How to Design a Printed Circuit Board (PCB) Reasonably?
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If the design of the printed circuit board is unreasonable, even if the components are assembled correctly, the expected work effect will not be achieved. This article will specifically introduce the method of rational design of printed circuit boards.
If the wiring of the printed circuit board is not properly designed, even if all the components of the complete working schematic are interconnected, the product may not work as expected in the end. Then there are many things that need to be paid attention to in the design of printed circuit boards. The following is a reasonable design method for printed circuit boards.
Take a look at the visible traces on the PCB in general. These will be covered by solder resist, which is a thin layer of lacquer-like polymer, covering the copper traces to prevent oxidation and short circuits.
This layer is usually green, but other colors can also be used. Please note that the white solder mask tends to make the traces the hardest to see. In most cases, just use standard green.
In addition, only the top and bottom layers are actually visible, and if the board has more than two layers, you will not see the inner layers. Nevertheless, reviewing only the external layer should still provide some clues about the quality of the design.
Check whether all traces extend in straight segments without sharp bends. Sharp angles can be troublesome for certain high-power and high-frequency traces.
The location of the decoupling capacitor is very close to the power pin of the chip to filter out any high-frequency noise, so as not to have a negative impact on the chip. Generally, if a chip has multiple VDD pins, each such pin needs at least one decoupling capacitor, and sometimes more.
The physical location of these decoupling capacitors should be very close to the pins to which they should be decoupled. If this does not happen, its effect will be greatly reduced.
If your PCB design does not place a decoupling capacitor next to the power pins of most microchips, then this indicates that the design is incorrect.
PCB trace length
In designs that require precise timing relationships between multiple signals, the length of the PCB traces must match. For example, this is critical when routing high-speed clock signals to multiple chips or data and address buses that run between a microprocessor and RAM memory.
This ensures that all signals arrive at their destinations with the same delay, thus preserving the relationship between signal edges. This requires access to the schematic and knowing which set of signal lines requires precise timing relationships.
Then, follow the trace to see if a certain trace length equalization (called a delay line) has been achieved. These delay lines usually look like curved lines.
Note that vias in the signal path will cause additional delay. If these problems cannot be avoided, please check all traces that require precise timing relationships and make sure they have the same number of vias. Alternatively, you can use a delay line to compensate for the delay caused by the via.
If your design includes a radio transmitter, receiver, or transceiver (transmitter and receiver combined), it must have an antenna.
For best performance, the feed line between the radio frequency (RF) pins on the RF chip should match the impedance of the feed line connected to it. In turn, the feeder must match the impedance of the antenna. In order to maximize the power transfer between the antenna and the radio chip, this impedance matching is necessary.
Any mismatch will result in a reduction in the actual transmission power, thereby reducing the operating range. The feeder is just a PCB trace with a controlled impedance that matches the antenna impedance (usually 50Ω).
If the output impedance of the transmitter does not match the impedance of the feeder, a matching network composed of inductors and capacitors is usually used. In order to achieve controlled impedance, the feeder is a PCB trace whose calculated width extends on the ground plane. The width of the trace depends on the thickness of the copper trace, the thickness of the PCB substrate, and the dielectric constant.
In addition to placing decoupling capacitors, there are other considerations for placing components on the circuit board.
(1) If the circuit contains inductors, they should not be placed too close. The inductance generates a magnetic field. Placing them closely together, the especially end-to-end connection may cause unnecessary coupling between them.
(2) In addition, inductors should not be placed near large metal objects. The magnetic field induces a current in these objects, which changes the value of the inductor.
(3) Toroidal or toroidal inductors are usually not easy to generate stray magnetic fields, so their influence is small. If it is unavoidable to place the inductors close together, they should be placed perpendicular to each other to reduce unnecessary mutual coupling.
(4) If there are power resistors or any components that generate a lot of heat on the circuit board, you need to consider the effect of heat on other nearby components.
(5) If the circuit contains an onboard switching regulator, all components related to it should be physically located on a part of the PCB and as far away as possible from the part that handles small signals. These tend to produce obvious switching noise, which will have a negative impact on noise-sensitive circuit parts.
(6) If the PCB is directly applied with AC power to the power supply part, the AC side should be located in a part of the circuit board.
Trace width and routing
The size of the traces carrying large currents should be adjusted appropriately. Due to noise pickup issues, traces carrying small analog signals should not be parallel to traces carrying digital or rapidly changing signals.
Similarly, in general, the traces connecting the inductors should not exceed the required width. They may work like antennas and generate harmful radio frequency emissions.
For any moderately complex PCB, it is best to use at least a four-layer board, with two inner layers for power and ground.
If the design contains both analog and digital parts, the ground plane should be separated and connected only at the common point (usually the negative pole of the power supply). This can prevent the large ground current spike from the digital part from adversely affecting the analog part.
If only two layers are used, the wiring of each sub-circuit ground loop should be separated, and then all of them should be connected to the negative terminal of the power supply.
If you want to design a PCB with good performance, you must avoid the above possible design errors. If you want to learn more about printed circuit boards after reading the above content, you can get a more comprehensive solution by contacting us.
As a professional PCB product manufacturer, we have accumulated rich production and design experience in this field. We have a professional production team that manufactures in full accordance with strict standards and can provide customers with safe and high-quality products. We can also provide corresponding customized services and professional solutions according to customer needs. If you want to buy our printed circuit boards, please contact us immediately!