High-Speed Backplane and Mezzanine Connectors Continue to Rock
By Bob Hult, Bishop & Associates Inc.

The marching orders for just about all electronic devices and components continues to be faster, smaller, greater design flexibility, energy efficiency, RoHS compatibility, and of course, cheaper. This applies to connectors of all types, from processor sockets to I/O.

The merging of communication, entertainment, and computing functions into new generations of portable devices has driven consumers to demand lightweight products that feature simple intuitive interfaces that consume little power and are durable enough to survive the abuse handed down by a teenager.

The recently announced 10 Gb Thunderbolt I/O interface from Intel is a perfect example of these trends applied to a connector, with a possible question about cost, at least initially.

High-speed backplane and mezzanine connectors have experienced continuous evolution to satisfy requirements of higher pin counts, greater bandwidth, and design flexibility. The venerable 2mm HM-type pin and socket connector has morphed over the past 15 years into a series of highly sophisticated serial differential interfaces with carefully tuned impedance control and skew characteristics, while minimizing crosstalk. Mezzanine connectors have followed suit, with versions that feature minimum loss and distortion, and nearly infinite stacking height options.

There is no doubt that the improved performance of board-to-board connectors has been enabled by advanced serializer/deserializer chips that can compensate for losses and distortion created within the channel. Materials used to fabricate the backplane itself have been improved to minimize loss and distortion. The process of assembling the backplane, such as reducing the diameter and backdrilling of the plated-through-hole, has minimized the negative effects of the un-terminated stub. Major improvements in PCB design tools more accurately predict high-speed performance and optimize trace layout.

Backplane connectors that were originally designed to support 3.125 Gb/s performance have been upgraded using improved footprint designs, pin assignment, as well as advanced materials to allow published bandwidth to push 10+ Gb/s.

Suppliers, including Amphenol TCS, ERNI, FCI Electronics, Molex, TE Connectivity (previously Tyco Electronics), and 3M, dominate the multi-gigabit backplane connector market segment today. At last count, these suppliers offer more than 25 families of high-speed backplane connectors, with more in the development pipeline.

The ability to demonstrate performance headroom within a product family has become an important marketing issue. Experience with the characteristics of a particular connector is gained as a new interface is implemented into a new product. Engineers often prefer to leverage that experience when designing a new product, rather than start the learning curve over again with a new interface. In some cases, a connector product line is offered in good, better, and best versions, which allows a designer to select the level of performance required for a current application, and stay with the same product family as higher bandwidth and/or density is required by next-generation equipment.

For instance, 3M Interconnect Solutions has introduced the UHM connector. This backplane connector is based on standard 2mm HM technology, but the right-angle socket has been outfitted with internal shields that enable up to 7 Gb/s performance. The receptacle mates with standard 5+2 vertical headers so existing CompactPCI and VME 64x backplanes can be upgraded by simply installing new daughtercards that carry the new UHM receptacle.


The Amphenol TCS flagship XCede backplane connector family offers scalable performance from 8 to 25 Gb/s via the original version, the LC iteration without resonance damping for lower cost, and the new HD version that offers a 35% increase in signal density.

Although many designers are currently learning the intricacies of developing 6-10 Gb/s channels today, the new target appears to be focused on 25 Gb/s. Connector suppliers are gearing up to provide a bandwidth roadmap that will support next-generation equipment.

ERNI recently announced the ERmet ZDHD backplane connector system. This higher density connector system features 84 differential pairs per inch and an optimized footprint that enables performance to 25 Gb/s. Headers are press fit into downsized 0.46mm plated through holes.





FCI Electronics introduced the AirMax VSe, the next generation of AirMax high-speed backplane connectors that provide a migration path to 15+ Gb/s performance, while retaining the flexibility of an open pin-field design. These connectors are backward compatible with existing AirMax VS connectors with minimal footprint design changes. At DesignCon 2011, FCI demonstrated a 25 Gb/s channel using the VSe connector, opening the door to 4 X 25 Gb/s to achieve 100 Gb/s Ethernet or Infiniband channels.



The Molex Impact backplane connector system continues to be expanded with the addition of 85- and 100-ohm impedance versions, as well as a midplane orthogonal configuration.

Molex recently exhibited a new Impact Orthogonal Direct connector, which completely eliminates the midplane. Orthogonally oriented daughtercards mate directly with each other to minimize crosstalk, attenuation, and skew associated with backplane

All three connector systems are rated to 25 Gb/s.


