Power connectors maximize cooling in hot ICs

System designers are driving demand for power connectors that deliver higher current ratings in an equal or smaller footprint. But they also need to maximize cooling in shrinking designs packed with hot ICs and beefy power supplies. And they know that system temperatures affect the current-carrying capability of the power connectors.

The design of a connector has a direct impact on airflow, said Michael Bean, product manager for Molex Inc. But system designers can't rely solely on the connector design to solve thermal problems, he said.

To optimize a system design, Bean said, a designer also has to look at other elements—such as the amount of copper on the board—that can help draw heat away from the connector interface.

Nonetheless, connector manufacturers can address thermal issues and are taking steps to do so. One way is with power connector designs that have lower profiles to maximize airflow and thus increase cooling.

Lower profiles aren't always the answer, however, since lower-profile designs also tend to be wider. For applications that don't have the width, but have plenty of room for a taller connector, Tyco Electronics Corp. has developed the MiniPak HDE stacked 2x3 connector with 21.5mm height and a maximum current density of 200A per inch.

Similarly, Molex touts its Power Dock Sr. board-to-board connector as the highest-current-density power connector in the market, with 350A per linear inch. Molex is also working on the Ten50, a connector design that it says will offer a higher current-carrying capability with a low profile.

Other ways that connector makers are addressing thermal issues are with materials, housings and contact designs. Many are already using higher-conductivity copper alloys, which allow current to pass through a system with less heat buildup. They are also using new contact beam designs and thermally conductive housings.

Tyco's MultiBeam XLE yields 20 percent more current than its XL.

Finessing the contacts
New contact designs are also helping. One Tyco engineer has developed a stamped and formed contact that gets rid of heat and provides as much current-carrying capacity as screw-machined types. He took a cross-sectional area of a round conductor and flattened it to provide about 50 percent more surface area. Developed for the AdvancedTCA telco market, the connector carries more current and costs less than screw-machined contacts, said Mike Blanchfield, product manager for power interconnect products at Tyco.

According to Molex, designers need new power-connector-modeling software, and the company is working to fill that need.

Bean noted that current-rating calculations are evaluated as temperature rise above ambient, or T-rise, and are based on the amount of current that can be pushed through a contact or contacts until the temperature interface reaches 30°C above ambient. Such tests are typically conducted at still air for a baseline. "Since heat is the element being measured, any positive influences to aid with heat dissipation, such as additional copper on the PCB or airflow over the connector, will allow additional current to be passed through the connector interface," Bean said.

Some system designers are pushing the envelope past a 30°C T-rise in exchange for more current capacity in space-constrained applications, he said.

Designers today are more limited than in the past, when they typically derated a connector by 50 percent. If the part was rated for 10A per pin, they derated it to 5A, which translated into more pins and larger connectors.

But designers can't afford to design-in larger connectors today, and they don't have the luxury of derating, Bean said. "They have to take the 30° T-rise chart and decide how much of a rise in temperature they can go over ambient." If the spec happens to be 10A, then they are probably rating the part very close to 9-10A, Bean said.

"But if they want to push 12A through the connector and they have airflow, they're willing to take the chance to reduce the pin count because they know that the connector and contacts can take it," he said. "So they rely on airflow to keep the connector cooler—but it's not a science because there is nothing that can model it."

Molex's work on new modeling software will take into account such design issues as available space, connector type, connector size, current requirements, airflow, PCB design, amount of copper and ambient temperature.

- Gina Roos
eeProductCenter