ICE-Lok™ : Thermally Enhanced Wedgelocks for Embedded Computing
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ICE-Lok™ : Thermally Enhanced Wedgelocks for Embedded Computing

Embedded computing systems are rapidly increasing
in power densities, making thermal solutions a major design concern. In most cases, designers
prefer a predominantly conduction cooled approach, which provides the highest reliability.
ACT’s Isothermal Card Edge, or ICE-LokTM wedgelocks, are designed to enhance card-to-chassis
conduction by enhancing the heat flow through the wedgelocks by making additional contact
between the card and the chassis. This wedgelock design offers a 30% improvement in thermal
resistance compared to similar sized commercial off the shelf wedgelocks. This enables reduction
of component temperatures of up to 10°C in some 100W card applications. ICE-Lok™ wedgelocks
have been thoroughly tested for thermal and mechanical stability with repeated insertion/removal
testing. They are compatible with VITA 3U, 6U and 9U cards; and the friction lock feature
ensures card deformation is avoided. Let’s see how it works. In this example, the ultimate cooling is provided
by a liquid cold plate along the base of the chassis which runs fluid at 55 degrees C.
The electronics board is generating 50 W concentrated near it’s center and has additional components
totaling 50 W distributed across the board. To successfully reject the waste heat to the
liquid cooled base, the heat must conduct from the components to the conduction card
frame edge, through the mechanical retainer or wedge lock and down the card guides to
the liquid base. In the baseline example, we are assuming all components are aluminum
and the wedgelock is an off the shelf design. As we analyzed the base model, you’ll notice
significant temperature rise from the cold plate to the max card temperature. The total
delta T is 69 C. In most cases, that delta T is not suitable for successful operation,
therefore designers must find ways to reduce the thermal resistance. The largest delta T in the system is from
the centralized component to the card edge, which means the design is limited by the thermal
conductivity of aluminum. By strategically embedding heat pipes, you can greatly enhance
the bulk thermal conductivity of the heat spreader. The resultant embedded heat pipe
card frame is known as a high thermal conductivity or HiK™ plate. After reinserting a HiK™ frame in place
of the aluminum conduction card frame the max temperature of the card drops from 124C
to 96C. HiK™ plates in 6U form factors can routinely achieve thermal conductivities of
600-800 W/m-K, dependent on component placement. The next area for thermal enhancement is at
the frame to chassis interface. Off the shelf wedgelocks provide mechanical attachment,
but are not efficient heat transfer devices. Due to limited surface area and poor thermal
path through metal to metal interfaces, the overall delta T is pretty significant for
a short conduction path. ACT’s ICE-Lok™ was designed to address both challenges- The
design expands in all directions, contacting an additional surface on both the board frame
and chassis. This provides more surface area while also bypassing metal to metal interfaces
as the primary thermal path. By changing from an off the shelf wedgelock
to the thermally superior ICE-Lok™, the designer continues to reduce the overall delta
T of the system. The card max temperature is now 92 C, which is a total delta T of 37
C. With these two minor changes, neither of which significantly effects geometry or weight,
the system operates over 30 degrees cooler than the baseline model. The final area effecting overall delta T is
the conduction through the card guide or chassis. Each sidewall must conduct heat from the card
interface to the liquid cooled base. Again, the baseline is aluminum with a thermal conductivity
of 167 W/m-K. To reduce this gradient, we convert the chassis to a HiK™ sidewall by
embedding heat pipes. This final change drops the overall delta
T by an additional 13 C. The max card temperature is now 79 C, which is safe operating temperature
for most electronics. From the baseline to the fully thermally enhanced model, the thermal
savings was 45 C. This type of savings can allow for higher power densities or added
margin to the system. Thanks for joining us for this example of
how ACT’s ICE-Lok wedgeloks can improve thermal performance.
For more technical information about ICE-LokTM, as well as to access an installation guide,
visit our website at ICE-LokTM wedgelocks are aluminum-based material available
in both three eighths and one quarter inch cross sections with standard 3U, 6U and 9u
lengths. A variety of coatings are also available including: Clear Chem Film, Electroless Nickel,
Black Anodized and Teflon Hard Coat. The Thermal Experts at ACT are waiting to discuss your
embedded computing systems application and help you choose the right ICE-LokTM wedgelocks
for you.

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