Flexible Planar Heat Pipe for Space Electronics Thermal Stress
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Solution Overview
Problem
In space-based electronic devices, the coefficient of thermal expansion mismatch between metal heat sinks and ceramic devices leads to lateral stress on interconnection structures like BGA or CGA, causing potential failure due to thermal cycling and vibrations, and existing heat removal methods in vacuum environments are inefficient and may rely on undesirable static loads.
Innovation Solution
A planar heat pipe with a flexible serpentine portion that compensates for thermal expansion mismatch by flexing in three degrees of freedom, coupled with a thermally conductive housing containing a sintered wicking material and working fluid, allowing efficient heat transfer without significant stress on interconnection structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a metal heat sink is used to remove heat from the device, then heat removal efficiency is improved, but CTE mismatch with the ceramic device causes lateral stress on BGA/CGA interconnections
Solution Approach 1:
The patent employs a flexible membrane structure as the thermal interface material between the heat sink and the electronic device. This flexible membrane can accommodate thermal expansion differences through its inherent flexibility, eliminating lateral stress on the interconnections while maintaining effective thermal contact. The membrane acts as a compliant layer that adapts to dimensional changes without compromising the thermal conduction path.
Solution Approach 2:
The invention uses a composite structure combining a rigid heat sink with a flexible membrane interface. The heat sink provides high thermal conductivity for efficient heat removal, while the flexible membrane component provides compliance to accommodate CTE mismatch. This composite approach allows each material to perform its optimal function without the drawbacks of using a single material type.
2Temperature
If a large thermally conductive structure is used for heat removal in space applications, then heat dissipation is improved, but the structure requires bolting or gluing to the PCB which increases complexity and stress
Solution Approach 1:
The patent replaces the traditional mechanical mounting system (bolts, screws, or adhesive bonding) with a flexible membrane-based attachment system. The flexible membrane naturally conforms to the device surface and maintains thermal contact through its elasticity rather than mechanical fastening. This substitution eliminates the complexity of mounting hardware and the associated stress concentrations on the PCB and interconnections.
3Reliability
If non-metallic elastomeric materials are used as heat sinks, then CTE mismatch stress is reduced, but significant sustained compressive loads are required which may be undesirable long-term
Solution Approach 1:
The flexible membrane in the invention provides the necessary compliance to reduce interconnection stress while requiring minimal compressive load. Unlike bulk elastomeric materials that need significant sustained compression to maintain thermal contact, the thin flexible membrane maintains contact through its inherent flexibility and small deflection capabilities, dramatically reducing the required compressive force while still accommodating CTE mismatch.
4Temperature
If the heat pipe structure is rigid to maintain thermal contact, then heat transfer efficiency is improved, but thermal cycling and vibrations cause stress on interconnections
Solution Approach 1:
The patent transitions from a static rigid heat pipe structure to a dynamic flexible membrane structure that can adapt to changing conditions. The flexible membrane's ability to dynamically adjust its shape and compliance in response to thermal cycling and vibrations allows it to maintain thermal contact while absorbing mechanical stresses, preventing stress transmission to the interconnections during dynamic operating conditions.
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 planar heat pipe effectively reduces stress on interconnection structures and enhances heat removal efficiency in space-based electronic devices, improving device longevity and performance by accommodating thermal expansion and vibrations without relying on static loads.
Implementation Method 1
The working fluid is a liquid at low temperature, and when it is heated by the device, turns into a vapor that travels through the chamber from a hot end of the heat pipe to a cold end of the heat pipe where it condenses back into a liquid.
Implementation Method 2
The liquid is then returned to the hot end of the heat pipe through the wicking material under capillary action that occurs as a result of the water being vaporized at the hot end.
Implementation Method 3
the coefficient of thermal expansion mismatch between metal heat sinks and ceramic devices leads to lateral stress on interconnection structures
Implementation Method 4
A planar heat pipe with a flexible serpentine portion that compensates for thermal expansion mismatch by flexing in three degrees of freedom, coupled with a thermally conductive housing containing a sintered wicking material and working fluid, allowing efficient heat transfer
Data Source
Figure 1
Figure 2~6
Figure 3~4
AI summary
A planar heat pipe for removing heat from an electronic device. The heat pipe includes a planar portion (32) defining a cool end of the heat pipe and a plate portion (40) mounted to the electronic device and defining a hot end of the heat pipe. The heat pipe also includes a serpentine portion (44) coupled to the planar portion and the plate portion, where each of the planar portion, the plate portion and the serpentine portion include an internal chamber being in fluid communication with each other and containing a working fluid. The serpentine portion can include a plurality of elements where each element is coupled to an adjacent element at substantially a 90° angle so as to allow the serpentine portion to flex in three-degrees of freedom.