PCB is short for Printed Circuit Board. In general, a conductive pattern made of a printed circuit, a printed assembly, or a combination of the two is formed on a dielectric material in a predetermined manner and is referred to as a printed circuit.PCB was born in 1936 and was used in a large number of military radio by the United States in 1943.Since the mid-1950s, PCB technology has been widely adopted. At present, PCB has become the "mother of electronic products", its application is almost infiltrated in the various terminal areas of electronics industry, including computers, communications, consumer electronics, industrial control, medical equipment, defense industry, aerospace and many other areas. So, how does the PCB design out?
It should include component libraries and schematics. Before PCB design, you must firstly prepare the schematic SCH component library and the PCB component package. The PCB component package is best built by the engineer based on the standard size of the selected devices. In principle, the PC component package library should be established before the schematic SCH component library.
The requirements of PCB component package library are higher, which directly affects the PCB installation; though schematic SCH component library are relatively loose, you still need notice the correspondence of pin properties and PCB components package library.
2. PCB structure design
According to the board size and mechanical positioning, drawing PCB frame in design environment, and placing connectors, buttons/switches, screw holes and assembly holes based on the positioning requirements. Additionally, you should fully consider and determine the wiring and non-wiring area (the scope around the screw hole is the non-wiring area).
3. PCB layout design
Layout design is the component placement on the PCB board frame in accordance with the design requirements. You can create a net list in the schematic tool which can be imported into the PCB software
. After that, the net list will exist in the software background where all the part pins are suggested for connection through the placement operation, and then the component layout can be designed.
As the first important process in PCB design process, PCB layout design will affect the degree of difficulty to achieve the later wiring, especially for those more complex ones.
What’s more, the layout design relies on the knowledge and experience from designers, thus it has a higher level of requirements for the circuit board designers. The primary circuit board designer is suitable for the design tasks of small module and low difficulty.
4. PCB wiring design
PCB layout design is of the largest workload in the PCB design, directly affecting the performance of the PCB board.
In the design process, PCB wiring generally has several meanings:
Routing comes first as it is the most basic entry requirement of PCB design;
The electrical performance follows, which is a standard to measuring whether a PCB board is qualified. You should carefully adjust the wiring after routing so that it can achieve the best electrical performance;
Last but not least, you should ensure the PCB board is neat and clean instead of chaotic wiring. Otherwise, it will be troublesome for the late board optimization, testing and maintenance even if the electrical performance is good. Hence, you must confirm the wiring is uniform.
5. Wiring optimization and silk screen display
There are several sayings like "There is not the best PCB design except better", "PCB design is a defective art", which is mainly because the PCB design aims to achieve all aspects of hardware design requirements, while the conflicts may exist between them.
For example, a PCB project is designed into a 6-layer board through the circuit board designer, but a 4-layer board may be the final choice considering cost. So, the signal shield has to be sacrificed, resulting in increased signal crosstalk and reduced signal quality between adjacent wiring layers.
The general design advice is that the optimizing time is as twice as the initial wiring. After PCB layout optimization, you should take the post-processing including the treatment of silk screen logo. The silk screen characters in the bottom layers are required to be mirror-imaged, avoiding the confusion with top silk screen.
6. DRC and structural inspection
Quality control is an important part of PCB design process, the general quality control methods include: design self-test, design mutual inspection, expert review meeting, and special inspection, etc.
Schematic diagram and structural elements are the most basic requirements; network DRC and structural inspection are two input conditions for respectively confirming the PCB design meet the schematic net list and structural elements.
Generally, the circuit board designers will have their own accumulation of design quality checklist; some are from the specifications of company or department, others may come from their own experience. Special inspection includes the Valor and DFM inspection, which is concerned about the processing Gerber files from PCB design output back-end.
7. PCB Manufacturing
Before formal board processing, the circuit board designers need to communicate with PE in PCB board suppliers, replying to the manufacturers on the PCB board problems. This should include but is not limited to: PCB board model selection, adjustment of line width and spacing, impedance control adjustment, PCB stacking thickness adjustment, surface treatment processing technology, and aperture tolerance control and delivery standards.