vol 8, issue 7

Printed circuit board design tools

15 July 2013
By Caroline Hayes
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A multi-coloured PCB graphic

PCB design tools are offering enhanced functionality and flexibility

DesignSpark screen shot

RS Components provides DesignSpark free and hopes that users source components from the distributor

A sheet of PCBs being held up

The requirement for PCB design aids has grown rapidly

Multisim screen shot

The Multisim SPICE simulation environment focuses on the prototyping and simulation

Zuken screenshot

Zuken's CR-8000 offers the versatility of input modes and 2D and 3D views of the PCB

Printed circuit boards now need to come in all shapes and sizes – and so the computer-based tools available to design them have to offer enhanced flexibility and functionality.

To many they are the unsung heroes of electronic devices. Printed circuit boards (PCBs) play an important role in devices and equipment from automotive, military and defence to aero, transportation and industrial products. PCBs route the electrical signals between components and connect the analogue and RF circuits in such a way that the electrical signals are passed efficiently to operate the functions as the technology designer intended.

The challenge met by designers now is how to squeeze more functionality into a smaller space. Every new smartphone requires more memory and more processing capability to fulfill enhanced data functions, but now in a smaller end-product.

As a result, the PCBs inside are smaller and multi-layered. "With the increasing performance and density of silicon, it is not uncommon for a design team to put double the functionality in a smaller form factor than a design from just a year ago," observes David Wiens, business development manager of the systems design division at Mentor Graphics, whose PADS (personal automated design system) entry-level PCB design tool is a long-established market contender.

In addition to the increase in power potentially causing integrity problems, the design has to be ready for manufacture at an attractive cost. Both of these aspects come down to board design. "PCBs now have to deliver over 20 voltage rails to power-optimised integrated circuits, generating fragmented power distribution networks and a power integrity nightmare," Wiens explains.

The company's own data indicates that over the last five years, average layer counts have reduced 12 per cent, the average area has decreased 35 per cent, while the average number of pins per square inch has increased 15 per cent. "Trade-offs between system performance, manufacturability and costs occur daily," adds Wiens.

Everything has to be done in the same time – or shorter – as the last revision. Adding to the pressure is the fact that, especially in consumer products, being second to market can mean the difference between establishing a dominating position and ending up scratching for sales amid low-value leftovers.

Market value

The PCB design and analysis market was valued at $600m in 2012 according to figures released by the EDA Consortium, the trade association of tools and services companies for the electronic design automation industry. PCB tools is one of the fastest-growing segments of EDA, with a compound annual growth rate of 6-7.5 per cent.

The growth is international. Companies like Sony, Samsung, and Panasonic are strengthening their positions in mobile and consumer markets, while the Americas, the US in particular, remain strong, with Europe a respectable contender.

In fact, in real terms the market has not really seen a downturn since the financial crisis hit the market in 2009, maintains Bhavesh Mistry, general manager, National Instruments, Toronto, Canada. Steve Chidester, head of international marketing at Zuken (the only PCB tool vendor headquartered in Japan) even discounts 2008/09, saying there have been no significant downturns since the mid-to-late 1980s. Based on 2011 figures, the latest available, industry analyst Gary Smith places Zuken with 19 per cent market share, behind Mentor Graphics which commands 41 per cent, and Cadence a close third with a market share of 16 per cent.

The grand scheme

The driving force for today's PCB design tools is to design and produce a board that is 'right first time', and that can be manufactured easily, cost-effectively, and in the shortest timeframe. Bhavesh Mistry breaks down the role of PCB design tools into three parts: schematic capture, simulation, and layout.

Schematic capture tools create the design by picking components from a list and placing them on the design scheme. Electrical rules are added, and the electrical connection between devices on a board is checked.

Simulation tools check signal integrity, magnetics, and physics; or they manipulate the model with SPICE (Simulation Program with Integrated Circuit Emphasis).

This general-purpose, open-source analogue electronic circuit simulator was originally developed by University of California at Berkley in 1969 and simulates the board's performance, e.g. what happens when a diode is placed in a position or when one methodology is used over another. Chip manufacturers like Texas Instruments (TI), Infineon, and Analog Devices, have all developed SPICE models to define their components' performances for use in design tool environments. The layout tools design and lay out circuits and packaging, ready for manufacture.

