23 February 2010

Back to front

No longer the 'back room boys', pcb designers are now among the first to be consulted on new projects

The pcb designer's image is changing, driven primarily by the technical challenges of high speed, low power and high density interconnect, plus the need to interact with mechanical designers. As a result, the pcb designer's role is expanding to embrace the whole product design flow.
Keith Felton, Cadence's group director of product marketing, said: "The consumer electronics market has already realised that packaging can be the most important aspect of a new product design. Today, designers start with the form factor. That determines the size and shape of the pcb; then they go to the chip level.

Corroboration came from Altium product manager Rob Irwin. "15 to 20 years ago, most electronic products were rectangular pcbs in boxes. It's not only consumer 'i-products' that have changed the game; even mundane products have added complexity. Most board designers are no longer designing single, simple boards: there might be nested boards, daughter boards or flexiboards. It's becoming much harder to do in the standard 2d design environment."

It seems that, over the last few years, there has been a steady expansion in the role of the pcb designer. "The walls between the electronic designer and the layout expert are breaking down. The board designer is having to learn more about electrical characteristics," Irwin continued.

"More of a design is often being done by the same person," added Felton. In larger teams, however, there are still dedicated experts for specialist tasks, such as rf design or signal integrity analysis.

"Board designers are moving out of their insular world, yet many do not realise they can have a major influence on electronics design," claimed Dionne Hayman of Zuken. "Through collaboration with electronic engineers on one side and mechanical designers on the other, they can make a big difference to the bottom line."

John Isaac of Mentor Graphics believed change is being driven by high speed. "Even the simplest designs can have high speed issues. Some years ago, only a few nets had signal integrity issues. Today, it is often 70 to 80%. Even if the board itself isn't high speed, it is likely to contain parts that operate at high speed."

Allied to the high speed issues is the increasing use of devices with very fast edges, coupled with the trend towards low supply voltages. "A few years ago, most ics operated at 5V, so a designer would slap down a 5V plane and a groundplane," Isaac remarked. "Life was good." Today, multiple supply voltages even in a single chip are common, requiring careful design, with stable power planes and control of power dissipation to ensure efficiency and avoiding voltage drops, noise and high currents.

The experts call it power delivery design and this is now regarded as a major technical board level challenge. "Yet," Isaac warned, "with multiple power distribution networks on a pcb, you can't be over conservative, as this can result in having to add layers, and therefore cost".

However hard designers try to reduce power dissipation, heat is a problem. "Getting the heat of the board and out of the product requires knowledge of the mechanical design. And this is not just a problem with portable products, but also with a wide range of high performance systems," Isaac added.

Meanwhile, Cadence sees the downwards shift in ic geometries having a knock on effect on pcb design. "Miniaturisation is one the key challenges facing pcb designers," Felton stated. The need to handle smaller component packaging has driven demand for high density interconnects and microvias.

According to Irwin, high performance – and now affordable – fpgas are the primary driver for the rapid uptake in microvias and high density interconnect (HDI) techniques. "FPGAs are highly attractive, providing significant gains in time to market, increased functionality and flexibility. But they tend to be in high density packages."

Isaac reinforced the case: "It used to be that only high end designers went to microvias, but fpgas and popular processors in high pin count bgas have provided the tipping point. Now, demand for HDI and microvia support in the tools is becoming more common." As a result, fpga/pcb codesign is a common feature, even on low cost platforms.

The move to microvias has introduced the concept of 3d design, although Cadence talks about the Z dimension, rather than 3d. "There's a definite trend towards greater use of the Z dimension," Felton claimed. Where additional layers were once added to solve interconnect issues, designers are now looking at burying devices in the substrate – and not just passives. "Bare ics and flip chips are thin enough to be incorporated into the board layers, thereby giving greater opportunity to shrink the x and y coordinates of the overall board," he explained.

For this reason, ic packaging design is increasingly associated with pcb design. "Foundries are more concerned than ever about packaging," Felton explained, primarily because their success is dependent on ensuring a new product moves into volume production as swiftly as possible. A complex interaction between board and chip designers is required to assess the trade offs between the various device package types and their impact on board design.

Interestingly, the tool vendors see pcb design as the pivotal point for cross discipline work, not only between electronic and layout tasks, but also with mechanical design and even software development. PCB designers are seen as critical to coordinating the interaction required when optimising a design for low power, high speed, signal integrity and thermal management.

Further, pcb design appears to be the centre point for allied tasks, such as ensuring regulatory compliance, component library management (and even procurement) and design for manufacture. It's a small step into data management systems covering all aspects of a design and project management functions.

Some conclusions can be drawn. First, it seems that a huge effort has gone into enhancing pcb design tools in recent years. Felton: "Tools have had to become more intelligent, more capable and more automated. We can no longer take the adjustable spanner approach, with one size fits all." Isaac added: "Because designers can no longer work in isolation, tools have to be integrated, easier to learn and to use. Engineers have to be able to pick up a tool they don't use every day and run it easily". Yet the software is substantially cheaper than it was a decade ago.

Second, board designers are finding themselves in the heart of product design, rather than on the edge. "Life as a pcb designer is still tough; multitasking and narrow profit margins are the name of the game," Felton concluded. But, it seems they have a greater opportunity to influence electronic and mechanical design. And the suite of tools now available is claimed to give them the potential to expand their skill set into project management, managing the trade offs between cost, time to market and performance, and facilitating the design flow into manufacture.

Author
Louise Joselyn

Supporting Information

Downloads
22687\P25-26.pdf

Websites
http://www.altium.com
http://www.cadence.com/
http://www.mentor.com/
http://www.zuken.com/

Companies
Altium Ltd
Cadence Design Systems Ltd
Mentor Graphics (UK) Ltd
Zuken Ltd

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Do you have any comments about this article?

I really enjoyed being interviewed by Louise Joselyn for her excellent 23 February article "Back to Front" about PCB design, but I wondered if I could make a point that a good number of your readers will identify with.
With a market share in Europe of more than 50%, Mentor not only serves small companies, but also mid sized to large enterprises. In these larger companies, we see a distinct challenge in product design that I think should have been given more press. These companies typically have design teams that are located in different facilities and may even be globally dispersed. They also have multiple engineers and CAD designers working on the product in order to meet tight time-to-market goals. We also find that multiple disciplines are involved in the development process (analogue, digital, RF, mechanical, FPGA, IC/Package, software, procurement, manufacturing, test and so on).
We strongly believe that our R&D investment focus is not just on the productivity and advanced technology capabilities in the core PCB design flow but also in creating concurrency and collaboration capabilities. This includes the ability for multiple engineers and CAD designers to work simultaneously on the same board, at the same time, without database split and re-join, and with the ability for all the members of the team to view each others' edits real time. As well, to enable real-time collaboration in the process by providing the ability to electronically communicate proposed design changes between the multiple disciplines, initiate a negotiation process, and update the design when the change is acceptable to all of the extended team.
So, the emerging trend is from a serial to a parallel process with real time, multidisciplined concurency and collaboration.

John Isaac
Mentor Graphics


Comment John Isaac, 04/03/2010

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