Tool Report article 2

The Need for a Web-Based High-Speed PCB Design System by Myoung Jin, Ph.D.

The Problem

Escalating demands on high performance and miniaturization have increased the complexity and clock speed of electronic equipments. With faster clock speed, the system performance becomes much more sensitive to the physical makeup of interconnects. Due to advancements of semiconductor technologies, it is now commonplace for the microprocessor chips inside desktop computers to run at more than 1 GHz. However, the hard-to-solve high-speed effect on interconnects still limits the system-level clock speed to around 300 MHz, which results in a huge performance gap between IC and system levels. Interconnects at the PCB and system level are now the limiting factor to greater system performance. In order to develop high performance products, it is essential to reduce the performance gap between the IC and system levels by achieving maximum performance from the PCB interconnects.

This increased design complexity and the difficulties of resolving the high-speed design issues result in added design iterations. To improve the design-to-manufacturing process and meet market competition, these design iterations must be reduced, but the electronics industry is impeded by a number of stumbling blocks:

Inefficient Communication Among Design Team Members

Design team members communicate with each other through meetings, e-mail and teleconferences. Although the Internet has a great potential for managing the design projects and improving communication, collaboration and data exchanges among geographically dispersed design team members, e-mail is the most widely used. But e-mail is inadequate because it does not tightly link together the engineers, buyers, suppliers and subcontractors to let them work in unison on design projects.

Sequential Design Process

Traditionally, the electronic design process has been sequential: logic design, physical design, analyses, prototyping and testing. If problems are found in a later stage of the design, the design team needs to go back to an earlier stage to resolve the problem. When the clock speed was lower, this design process worked well because the physical makeup of the PCB and system did not affect system performance very much, and the PCB was easier to manufacture. With greater clock speed and design complexity, it becomes much harder to resolve the high-speed design and manufacturing issues in the later stages of the design, which results in more design iterations. In order to eliminate or reduce the design iterations, multiple engineering disciplines must participate in the design process as early as possible and work in parallel throughout the design process.

The Need for a Web-Based High-Speed PCB Design System Continued…

Fragmented Design Tools and Databases

EDA tools have been developed to support each function of the sequential design process. Unfortunately, EDA design and validation tools are fragmented and each relies on its own proprietary database, which supports only the functionality of that tool. When the design process is moved from one tool to another for the next stage, only the data absolutely needed for input is passed to the new tool. Most of the intelligence used for design decisions is not passed to the tools employed later. This lack of communication among tools requires duplicated manual data entries and prevents the tool users from accessing all intelligent data used for previous design stages, which is needed to make correct decisions at the current design stage.

Design and Validation Tools Being Expert-Oriented

Each EDA tool is designed for use by experts, have many features, and be as stand-alone as possible. It takes a lot of effort to become an expert in using the tool, so unless their primary job function is using a particular tool, designers tend to be wary of it. This prevents the tool user from getting direct input on design constraints and parameters from other engineers and effectively sharing data with them.

Analysis Tools Separated from Design Tools

Analysis tools are involved in validating the physical designs through computer simulations; they include the tools for thermal, structural, signal integrity, EMI/EMC and manufacturing analyses. These tools are for the engineering specialists and are not integrated into the design tools, so the analyses cannot be done promptly during the design and after changes are made. Unfortunately, these tools are mostly employed after the design is completed, and this results in costly design iterations.

Use of Generic Parts

Generic part data is used with both schematic design and PCB layout tools - for the logical symbols and the package and footprint data, respectively. The actual manufacturer-specific parts are usually determined at the final stage of the design, mostly by the purchasing people. The parts with identical logical functions and package types can differ in the packaging materials, physical dimensions, power dissipation, and electrical characteristics of the IC and package, depending on the manufacturer. Use of the generic part data prevents the physical design validations from being employed in early design stages, which contributes to costly design iterations.

Expensive Design Software and Hardware

The fragmented EDA tools are expensive and run on expensive hardware. They're usually offered on a perpetual license or yearly lease. Although demand for the tool varies widely, the user ends up paying for peak usage. It's difficult to switch to a better tool later because of the interoperability problem among tools and the significant investment already made in the current tool.