Checking the integrity of circuits and predicting circuit behaviour before the design is a physical entity makes the board closer to 'right first time'. Bhavesh Mistry estimates that every redesign costs $2,000 to $5,000 plus five days of production – "and that is before the revision is tested again".

Simulation is a key part of National Instruments' Multisim, a schematic capture and SPICE simulation environment for low-frequency circuit designs. The tools simulate the interaction of amplifiers, diodes and other components on the board. They also check signal integrity, magnetics, and physics at the board level. Layout tools can take into account packaging restrictions; for example, the low profile of slim phones. Multisim also performs routing and design considerations for using RF.

Introductions change the real-world specifications. The so-called 'Internet of Things' is causing specifiers to re-evaluate board design, says Hemat Shah, product marketing director, at Cadence Design Systems. In the connected world, data has to be accessible wherever and whenever it is requested. This takes a lot of memory to store and a lot of processing horsepower to deliver.

"PCBs with a better power delivery system will enable the battery to run for longer," Shah reasons. "Battery analysis and power analysis for the whole system lets designers create efficient power management. More power within a confined space, mean that thermal issues also have to be looked at."

To reflect the diversity of design teams, Cadence provides Allegro PCB Designer for medium-sized groups, although it can scale to complex designs with options for specific features, such as miniaturisation or high-speed designs. It also has real-time checking for assembly. At the other end of the scale are OrCAD tools for small, or even single-person design teams. OrCAD Lite is a pared-down version, which is a free download for individual designs or prototypes.

A free market

The free design-tool concept is embraced by distributor RS Components, which makes its DesignSpark schematic capture and PCB layout tool available to download gratis. Launched in July 2010, it is now on its fifth edition, and has many of the features found in expensive tools, says the company's head of application strategy Martin Keenan.

Over 165,000 downloads of the tool have been activated, mainly by small-to-medium enterprises where the majority of designs use simple cable connections and are used in controller boards in vehicles and motor control in industrial equipment. Used in larger companies for prototyping, and in education, the tool can be also used in sophisticated designs too, claims Keenan, citing electro-hydro controllers for vehicles, ECU (engine control units) as well as medical and satellite systems.

April 2013 saw the introduction of version 5.0, which introduces support for digital buses in the schematic section and a real-time design rule checker. Traditionally, platforms cannot simulate both analogue and digital parts together allowing design errors to accumulate, or cascade, and manifest in the physical prototype. The result is that the PCB will need to be reworked at considerable cost and with delays to the design schedule.

In 2011, 3D visualisation was included, distinguishing DesignSpark as a free tool that was distinctly 'on-trend'. A 3D view provides an insight into the speed and how the functions work together, particularly in multiple board designs. Zuken's Steve Chidester describes it as the means to "make sure you are not putting 6lb in a 5lb can". The company's CR-8000 release has a native 3D environment, and can switch between 2D and 3D within the same environment.

Inter-board tracing views

Most importantly, 3D allows the design engineer to see how the system traces from one board to another as well as the route to package. "Routing on different layers can be viewed, for example – the model can be turned on its side to watch both traces being routed," says Chidester. Similarly, if another board layer is needed, it can be added without having to rework the whole board, using the 3D view.

This links in part to a trend identified by David Wiens: systems-aware engineering. "We are fond of saying that ICs don't float in space (that's to say that the package and PCB they sit on are a critical component of the overall system). Likewise, PCBs don't float in space either, they integrate with other boards, via connectors, wires and cables and are enclosed by a tight-fitting mechanical assembly." Design teams have to collaborate across the system, from IC to package, to PCBs to enclosures, to optimise performance, space, cost, and design efficiency.

All of the tools discussed operate on minimum hardware requirements, typically 500Mb/s, but 2Gb/s at most, despite the graphics and the multi-threading capabilities. They all run on 32-bit or 64-bit Microsoft Windows, some also run on Linux. The universality reflects the ubiquitous nature of PCBs.

They exist, with varying degrees of complexity, in products in industry to automotive, consumer to computing, telecoms to military/aerospace, and space. Design tool companies seem to be meeting the challenges of the diverse markets with zeal. A zeal matched only by the innovation of designers using the tools, whether hobbyist or members of international teams in large corporations.

