Pyrolytic Graphite Heat Spreader Anisotropic Orientation
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Solution Overview
Problem
Conventional heat spreaders made of solid thermally conductive metals have limited ability to efficiently dissipate heat due to their thermal conductivity characteristics, which are inadequate for managing the increasing heat dissipation requirements of smaller electronic components.
Innovation Solution
The use of pyrolytic graphite strips, cut and oriented such that their thermal conductivity in the xy plane is maximized, allowing for rapid heat transfer along the length and thickness directions while minimizing heat transfer across adjacent strips, thereby enhancing heat dissipation efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solid thermally conductive metal is used for heat spreader, then heat conduction is achieved, but thermal conductivity characteristics are limited and heat dissipation efficiency is insufficient
Solution Approach 1:
The patent uses pyrolytic graphite, a composite material with highly anisotropic thermal conductivity properties. The material combines carbon layers oriented to provide high thermal conductivity in the plane (a-direction) while maintaining low conductivity in the thickness direction (c-direction), creating a composite structure that optimizes heat spreading while limiting heat transfer to the sink.
Solution Approach 2:
The patent applies local quality by orienting the pyrolytic graphite strips such that their high thermal conductivity a-direction is parallel to the heat flow path from the heat source. This local optimization ensures that heat is efficiently conducted along the desired path while the c-direction perpendicular to the layers provides thermal resistance, creating different thermal properties in different directions and locations within the spreader.
2Speed
If pyrolytic graphite strips are cut and oriented at 90 degrees, then thermal conductivity in xy plane is maximized for rapid heat transfer, but heat transfer across adjacent strips is minimized
Solution Approach 1:
The patent divides the heat spreader into multiple discrete pyrolytic graphite strips arranged in a grid pattern. Each strip is oriented with its high-conductivity a-direction parallel to heat flow, while the c-direction perpendicular to the layers creates thermal barriers between adjacent strips. This segmentation allows efficient heat conduction along each strip while minimizing lateral heat transfer to adjacent strips, reducing energy loss.
3Area of stationary object
If multiple pyrolytic graphite strips are placed side by side, then heat spreading area is increased, but thermal conductivity characteristics must be optimized
Solution Approach 1:
The patent transitions from two-dimensional heat spreading to three-dimensional heat management by utilizing the anisotropic properties of pyrolytic graphite. The strips are oriented vertically with their a-direction parallel to heat flow, creating a 3D thermal conduction path that maximizes heat spreading area while optimizing thermal conductivity through proper orientation of the crystalline structure in multiple dimensions.
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
This configuration enables more effective heat transfer from electronic components to heat sinks, offering improved thermal conductivity and weight savings compared to traditional materials like copper.
Implementation Method 1
Heat is conducted from the heat source into the first strip and second strip. Heat is conducted through the heat spreader in the direction of the a directions or axes of the pyrolytic graphite strips.
Implementation Method 2
Thermal conductivity in the xy plane of the pyrolytic graphite sheet is greater than in the z direction. The thermal conductivity of the sheet in the z direction or as is commonly referred to as the c direction is relatively low as compared to the thermal conductivity in the xy plane or as is commonly referred to as the a directions or axes.
Data Source
AI summary
A heat spreader having at least two adjoining strips of pyrolytic graphite material is made by cutting a strip from a sheet of pyrolytic graphite in the z direction. Thermal conductivity in the xy plane of the graphite sheet is greater than in the z direction. The z direction cut provides strips which are then each individually oriented 90 degrees such that the thickness direction of the original pyrolytic graphite sheet becomes the width or length of the cut strip. A face on the side of a first strip adjoins a face on the side of a second strip. Due to the greater thermal conductivity in the xy plane of the strips as compared to in the z direction heat transfers more rapidly in the length and thickness direction of the strips than across adjoining sides of the oriented strips.