In the electronics industry is driven by Moore's Law, the product more powerful, more integrated, faster and faster rate signal, the product development cycle is getting shorter, PCB design also entered the High-speed PCB design era. PCB no longer merely fulfills the function of interconnecting the carrier, but all electronic products as a very important component. In this paper, to achieve high-performance PCB design engineering point of view, a comprehensive analysis of the IT industry in all aspects of high-performance PCB design.
High-performance PCB design must first have a high-quality PCB design team.
A, PCB design team recommended the formation
Since entering the high-speed PCB design era, schematics, PCB design by hardware engineers solely responsible practices on gone, dedicated PCB engineers also emerged.
A mature large and medium-sized PCB design team composition should include the following types:
Package library Engineer: building a database of full-time, well-known in today's mainstream mill, patch vendor process capability, technical parameters, combined with the company's products, the actual, and accordingly the work of building a database to complete the PCB package under the current high-speed high-density conditions.
PCB Design Engineer: designers must have extensive knowledge surrounding PCB, such as basic knowledge of the basics of electronic circuits, PCB production, chip processing, DFX (DFM / DFC / DFT) design, but also need to have high-speed PCB stacking design, impedance design, signal integrity knowledge, EMC knowledge, considering the requirements of modern PCB design, PCB layout complete the wiring job.
SI Engineer: uncover hidden in the PCB transmission line in the "hidden schematic" face reflecting the high-speed era, crosstalk, timing issues. Before and after the simulation to ensure signal quality, improve the success rate of a product, PCB to ensure stable and reliable work.
EMC Engineer: As a source of EMC design considerations, is responsible for including circuits, devices, PCB board-level EMC design related. Reduce their external radiation and increase resistance to outside interference.
Thermal Design Engineer: In the pursuit of beautiful, small R & D team, the thermal design engineer indispensable. Analysis by heat distribution, rational design of duct systems, temperature control system to ensure stable and reliable work. Hard to imagine a notebook design team did not participate in the thermal design engineer can make a reliable and stable notebook products. (Note: some companies by the structural engineer and negative thermal simulation PCB thermal design).
Process Engineer: PCB processing for our vendors, process capability placement equipment / manufacturer, to develop the process parameters of the company's PCB design. Involved in specific boards, PCB design, PCB to ensure manufacturability, machinability.
Taking into account its own exchange, technology upgrading, backup personnel needs, each of these types of jobs, at least not less than three people. Group size is limited to its own R & D needs of larger companies and downs, appropriate reserves of some complex rounder and according to their needs is appropriate to seek external resources to solve their own research short planks wise.
We take a look at the IT industry giants PCB design team building process:
In 1980, the company's internal hardware engineers cater to PCB design;
1990, CAD engineers specialized departments gradually as independent;
In 1995, professional PCBDESIGNHOUSE became popular in North America, Japan
In 2000, the specialized division of labor is getting smaller, built libraries, PCB design, SI, EMC, thermal design, technology and other types of gradual independence; North America, Japan, more than 50% of the PCB design is completed by a professional design company; SI, EMC and other types of gradual self-contained;
In 2003, a Bo technology-led professional design companies to outsource PCB design concepts into China;
In 2008, a clear division within the company, complete trades. And reasonable uses of resources outsourcing, staggering design, technology outsourcing become the trend.
Second, the hardware necessary basis for the design of high-performance PCB
Since entering the high-speed PCB design era to the transmission line theory-based knowledge of signal integrity momentum overshadowed the hardware basics. It was suggested that the hardware design years later only the front and rear (front-end IC design refers to the backend refers PCB design). As long as there is a system engineer to integrate them about enough. It is very easy to learn basic knowledge of hardware necessity suspicion. In fact, whether engineers or PCB IC engineer must have, such as R, L, C, and basic knowledge of the gate.
Inseparable from the power of high-performance PCB design basics, ultimately, FPGA knowledge. Even if the signal integrity analysis based on transmission line theory but also from research to R, L, C-based micro-element to consider.
PCB design engineer must have a basic knowledge of the basic circuit, such as high-frequency, low frequency, digital circuits, microwave, electromagnetic fields and electromagnetic waves. Familiar with and understand the basic functions and basic knowledge of hardware design of products, is the basic condition to complete a high-performance PCB design.
Third, the high-performance PCB design challenges and works to achieve
PCB design is an art not only the best better, a good performance PCB design, are often faced with the following challenges.
A challenge. Development cycle
Statistics show that a laptop's design, from the project to the market, generally only half the time. A mobile phone R & D, from the project to the market, an average of only 3 months. Product development as an important part, PCB design time have gradually been compressed, compressed and then compressed.
April 1985, Tetsuya Mizoguchi Toshiba engineers devised a machine named T1100 pocket, leading to the rise of the computer industry. Since then, the computer's motherboard also significantly accelerate the development cycle rhythm.
Design cycles (days)
In EDADOC, notebook PCB design basic control in less than three weeks, the phone's PCB design time general customer expectations time is 10 days.
