AdvancedMC modules for Rugged MicroTCA

A "worst case" was defined to provide a test template for AdvancedMC modules compliant with the MicroTCA.1 specification:

• Peak acceleration rates of 25 g for shock testing and 3 g for vibration testing
• Maximum permissible weight of 700 g per module

This requirement was met with an additional screw interlock on the AdvancedMC modules. A patent application has been submitted for this solution. The AdvancedMC module faceplates have to be made longer vertically at both ends (flange) and must be fastened to the MicroTCA systems.

Making things more difficult is the requirement for the interlock to be made without any force being applied to the connector on the MicroTCA backplane. When turned to tighten, a "normal" screw would push the PCB on the AdvancedMC module toward the backplane to an extent which is not defined, thereby exerting force on the connector.

Schroff offers a working and tested AdvancedMC module fastener which meets the requirements of the MicroTCA.1 specification (i.e. interlock without exerting pressure on the connector) in full.

Schroff's AdvancedMC module fastener: 1 = MicroTCA front panel, 2 = AdvancedMC front panel, 3 = front panel with flange, 4 = additional screw interlock, 5 = Torx screw head T10

Diagram showing screw interlock on AdvancedMC modules

Application of the fastener

An expansion bolt (green) with an internal cone fits into a bushing (blue), which has been welded to the front panel. The screw (gray) is shaped to match the expansion bolt's cone. When the screw is tightened by turning, the bolt expands, forming a positive-fit connection with the bushing fastened to the front panel. As such, no force is exerted in the direction of the backplane connector.

This solution, for which Schroff has a patent pending, is an integral component of the MicroTCA.1 specification.

Schematic diagram of Schroff's interlock screw, patent pending: 1 = expansion bolt, 2 = knurled screw, 3 = bushing, 4 = front panel, 5 = welded, 6 = threaded bar, 7 = MicroTCA subrack

Schroff retention device

Excerpt from the Rugged MicroTCA Specification PICMG MTCA.1, attachment B.2:

Figure B-1 shows the Schroff retention device, part no. 61850-100 (included in delivery: 1 x knurled thumbscrew M3, 1 x sleeve, 1 x collet; assembled).

Figure B-1: Schroff retention device, assembled

Tests

Earthquake test on a MicroTCA subrack (MicroTCA.0)

Special enclosure for testing the interfaces (AdvancedMC interlock and MicroTCA connector)

Schocktest

Shock test at 25 g with Schroff MicroTCA.1 module screw connection

Shock test at 25 g without Schroff MicroTCA.1 module screw connection