Cool Connections are Hot in High-Power Designs
By Bob Hult, Bishop & Associates Inc.

Doctors tell us that smoking is dangerous to our health, and that also certainly applies to electronics products. Who can forget the uproar when rechargeable batteries in certain laptop computers decided to self-destruct?

The failure of a power connector can be a dramatic event and may have serious safety implications. Fortunately, catastrophic failure of power connectors is a relatively rare occurrence. Examination of connectors returned to the vendor for analysis often reveals that a component elsewhere in the system, such as a capacitor or PCB trace, shorted and grossly overloaded the connector.

In order to insure that power distribution systems are robust, designers may cut the published power rating of a power connector in half to insure that they have plenty of design margin. They accomplish their goal, but the resulting connector often consumes more space then necessary, and incurs more cost. Increasing system power demand and packaging density are driving the connector industry to reconsider how these potentially conflicting objectives can be satisfied.

Semiconductor manufacturers recognized years ago that the race for processing speed was driving power demand to unacceptable levels. Suppliers have responded with entirely new families of processors, field programmable gate arrays, and memory that consume less power per instruction cycle. Via Technologies staked out the low-power microprocessor market several years ago, and promotes their devices with Adaptive PowerSaver technology. Intel recently introduced the Atom processor, which is aimed at low-power portable applications. Typical Intel mobile Core 2 Duo processors are designed for a thermal design power rating of 35 watts, while the new Atom will run at 0.6 to 2.5 watts. Multi-core processors from Intel and AMD can distribute a complex task among its cores—requiring none of the cores to push speed and power demand limits. Advances in dielectric materials and processes have reduced static gate losses, a major source of wasted energy. Advanced operating system software is able to shut down unneeded portions of a chip to conserve energy and reduce the generation of heat.

The problem is that systems have become more densely packaged. What was once a rack-mounted server has become a pluggable blade in a rack of blades. Printed circuit boards are packed with active devices, each of which consume power and generate heat. Individually, they may draw less power, but demand at the board level is increasing. Power distribution systems must support this increased demand without adding to loss and heat budgets.

The power connector is a key element in the distribution system, and is being pressured from several potentially conflicting perspectives. Designers want power connectors that can handle increased power more efficiently. A lossy power connector results in voltage drops and generates additional heat, so contacts that feature greater conductivity are desirable. The traditional method by which the power rating of a contact is increased is to make it larger. More copper and a greater contact surface area results in lower bulk and contact resistance. The problem is that designers want smaller—not larger—connectors.

Systems often require the distribution of multiple voltage levels. Feedback circuits that monitor power delivered to the loads require many low level signal lines, generating the need for more power and signal contacts in a smaller envelope. Increasing contact and power density raises some challenging design issues.

Thermal management, the strategy by which heat is transferred out of the box, has become an early consideration in the design of new equipment. With components tightly packed together, it is essential that heat is not allowed to build beyond established limits. Semiconductors are rated for maximum operating temperatures. Once those limits are exceeded, reliability goes down dramatically. Today, most systems are passively cooled by conduction to outer surfaces or actively by fan-driven air. Typical card rack enclosures include one or more fan trays designed to circulate air within the box, and exhaust it away from components. Some systems rely on local room temperature air, while larger server farms and data centers must use refrigerated air to keep systems running. The energy consumed by the cooling equipment may exceed the energy required to power the electronic systems. Designers must be careful to select components that maintain a low profile to minimize obstruction of cooling airflows, including connectors. As enclosure sizes shrink, the space available for connectors is reduced. Designers need power connectors that can be adapted to unique spaces.

Traditional power connectors had a difficult time satisfying these requirements. They were often large, available in limited configurations, and costly. Proprietary designs offered few second sources, making users captive to a single supplier.

Much of that has changed. Leading suppliers have recognized industry needs for new power connector designs that offer greater power density, design flexibility, and compatibility with thermal management strategies, and they are creating novel products to help further these goals.

One of the first new products to break the mold was the result of the Server System Infrastructure (SSI) specification that defined a new modular power connector. It was subsequently tooled by FCI Electronics as their PwrBlade family, and licensed to Tyco Electronics, who markets a compatible Multibeam XL connector. The introduction of the SSI power specification seems to have stimulated the industry to develop more flexible, high-performance, and user-friendly power connectors. The last two to three years have been particularly productive in the introduction of new power connectors that offer greater density, modular design, and lower profiles, all of which facilitate thermal management of the system.

Established power connector suppliers, including Anderson Power Products and Positronic Industries, continue to expand their portfolios, but several broad product line connector industry leaders have recently decided to commit major resources to this market, resulting in many new options for designers.

Amphenol introduced several new cable-to-board connector systems using RADSOK contact technology. These internal spring assemblies greatly increase the number of contact points within an interface, resulting in lower contact resistance and higher current ratings. The current ratings of these enhanced contacts has been reported to be nearly double that of the original design.