Lack of Experts in High-Speed Design

As more and more electronic designs move to high speed, there is an acute, industry-wide shortage of experts to deal with high-speed design issues. Hiring experts such as signal integrity and EMC engineers is expensive and difficult. Many companies try to resolve their high-speed design issues by having non-experts learn the signal integrity and EMC analysis tools, usually without much success.

The Solution

Clearly, a need has long existed for an Internet-based design environment with a PCB design system that would eliminate these troublesome problems. Facilitated by a DESP (design environment service provider), this new type of system would support collaborative parallel design processes that allow multiple engineering disciplines to participate throughout the design process. With the participation of multiple engineering disciplines, design and engineering issues are resolved in the early stages, thus reducing design time, increasing product quality, and cutting product cost.

Deployed entirely on the Web, this new design environment/PCB design system would enable:

• Integrated communication and design/data management
• A unified design database
• Common tools for multiple engineering disciplines
• Interfaces to third-party EDA tools
• Complete design and validation tools
• Automatic generation of high-speed design constraints
• Embedded analysis capabilities
• A tight link to manufacturing
• Redlining and mark-up
• Online document and support
• A cost-effective delivery/license model
• Expert services

The Need for a Web-Based High-Speed PCB Design System Continued…

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 Figure 1
A Universal Design Environment captures project and parts management, design collaboration, as well as partners, suppliers, and customers into a single Web-based environment.

Integrated Communication and Design/Data Management

This aspect of the Web-based PCB design environment would work with other system components for peer-to-peer communication, design data sharing, and server-based design management and part data management. This provides an environment for a geographically dispersed team of design engineers, engineering specialists, purchasing people, suppliers, subcontractors, and contract manufacturers to effectively communicate with each other and manage the design and design data.

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 Figure 2
A Unified Design Datafile is critical to capturing the logical, physical, manufacturing, and simulat ion data in the PCB design process. A Universal Design Environment provides multiple-discipline part icipation early and throughout the process.

Unified Design Database

A unified design database would address the problems resulting from the fragmented EDA design and validation tools and would be accessed by tools that can be commonly used by multiple engineering disciplines. A single Java binary jar file could be used to store the entire data of a PCB design needed to support a suite of design and validation activities throughout the design cycle. It would contain the design constraints, materials, parts, schematic (logical) design data, physical layout data, and the analysis parameters, models and simulation results of thermal, signal integrity, EMI and manufacturing analyses.

Stored on the unified design database would be:

• General Information -- identifiers and key attributes of the design, e.g., design name, version number, when last updated, and length unit.
• Schematic Design Data -- schematic drawing, part list and net list.
• Material Data -- names and electrical and thermal properties of materials used for the PCB and interconnects.
• Part Data -- data of entire parts used for the design, e.g., part name, manufacturer, functional type, description, and datasheet link URL, logic symbol, package and footprint data, placement and routing constraints, thermal properties, and electrical properties of each pin.
• Board Properties -- outline, cutouts, placement boundary, routing boundary, and layer stack-up data.
• Design Constraints -- electrical, thermal boundary, component placement, routing, and manufacturing constraints from various sources.
• PCB Layout Data -- locations of the placed components and the shapes and locations of the traces, vias, pads, and planes of the routed board.
• Manufacturing Drawing -- silkscreen and assembly top and bottom drawings for use in PCB manufacturing.
• Parameters and Models, with Analysis and Simulation Results -- for thermal, signal integrity, power/ground, EMI/EMC and manufacturing.

Common Tools for Multiple Engineering Disciplines

Employing the unified design database and easy-to-use Java GUI, the PCB design system would allow multiple engineering disciplines to learn the tools quickly and commonly use them for specifying design constraints, designing, validating the designs, and making design changes through dynamic collaborations. The engineering specialists directly access the design tools and data, working on the design instead of passing data to design engineers in the form of design constraints and hoping the design engineers take care of all these constraints. These commonly usable tools would permit multiple engineering disciplines to participate in the design at early design stages and work in parallel throughout the design process.

The Need for a Web-Based High-Speed PCB Design System Continued…

Interfaces to Third-Party EDA Tools

Companies that have already invested heavily in EDA tools and design methodologies cannot quickly adopt new ones. Accordingly, it's important for them to be able to use their existing EDA tools -- e.g., Cadence, Mentor and Innoveda -- in parallel with the new system via bi-directional interfaces.

