As the industry moves to faster signal speeds, interconnections are becoming far more complex. Maintaining signal integrity is becoming more difficult, requiring more analysis both before and after board layouts.

"When you get above 200 MHz, interconnections are no longer transparent, you can't just slap things together," said Eric Bogatin, founder of Bogatin Enterprises, a consulting firm.

He explained that in these higher frequency domains, ensuring signal integrity requires paying attention to aspects of the design that are often ignored by many engineers and layout specialists. "Signal integrity is all about the white space on the schematic. You can see the chips, packaging, wiring and the other components. Signal integrity is all about the spaces between those components," Bogatin said.

Bogatin, who calls himself an evangelist for signal integrity, will describe some of the habits that board designers can use during one of the IPC Summer School 2010 Webinars. The hour-long session, which will be on July 29, 2010 at 10:00 a.m. Central time, is entitled "What Every Layout Designer Needs to Know About Signal Integrity."

Those habits help out during basic decision making, helping layout specialists avoid subtle high-speed problems or figure out what's causing them when some inevitably arise. One of these habits is to make extensive use of return vias. Many board designers have the perception that when they use vias to go from one layer to another, routing the signal line is all that needs to be done.

"People often don't pay attention to the return layer, which can introduce noise into the planes," Bogatin said. "Simply adding a return via adjacent to the signal via can dramatically reduce high frequency noise, but that fact is not well known."

As with most aspects of high frequency design, adding a return via isn't as simple as sticking the opening next to a signal line. Layout specialists must ensure that both the vias have the same voltage. If they don't, a signal line must come up to the surface and a blocking capacitor has to be added to make the adjustment.

Another benefit of using return vias is the reduction of EMI emissions. That's becoming a growing factor in many fields as electronics move to higher frequencies, generating more EMI, and a growing number of electronic modules increases the likelihood of problems that come when EMI isn't controlled.

Bogatin also stresses the importance of examining signal integrity during many phases of system development. Development teams create design rules that set the constraints for board layout. But board designers can't work only with those constraints. They must also take interactions into account.