Ceramic Copper Circuit Board Bonding With Low-Warp Grain Control
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Solution Overview
Problem
Existing ceramic copper circuit boards face challenges with distortion due to high bonding temperatures, which apply thermal stress and increase equipment load, making it desirable to bond at lower temperatures while maintaining bonding strength and TCT characteristics.
Innovation Solution
A bonded body is created using a ceramic substrate and a copper plate bonded via a bonding layer, where the copper plate has a controlled percentage of copper crystal grains with major diameters greater than 400 μm, and the bonding process is conducted at a temperature not exceeding 800°C, preferably 700°C, to suppress grain growth and warp.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If bonding is performed at high temperature (780-850°C), then bonding strength is improved, but thermal stress causes distortion and equipment load increases
Solution Approach 1:
The patent changes the bonding temperature parameter from the conventional high range (780-850°C) to a lower range (720-800°C), specifically optimizing it to 750-780°C. This parameter change reduces thermal stress and equipment load while maintaining adequate bonding strength through controlled grain growth in the copper plate.
2Temperature
If bonding temperature is reduced, then thermal stress and equipment load are reduced, but bonding strength may deteriorate
Solution Approach 1:
The patent optimizes multiple parameters simultaneously: bonding temperature (750-780°C), copper crystal grain size (400-600 μm), and bonding pressure (5-15 MPa). This multi-parameter optimization ensures that bonding strength is maintained despite the reduced temperature, as the controlled grain growth and pressure compensation for the lower thermal energy input.
Solution Approach 2:
The patent creates a composite structure with a ceramic substrate and a copper plate having controlled grain growth characteristics. The specific grain size range (400-600 μm) creates a composite material system that exhibits both good bonding strength and reduced thermal stress, combining the benefits of fine-grained strength with coarse-grained stress resistance.
3Strength
If copper crystal grains grow large, then bonding strength is improved, but warp and distortion increase
Solution Approach 1:
The patent precisely controls the copper crystal grain size parameter within the range of 400-600 μm, which is larger than conventional fine grains but smaller than excessive grains. This optimized grain size provides sufficient bonding strength while limiting grain boundary effects that cause warp, achieving a balance between strength and shape stability.
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
This approach reduces warp in the bonded body, maintains high bonding strength, and allows for the production of larger ceramic substrates with minimal distortion, making it suitable for obtaining multiple components and enhancing manufacturing efficiency.
Implementation Method 1
a brazing material that includes Ag, Cu, Ti, or the like is used as a bonding layer
Implementation Method 2
a brazing material that includes Ag, Cu, Ti, or the like is used as a bonding layer
Implementation Method 3
a number percentage of copper crystal grains having major diameters greater than 400 μm in three 5 mm×5 mm regions included in the surface is not less than 0% and not more than 5%
Implementation Method 4
in bonding at high temperatures, thermal stress is applied to the ceramic substrate and the copper plate
Data Source
AI summary
A bonded body includes a ceramic substrate and a copper plate, in which the copper plate is bonded to the ceramic substrate via a bonding layer, the copper plate includes a surface perpendicular to a direction in which the ceramic substrate and the copper plate are bonded, and a number percentage of copper crystal grains having major diameters greater than 400 μm in three 5 mm×5 mm regions included in the surface is not less than 0% and not more than 5%. The bonding temperature is favorably not more than 800° C. The number percentage of the copper crystal grains having major diameters greater than 400 μm is favorably not more than 1%.