Power Module Substrate Copper Ceramic Bonding Thermal Stress
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Solution Overview
Problem
Power module substrates using aluminum sheets for the circuit layer suffer from inadequate heat dissipation due to lower thermal conductivity compared to copper, and the Ag-Cu eutectic structure layer formed during copper-ceramic bonding is prone to cracking under thermal stress due to differing expansion coefficients.
Innovation Solution
A power module substrate with a copper sheet bonded to an Al2O3 ceramic substrate, featuring an oxide layer containing Ti, Hf, or Zr, and an Ag-Cu eutectic structure layer of 15 µm or less, which allows for deformation and prevents cracking during thermal cycles, and includes a heat sink for effective heat dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If copper sheet is used for the circuit layer to improve heat dissipation, then thermal conductivity is improved, but the Ag-Cu eutectic structure layer becomes very hard and prone to cracking under thermal stress
Solution Approach 1:
The patent changes the chemical composition parameters of the brazing material by adding specific elements (Ti, Zr, Hf, Nb) to form an oxide layer, which modifies the properties of the Ag-Cu eutectic structure layer to reduce hardness and improve crack resistance while maintaining heat dissipation capability
Solution Approach 2:
The patent creates a composite bonding structure consisting of multiple layers: oxide layer, Ag-Cu eutectic structure layer, and additional elements (Ti, Zr, Hf, Nb) that work together to provide both thermal conductivity and mechanical flexibility to prevent cracking
2Ease of manufacture
If aluminum sheet is used for the circuit layer to reduce cost, then manufacturing cost is reduced, but thermal conductivity and heat dissipation capability deteriorate
Solution Approach 1:
The patent changes the material parameter from aluminum to copper for the circuit layer, accepting the higher cost in exchange for significantly improved thermal conductivity and heat dissipation capability, which is critical for high-power density applications
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 solution effectively suppresses ceramic substrate cracking and ensures reliable bonding, enabling efficient heat transfer and dissipation, even with increased power density.
Implementation Method 1
an oxide layer is formed on the surface of the ceramic substrate between the copper sheet and the ceramic substrate, and an Ag-Cu eutectic structure layer is formed on the oxide layer
Implementation Method 2
shear stress caused by a difference in thermal expansion coefficient between the ceramic substrate and the copper sheet is applied during loading of a thermal cycle
Implementation Method 3
the Ag-Cu eutectic structure layer is not deformed and there is a problem in that cracking or the like occurs in the ceramic substrate
Implementation Method 4
the thermal conductivity of aluminum is lower than that of copper. Accordingly, in the case of using an aluminum sheet as the circuit layer, heat from a heat generating body such as an electrical component or the like which is mounted on the circuit layer cannot be spread and dissipated
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
A power module substrate according to the present invention is a power module substrate in which a copper sheet made of copper or a copper alloy is laminated and bonded onto a surface of a ceramic substrate (11), an oxide layer (31) is formed on the surface of the ceramic substrate (11) between the copper sheet and the ceramic substrate (11), and the thickness of aAg-Cu eutectic structure layer (32) is set to 15 µm or less.