LISLE, Ill. — The Slot 2 connectors that Molex Inc. will roll out next week for Intel Corp.'s Pentium II Xeon processor will employ novel techniques to satisfy requirements set by Intel and Molex when they began working together in 1994. The connectors borrow circuit board techniques to handle higher speeds while increasing contact density.

The HiSpec card edge connectors are designed for servers and other high-end applications that require Xeon, which was introduced in June. The connector itself is only slightly larger than the Slot 1 connector found on many desktop systems, but it has 110 extra contacts and can handle signals that are more than twice as fast. Some of the techniques implemented on the Slot 2 connector are already being employed in other Molex connectors.

Molex and Intel worked for four years to get more lines running at higher frequencies. The challenge was heightened because the characteristics were to be achieved without making manufacturing more complex for Molex or for the system houses and contract manufacturers that will use it.

"We had plenty of goals: we had to hit Intel's speed and density requirements, and we had to carry enough power for future generations of the chip which will draw more power and have more simultaneous switching," said Jim McGrath, strategic product manager at the Computer Strategic Business Unit of Molex. "This couldn't use new manufacturing techniques. It had to hit the manufacturing floors at our plants and our customers and be running right away."

It took an international team of Molex designers to come up with the complete system for the interconnection system. Though Intel was setting the guidelines, Molex was able to adjust them so that installed costs for the connector could be decreased.

"Intel originally wanted a 0.025-inch pinch, but we ended up with a 0.030-inch pitch," McGrath said. "We said 0.025 would be difficult at our end, but it would be a nightmare at theirs. In the module, there would be a much greater chance of solder bridging and the ability to route to the contacts would be much harder at the finer pitch. They might have had to add substrate layers to route at that density, and that would add to costs."

The connector has several more pins than its desktop counterpart. The Slot 2 connector puts 330 card edge contacts in a housing that is 5.66 inches long, while the Slot 1 connectors found on desktops have 242 contacts in 5.23 inches, with a pin pitch of 1 mm.

To meet the goal, Molex came up with the idea of staggering the pads. That allows a 0.030-inch pitch for the edge contacts while providing pad widths of 0.032 inches. That matches the tolerances of conventional PCI connections, which helps the connectors to fit existing production techniques.

The combination of density and high performance forced Molex to come up with a novel concept it calls complementary contacts. Metal contacts are the same size in most connectors, but Molex has made the power and ground contacts much larger than those which carry signals.

The larger surfaces look and act more like ground planes. Use of the smaller contacts for signals lets Molex put more contacts in a given amount of space. The signal lines employ microstrip and stripline techniques like those used on circuit boards to provide high speeds.

The microstrip and stripline techniques are complemented by a number of power/ground contacts. Many high speed connectors employ a 1:1 ratio of ground and signal lines to minimize crosstalk, but Molex and Intel couldn't afford the space required for that many contacts. Instead, they employed larger contacts for power and ground signals, and placed two smaller ones between each pair of ground connectors. While grounding is important, power handling is equally critical for future products.

"As we see continued drops in voltage, wattage doesn't change, so current goes up," McGrath said. "In processor applications it's not just the processor, but the L2 cache runs as fast as the chip, so you need more current."

Though Molex is prepared to license the technology to other connector makers, it is currently a sole source supplier for Intel, and no other manufacturer has signed on as yet. The company does not expect that to be a problem, however.

"We have 50 percent more capacity than the highest demand estimate," McGrath said. "We're probably okay for three years."

Other Molex groups are already adopting the complementary contacts technology. Molex is also preparing to introduce connectors for Rambus memory modules, and will use multi-sized contacts in that product. Other Molex operations are also exploring possible uses for the contacts.