PCB News - What factors should be paid attention to in the PCB evaluation process

For articles on PCB technology, the author can elaborate on the challenges faced by PCB design engineers in recent times, because this has become an indispensable aspect of evaluating PCB design. In the article, you can discuss how to meet these challenges and potential solutions; when solving PCB design evaluation problems, the author can use Mentor's PCB evaluation software package as an example.

As a researcher, what I consider is how to integrate the latest advanced technology into the product. These advanced technologies can be embodied in excellent product functions, but also in reducing product costs. The difficulty lies in how to effectively apply these technologies to products. There are many factors to consider. The time to market is one of the most important factors, and there are many decisions around the time to market that are constantly updated. There are a wide range of factors that need to be considered, including product functions, PCB design and implementation, product testing, and whether electromagnetic interference (EMI) meets the requirements. It is possible to reduce the repetition of PCB design, but it depends on the completion of the previous work. Most of the time, it is easier to find problems in the later stages of the product PCB design, and it is more painful to make changes to the problems found. However, although many people know this rule of thumb, the actual situation is another scenario, that is, many companies know that it is important to have a highly integrated PCB design software, but this idea is often compromised by high prices. This article will explain the challenges faced by PCB design and what factors should be considered when evaluating a PCB design tool as a PCB designer.

The following are the factors that PCB designers must consider and will affect their decision:

1. Product function

A. Basic functions covering basic requirements, including:

A. Interaction between schematic and PCB layout

B. Wiring functions such as automatic fan-out wiring, push-pull, etc., and wiring capabilities based on PCB design rules constraints

C. Precise DRC checker

B. The ability to upgrade product functions when the company is engaged in a more complex PCB design

A. HDI (High Density Interconnect) interface

B. Flexible PCB design

C. Embedded passive components

D. Radio Frequency (RF) PCB Design

E. Automatic script generation

F. Topological placement and routing

G. Manufacturability (DFF), Testability (DFT), Manufacturability (DFM), etc.

C. Additional products can perform analog simulation, digital simulation, analog-digital mixed signal simulation, high-speed signal simulation and RF simulation

D. Have a central component library that is easy to create and manage

2. A good partner who is technically in the industry’s leadership and devotes more effort than other manufacturers, can help you design PCB products with the greatest efficiency and leading technology in the shortest time

3. Price should be the most important consideration among the above factors. What needs more attention is the rate of return on investment!

There are many factors to consider in PCB evaluation. The type of development tools that PCB designers are looking for depends on the complexity of the PCB design work they are engaged in. As the system is becoming more and more complex, the control of physical wiring and electrical component placement has developed to a very wide range, so that it is necessary to set constraints for the critical path in the PCB design process. However, too many PCB design constraints have restricted the flexibility of PCB design. PCB designers must have a good understanding of their PCB design and its rules, so that they know when to use these rules.

A typical integrated system PCB design from front to back. It starts with the PCB design definition (schematic input), which is closely integrated with constraint editing. In constraint editing, PCB designers can define both physical constraints and electrical constraints. The electrical constraints will be analyzed before and after the layout of the network verification drive simulator. Take a closer look at the PCB design definition, it is also linked with FPGA/PCB integration. The purpose of FPGA/PCB integration is to provide two-way integration, data management, and the ability to perform collaborative PCB design between FPGA and PCB.

In the layout stage, the same constraint rules for physical realization are entered during the PCB design definition. This reduces the probability of errors in the process from file to layout. Pin swapping, logic gate swapping, and even input-output interface group (IO_Bank) swapping all need to return to the PCB design definition stage for updates, so the PCB design of each link is synchronized.

During the evaluation, PCB designers must ask themselves: What standards are critical to them?

Let’s look at some trends that force PCB designers to re-examine the features of their existing development tools and start ordering some new features:

1.HDI

"The increase in the complexity of semiconductors and the total amount of logic gates has required integrated circuits to have more pins and finer pin pitches. It is commonplace to design more than 2000 pins on a BGA device with a pin pitch of 1mm, not to mention arranging 296 pins on a device with a pin pitch of 0.65mm. The need for faster and faster rise times and signal integrity (SI) requires a larger number of power and ground pins, so it needs to occupy more layers in the multi-layer board, thus driving the high level of micro-vias. The need for density interconnection (HDI) technology.

