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The challenges of printed circuit board design and debug

January 26, 2015

Bernard Cole-January 26, 2015

Of all the various elements that must be considered in any embedded systems design, printed circuit board development and debug is in many ways the most challenging of all. The printed circuit board is the point at which all of the design decisions made earlier come together and where unforeseen problems related to performance, power, signal integrity and noise mismatching make themselves known and where they must be resolved.

But  as you''ll see in this week's Tech Focus Newsletter, resolving these problems is getting harder as integrated circuit design geometries get smaller and become more sensitive to issues of crosstalk, electromagnetic interference and jitter. Similar issues arise in packaging and in the PCB itself, where efforts to increase the functional density of a design through multichip packaging and new smaller dimension pinout approaches present their own sets of signal integrity issues. As a result, debugging a board often requires the skills of a detective to sort out the innocent from the guilty.

As Dunstan Power points out in "11 steps to successful hardware troubleshooting in PCB development and debug” it is always important to keep in mind that board design work is carried out by a person who is not only fallible, but may also be working with incomplete or incorrect data.

"Some bugs are inevitable on all but the simplest designs and so the art of troubleshooting these bugs is all-important," he writes. "Bugs can range from something going BANG the first time power is applied to intermittent glitches reported in association with completely unrelated things like 'it was raining' or 'it only happens on his bench, not on mine'. Consequently the ease of fixing bugs similarly ranges from a five-minute job to months of work."

Included in this week's Tech Focus newsletter are a range of techniques and methodologies that can be employed to anticipate and prevent the many gotcha’s that can pop up at any time, and procedures to follow when, as Dunstan points out, the inevitable does occur. At the top of my Editor's Top Pick list are several articles that should be of help:

Bringing experimental development methods to PCB design and manufacturing
By necessity PCB design and assembly have become the proving grounds for setting up and evaluating new design techniques. But to be successful, they must be done by electronic manufacturing service providers skilled in design of experiment (DOE) methods.

Overlooking design-for-test can lead to costly PCB design rework
To avoid costly printed circuit board rework, it is important to have an effective design-for-test (DFT) strategy in place, based on a close partnership between the design and test engineering teams.

The basics of printed circuit board design
This series of articles discusses the basics of the PCB design flow, from basic terminology to the primary steps required to move a design through the schematic, layout, and manufacturing stages.

Another good resource for printed circuit board design and debug techniques and tools is the 2015 DesignCon which opens tomorrow at the Santa Clara, Ca., Convention Center. Be sure to register and attend as many of the presentations in the three tracks devoted to printed circuit board issues as you can: System Co-Design Chip/Package/Board Modeling & Simulation; PCB Materials/Processing Characterization; and Applying PCB Design Tools.

PCB design is like every other aspect of embedded systems design in that it is not done in isolation; it is connected to issues relating to IC, packaging and interconnect. So, do not ignore the other hundred or so talks, presentations and panels at the conference, some of which will have useful perspectives in PCB design. Three tracks I would pay particular attention to include: Detect and Mitigate Jitter, Crosstalk, and Noise; Applying Test and Measurement Methodologies; and Electromagnetic Compatibility/Mitigating Interference.

Embedded.com Site Editor Bernard Cole is also editor of the twice-a-week Embedded.com newsletters as well as a partner in the TechRite Associates editorial services consultancy. If you want to see a calendar of topics for the weekly Tech Focus newsletter or have a topic you would like to see covered, he welcomes your feedback. Send an email to bccole@acm.org, or call 928-525-9087.

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