The second component that was identified for improvement was the latch plate, which is the component that separates the bottom port from the upper port. This component also houses the light pipes that transmit light from LEDs mounted on the PCB to the front face of the cage assembly. Industry standards dictate the design of the latching mechanism, so this was left unchanged. But, within the latch plate a secondary component was added to improve EMI performance and prevent leakage. Since this component is integral to the cage body there is no difference in appearance or functionality between standard SFP+ stacked cages and SFP+ stacked enhanced cage assemblies. See figure 3 for detailed view of the latch plate. The optimisation of the gasket retention plate and the addition of the
component to the latch plate yielded a significant improvement in EMI performance in the 10-15 Ghz range. Test results are shown in figure 4.
figure 4
Standard SFP+ stacked 2x4 cages were tested in order to establish baseline test data, which could be compared against thermally enhanced cages. The test setup consisted of three cages mounted to a mock PCB with half-inch spacing between each cage. The PCB was then placed within a wind tunnel that allowed the front face of each cage to protrude through a bezel. Each port was simultaneously populated with a modified SFP+ module that allowed the use of thermocouples for measurement data and allowed testing of various wattages. Thermocouples were also attached to the top, sides and back of the cage to record surface temperatures. An adjustable baffle was added to the exit end of the wind tunnel to induce backpressure. The following parameters were used for the baseline testing and follow up testing with enhanced cages:
» Airflow: 500 LFM » Backpressure: 0.25” H20 » Altitude: Sea level
Test data using 1.5 watts per transceiver indicates thermally enhanced cages outperform standard SFP+ cages by a 3% reduction in temperature, in this particular test environment. This testing also verifies that the lower inner row of ports is the most difficult to effectively draw heat away from and will remain a challenge as data rates continue to increase. TE’s thermally enhanced 2xN cages include the same EMI enhancements mentioned above.
figure 5 figure 6
Thermal enhancemenTs The real estate that the latch plate provides was also used to create an airflow channel throughout the cage body in order to allow for the cooling of the lower row of SFP+ ports. This included the addition of square shaped perforations to the outside cage walls and vertical port separators, as well as two thermal vent holes in the front of the latch plate. These perforations were optimized in size and shape in order to maintain the same improved level of EMI performance, and the two thermal vents holes added to the front of each latch plate still allow for the use of two light pipes per column. Figures 5 shows a side view of cage assembly that includes side wall perforations. figure 6 gives a detailed view of the latch plate that includes the two thermal vent holes.
figure 2 figure 3
conclusion These SPF+ EMI and thermal enhancements demonstrate TE’s commitment to providing engineered electronic components for data communications applications, while providing innovative solutions to market demands. Avnet Abacus’ longstanding relationship with TE enables rapid adoption of these and all of TE’s products.
conTribuTors Matthew Schmitt, Product Engineer, TE Connectivity Dave Dedonato, Test Engineer, TE Connectivity Patrick Recce, Product Engineer, TE Connectivity Matt Burns, Global IP&E Technical Marketing Specialist, Avnet Electronics Marketing
For more information email
te@avnet-abacus.eu
Reprinted with permission from Avnet Electronics Marketing’s AXIOM publication, March 2013.
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focus magazine - issue 16
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