Copper-Ceramic Bonding with Grain-Controlled Copper Purity
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Solution Overview
Problem
Existing methods for bonding copper and ceramic substrates often result in coarsening and non-uniformity of copper crystal grains, leading to issues with ultrasonic inspection accuracy, surface undulations, and increased thermal resistance, particularly under temperature cycles.
Innovation Solution
A method involving a copper member with specific impurity content and crystal grain size control, including P, Pb, Se, Te, and other elements, to suppress crystal grain growth and ensure uniform bonding, using a pressing load and heating within defined ranges to maintain grain size and aspect ratio, and employing EBSD for orientation mapping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If copper plates are bonded to ceramic substrate at high temperature (800°C or higher), then bonding strength is improved, but crystal grains of copper plates become coarse
Solution Approach 1:
The invention changes the chemical composition parameters of the copper plate by strictly controlling impurity content (P≤2ppm, Pb+Se+Te≤10ppm, S≤20ppm, total impurities≤30ppm). This compositional parameter change modifies the material's recrystallization behavior, allowing high-temperature bonding while suppressing crystal grain coarsening through controlled impurity levels that affect grain boundary energy and mobility.
2Ease of manufacture
If crystal grains become coarse in copper plates, then bonding process is simplified, but external appearance and inspection accuracy deteriorate
Solution Approach 1:
The invention changes the material parameters by precisely controlling impurity content to maintain fine crystal grain structure (average grain size 10-500μm with aspect ratio ≤2). This parameter control ensures uniform grain structure that allows ultrasonic waves to propagate accurately without scattering from large grain boundaries, thereby maintaining inspection accuracy while enabling reliable bonding.
3Manufacturing precision
If S content is increased to suppress crystal grain growth, then grain size control is improved, but local coarsening and non-uniformity occur
Solution Approach 1:
The invention optimizes the S content parameter within a specific range (≤20ppm, preferably 2-20ppm) rather than simply increasing it. This controlled parameter change provides sufficient grain boundary strengthening to suppress coarsening while avoiding excessive S that would cause local precipitation and non-uniform grain structure. The balanced composition ensures uniform grain size distribution throughout the copper plate.
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 method effectively suppresses coarsening and non-uniformity of copper crystal grains, ensuring accurate ultrasonic inspection and maintaining surface integrity even under temperature cycles, thereby enhancing the reliability of copper/ceramic bonded bodies and insulating circuit boards.
Implementation Method 1
a bonding step of bonding the copper member and the ceramic member which are laminated to each other by pressing the laminated copper member and ceramic member in a laminating direction and heating
Implementation Method 2
an average crystal grain size of the copper member before bonding is set to 10 μm or more, an aspect ratio, which means a ratio of a major axis to a minor axis of a crystal grain on a rolled surface, is set to 2 or less
Data Source
Figure 1~2
Figure 3A
Figure 3B
AI summary
A method of producing a copper/ceramic bonded body, the copper member having a composition having a Cu purity of 99.96 mass % or more, a balance of inevitable impurities, a P content of 2 mass ppm or less, and a total content of Pb, Se and Te of 10 mass ppm or less, the method includes bonding the laminated copper member and the ceramic member by pressing and heating, wherein an average crystal grain size of the copper member before bonding is 10 µm or more, an aspect ratio is 2 or less, and a pressing load is 0.05 MPa or more and 1.5 MPa or less, a heating temperature is 800°C or higher and 850°C or lower, and a holding time at the heating temperature is 10 minutes or longer and 90 minutes or shorter.