6. The design of PCB-- related skills

9. PCB design related skills
 Juvtmall ( a company supply PCB PrototypingPCBA service and sell kinds of components, modules and so on) 

PCB design setting technique

The PCB design needs to be set different points in different stages. In the layout phase, the device layout can be used in the large lattice point.
For large devices such as IC and non-locating connectors, the lattice site of 50~100mil can be selected for layout, and the grid point of 25mil can be used for the distribution of passive devices such as resistance capacitance and inductance. The precision of the large lattice point is beneficial to the orderliness and beauty of components.

PCB layout rules

1. In general, all components shall be decorated on the same side of the boards, only the top-level element too close, set some highly limited and calorific value small devices on the bottom., such as SMD resistor, SMD capacitors, SMD IC, etc.
2. Under the premise of ensuring electrical performance, the components should be placed on the grid and arranged in parallel or vertically, in order to be neat and beautiful, and not allow the components to overlap in general; The arrangement of components should be compact, and the elements should be evenly distributed and consistent on the board.
3. The minimum spacing between the different components on the circuit board and land pattern shall be more than 1MM.
4. The distance from the edge of circuit board is generally not less than 2 mm. The best shape for circuit board is rectangle, the ratio of length to width is 3:2 or 4:3. The size of circuit board is greater than 200 mm *150 mm, should consider the mechanical strength that circuit board can withstand.

PCB design layout techniques

In the layout design of PCB, the unit of the circuit board should be analyzed. According to the function to layout, the following principles should be met :
1. Arrange the location of each functional circuit unit according to the process of the circuit, make the layout easy to circulate and keep the signal as consistent as possible.
2. Centered around the core components of each functional unit, surrounding it for the layout. The components shall be uniformly, whole and compact on the PCB, minimizing and shortening the leads and connections between the components.
3. The circuit that works at high frequency should consider the distribution parameters between components. The general circuit should be arranged in parallel with the components as much as possible, so that it is not only beautiful, but also easy to install and mass production.



When PCB is designed, the following points should be paid attention to:

(1) the length of the tracing as short as possible to prevent the minimization of the lead inductance.
In low frequency circuits, the ground current of all circuits flows through the public grounding impedance or grounding plane, so avoid multi-point grounding.
(2) the public land line should be arranged on the edge of printed circuit board. The circuit board should retain as much copper foil as possible, which can enhance the shielding ability.
(3) the double board can be used with ground surface, and the purpose of the ground surface is to provide a low impedance geodesic.
(4) in the multi-layer printed circuit board, the strata can be set up and the strata are designed into a network.
The spacing of ground wire mesh cannot be too large, because a main function of ground wire is to provide the signal backflow path. If the spacing of the grid is too large, it will form a larger area of signal loop.
The area of the big loop causes radiation and sensitivity problems.
In addition, the signal reflux actually takes the path of small area, and other ground lines do not work.
(5) the groundline-plane can minimize radiation circulation.

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