Electronic Design - PCB design company decrypts circuit board design technology

Designing a circuit is a necessary hard work, but no matter how perfect the principle design is, if the circuit board design is unreasonable, the performance will be greatly reduced, and it may even not work properly in severe cases. Summarize the following points that should be paid attention to in PCB design, and I hope it will give you some enlightenment.

No matter what software is used, there is a general procedure for PCB design, which will save time and effort in order. Therefore, I will introduce it according to the production process. Schematic design is the preliminary work. I often see beginners directly draw in order to save trouble. PCB board, this will outweigh the gains. For simple boards, if you are proficient in the process, you can skip it. But for beginners, you must follow the process, so that on the one hand, you can develop good habits, and on the other hand, the only way to avoid mistakes for complex circuits.

When drawing a schematic diagram, pay attention to the final connection of each file into a whole when designing the hierarchy, which is also of great significance for future work. Due to differences in software, some software may appear to be connected but not connected (in terms of electrical performance). If you don’t use related testing tools, in case something goes wrong, it’s too late to find out when the board is ready. Therefore, the importance of doing things in order has been repeatedly emphasized, and I hope to attract everyone's attention.

The schematic diagram is based on the designed project, as long as the electrical connection is correct, there is nothing to say. Below we focus on the problems in the specific board-making procedures.

One, make the physical border

The closed physical frame is a basic platform for the future component layout and routing, and it also plays a constraining role for the automatic layout. Otherwise, the components coming from the schematic will be at a loss. But you must pay attention to accuracy here, otherwise installation problems in the future may be troublesome. In addition, it is best to use arcs at the corners. On the one hand, it can avoid sharp corners from scratching workers, and at the same time, it can reduce the effect of stress. In the past, one of my products always had the PCB board of the face shell broken during the transportation process, and it was just fine after switching to the arc.

2. The introduction of components and networks

It should be very simple to draw the components and the network in the good frame, but there are often problems here. You must carefully solve the errors one by one according to the prompts. Otherwise, it will take more effort. The problems here generally include the following:

The package form of the component can not be found, the component network problem, there are unused components or pins, these problems can be solved quickly by comparison.

Third, the layout of the components

The layout and wiring of the components have a great impact on the life, stability, and electromagnetic compatibility of the product, so special attention should be paid. Generally speaking, there should be the following principles:

(1) Placement order

First place the components related to the structure at a fixed position, such as power sockets, indicator lights, switches, connectors, etc. After these components are placed, use the LOCK function of the software to lock them so that they will not be moved by mistake in the future. Then place special components and large components on the circuit, such as heating components, transformers, ICs, etc. Finally, place the small device.

(2) Pay attention to heat dissipation

Particular attention should be paid to heat dissipation in the component layout. For high-power circuits, the heating elements such as power tubes, transformers, etc. should be placed as close to the side as possible to facilitate heat dissipation. Do not concentrate in one place, and do not have high capacitors too close to avoid premature aging of the electrolyte.

Four, layout wiring

The knowledge of wiring is very advanced, everyone will have their own experience, but there are still some common layout wiring principles.

▪ High-frequency digital circuit traces should be thinner and shorter.

▪ The isolation between high current signal, high voltage signal and small signal should be paid attention to (the isolation distance is related to the withstand voltage, under normal circumstances, the distance between the board should be 2mm at 2KV, and it will be increased in proportion to this. For example, if you want to withstand the 3KV withstand voltage test, the distance between the high and low voltage lines should be above 3.5mm. In many cases, to avoid creepage, slots are also slotted between the high and low voltages on the printed circuit board.)

▪ When wiring two panels, the wires on both sides should be perpendicular, oblique, or bent to avoid parallel to each other to reduce parasitic coupling; printed wires used as the input and output of the circuit should be avoided as far as possible. In order to avoid feedback, it is best to add a grounding wire between these wires.

▪ The corners of the routing should be greater than 90 degrees as much as possible, avoid corners below 90 degrees, and use 90-degree corners as little as possible.

▪ The same address line or data line, the length of the trace should not be too different, otherwise the short line part will have to be artificially bent for compensation.

▪ The trace should be placed on the soldering surface as much as possible, especially the PCB with through-hole technology.

▪ Use as few vias and jumpers as possible.

▪ Single-panel pads must be large, and the lines connecting the pads must be thick, and teardrops can be placed when teardrops can be placed. The quality of general single-panel manufacturers will not be very good, otherwise there will be problems with soldering and RE-WORK.

▪ A large area of copper should be covered with a grid to prevent bubbles and bending of the board due to thermal stress during wave soldering. However, in special occasions, the flow direction and size of the GND should be considered. You cannot simply fill the matter with copper foil., But it needs to be routed.

▪ The components and traces should not be placed too close to the side. The general single-sided boards are mostly paper boards, which are easy to break after being stressed. If they are connected or placed on the edge, they will be affected.

▪ The convenience of production, debugging and maintenance must be considered.

It is very important for analog circuits to deal with the ground problem. The noise generated on the ground is often inconvenient to predict, but once it is generated, it will bring great troubles. For the power amplifier circuit, extremely small ground noise will have a significant impact on the sound quality due to the amplification of the subsequent stage; in the high-precision A/D conversion circuit, if there is a high-frequency component on the ground wire, a certain temperature drift will occur. The work of the amplifier. At this time, you can add decoupling capacitors to the 4 corners of the board, one pin is connected to the ground on the board, and the other pin is connected to the mounting hole (connected to the housing by screws), so that this component can be taken into account, and the amplifier and AD are also It's stable.

Five, adjustment and perfection

After completing the wiring, all you need to do is to adjust the text, individual components, wiring, and apply copper (this work should not be too early, otherwise it will affect the speed and bring trouble to the wiring), also for the convenience of production, Commissioning and maintenance.

Six, check the network

Sometimes the network relationship of the board drawn is different from the schematic diagram due to misoperation or negligence. At this time, it is necessary to check and verify. Therefore, after drawing, you must not rush to hand it to the PCB manufacturer, you should check it first, and then do the follow-up work.

Seven, use the simulation function

After completing these tasks, software simulation can be carried out if time permits. Especially for high-frequency digital circuits, some problems can be found in advance, which greatly reduces the amount of debugging work in the future.