Coexisting with other EDA tools, the new system could be most effectively used at the front end to resolve the design and engineering issues early in the design stage. This includes part selection, specifying design constraints, determining the board layer stack-up, placing components, routing critical nets, performing thermal validation, and running pre-design signal integrity analysis to obtain high-speed routing constraints. The partially completed design data is passed to other PCB layout tools for the final layout.

The system could also be used effectively for validating design and correcting problems for designs completed in other EDA tools.

Complete Design and Validation Tools

The ideal PCB design system would include a complete, modular design and validation tool set, with all modules operating on a common database to eliminate the need for duplicated data entries throughout the system. For physically designing and validating PCBs, one module could be used for either creating a new design from scratch or for bringing in completed or partially completed designs in other EDA tool data formats; this design data could also be output into other EDA tool data formats.

Other modules would include:

• Part Editor -- for creating, viewing, and editing data of manufacturer specific parts; importing part data in third-party EDA tool formats; and producing part data in third-party EDA tool formats.
• Material Editor -- for creating, viewing and editing data of materials used for PCBs and interconnects.
• Device Modeler -- for creating, viewing and editing driver, receiver, and terminator models of individual package pins used for signal integrity and EMI/EMC validations, with support for the linear, IBIS and transistor-level Spice models.
• Schematic Capture -- for schematic design; support of hierarchical designs; and bi-directional interfacing to EDIF 300.
• System Level SI -- for constructing system level net list and performing signal integrity analysis.
• Power Integrity Analysis -- for simultaneous switching noise and power-drop/ground-bounce analyses and for EMI/EMC calculations.

Automatic Generation of High-Speed Constraints

With faster clock speed, interconnection problems -- such as timing delays, reflections, signal distortions, cross-talk noises, simultaneous switching noises, and electromagnetic radiations -- increase exponentially. Resolving these high-speed design problems requires eliminating impedance mismatches throughout the signal paths and tightly controlling the routing paths. As a result, the high-speed design constraints would come in the form of trace width to use for each signal layer, pin ordering, maximum stub length, maximum driver pin to receiver pin wiring length, and others.

Most EDA tools now allow the user to specify the high-speed design constraints. But the real difficulty is how to get the constraints. Usually, signal integrity specialists are employed for obtaining the high-speed design constraints through some simple calculations or complex computer simulations. With the ratio of critical nets, requiring the high-speed design constraints, to the entire nets of a typical PCB design exceeding 80 percent now, obtaining the constraints becomes a daunting task.

With embedded electromagnetic and signal integrity simulators, the new PCB design system would be capable of automatically producing the high-speed design constraints via three major functions:

• Termination Analysis -- Analyzes unrouted nets to see that the termination of the nets' signals have been adequately addressed, assuming the nets are routed with the target line impedances. If a termination problem is detected for a net, the system returns with a recommendation on the termination method and the value to use.
• Layer Stack Optimization - Enables the user to vary the PCB layer structure by selecting the location, material and thickness of each signal, dielectric, power and ground layer and to quickly see the electromagnetic effect on the traces and vias. The user can even let the system find the trace width of each signal layer to match the actual trace line impedance with the target line impedance of individual net. Also, the user can quickly arrive at the PCB layer structure and trace and via sizes that eliminate the impedance mismatch problems.
• Pre-Design Signal Integrity Analysis -- Generates routing constraints of individual nets after determining the PCB layer structure and the trace and via sizes to use for each signal layer. Through simulations, the routing constraints are obtained from converting the electrical design constraints of the nets to the physical design constraints.

The Need for a Web-Based High-Speed PCB Design System Continued…

Embedded Analysis Capabilities

The thermal, signal integrity, power/ground, EMI and manufacturing analysis capabilities would be embedded in the new PCB design system. Each design decision made throughout the design process could be validated almost immediately with the use of built-in analysis capabilities, and analysis results are instantly available to all design team members.

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 Figure 3
An integrated design process - which incorporates project and parts management, design, and validation - improves the performance, reliability, and manufacturability of PCBs. Thermal, signal integrity, and power/ground bounce analyses are an integral part of both the process and the design data.

