PCB Tech - High-quality PCB design should pay attention to the disk

In high-quality PCB design, reasonable component layout is the basic prerequisite for designing high-quality PCB diagrams.

1. Component layout

The requirements for component layout mainly include six aspects: installation, force, heat, signal, and aesthetics.

1.1. Installation

Refers to a series of basics proposed in order to smoothly install the circuit board into the chassis, shell, slot, etc., without space interference, short circuit and other accidents, and make the designated connector in the designated position on the chassis or shell under specific application occasions. Require. I won't repeat it here.

1.2. Force

The circuit board should be able to withstand various external forces and vibrations during installation and work. For this reason, the circuit board should have a reasonable shape, and the positions of various holes (screw holes, special-shaped holes) on the board should be arranged reasonably. Generally, the distance between the hole and the edge of the board should be at least greater than the diameter of the hole. At the same time, it should be noted that the weakest section of the plate caused by the special-shaped hole should also have sufficient bending strength. The connectors that directly "extend" out of the device shell on the board must be reasonably fixed to ensure long-term reliability.

1.3. Heated

For high-power devices with severe heat generation, in addition to ensuring the heat dissipation conditions, they should also be placed in appropriate locations. Especially in sophisticated analog systems, special attention should be paid to the adverse effects of the temperature field generated by these devices on the fragile preamplifier circuit. Generally, the part with very large power should be made into a module separately, and certain thermal isolation measures should be taken between the signal processing circuit and the signal processing circuit.

1.4. Signal

Signal interference is the most important factor to be considered in PCB layout design. The most basic aspects are: the weak signal circuit is separated or even isolated from the strong signal circuit; the AC part is separated from the DC part; the high frequency part is separated from the low frequency part; pay attention to the direction of the signal line; the layout of the ground line; proper shielding and filtering And other measures. These have been repeatedly emphasized in a large number of treatises, so I won't repeat them here.

1.5. Beautiful

It is not only necessary to consider the neat and orderly placement of components, but also the beautiful and smooth wiring. Because ordinary laymen sometimes emphasize the former more in order to one-sidedly evaluate the pros and cons of the circuit design, for the image of the product, the former should be given priority when the performance requirements are not harsh. However, in high-performance occasions, if you have to use a double-sided board, and the circuit board is also encapsulated in it, it is usually invisible, you should give priority to the aesthetics of the wiring.

2. PCB wiring principle

The following is a detailed introduction to some uncommon anti-jamming measures in the literature. Taking into account that in practical applications, especially in the trial production of products, a large number of double panels are still used, the following content is mainly for double panels. Avoid right angles when turning, and try to use diagonal or arc transitions.

The wiring should be neat and orderly, arranged in a centralized manner, which can not only avoid the mutual interference of signals of different natures, but also facilitate inspection and modification. For digital systems, there is no need to worry about interference between signal lines (such as data lines, address lines) in the same camp, but control signals such as read, write, and clock should be independent, and it is best to use ground protection. stand up.

When laying a large area (discussed further below), try to keep a reasonable and equal distance between the ground wire (actually should be the ground "plane") and the signal wire, and try to be as close as possible under the premise of preventing short circuit and leakage.

For the weak current system, the ground wire and the power wire should be as close as possible.

For systems using surface mount components, the signal lines should be routed to the front as much as possible.