PCB News - Discussion on PCB Evaluation Skills in PCB Design

PCB evaluation skills talk: see which factors you need to pay attention to
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, design implementation, product testing, and whether electromagnetic interference (EMI) meets the requirements. It is possible to reduce the repetition of the 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 product 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 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:

I. Interaction between schematic and PCB layout

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

Iii. Precise DRC checker

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

I.HDI (High Density Interconnect) interface

Ii. Flexible design

Iii. Embedded passive components

Iv. Radio Frequency (RF) Design

V. Automatic script generation

Vi. Topological placement and routing

Vii. 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 leadership of the industry and has devoted more effort than other manufacturers, can help you design products with the greatest efficacy 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 tool that designers are looking for depends on the complexity of the 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 design process. However, too many design constraints have restricted the flexibility of design. Designers must have a good understanding of their design and its rules, so that they know when to use these rules.

A typical integrated system design from front to back. It starts with the design definition (schematic input), which is closely integrated with constraint editing. In constraint editing, the designer 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 design definition, it is also linked to FPGA/PCB integration. The purpose of FPGA/PCB integration is to provide two-way integration, data management, and the ability to perform collaborative design between FPGA and PCB.

The same constraint rules for physical realization are entered during the layout phase as during the design definition. This reduces the probability of errors in the process from file to layout. Tube exchange, logic gate exchange, and even input and output interface group (IO_Bank) exchange all need to be returned to the design definition stage for update, so the design of each link is synchronized.

During the evaluation period, designers must ask themselves: What criteria are critical to them?

Let’s take a look at some trends that force 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 common today 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.RF design

For RF design, the RF circuit should be directly designed as a 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" design. Therefore, the differences between the data models and the resulting design conversion problems will disappear. First, designers can directly interact between system design and RF simulation; second, if designers perform a large-scale or quite complex RF design, they may want to distribute circuit simulation tasks to multiple computing platforms running in parallel, or They want to send each circuit in a design composed of multiple modules to their respective simulators, thereby reducing 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 be designed with high precision, 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, all factors that affect the assembly process must be considered. A designer 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 design to ensure that the design points will not cause the conductor to break and peel off due to the stress of the bending 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 design and decide whether your product allows you to create a rigid flexible 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.

The type of typical design problems encountered in a parallel bus and serial-to-parallel conversion design. The limitation of parallel bus design lies in system timing changes, such as clock skew and propagation delay. Due to the clock skew on the entire bus width, the 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 design issues have arisen. 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 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 the loss effects of IC packages, PCB boards, cables and connectors.

6. The practicality of the design kit

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