ERNI has added a power module to complement their MicroSpeed mezzanine connectors. MicroSpeed power modules are available in stacking heights of 5mm to 20mm with surface-mounted contacts rated from 6 to 8 amps each. 

The FCI Electronics Power Solutions portfolio added several new power connector families, expanding on the successful PwrBlade concept.

Pwr TwinBlade is a cable-to-PCB connector that features right-angle receptacles, touch-proof housings, and up to 100 amp contacts.

The HCI connector extends the power rating of the TwinBlade and offers the ability to mix power and signal contacts in a low-profile housing that is vented to dissipate heat within the connector.

Additionally, FCI offers power-edge connectors, as well as high-current connectors designed to support 2mm backplane interconnect systems. Their extensive power connector product line is now the subject of a separate 28-page catalog.

Molex has long been recognized for its popular lines of soft shell power connectors, which are used in the appliance industry.

More recently, they have expanded into the power supply, computing, and telecom markets with new products that satisfy the unique needs of these industries. Marketed under the banner EXTreme Power products, Molex offers a complete menu of low-, medium-, and high-power connectors.

EXTreme LPHPower is a hybrid modular board-to-board connector with 4 to 10 power contacts and up to 40 signal contacts. Each power contact is rated up to 30 amps.

The complete product family includes EXTreme PowerDock, EXTreme ZPower, EXTreme Power Bus Bar Connector (BBC), EXTreme PowerPlus (SSI), EXTreme PowerMass, EXTreme MicroPower, and EXTreme PowerEdge.

The EXTreme Ten50Power is a more recent addition to the family and represents the highest power density available. The housing is only 10mm high, yet can deliver up to 200 amps per linear inch. A variety of power and signal contacts are available in this modular housing.

Tyco Electronics has historically offered a broad range of power connectors and has continued to aggressively expand their offerings. Tyco recently upgraded their Multi-beam XL with the XLE version.

This new blind mate modular connector is designed to offer high-power 50 amp contacts, low-power 25 amp contacts, and signal contacts in the same vented housing.

It features reduced mating forces, as well as true hot-mating contacts. Thinner guide-sockets consume less PCB space.

The MiniPak HDL is the lowest profile modular power connector on the market today, at 8mm total height from the surface of the board. Power contacts rated at 16 amps each are available in increments of two. Signal contacts are reliable HM style. Power contacts use six compliant pins per blade to distribute current to the PCB.

Integrated alignment features assure reliable blind mating.

MiniPak HDL achieves current densities of 140 amps per linear inch.

New high-density interconnect systems designed to handle increased current in board-to-board, cable-to-board, and even mezzanine stacking configurations continue to bring welcome options to system engineers. This market, once considered a niche, is finally getting the attention it deserves.

Bishop & Associated Comments:

1. Power connectors introduced over the past several years have reinvigorated the industry with innovative features that address industry needs.

2. Modular housings simplify the creation of custom configurations. Laminated tooling allows quick changes, with little or no tooling charges.

3. Hybrid design integrates power and low-level signals in the same housing, improving the packaging density of the system.

4. Low-profile housings facilitate better packaging density and reduced airflow obstruction.

5. Higher contact current ratings result from using higher conductivity and thicker contact materials. Improved contact designs reduce contact resistance. Vented housings keep the contacts cooler and increase current ratings. Power connectors are designed to support hot mating without damage to the separable interface.

6. Designers are benefiting from a much broader range of power connector options than ever before. There has been some movement toward multiple sources, but this is far from universal. Connectors designed to the SSI specifications allow true second sources.

7. The race among a greater number of suppliers to create higher current ratings in smaller modular housings has kept prices competitive.

8. Printed circuit board connectors of all types, including backplane and mezzanine, are adding power options.

9. Connector designers are considering airflow in their connector designs, both to minimize obstruction as well as keep the contacts cooler.

10. At some point, the ability to transfer sufficient heat out of the box will not be possible using circulating air, forcing consideration of liquid-cooling alternatives. This technology is being implemented in high-performance systems now, and will likely migrate downward as costs decline. The market may be ripe for backplane connectors that feature self-sealing valves that can bring cooling liquid to the daughtercard.

Robert Hult
Director of Product Technology, Bishop & Associates, Inc.
Robert Hult has been in the connector industry for more than 36 years. Hult began his career as a sales engineer for Amphenol. He joined AMP in 1972 and served in several management positions through 1996. In 1997, Hult joined Foxconn as group marketing manager for Intel in Chandler, Arizona, USA. Prior to joining Bishop & Associates, Hult was the regional application engineering manager for Tyco Electronics.

Hult graduated in 1968 from Bradley University with a Bachelor of Science degree in electronics technology and a minor in business.