Design Subtleties Determine Success for High Frequency Boards

Very speedy chips can be placed on laminate boards, but it takes a lot of care attention to make high frequency boards that are reliable and cost effective.

One of the constants in the electronics industry is that as speeds rise and new technologies emerge, people start predicting that older technologies will be replaced and fade away. But makers of these entrenched technologies typically increase their efforts and postpone their demise.

Resistors and capacitors still consume plenty of board space despite predictions that ASICs and other chips would integrate most passives. Plus, laminates are still the dominant printed circuit board technology even though some observers predicted that laminates couldn't handle speeds that are now considered pedestrian.

"There's a real mystique about speed. Twenty years ago, people said it would be difficult if not impossible to build a 300 MHz system using epoxy laminates. Now you hear folks saying 10 Gbits/second is too fast for laminates," said Mike Freda, interconnect specialist for semiconductor packaging & PCB technology at Oracle.

When engineers develop high frequency boards, they must focus on many nuances. Freda noted that that overall speed isn't the only factor that determines whether the system can be built using conventional circuit board technologies.

"The truth is that it depends how far your signals go as to the total signal loss. It is much easier (relatively)to go at high-speed for short distances," he said.

Many subtleties must be addressed to provide high reliability for high frequency designs. Both design and manufacturing technologies must be considered to get a holistic end product that meets all requirements. As more boards have been outsourced, it's become more difficult for young engineers to learn the subtleties of each side of production. Much of the communication that came when both manufacturing and design personnel worked for the same company has disappeared.

"Most people today don't know about the full vertical supply chain, there aren't any companies that start with laminate on one end of their line and ship out computers out the other end," Freda said. "Fabricators know how to build boards, but their understanding of signal integrity is often lacking."

Freda, who's worked on boards for a few decades, will provide some pointers in a presentation entitled How to Achieve Higher Speeds Without Breaking the Bank. His speech is the technology opener during the IPC Executive Summit, taking place August 21-22 in Schaumburg, Ill. The Summit is being held in conjunction with the IPC Midwest Conference and Exhibition.

His discussion will address necessary steps from the start of design through manufacturing. Early on, engineers must adopt design techniques that have been gaining strength for several years.

"You need to do modeling, simulation and validation. You can't build this stuff without modeling, and you must validate your models with real test boards," Freda said.

Even when circuit boards are validated using these models, there's a chance that problems will creep in. Freda noted that engineers will need expensive testing tools to understand the many intricacies that can cause problems, particularly when they're tricky intermittent failures.

"One key to doing high speed boards at lower cost with good quality is to hire good engineers and give them the budget to build test board to validate high-speed structures on half-million-dollar pieces of test equipment so they can understand why certain things work and don't work," Freda said.