Feature: Embedded
rate will decrease. Terefore, simply passing a lab test can’t be considered proof of compliance, as this can only be determined aſter carrying out accurate measurements. Tis motivated Congatec engineers to build specific test labs and equipment; see Figure 2. Working in a safe zone increases system accuracy and efficiency. Technicians first optimise designs with simulation, although this requires extensive receiver (Rx) and transmitter (Tx) compliance measurements to verify the optimisations. To prepare high-speed interfaces such as COM-HPC,
Congatec set up a test station to characterise new generations of transmitters and receivers, including PCIe Gen 5.0, USB 4.0 and others.
Developers must focus on early compliance testing to guarantee their solutions’ efficient operation during testing and in the field
Heat losses As thermal and electrical properties interact with each other, heat stress becomes yet another problem when establishing compliance, particularly crucial as COM-HPC server and COM-HPC client module connectors handle power to 300W and 200W respectively. Heat loss should also be optimised for all semiconductor
and power elements as well as the CPU. A successful thermal connection suggests a successful electrical connection with possible interference on signal lines. Tere are two types thermal simulations that can help with optimisation: a purely thermal one that mainly prioritises component heat, and one that relies on electrothermal simulation by considering the currents in the circuit board – and specifically in the power supply. Vias distribute the heat to large copper surfaces of the ground plane, making their positioning very important; see Figure 3. Heat from the circuit board also impacts the resistance of the
nearby signal lines, affecting signal quality. When signal clarity is affected, a domino effect occurs that ultimately impacts the cooling concept.
Gaining compliance Te most fundamental goal in gaining compliance is collecting data to prove it, confirmed through measurement. To successfully show proof of compliance, the entire unit, including the COM and matching carrier board, should be tested. Teams such as Congatec’s then work toward ruling out any technical difficulties that might occur, effectively guaranteeing that customers can pass their own compliance tests.
Figure 2: The Congatec test lab uses advanced precision test instruments that measure to 36GHz
Figure 1: Establishing the compliance of a large number of high-speed interfaces is a significant obstacle when it comes to COM-HPC server modules
Figure 3: Copper thicknesses and the number and placement of vias greatly impact temperature. This graph shows how temperature decreases by about 12% in seven iterations
www.electronicsworld.co.uk May 2021 27
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