Copper-Ceramic Substrate Grain Structure for Thermal Fatigue
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Solution Overview
Problem
Copper ceramic substrates used in electronic power modules face challenges with thermal fatigue resistance due to differing thermal expansion coefficients of ceramic and copper materials, leading to delamination and fissures under thermal stress, which affects the component's lifetime.
Innovation Solution
A copper ceramic substrate with a copper layer comprising two layers of different grain sizes, where the layer facing the ceramic carrier has a coarser grain size for improved thermal fatigue resistance and the outer layer has a finer grain size for increased hardness and strength, achieved through specific heat treatment or using different copper materials like Cu-ETP and Cu-OF.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the copper layer has a uniform fine grain size to improve surface homogeneity and strength, then the thermal fatigue resistance decreases due to higher proof stress under thermal expansion differences
Solution Approach 1:
The copper layer is divided into two regions with different grain sizes: a first region (10-50 μm) facing the ceramic carrier for thermal fatigue resistance, and a second region (1-10 μm) facing outward for surface homogeneity and strength. This local differentiation resolves the contradiction by optimizing each region for its specific function.
Solution Approach 2:
The copper layer is segmented into a first copper layer and a second copper layer with distinct grain size characteristics. The first layer provides coarse-grained thermal stress accommodation, while the second layer provides fine-grained surface quality, together solving the overall contradiction.
2Reliability
If the copper layer has a coarse grain size to improve thermal fatigue resistance, then the surface homogeneity and fine structure decrease
Solution Approach 1:
Different regions of the copper layer are assigned different grain sizes based on functional requirements: coarse grains (10-50 μm) at the ceramic interface for thermal fatigue resistance, fine grains (1-10 μm) at the outer surface for homogeneity and fine structure.
Solution Approach 2:
The copper layer is divided into first and second layers with distinct grain size characteristics, allowing the coarse-grained first layer to provide thermal fatigue resistance while the fine-grained second layer provides surface homogeneity.
3Strength
If the copper layer has high proof stress to increase strength, then the thermal fatigue resistance decreases due to higher sensitivity to thermal expansion differences
Solution Approach 1:
The first copper layer has lower proof stress (coarse grains) to accommodate thermal expansion differences and provide thermal fatigue resistance, while the second copper layer has higher proof stress (fine grains) to provide overall strength and surface quality.
Solution Approach 2:
The copper layer is segmented into first and second layers with different proof stress levels, allowing the first layer to be compliant under thermal stress while the second layer provides structural 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 substrate exhibits enhanced thermal fatigue resistance, improved mechanical strength, and better workability with a homogeneous fine surface structure, optimizing the copper layer's properties for various requirements without compromising other properties.
Implementation Method 1
achieved through specific heat treatment or using different copper materials like Cu-ETP and Cu-OF
Implementation Method 2
the first layer having an average grain size of greater than 100 μm and the second layer having an average grain size of less than 100 μm
Implementation Method 3
heating the composite to a process temperature of between 1060° C. and 1085° C. This produces a eutectic melt on the copper layer, which produces an integral join to the ceramic carrier
Data Source
AI summary
The present invention relates to a copper ceramic substrate incorporating a ceramic carrier, and a copper layer joined to a surface of the ceramic carrier, wherein the copper layer incorporates at least one first layer, which faces the ceramic carrier and has an average first grain size, and a second layer, which is arranged on the face of the copper layer facing away from the ceramic carrier and has an average second grain size, the second grain size being smaller than the first grain size.