HDI is an interconnection technology being developed in response to the above-mentioned needs. Micro vias and ultra-thin dielectrics, finer traces and smaller line spacing are the main features of HDI technology.

2. RFPCB design

For RFPCB design, the RF circuit should be directly PCB designed into the system schematic diagram and system board layout, and not used in a separate environment for subsequent conversion. All the simulation, tuning and optimization capabilities of the RF simulation environment are still necessary, but the simulation environment can accept more primitive data than the "real" PCB design. Therefore, the differences between the data models and the resulting PCB design conversion problems will disappear. First, PCB designers can directly interact between the system PCB design and RF simulation; secondly, if PCB designers perform a large-scale or quite complex RFPCB design, they may want to distribute the circuit simulation tasks to multiple calculations running in parallel Platform, or they want to send each circuit in a PCB design composed of multiple modules to their respective simulators, thereby shortening the simulation time.

3. Advanced packaging

The increasing functional complexity of modern products requires a corresponding increase in the number of passive components, which is mainly reflected in the increase in the number of decoupling capacitors and terminal matching resistors in low-power, high-frequency applications. Although the packaging of passive surface mount devices has shrunk considerably after several years, the results are still the same when trying to achieve the maximum density. The technology of printed components makes the transition from multi-chip components (MCM) and hybrid components to SiP and PCBs that can be directly used as embedded passive components today. In the process of transformation, the latest assembly technology was adopted. For example, the inclusion of a layer of impedance material in a layered structure and the use of series termination resistors directly under the uBGA package greatly improve the performance of the circuit. Now, embedded passive components can obtain high-precision PCB design, eliminating the need for additional processing steps for laser cleaning of welds. Wireless components are also moving in the direction of improving integration directly in the substrate.

4. Rigid flexible PCB

In order to design a rigid flexible PCB for PCB, all factors that affect the assembly process must be considered. PCB designers cannot simply design a rigid flexible PCB like a rigid PCB, just as the rigid flexible PCB is just another rigid PCB. They must manage the bending area of the PCB design to ensure that the main points of the PCB design will not cause the conductor to break and peel off due to the stress of the curved surface. There are still many mechanical factors to consider, such as minimum bend radius, dielectric thickness and type, metal sheet weight, copper plating, overall circuit thickness, number of layers, and number of bends.

Understand rigid flexible PCB design and decide whether your product allows you to create a rigid flexible PCB design.

5. Signal integrity planning

In recent years, new technologies related to parallel bus structure and differential pair structure for serial-to-parallel conversion or serial interconnection have been continuously advanced.

Figure 2 shows the types of typical PCB design problems encountered in a parallel bus and serial-to-parallel conversion PCB design. The limitation of parallel bus PCB design lies in system timing changes, such as clock skew and propagation delay. Due to the clock skew over the entire bus width, PCB design for timing constraints is still difficult. Increasing the clock rate will only make the problem worse.

On the other hand, the differential pair structure uses an exchangeable point-to-point connection at the hardware level to realize serial communication. Usually, it transfers data through a one-way serial "channel", which can be superimposed into 1-, 2-, 4-, 8-, 16-, and 32-width configurations. Each channel carries one byte of data, so the bus can handle data widths from 8 bytes to 256 bytes, and data integrity can be maintained by using some forms of error detection techniques. However, due to the high data rate, other PCB design issues are caused. Clock recovery at high frequencies becomes the burden of the system, because the clock needs to quickly lock the input data stream, and in order to improve the anti-shake performance of the circuit, it is necessary to reduce the jitter from cycle to cycle. Power supply noise also creates additional problems for PCB designers. This type of noise increases the possibility of severe jitter, which will make eye opening more difficult. Another challenge is to reduce common mode noise and solve the problems caused by loss effects from IC packages, PCB boards, cables and connectors.

6. Practicality of PCB designkit

PCB designkits such as USB, DDR/DDR2, PCI-X, PCI-Express and RocketIO will undoubtedly help PCB designers to enter the field of new technologies. The PCB designkit gives an overview of the technology, a detailed description, and the difficulties that PCB designers will face, followed by simulation and how to create wiring constraints. It provides explanatory documents together with the program, which provides PCB designers with an opportunity to master advanced new technologies.