1. Correctness

This is the most basic and crucial requirement for printed circuit board design. We should connect the relationship of the electrical schematic diagram and avoid the two simple and fatal mistakes of "short circuit" and "open circuit". This basic requirement is not easy to achieve in manual design and PCB design with simple CAD software. Usually, products have to go through more than two rounds of trial production and modification. CAD with strong functions has ability to ensure the integrity of electrical connections.

2. Reliability

This is the higher requirement in PCB design. A printed circuit board may look good, but reliability can't be ensured. For example, unreasonable board material selection, incorrect board thickness and installation, improper layout and wiring of components may all lead to issues.

Here's another example. Multi-layer boards are much easier to design than single- and double-sided boards, but they are not as reliable as these two. From this perspective, the simpler the structure, the smaller the use area. The fewer the number of board layers, and the higher the reliability.

3. Rationality

This is a more complicated principle in PCB design. Rationality is important to a printed circuit board assembly from manufacturing, inspection, assembly, commissioning to the assembly, commissioning of the whole machine, use and maintenance.

For example, if the board shape is not well selected, it is difficult to process. It is difficult to assemble if the lead hole is too small. It is difficult to leave no pilot height, and it is difficult to maintain if the connection outside the board is improperly selected, etc. Every difficulty can lead to increased costs and longer working hours.

Of couse, every cause of difficulty stems from design error. There is no absolutely rational design, only a process of continuous rationalization. It requires the designer's sense of responsibility and rigorous style, as well as the experience of constantly summarizing and improving in practice.

4. Economy

It's not difficult, but not so easy. That's interesting. You can choose a low price board. The size should be as small as possible. The connection is made of direct soldering wires. The surface coating is the cheapest, and the processing plant with the lowest price is selected.

However, don't forget that these cheap options may cause poor manufacturability and reliability, increase manufacturing costs and maintenance costs. The overall economic efficiency may not necessarily be resolved, so it is "not easy". "Must" is the principle of market competition. Competition is ruthless, and a product with advanced principles and high technology may die due to economic reasons.

Other tips for designing

There must be a reasonable direction. We are talking about input/output, AC/DC, strong/weak signal, high frequency/low frequency, high voltage/low voltage, etc. They must not blend with each other. The purpose is to prevent mutual interference. The best direction is a straight line, but it is generally not easy to achieve. The most unfavorable direction is a circle. Fortunately, isolation can be set to improve. For DC, small signal, and low voltage PCB design requirements can be lower.

Choose a good grounding point. It's impossible to overstate the importance of grounding point. Generally speaking, a common ground is required. For example, multiple ground wires of the forward amplifier should be merged and then connected to the trunk ground, etc. It is difficult to do it completely due to various restrictions, but we should try our best to follow it. This problem is quite flexible in practice. Everyone has their own set of solutions.

Only a few power filter/decoupling capacitors are drawn in the schematic diagram. However it is not indicated where they should be connected. In fact, these capacitors are set for switching devices (gate circuits) or other components that require filtering/decoupling. Arrange these capacitors as close as possible to these components.