TE Connectivity (TE) (previously Tyco Electronics) continues to push the envelope of backplane connector performance. The most recent addition to their high-speed backplane stable is the STRADA Whisper. Initially offered as a 25 Gb/s interface, test results indicate bandwidth capability well above that data rate. Offering a product that supports 25Gb chips—that do not yet exist—provides design headroom for several iterations of next-generation equipment.

STRADA Whisper is currently in a pre-production stage, and will be offered in 3.9mm and 4.5mm column pitch modules, with up to 65-pairs/inch signal density.

Mezzanine connectors are following a similar performance and density curve, with suppliers expanding their product offerings.





Amphenol TCS recently introduced a new high-speed InfinX™ mezzanine connector designed to support 25+ Gb/s channels. InfinX uses Amphenol 3D shield technology that results in exceptionally low crosstalk and resonances. The first tooled parts are 4-pair (44 differential pairs/inch) and 6-pair (61 differential pairs/inch) versions, with stacking heights ranging from 10mm to 40mm.
















The FCI Electronics TwinMezz™ connector provides 161 pairs per square inch density in an open-pin field design, and is capable of supporting 20+Gb/s channels.




Hirose Electric has been building up their portfolio of high-performance mezzanine connectors. Rather than utilizing a two-piece approach, Hirose has chosen to base their designs around a three-piece concept. A common header is applied to the surface of each of the two parallel boards, and an interposer establishes the stacking height.

The IT-5 connector is the most recent addition and provides 73 differential pairs and is rated to 25 Gb/s. The unique interposer module mates with existing IT-3 PCB headers to simplify the upgrading process. IT-5 modules will be available in production quantities later in 2011, and will be offered in 85- and 100-ohm versions.

Meritec recently entered this market segment with their new 480-position mezzanine connector system. Instead of using a traditional pin and socket design, the Meritec connector is a hermaphroditic interface. The primary advantage is that only one part number is required to produce the two-piece interface. The connector features low insertion and high normal forces for reliability in rugged environments, and has been tested to 5 Gb/s.




The Molex HD Mezz connector is rated to 12.5 Gb/s in circuit sizes from 91 to 403. This connector features improved solder-attach technology and is offered in stack heights that range from 16mm to 38mm.









Samtec has built an extensive array of mezzanine connectors. Their SeaRay connectors feature high density and bandwidth up to 9 GHz. As an alternative to BGA attachment, SeaRay uses unique solder-charge technology that assures consistent surface mount terminations.

SeaRay was selected as the defined interface for the Computer on Module Interconnect Technology (COMIT).




TE offers an array of stacking connector systems, including its new hybrid STRADA Mesa mezzanine connector, currently rated to 15+ Gb/s. Offered in heights from 8mm to 42mm, this unique interface features integrated power contacts rated at 14 amps each.

When fully tooled, STRADA Mesa will feature 40, 80, and 120 differential pair configurations with press-fit PCB termination.






The TE Mezalok connector system addresses the emerging market for connectors that must survive harsh environments. Designed to support the VITA 61 specification, Mezalok mezzanine connectors are targeted for extreme military and aerospace applications, and are based on Mil-C-55302 Mini-Box technology.

These connectors are rated to 5+ GHz and are BGA-attached. Connectors are available in 10, 12, and 18mm stack heights. 60- and 114-position sizes are tooled.

Bishop & Associates Comments:

• A continuous progression of high-speed/high-density backplane and mezzanine connectors are entering the market, fueled by demand for faster, smaller, more reliable interfaces.

• Connector manufacturers are continuing to refine their high-speed interfaces with improvements in shields, footprints, and materials to increase their rated bandwidth.

• Most high-speed backplane and some mezzanine connectors are now offered in both 85- and 100-ohm impedances.

• A select group of industry leaders have made the investments in technical expertise and equipment necessary to participate in these rapidly evolving market segments.

• Ball-grid attachment is the termination process of choice for mezzanine connectors, but has had limited use in backplane interfaces due to concern about solder joint fracture.

• The majority of high-speed backplane connectors have licensed second sources that offer identical electrical and mechanical performance. Second sourcing in the mezzanine segment is somewhat less prevalent, but a growing trend.

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, U.S. 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.