Who should lay out my printed circuit boards?

Satcam & RTD Circuit Design
http://www.satcam.com.au/
By Rob Leslie*
Tuesday, 10 April, 2007



As ever shortening product lifetimes impose tighter and tighter time-to-market pressures, the variety of CAD/EDA software looks more and more bewildering and the make-or-buy question for PCB design remains as hotly argued as ever.

As with much in life, there is an abundance of truths, half-truths and misconceptions about the benefits and disadvantages of using an independent CAD bureau to perform printed circuit board design.

Typical topics include cost-effectiveness (including use of both capital and expense resources), fear of communication difficulties, concern about loss of project control, the 'not-invented-here' syndrome and maintainability and portability of the resulting design.

Typically, the R&D team of an electronics manufacturing company might comprise mechanical, electronic hardware and software engineers, technicians and drawing staff. Once marketing and management have agreed on the specification for a new product, industrial designers and mechanical engineers will work to produce a set of project drawings that will include profile drawings for the circuit boards and concurrently the electronic hardware design engineers will work towards producing a suite of schematics.

Who is going to combine the mechanical drawings and circuit schematics to generate the printed circuit board layout? If the organisation's circuit board design workload is not consistent enough to justify a dedicated full-time PCB designer, there are three or perhaps four other choices: use a mechanical draughtsman who has some 'spare time' and has 'done a few boards before'; distract an electronic design engineer or technician from his circuit design and analysis long enough to learn the vagaries of your EDA system and do the design; hire a contractor to do the job in-house using your EDA system; or outsource the task to a CAD bureau.

The significant difference between the first three of these options and the fourth is ownership of an EDA system. The decision to invest in a CAD system has a number of apparent benefits as well as a number of disadvantages, perhaps the most oft-quoted advantage being the ability to maintain 'complete internal control over your designs'.

While the prospect of being master of one's own destiny is undeniably attractive, it is also something of an illusion, as access to the tools is only part of the exercise.

Even the most sophisticated and user-friendly tools are useless without competent tradesmen. In fact, it is frequently the case that the more powerful the system, the more training-intensive and operator-skill-dependent it can become.

Thus the initial decision to purchase involves more than just a capital commitment, it imposes an ongoing financial obligation to the maintenance of skilled manpower resources.

The use of the adjective 'skilled' is significant, for it is perhaps here that we come to the crux of the argument in favour of engaging the services of a bureau. For a bureau to justify the investment of its proprietors, it must process a certain volume of design work and it must do this in a reasonable time frame.

To fulfil these requirements, each designer must be fully conversant with software and equipment capabilities and shortcomings. This familiarity grows naturally from an intimate 35-hour-a-week (or more) relationship with the mouse, keyboard and monitor.

In the usual environment of small- to medium-sized R&D departments, it is uncommon for staff to be available continuously for the sole task of PCB design.

As a result, the skills and familiarity tend to lose their edge between jobs or perhaps are never fully honed in the first place. It is this familiarity which enables a bureau operator to confidently commit to both a price and a delivery schedule for a design task.

Further, because circuit boards are its main or sole business, a bureau will generally be in close contact with both PCB manufacturers and assemblers. In addition to expertise in the use of design resources (hardware, software and human), a bureau will consequently be able to offer an understanding of manufacturing cost savings which may be achieved by slight changes in layout or by different assembly techniques.

These experience-related points may not be appreciated by in-house R&D staff to whom PCBs are merely an intermittent diversion from other tasks.

Another major benefit of using a bureau is that of resource availability and workload. Frequently the development cycle of a project is such that board design is a 'feast-or-famine' affair, with a number of PCB designs all being required simultaneously and with engineers' circuits all becoming available around the same time.

To produce designs for many boards at once requires a number of workstations and designers which would be impossible to justify, potentially lying idle for a large proportion of the year.

With a continuous year-round flow of circuit board design work from a number of clients, a bureau will be far better equipped to deal with intermittent loads from each client.

Considering the aspect of cost control, any reputable bureau can prepare a quotation for whatever work is required, including the provision of all necessary support documentation such as parts lists, net lists, Gerber (phototool) files, drill files and manufacturing specification drawings.

Although it may be frightening to have the entire cost of the development of a circuit board presented in a single quote, it is not difficult to demonstrate that the cost of using a bureau can indeed be less than the cost of maintaining one's own equipment and staff.

It's just that many of the real costs can tend to be ignored, overlooked or deliberately hidden within the company's accounting structure and it is often easy to lose sight of the real cost of a particular design.

A common objection to the idea of using a bureau is that of losing control of the design, and a frequent comment is:

"I don't have time to prepare the documents to brief somebody about component types and critical placements."

Both of these are fallacious.

The reality is that while dealing with a bureau might impose a discipline which is often absent when the design process is internal to the organisation, the procedures involved are nonetheless an essential part of project management.

Whether the design is done internally or externally, the PCB designer needs to know all component types, mechanical details and critical layout constraints.

The choice is really one between the confidence derived from fully and clearly defining these details at the beginning and a reliance on a 'she'll be right' approach to the design, often depending on ad hoc assumptions and guesses.

In any event, a design bureau will provide a set of checking documents before the job is declared complete, and frequently progress prints for areas of particular concern. Netlist checking ensures that the PCB layout is an exact electrical representation of the circuit schematic and a plot of a manufacturing specification drawing will permit checking of dimensions, hole sizes and fabrication details.

A bureau may not be the answer to every single PCB design challenge, but it certainly offers significant and demonstrable benefits in a wide variety of situations, especially considering that a quotation is only a phone call away.

*Rob Leslie is an electronics engineer currently with RTD Circuit Design, a Sydney-based independent design bureau which has a continuous history of more than 20 years in the industry.

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