In electronic design, PCB is the physical carrier of our design content, and the final realization of all our design intentions is represented by PCB. Such PCB design is an indispensable link in any project.
However, in the previous design, due to the low frequency, low density and large distance between devices, PCB design was designed for the purpose of connectivity, without any other functional and performance challenges. So for a long time, the position of PCB design in the whole project is very low. Usually, the physical connection of PCB is made by the designer of hardware logic connection. At present, some small products still have this development mode.
With the rapid development of electronic and communication technology, today’s PCB design is facing a completely different and brand-new challenge. Mainly in the following aspects:
1. The edge rate of the signal is getting faster and faster, and the on-chip and off-chip clock rates are getting higher and higher. Now the clock frequency is no longer a few megabytes in the past, and hundreds of megabytes and gigabytes of clocks are becoming more and more common on single boards. With the rapid development of chip technology, the edge rate of signal is getting faster and faster. At present, the rising edge of signal is about 1ns. This will lead to more prominent problems of system and board level SI and EMC;
3. The time for product research and development and marketing is decreasing, which makes us have to face the severe challenge of successful one-time design; Time is cost, and time is money. In the field of electronic products, where the upgrading is particularly fast, the earlier the product comes out, the bigger the profit opportunity window will be.
4. Because PCB is the physical carrier of product realization. In high-speed circuits, the quality of PCB is related to the function and performance of products. The same devices and connections, different PCB carriers, their results are different.
So, now the design process has been slowly changing. In the past, the design of logic function often accounted for more than 80% of hardware development and design, but now this proportion has been declining. At present, the design of logic function only accounts for 50% of hardware design, and the design of PCB also accounts for 50% of the time. Experts predict that in the future design, the cost of logic functions of hardware will be smaller and smaller, while the cost of developing design rules and other high-speed PCB designs will reach 80% or even higher.
All of these just show that PCB design will be the key and difficult point in present and future design.
Generally, our PCB design mainly focuses on the following points:
1. Realization of functions
2. Stability of performance
3, the simplicity of processing
4. The veneer is beautiful.
The realization of functions is the first step of our PCB. In the past design, due to the low signal edge rate and clock frequency, as long as there is no error in logical connection, the quality of physical connection will not affect the performance of use. But this view is not used in the current design. There is an example to illustrate this point:
The circuit board designers of a famous American image detection system manufacturer recently encountered a strange thing: a product that was successfully designed, manufactured and put on the market seven years ago has always been able to work very stably and reliably, but the product that recently rolled off the production line has problems, and the product can’t run normally.
Therefore, the true connection of logic can’t make the function true. The quality of physical connection is also the main condition for the realization of functions.
The guarantee of performance depends on the design of PCB. Everyone knows this point. The same logical connection, the same device, and different PCBs have different performance test results. Good design not only has high product stability, but also can pass various demanding tests. However, it is impossible to achieve such an effect if the design is not ideal. In some low-end products, many manufacturers use the same chipset, and the logical connections are similar. The only difference is the level of PCB design, and the difference of products is mainly reflected in the design of PCB.
The ease of processing is also an important index of PCB design. Good PCB design is convenient for processing, maintenance, testing and manufacturing. The quality of PCB is not only related to the production efficiency of PCB manufacturers and SMT manufacturers, but also closely related to our convenience of testing and debugging.
Elegance is also an important factor in PCB design. The overall beauty and atmosphere make people feel comfortable when they see it. PCB is also a handicraft. A good PCB will make people linger.
PCB design is a comprehensive subject, which is the product of the coordination of quality, cost and time. There is no best in PCB design, only better. In a word, the design of high-speed PCB is a serious challenge in today’s system design field. No matter the design method, the design tools, the composition of the design team and the design ideas of engineers, we should actively and seriously deal with it.