With the analysis parameters and models set up by engineering specialists, the analysis runs could be performed by anyone. For subsequent minor design changes, the design engineer would run the analyses for the validation without having to call the engineering specialists. This reduces the design time and frees the engineering specialist to support more designs. When the design engineers have greater exposure to the analyses, they can make better design decisions with their newly acquired engineering knowledge.

Tight Link to Manufacturing

Miniaturization and increased complexity cause additional problems in the manufacturing of electronic products, and these need to be resolved during the design stage. The new PCB design system would allow users to address manufacturing issues throughout the design process by using manufacturer parts, entering manufacturing constraints, performing manufacturing analysis, creating manufacturing drawings such as silk-screens and assembly drawings, outputting manufacturing data files such as Gerber and Valor ODB++ files, and planning the PCB paneling with the use of a built-in panel editor.

Redlining and Mark-Up

The system would also allow users to redline and mark-up on the drawings, tables and graphs displayed by the system, including the selection of colors, line widths and font sizes. Combined with the original drawings, texts and graphs, the redlining and mark-up data is stored in separate files for later viewings. This capability could be well utilized for exchanging design and design change ideas among design team members.

Online Document and Support

Users of the new PCB design system would always be connected to the DESP servers, which would provide constant online link between the DESP and its customers. The user always has access to the user manuals and application notes offered online, and the updated online documents are instantly available to all users. While using the applications, the user can instantly send inquiries and bug reports to the DESP and receive instant help in return.

Cost-Effective Delivery/License Model

The ideal PCB design system would be offered as a true floating license on a monthly subscription basis depending on maximum simultaneous accesses. There would be no hardware node-lock, and access to the system would not limited to specific users. Moreover, the subscription could be varied from month to month to reflect the expected usage requirements.

A monthly subscription would allow a user rights of access to all the design and validation capabilities within the system, unlike the multiple, separate licenses currently required by other EDA vendors for each individual tool. The system's EDA applications would run on the client machines, thus allowing the intellectual properties of designs to remain behind the customer's firewall; reducing delivery costs; and preventing the system performance from being degraded by increased simultaneous user access.

The Need for a Web-Based High-Speed PCB Design System Continued…

Expert Services

While designing high-performance electronic products requires collaboration among many multiple engineering disciplines, many companies do not have all the engineering experts needed. The DESP that administers the Web-based PCB design system could also address this problem by offering professional services, such as:

• Part Data Service - This service takes the customer's order online and delivers the complete package and footprint data of manufacturer's parts that can be used for the PCB layout and manufacturing validations. As a result, the customer's cost for creating the part data internally is greatly reduced.
• PCB Routing Service -- Unrouted or partially routed PCB designs are taken online and returned with completely routed PCB designs that satisfy the routing and manufacturing constraints the customer established within the PCB design system. This service eliminates the customer need to have board designers and expensive PCB layout tools in-house.
• Signal Integrity Specialist Service - The DESP-provided signal integrity specialist becomes a member of the customer's design project team and works on resolving high-speed design issues throughout the design process. The Web-based system enables the specialist to work on the customer designs without ever meeting with the other design project members. The service could be offered on a monthly contract, renewable for subsequent months.
• Thermal Analyst Service - The DESP-provided thermal analyst becomes a member of the customer design project team and works on determining thermal requirements and thermal boundary conditions of the design and resolving thermal problems throughout the design process. With this service as well, the PCB design system would enable the specialist to work on the customer designs without ever meeting with the other design project members and could be offered on a renewable monthly contract.

Summary

The foregoing scenario may seem like pie in the sky, but with the advent of DESPs such as Syncron Technologies and solutions like their new Universal Design Network, the Web-based design environment has become a reality, helping PCB designers solve the hard issues that have long plagued them. The pie is down from the sky, ready to be sliced up and enjoyed by all members of the design engineering team -- wherever on Earth they may happen to be.

Myoung Jin is chief technical officer at Syncron Technologies, a recently launched DESP focused on process innovation in the design-to-manufacture of high-speed electronic products. Dr. Jin has more than 15 years of experience in developing leading-edge EDA solutions. As head of technology for Pacific Numerix, he developed a wide range of highly accurate automated design and analysis software tools that provided a cost-effective way to validate electronic designs.