Facing the market is expected to continue to shorten the development, PCB engineers how to face this challenge?
First, the use of first-class EDA tools
Efficient EDA software tools to bring more than just efficiency, it is revolutionary design concept. Among the many EDA tools software, Cadence PSD series will undoubtedly occupy the role of industry flagship. From man operation 10 years ago, and later the "sub-drawing", to today's "partition", people CadenceAllegro originally designed to provide a parallel development cycle can not become a reality. In EDADOC, 92% of the PCB design will be used in parallel design.
Secondly, early intervention product development processes, reduce subsequent rework.
In the overall scheme design stage, PCB engineers involved in research and development that focus on participation in the system architecture design of products, demonstration; overall design stage, to carry out the initial PCB design feasibility assessment; during the detailed design phase, synchronous design principles involved in device selection, structural design, thermal design, so that when the R & D into the PCB design process, the main work will be simplified, while reducing the volume because the device is too large, the driving ability is not enough to bring the topological structure of the program is not feasible, and issues such as PCB thermal design process rework.
Third, "a board success" design philosophy
Senior Consultant IBM's R & D team has pointed out the existence of a domestic problem: "There is no time to do a one-time thing, but there is time to do the things I do," in the current market environment, has experienced PCB Design engineer, sound design process, and with a variety of software tools, and strive to a board success. Less to do more than just saving a PCB board costs, it is a whole process of saving development cycle. Window of opportunity to win the market for the product. Whether PCB engineers themselves, or product development manager, must have PCB R & D, "a board success" philosophy.
Finally, the module reuse, attention to technical precipitation
In a number of well-known companies I contacted, they attach great importance to the module reuse, ensuring technical precipitation, but also effectively shorten the PCB design time.
In short, we want the design concept, early intervention research, parallel design, the adoption of a board is successful, the idea of reducing the number of research and development, coupled with advanced software tools CadencePSD such, we do not need excessive overtime, but do not need two or even three classes PCB shifts can solve the problem of the development cycle.
2 Challenges costs
PCB costs include explicit and implicit costs
Explicit costs include the production of PCB, chip cost.
For the control of the dominant cost, we can be familiar with, understand the process requirements of conventional mill process capability, chip equipment, choose a reasonable number of layers, setting reasonable layered structure, the dominant design parameters to reduce the cost of PCB design.
Hidden costs including personnel during the PCB design inputs, technology risks, especially the opportunity cost of time cost listed on the window of opportunity.
In fact, the hidden costs of PCB design is far greater than the dominant cost.
For example, the general phone market window of opportunity is about six months, because of a problem if a PCB designed to increase research and development, mobile products for fashion is not just caused by the loss of 1-2 months time, it is failure of the entire product.
For the control hidden costs, company executives and R & D executives to have grasp the core, release peripherals, powerful combination, a successful concept, consider the cost of the initial design. Rational use of external resources to solve the problem of short planks own R & D, reduce the hidden costs of product development.
3 high-speed challenge
With the rising rate of the signal, signal integrity and constantly plagued by R & D personnel, including bus drive capability, signal reflections, crosstalk, overshoot, ringing, back to the ditch, attenuation; sometimes classified to the timing signal integrity range inside. Allegro Signoise IBIS simulation module based on the model, you can easily build a topology emulation.
Allegro simulation tools and wiring this platform has a good interface, after the PCB layout is complete, you can also extract directly from the PCB layout parameters to Signoise platforms to validate the simulation results after the wiring.
Simulation extracted routing constraints can be imported directly into the Allegro electrical rule manager, the manager can easily rule on the timing requirements of equal length constraints, in the wiring, when the length does not comply with the rules stipulated, Allegro in real time be alert.
4 Challenge density of
Let's look at a set of data:
In recent years, the device package changes:
Over the past 20 years the number of single device PIN IT industry as well as the total number of single-block veneer PIN changes:
Over the past 20 years in the IT industry veneer layers changes:
Over the past 20 years veneer PIN density (Pindensity, Pins / sqin): Changes:
Figure 5: Changes in the density of the board PIN
The above data which we can deeply feel more and more high-density PCB design pressure jumper from 20 years ago, fly the full board, to the later development of double sided, multilayer, to the device package of changes, as well as In recent years, the mobile phone industry to promote the rise of HDI technology, including the recent launch of the Intel Menlow platform, which takes HDI technology to the PC industry.
PCB design face rising density, PCB engineers must keep up with the industry's cutting edge, learn about new materials, new technology, can support high-density PCB design using first-class EDA software, so as to meet the product development process is facing increasingly high density challenge. Allegedly, the upcoming HDI PSD16.2 will be designed to have a major breakthrough, looking forward.
5 Challenges for power, ground noise
Power ground plane as a reference plane signal line, return channel, power, ground noise directly into its string signal reference plane. An important factor in problem solving power, ground noise, not only consider their own level and stable power supply problem, or solve the reliability problems of high-speed signals.
High-speed PCB design must first sort out the power supply tree, analyze supply channels reasonable.
