The MicroTCA standard has the potential to benefit from the advantages of today's industrial PCs while compensating for their shortcomings. Accordingly, MicroTCA is already also finding applications in various industries outside telecommunications. Yet there are areas in which, on account of higher requirements, the boundary conditions set out in the specification for shock and vibration are insufficient. Such areas include railway and transport technology, traffic systems, mechanical engineering, safety engineering and defence technology (Fig. 1).

Since the start of 2007 the PICMG working group "Rugged MicroTCA" has been engaged on solutions for more demanding requirements in the ruggedized sector on the one hand, particularly in regard to shock and vibration resistance, and on the other with effective heat removal in a situation of increasing demand as chips continue to increase in power. Appropriate specifications have been created in three steps. First: MicroTCA.1 - air-cooled ruggedized AdvancedMC modules and MicroTCA systems with solutions for air-cooled AMC.0 modules with greater mechanical and physical requirements. Second: MicroTCA.2 - conduction-cooled ruggedized AMC modules and MicroTCA systems with solutions for “contact-cooled” AMC modules with increased requirements, e.g. using so-called cold plates placed in contact with hot spots. And third: market-specific layered dot specifications: other requirements.

Test methods, testing systems and test procedures for the various MicroTCA components are described in the MicroTCA.1 specification on the basis of existing test specifications. This makes possible an objective comparison of the products of different manufacturers. The specification is expected to be published in September 2008, thus making specified ruggedized solutions based on AdvancedMC modules and MicroTCA systems available to the above-mentioned industry sectors as soon as possible. Implementation of MicroTCA.2 - conduction-cooled ruggedized AdvancedMC modules and MicroTCA systems - is more complex and is being carried out by a separate working group.

Cases, subracks and systems as set out in the MicroTCA.0 basic specification must pass the shock and vibration tests of IEC 61587-1 grade DL1, i.e. they must withstand accelerations of 7 g in the shock test and a vibration load of 0.5 g acceleration amplitude. The DL1 classification is designed for general industrial applications. In the IEC standard this is defined with examples such as use in power stations or situations in which low-energy impacts such as localised explosions may occur. The minimum thermal requirement was declared to be the temperature range -5°C to +45°C as per ETSI EN 300 019-1-3.

The minimum mechanical requirement of the MicroTCA.1 specification includes IEC 61587-1 grade DL3 and assumes peak accelerations of 25 g in the shock and 3 g in the vibrations tests - almost 4 and 6 times the MicroTCA.0 requirements respectively. Such systems are employed in situations with high levels of vibration such as on rotating machines (offset printing) and in railway and marine technologies. Thermal requirements under IEC 61587-1 level C3 assume ambient temperatures in the range -40°C to +85°C. These increased mechanical requirements for the ruggedized sector cater for some 85 % of applications. Many of the measures by which mechanical robustness can be enhanced, such as plate thickness, stiffening beads or strutting, are given sufficient scope by the 'normal' MicroTCA.0 standard. The MicroTCA subracks and chassis now available can thus simply be appropriately upgraded. Of particular importance are the interfaces to the modules and the robustness of mechanical connections.

Observing the 'worst-case' test specification for MicroTCA.1, AdvancedMC modules must be used with the maximum permitted weight of 700 grammes per module. This requirement, however, cannot be met with the standard AdvancedMC module locking system. Only standard AdvancedMC modules carrying up to 525 grammes were able to withstand the loading.

The very rigorous mechanical requirements of MicroTCA.1 can be satisfied with the necessary additional locking mechanism fitted to the AdvancedMC modules. For the front panels of the AdvancedMC module this means that the locking mechanism must extend in both vertical directions and fix onto the MicroTCA systems. It is particularly important that the locking operates without any force being applied to the MicroTCA backplane connector. An 'ordinary' bolt would, when turned, press the AdvancedMC subassembly board uncontrolled in the direction of the backplane and so apply a force on the connector. The use of a conventional bolt is therefore excluded. In early March 2008 Schroff presented, as the sole manufacturer, a functioning, electronically and mechanically tested AdvancedMC module fixing (Fig. 2) that fully meets the requirements of the MicroTCA.1 specification and allows locking without applying pressure on the connector.

This solution, for which Schroff has registered a patent, will be an element of the MicroTCA.1 specification. One of the bushings fitted to the front panel (blue) serves to receive an expansion anchor bolt (green) with an inner funnel. The bolt (grey) has a geometry that corresponds to the funnel of the plug. When the bolt is screwed in, the plug splays out and jams with a positive fit against the bushing fixed to the front panel. No resultant force (pressure) occurs in the direction of the backplane connector. This solution - as the only one tested to date - will be documented visually with its Schroff order number in the appendix to the specification.

The connectors to be used with ruggedized MicroTCA must also satisfy the higher requirements concerning shock and vibration resistance. Here tests such as vibration and shock resistance tests are carried out with AdvancedMC type 2 modules and the contact resistance measured. Continuity failures are then documented and the mechanical connector parts inspected visually.

In addition to telecommunications applications, MicroTCA system solutions are used in areas such as industrial automation (image processing, networking via Ethernet and controlling complex movement procedures under real-time conditions) medical technology (diagnostic instruments for ultrasound, computer tomography, magnetic resonance imaging and digital radiography systems), transport (trains with video monitoring systems, trains and aircraft with information or entertainment systems for passengers) and in military applications (similarly to telecommunications uses). In order to fulfil the high demands of telecommunications networks, the MicroTCA specification defines a comprehensive shelf management, though in non-telecomms applications this is often not required. In industrial applications the shelf management can usually be reduced to a minimum, which helps to optimise costs. On the other hand, however, it is necessary to respond to the increased mechanical stressing.