Not so long ago, the rise and fall times of signals, the coupling from one trace to another, and the de-coupling of power distribution on a PCB were tasks that were routinely handled by a few simple rules. Occasionally, you might use the back of an envelope, scribbling down a few equations to make sure that the design would work.

Those days are gone forever. Subnanosecond, single-ended I/O rise and fall times, 3 to 10 Gb transceivers, and tens of ampere power needs at around 1V have all led to increased engineering requirements.

Your choice is simple: simulate now and have a working result on the first PCB, or simulate later after a series of failed boards. The cost of signal integrity tools more than outweighs the cost of making the board over and over with successive failures.

In keeping with the theme of this special issue, here are my 10 best reasons why signal integrity engineering is a good idea:

1. You’re tired of making PCBs over and over and still not having them work.
   Seriously, without simulating all signals, as well as power and ground, you risk making a PCB that will just not work. IR (voltage) drop, inadequate bypassing or de-coupling, crosstalk, and ground bounce are just a few of the possible problems.
2. You’re tired of being late to market and watching your competition succeed.
   Every time you have to fix a problem with a PCB, it necessitates a new or changed layout, a new fabrication, and another assembly cycle. It also requires the re-verification of all parameters. Taking the time to do these things right has both monetary and competitive advantages.
3. You’re tired of spending all this money, only to scrap the first three versions of PCBs and all of the components that went with them.
   See reason number two.
4. Your eye pattern is winking at you.
   If the eye pattern of a high-speed serial link is closing, or closed, it’s likely that the link has a serious problem and will have dribbling errors – or worse, will be unable to synchronize at all. You must simulate every element of the design to assure an error-free channel.
5. All 1s or all 0s suddenly breaks the system.
   Unfortunately, many systems do not have a choice of what data may be processed. Often the data pattern will create conditions that, if not simulated a priori, will cause errors in the system.
6. Hot and cold, fast and slow, and high and low voltages cause failures.
   Without simulating the “corners” of the silicon used as well as the environmental factors, you’re playing Russian Roulette with five of the six chambers loaded.
7. You cannot meet timing, and you are unable to find out why.
   Poor signal integrity is the primary cause of adding jitter to all signals in a design. Ground bounce, crosstalk, and reflections all conspire to add jitter. And once added, jitter is virtually impossible to remove.
8. The FCC Part 15 or VDE EMI/RFI test fails every time you test a board.
   Radiated and conducted radio frequency emissions, as well as susceptibility to radio frequency sources, is a sign of poor SI practices. Fixing the problem by shielding increases the system cost substantially, and may not even be possible in extreme cases.
9. Customers complain, but when you get the boards back, you don’t find any problems.
   One of the biggest problems with SI is that the errors and failures observed are difficult to correlate and sometimes impossible to find. Was it a problem with voltage, temperature, or with the data pattern itself? It might have been someone turning lights on and off (ground disturbance). Don’t risk a return that cannot be fixed. And last, but certainly not the least:
10. Your manager has suggested that you look for other employment.
    Do not let this happen to you. Stay current, educated, and productive. Get the right tools to do the job. Realize that signal integrity engineering is a valuable and irreplaceable skill in great demand in today’s design environments.