SMA Thermal Interface for Heat Sink Contact Pressure
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Solution Overview
Problem
Thermal cycling caused by coefficient of thermal expansion mismatch between metal heat sinks and ceramic electronic devices leads to premature failure of solder joints in electronic devices, especially in space-based applications where controlled cooling methods are lacking.
Innovation Solution
Incorporating shape memory alloy (SMA) elements between a heat sink and a thermally conductive device to adjust contact pressure based on temperature, reducing thermal cycling by increasing heat transfer when the device is active and reducing it when inactive.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a metal heat sink is used to cool the electronic device, then heat dissipation is improved, but thermal cycling stress increases due to CTE mismatch between metal and ceramic
Solution Approach 1:
The patent changes the physical state and mechanical properties of the intermediate layer by controlling its transition temperature. The intermediate layer transitions from a rigid state at high temperature to a compliant state at low temperature, dynamically adjusting its properties to match operational conditions and reduce thermal cycling stress on solder joints.
Solution Approach 2:
The patent uses a composite structure consisting of a metal heat sink, an intermediate layer with specific CTE properties, and the ceramic electronic device. This composite design allows the system to benefit from the high thermal conductivity of metal while mitigating thermal expansion mismatch through the specially designed intermediate layer.
2Temperature
If the thermally conductive device is firmly coupled to the heat sink, then heat transfer efficiency is improved, but stress on BGA/CGA connections increases during thermal cycling
Solution Approach 1:
The patent makes the mechanical coupling dynamic rather than static. The intermediate layer's stiffness changes with temperature, providing firm coupling when hot (for efficient heat transfer) and compliant coupling when cold (to reduce stress on connections), thus adapting to operational conditions.
Solution Approach 2:
The intermediate layer acts as a pre-designed cushioning element that anticipates thermal expansion differences. It is specifically engineered to absorb and accommodate the differential expansion between the metal heat sink and ceramic device during thermal cycling, protecting the solder joints from excessive stress.
3Temperature
If controlled cooling methods (fans, liquid cooling) are used, then heat removal is improved, but device complexity and reliability in space environments worsens
Solution Approach 1:
The patent implements a self-regulating passive cooling system. The intermediate layer automatically adjusts its mechanical properties in response to temperature changes, providing stress compensation without requiring external control systems, power, or complex mechanisms - essential for space-based applications.
Solution Approach 2:
The patent extracts and eliminates the need for active cooling components (fans, pumps, control systems) by designing a passive thermal management system that relies on the inherent thermomechanical properties of the intermediate layer to manage thermal stress automatically.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The SMA elements help maintain a relatively constant temperature and reduce stress on electronic connections, thereby extending the lifespan of electronic devices by mitigating thermal cycling effects.
Implementation Method 1
one or more shape memory alloy (SMA) devices coupled to a thermal rail mounted to the heat sink and a thermally conductive device
Implementation Method 2
the SMA devices increase and decrease the contact pressure between the rail and the thermally conductive device depending on temperature
Implementation Method 3
a thermally conductive device to which the electronic device is mounted
Data Source
AI summary
A thermal transfer system for reducing temperature cycling of an electronic device. The thermal system includes a thermally conductive device to which the electronic device is mounted, a heat sink and a thermal rail mounted to the heat sink. The thermal system further includes a plurality of shape memory alloy (SMA) elements extending through aligned openings in the rail and the thermally conductive device, where the SMA elements are shaped in a deformed wire-like configuration and attempt to return to an undeformed spring-like configuration when the plurality of SMA elements are heated above a transition temperature so as to increase a heat transfer contact pressure between the thermally conductive device and the rail.