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Double PCB board layout design steps

2019-05-20

The double-layer PCB is a type of multilayer board, and there are still a large number of devices used in circuits where the degree of circuit integration is relatively simple. As a PCB engineer, the PCB design companies on the market now generally require that the number of layers be more than 6 layers. Before mastering the design of the multilayer board more than 6 layers, it is best to learn the progressive painting method, that is, 2-4-6 layers.

Due to the double layer board, the circuit board has wiring on both sides. Therefore, there must be a small hole in the middle that is full of metal or coated with metal, that is, a guide hole. The vias connect two layers of wires for current and signal transmission. In the placing position of the components, it is recommended that the DIP components that do not have special requirements when drawing the PCB are placed on the top layer by default. The pads are placed on multiple layers by default, and the SMD components and pads are placed on the top layer or the bottom layer.

Double PCB Board layout design steps

First, you need to prepare the circuit schematic, then create a new pcb file and load the component package library and the planning circuit board. The network tables and components are loaded into the EDA software using component auto-layout tools, and manual layout adjustment of network density analysis is performed after completion. Next, you can use the auto-route tool to manually adjust the wiring for more special lines.

Double PCB board signal line wiring

After the two-layer board is drawn in the EDA software, the next step is to design the power cable, sensitive cable, high-frequency cable, and low-frequency cable. The critical lead is preferably a separate power supply, ground loop, lead and very short, so sometimes a ground wire is placed close to the signal line on the edge of the critical line to allow it to form a minimal working loop.

The signal line of the double layer board is the signal line of the key crystal, crystal oscillator circuit, clock circuit, CPU, etc. First, the principle that the circulation area is as small as possible must be observed. When the PCB's IC circuit works, many references are made to the circulating current area. Actually, its source is in the concept of differential mode radiation. Such as the definition of differential mode radiation: the circuit operating current flows in the signal loop. This signal loop generates electromagnetic radiation. Since this current is differential mode, the radiation generated by the signal loop is called differential mode radiation. There is a formula for the field strength: It can be concluded that the radiation field strength in the circuit space γ of E1---differential mode copying board printed board can be seen by the differential mode radiation formula, the radiation field intensity and the working frequency f2, circulation area A, the working current I is proportional to, such as when the operating frequency f is determined, the size of the circulating current area is a key factor that can be directly controlled in our design, while circulating current speed, current as long as the reliability is satisfied, not the bigger the better, the signal jumps The narrower the jump edge along the next, the greater its harmonic components, the wider the electromagnetic radiation, the greater the power, the greater the current, which we do not expect.

Below are given several kinds of logic circuit that can meet the circulating current area reference value allowed by the radiation class B standard. It can be seen that the faster the circuit switching speed, the smaller the allowable area. The key link, if possible, is surrounded by ground wires. After the wiring of the PCB copying board is completed, all the voids can be covered by the grounding wire, but it must be noted that these covered grounding wires should be short-circuited with the low-resistance conglomerates of the large strata, and this can achieve good results.

Two-layer PCB board general wiring skills

In general, we use automatic routing for efficient work. In most cases, automatic routing will not cause problems for purely digital circuits, especially for low-frequency signals and low-density circuits. However, when trying to use the auto-wiring tools for analog, mixed signal, or high-speed circuit wiring, some problems may arise, and it may cause extremely serious circuit performance problems. There are many things to consider when wiring. The biggest problem is grounding. If the grounding path starts from the upper layer, the grounding of each device is connected to the ground via a pull wire on the layer. For each device in the lower layer, a ground loop is formed by connecting the through hole on the right side of the circuit board to the upper layer. The immediate red flag that you see when you examine the wiring method indicates that there are multiple ground loops. In addition, the underlying ground loop is at a horizontal position. This reduces the effect of digital switching δi/δt on analog circuits. However, it should be noted that these two dual-layer boards have a ground plane on the lower layer of the circuit board. This is designed to allow engineers to quickly see the wiring when troubleshooting, and this method often appears on the device manufacturer's demonstration and evaluation board. But the more typical approach is to lay the ground plane on the top of the circuit board to reduce EMI.

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