Ceramic-Copper Composite Grain Control for Thermal Stress
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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 affect the reliability and durability of power modules, especially in high-power and high-integration applications like electric vehicles.
Innovation Solution
A ceramic-copper composite with a specific structure, including a ceramic layer, a copper layer, and a brazing material layer, where the copper crystals in the vicinity of the ceramic layer have an average grain size of 30 μm to 100 μm, and the use of a brazing material containing Ag, Cu, Ti, and Sn/In, bonded at temperatures between 770°C and 830°C, to reduce thermal stress and prevent cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional brazing materials and bonding methods are used, then bonding strength is achieved, but thermal stress causes cracks at the bonding interface under repeated thermal cycles
Solution Approach 1:
The invention changes the physical and chemical parameters of the copper layer by controlling the average crystal grain size to be 30 μm or more and 100 μm or less. This parameter control allows the copper layer to effectively absorb thermal stress through grain boundary sliding, preventing crack propagation while maintaining bonding strength at the ceramic-copper interface under repeated thermal cycles
Solution Approach 2:
The invention creates a composite structure with specific copper crystal grain characteristics integrated with the ceramic layer and brazing material layer. The controlled copper grain structure acts as a stress-absorbing component within the composite, enabling the overall structure to withstand thermal expansion differences between ceramic and metal without developing cracks
2Power
If higher power output and higher integration are implemented, then functionality is improved, but thermal stress increases due to higher heat generation
Solution Approach 1:
By controlling the copper crystal grain size parameter within the specified range, the material's ability to dissipate thermal stress is enhanced. This allows the power module to operate at higher power levels where heat generation is increased, as the controlled grain structure provides a mechanism for stress relief that prevents thermal failure
3Reliability
If stricter thermal cycle test conditions are applied, then durability evaluation is improved, but crack occurrence increases due to higher stress
Solution Approach 1:
The controlled copper crystal grain structure serves as a pre-established stress-absorbing mechanism that cushions against thermal shocks before cracks can initiate. During stricter thermal cycle testing, this pre-configured grain structure enables the bonding interface to withstand higher stress levels without developing cracks, thereby improving durability evaluation results
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 reduces the occurrence of cracks during thermal cycle tests, enhancing the reliability and durability of power modules by managing thermal stress through grain boundary sliding and improved bonding strength.
Implementation Method 1
a brazing material layer 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 within 50 μm on a side of the copper layer from an interface between the ceramic layer and the brazing material layer is 30 μm or more and 100 μm or less
Data Source
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.