Further information

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Product briefing – National Instruments: Multisim

Multisim from National Intruments (NI) 12.0 has special editions for education. The latest version of the SPICE simulation environment is available as 'professional' and 'educational' editions. The education edition has analogue and digital system-level simulation allowing the user to simulate libraries via the desktop to demonstrate and teach students controls, energy, power and mechatronics. The professional edition is based on industry-standard SPICE simulation and includes simulation tools to minimise errors and prototype iterations with customisable analyses and intuitive measurement instruments. This version increases the level of integration with the company's LabVIEW system design software for closed-loop simulation of both analogue and digital systems. Engineers can now validate FPGA (field-programmable gate arrays) digital control logic alongside analogue circuitry, commonly required in power applications, before leaving the desktop simulation stage.

The educational edition is designed to help students engage with a hands-on approach to investigating and understanding circuit behaviour. Analogue and digital system-level simulation afforded by the use with LabVIEW, simulates complete laboratories via the desktop to explore circuit design control and power theories. It is complemented with hardware, textbooks, and courseware. New capabilities in this edition expand the experience to understanding mechatronics, power and digital design through its interactive components, simulation-driven instruments and NI Educational Laboratory Virtual Instrumentation Suite. New pin-accurate connectors ease to the company's educational hardware, such as myDAQ educational hardware platforms. NI offers a portfolio product, Ultiboard, which is used for PCB layout and routing of electrical signals. Schematics developed in Multisim can be translated to PCB board layout in Ultiboard and then physically prototyped.

Product briefing – Zuken: CR-8000 Design Force

One hand or two? 2D or 3D? Offering native 2D and 3D views and a choice of inputs, the CR-8000 multi-board system design from Zuken is claimed by its makers to have the fastest system performance available. Design Force is the native 3D PCB and IC package design environment which allows the user to 'convert' between the 2D and 3D views with the flip of a switch. As well as supporting 2D and 3D design, it uses accelerated graphics, developed for the video games industry with almost instantaneous rendering and refreshing of views. Users can use both hands to design, wielding a mouse in one hand and a touchpad in the other.

Signal integrity, EMC, and power integrity analysis can be conducted concurrently in a single environment, which also manages constraints and auto-routes a board.

The ability to use a 2D and a 3D architecture allows users to co-design a chip, package and board, optimise I/Os at each level, embed components in the dielectric of a stack-up intelligently, and verify manufacturing rules in real-time.

The 'system planner' environment carries out product planning, such as logical function block diagrams, 2D physical and 3D geometrical planning, so operators do not have to jump between tools, such as Excel, Visio, and AutoCAD. Another feature, 'design gateway', has signal integrity, analogue, digital, and multi-technology verification tools and also allows re-use of proven logic circuits.

For RF verification flow, CR-8000 Design Force interfaces with Agilent Technology, ADS and AWR's Microwave Office for RF and electromagnetic analysis. The DFM Center prepares and verifies fabrication and assembly for manufacture.

Product briefing – RS Components: DesignSpark 5.0

Electronics distributor RS Components relied on feedback from the DesignSpark user community to determine the features of its latest version of the software for schematic capture and PCB layout.The free design tool now includes online design rule checking (DRC) and buses, reflecting the trend for on-chip buses to transfer data.

DRC determines whether the physical layout of an IC satisfies recommended parameters, or design rules. Conducting these checks online is advantageous as designers can spot errors in real time during the design stage, before the design is finalised and before the final layout.

This saves reiterations and re-spins down the line. The other feature introduced in this version is the ability to represent wires used to transfer data, or buses, as a single bus wire. By representing these wires, bundled in multiples of eight, as a single entity, simplifies the final schematic as they do not have to be drawn or labelled individually. It also simplifies and reduces the errors in simulation and debugging.

Since its introduction in 2010, the company has introduced 3D visualisation of PCB layouts and increased the library management. Within 18 months of its introduction a simulation interface, design calculators and component grouping were added. A significant development was six months ago when access to ModelSource was introduced.

This gave DesignSpark users access to a component library of 80,000 part numbers. The same version also introduced a facility to provide a quote for materials and PCB manufacturing.

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