Solving the High-Speed Challenge for Space-Constrained Applications

By Chris Heard, Teradyne Hardware System Architect

With all of the many variations of high-speed connectors currently on the market, some applications require specific characteristics that are not fully satisfied with the current crop of products. Unique operating environments or performance requirements demanded by select classes of equipment or applications are the genesis of new connector development projects. The fruits of these efforts often push the boundaries of current interconnect technology and lay the foundation of the next step to enable even more advanced electronic systems.

Over the past several years, system designers have been concerned about the escalating demands for power and the required cooling. Efficient power distribution and thermal management have become key aspects of new system design. Teradyne offers several backplane interfaces that feature integrated high-speed and low-speed connectors with power modules to handle the increasing current loads. The next step was to address the issue of facilitating adequate airflow through low-profile chassis using midplanes.

Susceptibility to mating pin damage has been a persistent problem with traditional two-piece pin and socket backplane connectors. Users are demanding interfaces that can survive a high number of mating cycles, as well as resist damage through the manufacturing and assembly processes.

 The answer is the development of the new low-profile Aptera™ connector.

Application: Small form factor applications that are found in the storage market. Products would include controller cards used in disk arrays, JBODs (just a bunch of disks) and 1U-2U servers.

Problem: Achieving electrical performance and mechanical reliability in small form factor applications while balancing power and cooling requirements. Storage products, for example, are far less tolerant of mechanical failures than networking products.

 Considerations:

• Achieving speeds of 6.25 Gb/s with margin to spare

• Preventing bent pin nightmares in a product that is less tolerant of a hardware failure

• Distributing more power and cooling in a smaller space

Today's electronics packaging requires that backplane design, interconnect selection, and cooling be addressed at the same time, not in separate silos. Only a well-integrated system solution will balance performance and mechanical needs.

Achieving Speeds of 6.25 Gb/s with Margin to Spare
In disk array applications, the connector used for the controller needs to handle Fibre Channel, SAS, and SATA signal speeds up to12 Gb/s. However, there are very few low-profile interconnect options available for even reaching speeds of 6.25 Gb/s that can also provide the required headroom for future upgrades.

The need to measure cost performance in terms of gigabyte dollars per rack unit is becoming increasingly important. Drive array vendors are now forced to allocate as many square centimeters of rack space to disk drives as possible. Greater packaging density can also significantly increase the complexity of the design.

The emergence of SAS, SATA, and 2.5" drive form factors is changing drive array packaging from an implementation detail to an art form. In the past, the “box” design was routinely sent to a subcontractor for completion. Today, that design work is considered a core competency by many OEMs and part of their intellectual property portfolio.

Interconnect choices must be made that meet today's requirements, but they must also adequately take into consideration the complexity of the system design and the need for additional performance in the future. Connectors need the margin to improve the ratio of gigabyte dollars per rack unit without re-designing and replacing the midplane. Suppliers must be able to ship disk drive upgrades that can be  reliably hot-swapped for simple field replacement.
 

Preventing Bent Pin Nightmares
For storage products in particular, mechanical reliability is more crucial than in networking products. While there are some workarounds, such as re-routing traffic if a network I/O card should fail, the scenario for storage applications can be a nightmare. Most disk arrays have the ability to handle hardware failures, but connector-related intermittent problems are largely impossible to debug in the field and cannot be tolerated if you are in the middle of a disk drive write or read acknowledgement.  

A single bent pin on either side of a disk drive plug-in assembly can create a mechanical virus when blind-mating with the midplanes. Using a low-profile connector that provides plenty of wipe and guidance on the mating interface is crucial.

If meeting European design standards is important, low-profile connectors allow for a smaller card pitch so that more cards can be packed into a shelf. This is particularly important when designing for European standards in datacom and telecom switches, routers, and gateways — all of which are used to interconnect the vast packet and switched systems found in today's wired and wireless networks.

Managing Power and Cooling
As drive-packaging density continues to increase with the introduction of the 2.5" form factor, the product feature list doesn't get any shorter. Redundant power delivery, redundant cooling, and reducing chassis resonance due to rotational vibration are all still required.

Reducing drive resonance is commonly done with sheet metal or die cast carriers. These carriers can block airflow on the inlet side of the chassis. Cutouts in backplanes required for airflow can easily drive up midplane layer count and costs – the wrong direction for disk array suppliers.

Connectors on the midplane must be of a low enough profile so as not to block air flowing from the front of the chassis to the back of the chassis. A low profile connector construction that allows for optimal airflow may help to keep midplane costs in check by reducing the amount of cutouts required.

The Solution
The Aptera™ connector consists of a unique two-piece edge connector that can perform at speeds up to 6.25 Gb/s with signal densities of up to 46 single-ended lines per inch. The backplane half is compliant pin terminated to the board, while the daughtercard connector utilizes straddle-mounted contacts. The exceptionally low profile of the connector presents minimal obstruction to airflow, while the robust edge contacts resist damage. Dedicated power modules efficiently distribute up to 3 amps per contact and are packaged in the same low-profile configuration.

Chris Heard, Hardware System Architect, Teradyne Connection Systems

Chris Heard is a hardware system architect for Teradyne Connection Systems, and has more than 20 years experience in electronics packaging. Prior to joining Teradyne in 2002, he spent 11 years designing backplanes, chassis and cooling systems for networking and storage companies such as Chipcom, 3Com, and Cereva Networks. Heard holds patents on chassis level cooling, EMI containment, and disk drive packaging. He received a BSME degree from the University of Massachusetts at Amherst in 1983.