Ten PCB circuit board design questions and answers

PCB technology is very complex, involving many aspects of the problem, whether in the design stage or the production stage, I believe there will be a lot of problems to be answered.

Take you to understand, PCB circuit boarddesign technology ten frequently asked questions.

1, the design of a system containing DSP, PLD, from which aspects to consider ESD?

A: In terms of the general system, the main consideration of the body directly in contact with the part, on the circuit and the mechanism for appropriate protection. How much impact ESD will have on the system depends on the situation.

2. In EMC test, it is found that the harmonic of the clock signal exceeds the standard seriously. Only the decoupling capacitor is connected on the power pin. What aspects should be paid attention to in the design to suppress electromagnetic radiation?

A: The three elements of EMC are radiation source, transmission route and victim; The transmission channels are divided into space radiation transmission and cable conduction. So to suppress harmonics, first look at the way it travels. Power decoupling is the solution to conduction-mode propagation, in addition, the necessary matching and shielding is also required.

3. In the products designed with 4 layers of circuit boards, why are some surface paved and some are not?

A: The role of paving: 1, shielding; 2, heat dissipation; 3. Reinforce; 4. Technological processing needs. No matter how many layers of board paving, first of all to look at its main reason. Here we are mainly talking about high speed. Surface paving is good for EMC, but the copper paving should be as complete as possible to avoid islands.

4, frequency more than 30M plate, the use of automatic wiring or manual wiring?

Answer: Automatic or manual wiring depends on the support of software wiring function. Some wiring may be better than automatic wiring, but some wiring, such as check wiring, bus delay compensation wiring, automatic wiring effect and efficiency will be much higher than manual wiring.

5, in the design, the ground is usually divided into protective ground and signal ground; Power ground is divided into digital ground and analog ground, why to divide the ground wire?

A: The purpose of dividing the ground is mainly due to EMC concerns that the digital part of the power supply and ground noise will interfere with other signals, especially analog signals through the transmission path. No matter how divided, the final earth is only one.

6, in the cloth clock, is it necessary to add ground wire shield on both sides?

Answer: Whether to add shielding ground wire should be decided according to the crosstalk /EMI situation on the board. If the shielding ground wire is not handled well, it may make the situation worse.

7. What are the corresponding countermeasures for distributing clock lines of different frequencies?

A: For the wiring of the clock line, it is best to carry out signal integrity analysis, formulate the corresponding wiring rules, and carry out wiring according to these rules.

8, single-layer boardmanual wiring, how to represent the jumper?

A: The jumper is a special device in the design, only two pads, the distance can be fixed length, can also be variable length. Manual wiring can be added as required. There will be a straight line on the board, the material sheet will also appear.