3. Laying resistors, inductors (plug-in), electrolytic capacitors and other components below the cloth to avoid cloth through holes, so as to avoid after-wave soldering the hole and the component shell short circuit;

    4 components from the edge of the board side of the distance 5mm;

    5. The distance between the outer side of the mounting component pad and the outer side of the adjacent insertion component is more than 2mm;

    6. Metal shell components and metal parts (shielding boxes, etc.) can not collide with other components, not close to the printed lines, pads, the spacing should be greater than 2mm. Positioning holes, fastener mounting holes, elliptical holes and other square hole in the board outside the board from the board edge size greater than 3mm;

    7. heating element can not be close to the wire and thermal elements; high heat devices to be balanced distribution;

    8. The power outlet should be arranged around the printed board as far as possible. The outlet of the bus bar to which the power outlet is connected should be arranged on the same side. In particular, care should be taken not to place power sockets and other soldered connectors between the connectors in order to facilitate the soldering of these sockets, connectors, and power cable design and wiring. Power outlet and the layout of the welding connector spacing should be considered to facilitate the plug power plug;

    9. Other components of the layout: all the unilateral alignment of IC components, the polarity of a polar element clearly marked, the same printed board polarity marked no more than two directions, two directions appear when the two directions perpendicular to each other ;

   10. Board wiring should be properly densified, when the density difference is too large should be filled with mesh copper foil, the grid is greater than 8mil (or 0.2mm);

   11. Patch pads can not have through-holes, so as to avoid loss of solder paste component Weld. Important signal lines are not allowed to pass through the socket foot;

   12. Unilateral alignment of the patch, the characters in the same direction, the same package orientation;

   13. The polarity of the device in the same board to indicate the polarity of polarity as far as possible consistent.


Second, the rules of wiring components

   1, draw the wiring area from the PCB edge ≤ 1mm area, as well as within 1mm around the mounting hole, the prohibition of wiring;

   2, the power line as wide as possible, should not be less than 18mil; signal line width should not be less than 12mil; cpu into the line should not be less than 10mil (or 8mil); line spacing of not less than 10mil;

   3, the normal via hole is not less than 30mil;

   4, Double Inline: Pad 60mil, aperture 40mil;

     1 / 4W resistance: 51 * 55mil (0805 surface mount); straight when the pad 62mil, aperture 42mil;

     Promise capacitor: 51 * 55mil (0805 surface mount); straight when the pad 50mil, aperture 28mil;

  5, pay attention to the power cord and ground should be as radial as possible, and the signal line loop loop can not appear.


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