Advanced TCA and MicroTCA Find Their Niche
By Bob Hult, Bishop & Associates Inc.

Standardized hardware and software platforms offer a cost-effective and reduced design-cycle alternative to traditional proprietary system design. Telecommunications equipment manufacturers (TEMS) have been slowly migrating toward the use of standard system architecture over the past 10 years to address rapid changes in technology, as well as consumer demand for enhanced services.

One of the criticisms of adopting a standard architecture is that it tends to lock the design into what may quickly become old technology. The PCI Industrial Computer Manufacturers Group (PICMG) has addressed this concern by constantly upgrading existing standards and developing new platforms that offer backward compatibility and a clear migration path to utilization of higher performance hardware and software. A series of system platforms specifically targeted for the telecom industry demonstrates this evolution.

The Compact PCI specification was ratified in 1995, and was based on metric 3U and 6U card sizes. This PICMG standard platform offered a number of attractive features, including:

• Standard Eurocard dimensions

• High-density 2mm pin-and-socket connectors from multiple sources

• Vertical card orientation for good cooling

• Positive card retention

• Excellent shock and vibration characteristics

• Metal front panel

• User I/O connections on front or rear of module

• Standard chassis available from many suppliers

• Uses standard PCI silicon, manufactured in large volumes

• Eight slots in basic configuration, easily expanded with bridge chips

Compact PCI continues to find new applications, particularly in the embedded computer market.

The demand for enhanced features and bandwidth—together with a requirement for improved reliability, scalability, and the ability to support hot-swapping of daughtercards—led to the introduction of the Advanced Telecommunications Computing architecture (ATCA) in 2002. This full-featured platform was designed specifically to support next-generation carrier grade communication equipment.

PICMG 3.0 is the core specification defining architecture mechanicals, power, system management, fabric connectors, and Base interface (10/100/1000 Base-T).

Additional specifications were developed to support a variety of I/O interfaces:

• PICMG 3.1 Specification for Ethernet and Fibre Channel fabric interface.

• PICMG 3.2 Specification for InfiniBand fabric interface.

• PICMG 3.3 Specification for StarFabric*/Advanced Switching interface.

• PICMG 3.4 Specification for PCI Express* and Advanced Switching Fabric interface.

• PICMG 3.5 Specification for RapidIO

• PICMG 3.6 Specification for Packet routing switch

Typical systems consist of 14 slots using 12U or 13U daughtercards.

The backplane signal connector is the Z-Pack HM Zd connector from Tyco Electronics and the ERNI ERmet Zd connector. These high-speed connectors were specifically designed for multi-gigabit differential-pair signaling, and utilize integrated ground shields to minimize crosstalk and maintain consistent 100-ohm impedance though the connector.

Although this platform was introduced with much anticipation of quick adoption and huge volume, actual production equipment built on the ATCA specification has been slow to reach the market. Some of this delay may have been due to the severe telecom market downdraft that occurred in the 2000-2003 period. Manufacturers were looking to minimize the risk associated with the introduction of a totally new platform. Reluctance to transition from a proprietary to a standard platform, with the potential for losing control of the daughtercard market, was also a factor. The lack of volume kept prices higher than anticipated, which also slowed adoption.

Although this specification has been in the market for almost six years, several hardware suppliers feel that components that are defined by the ATCA specification are probably still in the late introduction or early growth stages. While telecom equipment has a relatively long design and development cycle, the market demand may now be ready to translate to volume production for this ATCA spec. Telecom manufacturers are considering the potential impact of advanced features, such as IPTV, as well as user-generated video. Chips that were designed for Compact PCI are reaching their end-of-life, and may be more difficult to source in the future, putting more pressure on equipment manufacturers to evolve to the next-generation platforms.

The Advanced Mezzanine Card (AMC) is typically used to support the various I/O protocols that OEMs use for external communication in ATCA equipment, and are designed to stack on ATCA carrier boards. AMC cards have evolved to include a wide variety of functions, are highly programmable, and enable a large degree of customization within the standard platform.

