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The basic principles and operation of PCB wiring

    With the rapid development of high-speed theory, PCB wiring can not be regarded as a simple interconnection carrier, but the transmission line theory should be used to analyze the influence of various distribution parameters.Now the complexity and density of PCB are also increasing, from the copper through-hole design to the micro-hole design, and then to the multi-stage buried blind hole design,buried resistance and buried volume.High density to the PCB wiring with a great difficulty at the same time, also need PCB design engineers more in-depth understanding of PCB production process and its process parameters.

    PCB wiring is divided into automatic wiring and manual wiring, automatic wiring can not meet the high standards of requirements in many ways,so it is generally manual wiring to achieve the DFM requirement.

1. Drilling

1) Mechanical drilling conventional recommended above 8mil, limit 6mil, try to ensure that the ratio between thicknessis and drilling in the 10: 1, the higher the ratio, the more difficult to process. Device hole annular ring should be more than 8mil per side, via annular ring should be at least 4mil per side, PCB manufacturer will optimize the working gerber,and the solder mask opening will be larger than the PAD 2-3mil per side.

2) The spacing between via to via can be 6mil for the same network,and 12mil for the different network.The spacing between device PTH to device PTH shoule be 16.8mil for the different network.

3) Generally speaking,the drill bit is larger than the original drill diameter 0.1mm, the drill bit is increasing in size of 0.05mmand then after the PTH and plating,the finish hole diameter will be the same as customer requirement.

4) Because there is a tolerance +/-0.13~+/-0.2mm of the outline, so the spacing of the NPTH to the outline edge shoule be more than 6mil so that the NPTH will not be broken, PTH to the PCB outline edge should be more than 10mil.

2. Etching

1)  0.5oz finish copper thickness, min. line width/space canl be 2.8/2.5mil;

2)  1oz finish copper thickness, min. line width/space can be 3.5/4mil;

3)  2oz finish copper thickness, min. line width/space can be 4/5.5mil;

4)  To aboid the PCB bow and twist,PCB wiring should be evenly distributed;

3. Impedance control and impedance continuity

1) Avoid sharp angle or right angle wiring;

2) As little as possible to use via for the key signal wiring;

3) High-speed signal line to consider the appropriate arc wiring;

4. Crosstalk or EMC and other interference control requirements

1) High-speed signal and low-speed signal to be layered partition wiring;

2) Digital signal and analog signal to be layered partition wiring;

3) Sensitive signal and interference signal to be layered partition wiring;

4) The key signal is to be distributed in the preferred layer,use the ground layer as the reference plane;

5) Any signal, including the return path of the signal, must avoid the formation of a loop, which is one of the important principles of EMC design;

5. Power supply and power signal wiring requirements

1) Power supply inlet circuit to do the principle of post-protection filtering;

2) Chip and its filter capacitor pins should be as short as possible, storage capacitor should be increase the hole design, reduce the inductance which bring by the PCB wiring;

6. Consider the heat in the wiring

1) Calculation of the wiring channel strictly to meet the current requirements;

2) Concerned about the current carrying capacity of the via, a reasonable distribution of the via number and location;

3) If under the chip with large heat, it can be added plane copper in a large area which without copper design to strengthen the heat dissipation;

4) In the high-power heat device area,please do not design high-speed lines and sensitive signal lines in all layers;

5) Add vias to the thermal pad to enhance heat dissipation;

Article from Shenzhen Vip Circuit Co.,Ltd

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