Ceramic-Copper Composite Grain Control for Thermal Cycle Cracking
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Solution Overview
Problem
Conventional ceramic-metal composites face issues with thermal stress and cracking due to differences in thermal expansion coefficients, particularly under stringent thermal cycle tests, which can lead to bonding defects and reduced thermal resistance, posing reliability concerns for power modules, especially in high-power and high-integration applications like electric vehicles.
Innovation Solution
A ceramic-copper composite with a brazing material layer containing Ag, Cu, Ti, and Sn/In, where the copper layer is formed using an oxygen-free copper grain control material, and the crystal grain size of copper crystals is controlled to be between 30 µm and 100 µm to reduce stress and prevent cracking, achieved through specific bonding conditions and material selection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ceramic-metal composite is used with standard bonding methods, then manufacturing process is simple, but thermal stress causes cracks at bonding interface under thermal cycle conditions
Solution Approach 1:
The invention changes the copper crystal grain size parameter to 30 μm or more and 100 μm or less, which optimizes the mechanical properties and thermal stress resistance of the copper layer, thereby improving bonding reliability under thermal cycling conditions without significantly complicating the manufacturing process
Solution Approach 2:
The invention uses a composite structure consisting of a ceramic layer, a copper layer with controlled crystal grain size, and a brazing material layer. This composite material system leverages the complementary properties of each material to achieve both high reliability and manageable manufacturing complexity
2Reliability
If copper crystal grain size is not controlled, then manufacturing process is simple, but cracks occur on ceramic material side under thermal stress
Solution Approach 1:
The invention specifies a precise parameter range for copper crystal grain size (30-100 μm) that balances crack resistance with manufacturing feasibility. This parameter control prevents ceramic cracking under thermal stress while maintaining reasonable manufacturing precision requirements
Solution Approach 2:
The copper crystal grain size is controlled during the bonding process itself, rather than requiring separate post-processing steps. This preliminary action of grain size control during manufacturing prevents crack formation before thermal cycling occurs, improving reliability without adding complex post-manufacturing steps
3Reliability
If brazing material layer is too thin, then bonding strength is sufficient, but stress relaxation capability is insufficient under thermal cycle
Solution Approach 1:
The invention optimizes the thickness parameter of the brazing material layer to balance two competing requirements: maintaining sufficient bonding strength to hold the ceramic and copper layers together, while providing adequate thickness for stress relaxation during thermal cycling. This parameter optimization improves thermal cycle durability without compromising bonding strength
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 composite effectively reduces the occurrence of cracks during stringent thermal cycle tests, enhancing the reliability and durability of power modules by managing thermal stress through controlled copper crystal grain sizes and improved bonding characteristics.
Implementation Method 1
a brazing material layer which is present between the ceramic layer and the copper layer
Implementation Method 2
an average crystal grain size D1 of copper crystals at least partially present in a region P1 is 30 μm or more and 100 μm or less
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
A ceramic-copper composite having a flat plate shape, including: a ceramic layer; a copper layer; and a brazing material layer present between the ceramic layer and the copper layer. When a region having a length of 1,700 µm in a long-side direction is a region P on a cut surface of the ceramic-copper composite obtained when the ceramic-copper composite is cut with a plane perpendicular to a main surface of the ceramic-copper composite, an average crystal grain size D1 of copper crystals at least partially present in a region P1 within 50 µm on a side of the copper layer from an interface between the ceramic layer and the brazing material layer in the region P is 30 µm or more and 100 µm or less.