How to ensure high performance design of PCB
With the rapid development of electronics and communication technologies, today's PCB design faces a completely new and different challenge. Mainly in the following aspects:
1. The edge rate of the signal is getting faster and faster, and the clock rate of the on-chip and off-chip is getting higher and higher. Now the clock frequency is no longer a few megabytes in the past. The clock of hundreds of megabytes is more and more common on the board. . Due to the rapid development of the chip process, the edge rate of the signal is also getting faster and faster, and the rising edge of the current signal is about 1 ns. This will lead to more prominent system and board level SI and EMC issues;
2. The integration scale of circuits is getting larger and larger, and the number of I/Os is increasing, which makes the density of single-board interconnections increase. As the functions become more and more powerful, the integration of circuits becomes higher and higher. The processing technology of the chip is also getting higher and higher. In the past, the DIP package almost disappeared on the current board, and the small-pitch BGA and QFP became the mainstream package of the chip. This increases the density of the PCB design.
3, product development and the time to market to reduce, so that we must face the severe challenges of one-time design success; time is cost, time is money. In the field where electronic products are updated so fast, the product opportunity window will be much larger one day before the product is available.
4. Since PCB is the physical carrier for product realization. In high-speed circuits, the quality of the PCB is related to the function and performance of the product. The same devices and connections, different PCB carriers, their results are different.
So, the design process is slowly changing. In the previous design, the design of logic function often accounted for more than 80% of the hardware development design, but now the ratio has been declining. In the current hardware design, only 50% of the logic function design is occupied, and the PCB design part also occupies. 50% of the time. Experts predict that in future designs, the hardware logic overhead will be smaller and smaller, and the overhead of high-speed PCB design such as development design rules will reach 80% or higher.
All of this is just an indication that PCB design will be the focus and the difficulty in current and future design.
In general, our PCB design focuses on the following points:
1, the realization of the function
2, stable performance
3, easy to process
4, the beauty of the veneer
The implementation of the function is the first step of our PCB. In the past design, because the signal edge rate and clock frequency are relatively low, as long as the logical connection is free of errors, the physical connection quality will not affect the performance of the use. But this view is not used in the current design. An example is a good indication of this:
Circuit board designers at a leading image detection system manufacturer in the United States have recently encountered a peculiar thing: a product that has been successfully designed, manufactured, and marketed seven years ago, and has been able to work very reliably and consistently. Recently, products that have been offline from the production line have had problems, and the products are not working properly.
Therefore, the true connection of logic does not make the function true. The quality of the physical connection is also the main condition for the implementation of the function.
The guarantee of performance depends on the design of the PCB. Everyone has experience. The same logical connections, the same devices, different PCBs, their performance test results are different. Good design is not only highly stable, but also through a variety of demanding tests. But an unsatisfactory design can't achieve this effect. In some low-end products, many manufacturers use the same chipset, and the logical connections are similar. The only difference is the level of their respective PCB design levels. The difference in products is mainly reflected in the design of the PCB.
The ease of processing is also an important indicator of the quality of PCB design. Good PCB design is easy to process, maintain, test, and manufacture. The quality of PCB is not only related to the production efficiency of PCB processing manufacturers and SMT manufacturers, but also closely related to our testing and debugging.
Beautiful and elegant is also an element of PCB design. The overall beauty and atmosphere make people feel comfortable when they see it. PCB is also a craft. A good PCB will make people stay in love.
PCB design is a comprehensive discipline, which is the product of quality, cost, time and so on. There is no best in PCB design, only better. In short, the design of high-speed PCB is a serious challenge in the field of system design today. Whether it is the design method, the design tool, the composition of the design team and the design ideas of the engineers, we need to actively and seriously deal with it.