Heterostructure Thermal Interface for CTE-Matched Heat Transfer
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Solution Overview
Problem
High-power semiconductor devices face mechanical stresses due to mismatched coefficients of thermal expansion (CTE) between the semiconductor device, die attach material, and metallic flanges, leading to potential damage and performance degradation during thermal cycling.
Innovation Solution
The use of heterostructure thermal interface materials with distinct volumes of conductive materials, such as alternating layers of copper and molybdenum, bonded to both the semiconductor substrate and metallic flange via a die-attach material, to facilitate effective heat transfer while minimizing CTE mismatch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional single-material thermal interface materials are used, then the structure is simple, but the CTE mismatch between semiconductor device, die attach material, and metallic flange causes mechanical stresses and potential damage during thermal cycling
Solution Approach 1:
The patent applies composite materials by creating a thermal interface material with multiple distinct volumes of different conductive materials (e.g., copper, aluminum, graphite, ceramics) arranged in specific configurations. This composite structure enables the thermal interface to have tailored thermal conductivity in different directions while providing CTE gradient to reduce mechanical stresses during thermal cycling, thus improving reliability without excessive complexity.
Solution Approach 2:
The patent implements local quality by positioning different conductive materials in specific locations within the thermal interface. For example, high thermal conductivity materials like copper are placed in regions requiring efficient heat transfer, while materials with specific CTE properties are positioned to match and transition between the CTE of the semiconductor device and metallic flange. This spatial differentiation of material properties optimizes both thermal performance and stress reduction.
2Reliability
If heterostructure thermal interface materials with multiple conductive materials are used, then thermal conductivity is enhanced and mechanical stresses are reduced, but the manufacturing process becomes more complex
Solution Approach 1:
The patent applies segmentation by dividing the thermal interface material into multiple distinct volumes or layers, each made from different conductive materials. This segmentation allows independent optimization of each material's properties and facilitates modular manufacturing approaches, where each layer or volume can be prepared and then assembled into the final heterostructure, making the complex manufacturing process more manageable.
Solution Approach 2:
The patent implements the nesting principle by arranging different conductive material volumes in nested or layered configurations within the thermal interface. This nested structure allows smaller functional elements to be integrated within larger structural components, enabling complex multi-material architectures to be built from simpler sub-components that can be manufactured separately and then combined.
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 approach enhances thermal conductivity and reduces mechanical stresses, thereby improving the reliability and performance of semiconductor packages by aligning the CTE of the thermal interface with the substrate and flange, preventing damage and degradation.
Implementation Method 1
The heterostructure thermal interface comprises a volume of a first conductive material and a volume of second conductive material that is physically distinct from the volume of first conductive material
Implementation Method 2
metallurgically bonding a top surface of a freestanding heterostructure thermal interface material to the bottom surface of the semiconductor substrate
Data Source
Figure 1A~1E
Figure 2
Figure 3
AI summary
A substrate is bonded to a conductive metallic flange via a free-standing heterostructure thermal interface material that includes physically distinct volumes of different conductive materials. The heterostructure thermal interface material (a bimetallic foil, for example) is metallurgically bonded to the bottom of the substrate on one side and metallurgically bonded to the flange on an opposite side. The constituent materials forming the thermal interface material and their dimensions can be chosen to achieve a desired thermal and/or electrical conductivity while allowing the coefficient of thermal expansion (CTE) to be matched to the substrate and/or the flange.