Feature: Rail electronics
One approach to thermally managing
a design is to use an aluminum board assembly to shield the critical heat areas; another is to lead the heat away from the components through the PCB’s copper layers. Both methods require space, which must be considered at the design stage. To minimise the thermal and
mechanical stress to the computing system, the hot components must have a reliable thermal connection to their cooling elements. Te connection to the CPU can snap if it’s too rigid or too much pressure is applied to it. To obtain constant pressure, Duagon offers a spring mechanism, which takes up minimal space on the PCB. By selecting the correct spring force, a constant pressure between the heat sink and the CPU can be generated. In addition, the PCB may creep over
time, due to pressure and temperature changes, and screw connections can
loosen. To prevent the thermal interface material from drying out, the use of high-quality materials is essential.
CCA housing For rail applications, a CCA (Conductive Cooled Assembly) housing is a good solution and meets the AAR Standard (Association of American Railroads) – even though until now it was frequently overlooked. In CCA systems, the housing serves as a heat sink; its large surface area acts as a cooling surface, easily managed through convection; see Figure 3. Such systems can have four modular
concept units with maximum 60W dissipation at 55o
C ambient temperature
(Figure 4), or even nine of them for a maximum 120W dissipation, also at 55o
ambient temperature, without needing forced air flow. Since the component surface of the cards can’t be directly connected to the housing wall, the heat
C
must be brought to the contact surface between the plug-in card and the housing. At the same time, this contact surface must be thermally maximised. In this process, assemblies are packed in aluminum and the heat is distributed to the housing via guide channels, which are made of solid aluminum. Te cards themselves are wedged with locks into the grooves of the guides. Te fixings ensure a mechanically- robust and thermally-effective coupling to the housing, and that the heat is dissipated optimally – the housing becomes a heat radiator. Also, choosing the right material is
also important here, like aluminum or copper. Secondly, the components must be positioned correctly within the housing, and the heat-transporting cooling blocks must have appropriate mass to ensure optimum heat transport. Using these methods minimises maintenance, compared to actively-cooled systems.
Figure 1: Half 19” rack for CompactPCI serial cards with replaceable fan tray
Figure 2: CompactPCI serial card with Intel TigerLake CPU
Figure 3: CCA housing for CompactPCI card CPU
Figure 4: CCA housing for four modular concept units
www.electronicsworld.co.uk March 2023 21
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