Publication date: 02 March 2010
HARTING MicroTCA(TM) connectors are extremely robust and therefore suitable for use in rugged environmental conditions. In these applications, connectors have to guarantee secure connections despite being subjected to shocks, impacts and vibrations. HARTING uses con:card+ and plug connectors also for telecommunications and other applications.
Originally deployed for the telecommunications industry,MicroTCA uses a robust mechanism that is suitable for simple industrial applications. Conventional MicroTCA systems are, however, limited to low shock and low vibration applications. In various tests, HARTING has now shown that solutions such as con:card+ can also be utilised in areas with strong vibrations (for example, in transport systems or aviation).
These tests were based on PICMG specifications. The ‘RuggedMicroTCA’ workgroup is currently developing various specifications that expand the existing MTCA.0 base specification. Additional requirements and tests for the use of MicroTCA in rugged environmental conditions are to be established. The requirements that connectors have to meet are already largely defined.
The requirement profiles are currently divided into three specifications, which target industrial and outdoor applications (MTCA.1), applications from the transportation market (MTCA.2) and aviation and defence applications (MTCA.3). The shock and vibration-resistance requirements are graduated within the three profiles, depending on the expected application areas.
The specifications are named after the cooling concept that, under MTCA.1, is known as ‘rugged air cooled’. This refers to air-cooling that is to meet additional requirements regarding vibration and shock testing and is planned, in particular, for industrial applications. As extended temperature ranges are also defined, MicroTCA is also interesting for outdoor applications (e.g. base stations for telecommunications).
MTCA.2 systems have to meet the ‘hardened air cooled Specification’, and are therefore to be designed for more extreme shock and vibration conditions. Air-cooling is also planned for these systems, however, with tougher requirements in terms of shock and vibration.
The MTCA.3 specification describes cooling without moving parts (‘hardened conduction cooled specification’). The modules are fixed in the system by means of wedge locks so that the heat can be discharged via cold plates.
In all three applications, the system is often exposed to enormous stresses. It is therefore absolutely essential that the connector withstand this stress without any contact interruption. This poses a great challenge for a card edge connector such as MicroTCA, and HARTING is the first company to meet this challenge.
To ensure that the HARTING MicroTCA connector can withstand these stresses, HARTING has carried out several tests and simulated the described conditions in an accredited laboratory. The aim was to prove that HARTING solutions already meet future requirements for MTCA.1 to MTCA.3. The test system was equipped with mechanical components accordingg to the MTCA.0 specification. Conventional AdvancedMC modules according to PICMG AMC.0 were used as test cards.
For MTCA.1, a sinusoidal vibration with an alternating frequency of 2 Hz to 200 Hz is planned. This frequency range will pass through ten times in three axes; the test setup will simulate three times the gravitational acceleration (30 m/s²). No contact interruptions should occur during the tests. The HARTING con:card+ connector passed this test successfully.
However, test conditions do not take into account the fact that much greater accelerations can develop in the system. In order to simulate an extreme case, the test cards used with the ‘double full size’ form factor weigh 700 grams. The card that, as in the real system, reveals a little play in the guide rails and fastening, gets in resonance when passing through a certain frequency range. In the axis of oscillation perpendicular to the test card, in the resonance range, up to 20 times the gravitational acceleration was measured on the test card close to the connector.
When subjected to these enormous stresses, no contact interruptions occurred in the HARTING con:card+ connectors tested. The high normal force of the contacts stabilised the test cards during high accelerations. This prevented any contact interruptions that could otherwise have been caused by increasing the resonance. The extreme case (vibration of the card against the insulator, which can cause permanent damage to the connector) was avoided.
In the vibration direction lengthwise of the connector slot, the GuideSpring acts as stabiliser. The original purpose of the GuideSpring is to offset any possible tolerance deviations by means of a defined positioning. The GuideSpring presses the card against the opposite wall and fixes it. During stronger shocks and vibrations, this fixing by the GuideSpring prevents any movement in the lengthwise direction of the connector and thus also any contact interruptions.
The vibration test is followed by six shocks in each of the three axes using the same test setup. These shocks simulate 25 times the gravitational acceleration. The HARTING con:card+ connector also passed this shock test without interruptions.
Besides the HARTING connectors, two conventional MicroTCA(tm) connectors without con:card+ features were also tested. In the test, the conventional MicroTCA connectors revealed regular contact interruptions in two out of three axes. These interruptions occurred in both the vibration and the shock test. These are precisely the two oscillation directions described in the above.
An optical evaluation of the test modules revealed the reason for the contact interruptions. The wear of the connector contacts on the gold pads (after 100 mating cycles and the vibration and shock test) shows that the test module moved in the connector. This movement was so great that the contact fell off the gold pad.
However, for the HARTING con:card+ connector, during mating cycles, the GuideSpring displaced the module somewhat towards the middle and held it securely in place during the vibration and shock test. The GuideSpring thereby makes a fundamental contribution to the good performance of the con:card+ connector compared with connectors without GuideSpring.
HARTING offers the plug connector as an alternative to the card edge and gold pads on the AdvancedMC card. The manufacturing tolerance of the plug connector is much lower than that of the PCB card edge. Contact interruptions that are based on the tolerance problems of the card edge are prevented from the outset. This was also shown in the vibration and shock test, which the plug connector passed successfully without any contact interruptions.
The specification for the MTCA.2 has only just started, however, the key requirements for the backplane connectors have already been more or less established.
A vibration test with random vibration will be defined as the test condition. The intensity of the vibration and thus the system stress is measured in the so-called PSD level (power spectral density). The test, as is discussed today in the PICMG, is to be carried out with the PSD level 0.1 g²/Hz. This corresponds to a maximum acceleration of 13 g. In tests, the con:card+ connector has met this and further requirements: it passed the test at a PSD level of 0.2 g²/Hz (max. 18 g). Nor did the shock with 40 g reveal any contact interruptions.
In the MTCA.3 specification, the AdvancedMC cards are firmly fixed to the system. After tightening the wedge locks, there is no more play in the guide rails. In the test for the hardened conduction cooled specification, the test setup is also fixed in this way. Only the contact area is tested but with higher requirements, however, the system is to withstand even higher stresses
A test with random vibration is also defined (in accordance with EIA-364.28). The test condition will be a PSD level of 0.2 g²/Hz. The con:card+ connector also passed this test successfully. In addition, the HARTING con:card+ has even passed this test at a PSD level of 1.5 g²/Hz without contact interruption.
The shock test for MTCA.3 is based on the VITA 47 and the MIL-STD-810 specification with 40 times the gravitational acceleration. HARTING increased this requirement again and tested successfully with 50 times the gravitational acceleration.
The PICMG will continue to work on a specification for a rugged MicroTCA system. It is expected that the specifications and requirements will be changed and adjusted during the course of the discussions. The tests show that the HARTING MicroTCA connectors can be used in systems under rugged environments, such as outdoor, transport, aviation and defence applications, and also offer high contact reliability. Conventional MicroTCA connectors, on the other hand, produced much poorer results and cannot currently be used in the same application spectrum.
Michael Seele is Global Product Manager for TCA Connectors, Germany, with the HARTING Technology Group. For Further Information Contact: michael.seele@HARTING.com
