Direct Power Substrate Integration on Heatsinks With CTE-Matched Insulation
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Solution Overview
Problem
Existing methods for integrating power electronics substrates onto heatsinks face challenges in optimizing heat dissipation and assembly processes, particularly due to the large thermal expansion coefficient differences between ceramic and heatsink materials, leading to stress and non-uniform thermal resistance, which affects semiconductor performance and reliability.
Innovation Solution
A method involving a three-layer stack of a top copper plate, an epoxy-based resin sheet, and a heatsink with a fin structure, integrated using an autoclave process with a metal baseplate and a single bagging film for multiple stacks, utilizing sealing rings or adhesive materials to ensure uniform pressure and reduced assembly steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ceramic plate (aluminum oxide) is used as the insulating layer in DBC, then high breakdown voltage and electrical insulation are achieved, but large CTE difference with copper heatsink causes stress and warping during soldering
Solution Approach 1:
The patent changes the material parameter (CTE) of the insulating layer by transitioning from ceramic (aluminum oxide) to epoxy-based resin with ceramic particles. The resin's CTE can be tailored to closely match copper, eliminating the large CTE difference that causes stress and warping during thermal cycling and soldering processes.
Solution Approach 2:
The patent uses a composite material structure: epoxy-based resin sheet with ceramic particles as filler. This composite combines the electrical insulation properties of ceramic with the CTE-matching capabilities of the epoxy resin matrix, achieving both high breakdown voltage and CTE compatibility with copper heatsinks.
2Ease of manufacture
If thermal grease is used as TIM to mitigate CTE stress, then assembly complications are reduced, but thermal conductivity is much smaller than solder and thickness is inhomogeneous leading to ununiform heat dissipation
Solution Approach 1:
The patent changes the material properties of the TIM by using epoxy-based resin with tailored thermal conductivity and CTE. The resin's thermal conductivity can be optimized through ceramic particle filler, while its CTE matches copper, providing both good thermal transfer and stress compatibility without the inhomogeneity issues of thermal grease.
3Reliability
If solder is used as TIM, then high thermal conductivity is achieved, but the soldering process causes large stress due to CTE difference and requires careful design to prevent warping
Solution Approach 1:
The patent changes the CTE parameter of the TIM material from solder (which has large CTE difference with ceramic DBC) to epoxy-based resin with ceramic particles (which has CTE closely matched to copper). This allows the use of solder for bonding the DBC to the heatsink without inducing various complications, as the resin layer accommodates thermal expansion differences.
4Strength
If multiple separate assembly processes are used for DBC and heatsink integration, then bonding strength is ensured, but production time and complexity increase
Solution Approach 1:
The patent merges the DBC substrate and heatsink into a single integrated component by directly bonding the copper plate of the DBC to the copper heatsink using the epoxy-based resin as both insulating layer and TIM. This eliminates the need for separate assembly processes and intermediate components, reducing production steps while maintaining bonding strength.
Solution Approach 2:
The epoxy-based resin sheet serves multiple functions simultaneously: it acts as the insulating layer (replacing ceramic), as the thermal interface material (replacing separate TIM), and as the bonding adhesive. This multi-functionality simplifies the overall structure and assembly process while ensuring electrical insulation, thermal transfer, and mechanical bonding.
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 heat dissipation efficiency, reduces production costs, and improves long-term reliability by ensuring uniform thermal distribution and simplified assembly, allowing for thicker copper plates and more effective heat dissipation from power semiconductor chips.
Implementation Method 1
an autoclave process is applied on the ensemble
Implementation Method 2
a bottom layer being a top side of a heatsink, wherein the fin structure is arranged such that an outer rim of the bottom side is left blank of the fin structure
Implementation Method 3
epoxy-based resin sheet with ceramic particles as the filler is developed as a substitute of the ceramic plate of the DBC
Implementation Method 4
each aperture has a groove along its outer perimeter, in which a sealing ring is inserted
Data Source
Figure 1~2
Figure 3~4
Figure 5~6b
AI summary
Proposed is a method of directly integrating a power electronics substrate onto a heatsink, comprising the steps of providing several three-layer stacks, each of which is made of a top layer of a metal plate, a middle layer of an electrically non-conductive res-in sheet and a bottom layer being a top side of a heatsink, wherein the heatsink comprises a fin structure provided at a bottom side of the heatsink, wherein the fin structure is arranged such that an outer rim of the bottom side is left blank of the fin structure; and providing a metal baseplate plate comprising multiple apertures, each of which is designed to receive one of the stacks, wherein each aperture has a size such that the fin structure of a stack can be completely inserted in the aperture. In one solution, each aperture has a groove along its outer perimeter, in which a sealing ring is inserted, In another solution, a sealing material is placed along an outer perimeter of each aperture and/or the outer rim of the bottom side of the heatsink. Further, generating an ensemble of metal baseplate plate and stacks is conducted by inserting the stacks into the apertures of the metal baseplate plate such that each outer rim of a stack at least partially overlaps with the metal baseplate plate in such way that the stack and the metal baseplate plate are sealed by the sealing ring or the sealing material. Further, a single sheet of bagging film is provided on top of the ensemble, wherein the bagging film has a size of at least the size of the metal baseplate plate, and the area below the bagging film is evacuated. Finally, an autoclave process is applied on the ensemble.