For printed circuit board, in order to save material and make the function of PCB board normal, the layout of PCB is very important.This article will explain PCB layout and techniques.
PCB layout rules
1, Normally, all components shall be located on the same side of the PCB, only when the top-layer components are too close, then put some parts with limited height and small calorific value on the bottom, such as SMD resistor, capacitors, IC, etc.
2. Under the premise of ensuring electrical performance, the elements should be placed on the grid and arranged in parallel or vertically to keep orderliness and beautiful, and not allow components be overlap in general; The array of components should be closely, and the layout should be evenly distributed and consistent.
3. The minimum space between different components on PCB board shall be more than 1MM.
4, Away from the PCB board edge is generally not less than 2 mm. The best shape for circuit board is rectangular, length-width ratio is 3:2 or 4:3. When the PCB area is greater than 200mm*150mm, should consider withstand mechanical strength for the PCB.
PCB design layout techniques
For the PCB layout design, the PCB unit should be analyzed. the layout design should be based on its function, the following principles should be met for all components layout in PCB :
1. Place each functional circuit unit according to circuit direction,to make the layout be easily for circulate and keep the signal as consistent as possible.
2. Center on the core components of each functional unit, surrounding it for the layout.The components shall be uniformly, wholely and compactly placed on the PCB, minimizing and shortening the components leads and connections.
3. When the circuit works at high frequency,should consider the distribution parameters between components.For general circuit components should be placed in parallel as much as possible, so that not only is beautiful, but also easy to be installed and for mass production.
Pay attention to following points when PCB design layout
(1) length of lines should be as short as possible to minimize the inductance minimizaiton.In low frequency circuits, because all the ground current of circuits flows through the public grounding impedance or grounding plane, so avoid multi-point grounding.
(2) the public ground line should be located on the edge of printed circuit board.The circuit board should retain as much copper foil as possible to be ground line, which can enhance the shielding ability.
(3) double sided PCB can use ground surface, and its purpose is to provide a low impedance geodesic.
(4) in the multi-layer printed circuit board, the ground layer can be set up and designed to be a network.The space of ground lines mesh cannot be too large, because a main function of ground lines is to provide signal backflow path. If the grid space is too large, it will form a larger area of signal loop.The big loop area will cause radiation and sensitivity problems.In addition, if the actual loop area is small when signal reflux, others ground lines do not work.
(5) the ground surface can minimize radiation circulation.