AMC cards were designed as a low-cost option, and utilize an edge connector interface on 0.75mm centerlines. In order to allow the removal of mezzanine cards from the front of the rack without removing the carrier board, a unique right-angle edge-card receptacle was developed. This connector is tooled in several configurations and is available from a variety of suppliers.

 

Recognizing the interest in platforms that are smaller, require fewer features, and are cost sensitive, PICMG approved the Micro TCA standard in 2006, where AMC cards plug directly into a backplane via a vertical edge card connector, eliminating the ATCA carrier board.

The resulting form factor offers a high degree of flexibility as users can choose from a growing library of available AMC cards. AMC cards have become the bridge between Advanced TCA and MicroTCA systems. Both are open standards, but address different segments of the market. ATCA can support large full function applications, where MicroTCA is attractive to applications that demand smaller footprints and greater modularity, as well as reduced performance and cost.

 

Each platform continues to penetrate their target markets. Suppliers of Advanced TCA connectors, card racks, and daughtercards are optimistic that products which have been in design and development for years are finally nearing introduction and volume production. Telecommunications applications demand both high availability, as well as long-term reliability. Verifying system design that satisfies these goals requires extensive testing that can extend to years. One cloud on this market is the potential for the current turmoil in global financial markets to spill into the equipment market, further delaying volume production.

MicroTCA has received much attention since its introduction, and applications in medical, industrial control, and military are appearing well beyond the target telecom market. Market sales projections for MicroTCA components are stimulating connector suppliers to enter the market. FCI Electronics, Harting, Tyco Electronics, and Yamaichi entered the market early. Molex and Samtec recently announced their intent to enter the MicroTCA connector market with identical fit, form, and function interfaces. These connectors all meet the mechanical and electrical specification, but differ in termination, to the backplane. FCI, Harting and Tyco offer compliant pin termination; FCI offers a surface-mounted version, while Yamaichi uses solderless compressive spring contact-to-gold pads on the backplane.

One issue involving AMC board tolerances has raised some concern within the industry. The AMC specification calls for the PCB contact finger width of only 0.48mm +/- 0.02mm. Contact pad centerlines are 0.75mm, leaving worst case 0.25mm spaces between the contacts. A slight misalignment of the AMC card in the receptacle can result in open or shorted contacts. Some concern has been expressed that AMC card vendors will find it difficult and expensive to maintain these tight tolerances. Since the specification calls for receptacle durability of 200 mating cycles, it may be possible that plastic wear at the connector end blocks could cause misalignment. One vendor noted that any lateral movement of the edge connector contact beam during mating can cause problems, and must be carefully controlled.

Connector manufacturers are addressing these concerns in a number of ways. Harting and ept are offering their Concard+ connector, which uses an integrated guide spring to compensate for tolerance deviations of the AMC circuit board. Tyco Electronics has added metal plates to the end blocks to insure that wear does not allow misalignment. Yamaichi goes one step further with the introduction of the MCH plug concept. By attaching a precision molded PCB tongue to the mating edge of the AMC card, the responsibility for mating interface tolerances are transferred from the PCB card to the connector manufacturer, who can control both halves of the separable interface.

The use of this two-piece concept adds cost and consumes valuable space on the AMC card, but it is a potential solution to the issue.

Further product enhancements are expected as connector manufacturers battle for market share.  Adding features and innovation to standardized products may provide the differentiation to achieving profitability in what may become a commodity product.

Bishop & Associates Comments:

• PICMG has been particularly aggressive in introducing hardware platforms that continue to evolve to incorporate advances in hardware and software technology.

• CompactPCI, Advanced TCA, and MicroTCA-based systems continue to penetrate new applications, often beyond their original telecom market.

• It is hard to measure the adoption rate of these standards, as the specified connectors are often used in many applications that are not related to the specification.

• MicroTCA appears to be well suited to address current market demands for highly scalable, lower cost, and highly reliable system platforms. The availability of a wide range of existing AMC cards should accelerate the adoption of this standard.

Robert Hult
Director of Product Technology, Bishop & Associates, Inc.
Robert Hult has been in the connector industry for over 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, Chandler, Arizona, U.S.A. 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.