First, the current carrying capacity of the wiring width must be allocated an appropriate margin in consideration of the premise; same time, since the actual circuit has a resistor with the voltage drop from the power output to the actual load on the route, and the high-speed circuit in particular core voltage of the device voltage often low, the pressure drop has a direct effect on the power supply. Current-carrying capacity, and the line width, inner and outer layers, copper thickness, allowing the temperature rise associated.
Secondly, in the power of the filtering effect, need to consider the impedance of the power supply. Because the power supply channel is actually not an ideal channel, but a resistance and impedance, high-speed power supply circuit requires the moment when the flip gate circuit, and the current from the power module to the various flip gate is needed to provide energy levels assigned path requires time, which is understood as a process of charging classification,
Figure 6: Flip the power supply path gate
You can see that at high frequencies, the current device pins on the first by the power ground plane consisting of a plate capacitor to power, because the power supply system composed by their resistance to a minimum. Supply the fastest, but this plate capacitor storage capacity is too small, they charge provided by a small filter capacitor, a small filter capacitor charge and then by the large energy storage capacitor provides BULK, then switch power to the capacitor through the current channel BULK charge, the reason for this is because the switching power supply only a few K at a frequency is low impedance, BULK capacitance at a frequency of only a few megabytes is low impedance, low frequency filter capacitor is only in the tens of megabytes to hundreds of megabytes of The following is a low-impedance current only through the layers of the charge, in order to reach the device pins, meet the needs of the instantaneous power. Cadence also provides a PI analysis module to analyze the impedance of the power consumption under different planes, and filter capacitor selection is reasonable.
The theoretical basis of the simulation tool is PI transmission line, using the finite element approach to the power plane to be divided, the power and ground planes corresponding to a pair of matching plate capacitor, and is divided into several areas, as shown:
Tools using frequency domain analysis approach, the impedance of the board to analyze the various pieces, and finally get each point impedance diagram:
If you find an area of resistance points above the target impedance, the power plane through the redistribution or increase the filter capacitor, reducing the target impedance at this point, and enhance the ability of the filtering device pins.
6.EMC question:
With the improvement of people's living standards and attention to include electromagnetic pollution, including environmental, EMC issue has become all electronic product development in the past does not turn around. As a "BlackMagic", EMC is increasingly plagued developers.
EMC design from the source. As a source of product EMC, EMC performance board / PCB increasingly cause for concern, many of the indicators in the EMC, most hardware engineers headache is RE indicators.
For restricted model, even if the industry recognized leading EMC simulation software, since it can not be simulated and actual test data that can be compared with data out. Radiation field which can only be given under certain specific conditions to simplify the distribution of a single radiation source, thus providing design.
EMC design experience so far mainly by EMC Engineer / Hardware Engineer to carry out the design. As engineering design, we do not make too much of the theoretical analysis, but we must have some general engineering design experience. The same time with some of the near-field probes and other auxiliary means to solve EMC problems. EMI Pictured physical space segment on the map by means of near-field probe measured RE targets and specific frequencies.
In the author's opinion, to the PCB board based EMC problems, we need to focus on the following three main areas:
1) Power
2) clock (and other strong radiation source)
3) interface circuit
Mention the power, we consider is the power (ground) issues as well as the integrity of the return channel power design;
Clock as the primary source of EMI board, bear more than 60% of the major sources of EMI;
Neglect any one interface design, EMC efforts throughout the product you are likely to come to naught.
As the project implementation, as long as the fuss around these three points, EMC issues throughout the product will succeed in sight.
7.DFM challenge
DFM problem solving, in addition to board our process engineers to develop appropriate technology standards, the need for PCB design engineers systematic and comprehensive DFM knowledge training, PCB engineers understand the need to keep the status quo PCB production and processing capacity of the industry, combined with the company's actual Choose an appropriate process route and design parameters. In terms of electrical performance and DFM choice, considering. In addition, the PCB footprint library, there must be a full-time staff of building a database to solve the problem from the source DFM.
Allegro has a dedicated building a database module, the device datasheet can easily design package library, as well as the pad package library. Good package design is based DFM design.
As a high-performance PCB design, these challenges are sometimes conflicting requirements, PCB design engineers need to fully utilize their experience, consider a compromise in the face of these challenges, to find an optimal combination of points, the final completion of a high-performance PCB design engineering achieved.
Fourth, we must first sharpen his tools
High-performance advanced PCB design is inseparable from the support of EDA tools. Cadence PSD series of powerful high-speed PCB design, the front and rear simulation module to ensure signal quality, improve the success rate of a product; using its physical, electrical rules, such as the difference can be realized intelligent routing, and so long control technical requirements; support concurrent design, shorten development time; support module reuse, attention precipitation technology to ensure the quality of design and improve design efficiency.
Having a high-performance EDA software tools, with experienced engineers, PCB design, high-performance PCB design implementation will have a tangible guarantee. As has more than 150 engineers, PCB design, EDADOC committed to high-speed, high-density, high-performance PCB design. Promote domestic high performance has become a vital force in the PCB design.
