Copper/Ceramic Bonded Body Grain Refinement
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Solution Overview
Problem
In insulated circuit substrates where a ceramic substrate and a copper sheet are bonded using the active metal brazing method, the formation of a compound layer at the bonded interface can lead to deformation and destruction of the active metal nitride layer when ultrasonic waves are applied, resulting in reduced bonding reliability.
Innovation Solution
A copper/ceramic bonded body is formed by bonding a copper member with a ceramic member, where the average crystal grain size of the copper member near the bonding surface is maintained small by controlling the crystal grain size ratio D1/D0 to be 0.60 or less, and diffusing Mg in the copper member to refine the crystal grains and enhance bonding reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a ceramic substrate and a copper sheet are bonded by the active metal brazing method, then bonding strength is improved, but the copper sheet becomes easily deformed and the active metal nitride layer may be destroyed when ultrasonic waves are applied
Solution Approach 1:
The invention creates a non-uniform crystal grain structure in the copper sheet where the crystal grain size near the bonding interface (within 50 μm) is deliberately kept small (D1/D0 ≤ 0.60), while the overall average grain size D0 is controlled. This local refinement at the bonding interface prevents deformation and protects the active metal nitride layer during ultrasonic welding, while the bulk material maintains its overall properties.
Solution Approach 2:
The invention changes the crystal grain size parameter of the copper sheet by controlling the D1/D0 ratio to be 0.60 or less. This parameter change is achieved through specific heat treatment processes that refine the crystal grains near the bonding interface, thereby improving resistance to ultrasonic-induced deformation while maintaining bonding strength.
2Ease of manufacture
If the crystal grains of the copper sheet are coarsened by heating, then ease of manufacture is improved, but the copper sheet becomes easily deformed when ultrasonic waves are applied
Solution Approach 1:
The invention applies local quality by creating a gradient in crystal grain size where the region near the bonding interface has refined grains (small D1/D0 ratio) while the bulk material can have larger grains. This is achieved through controlled heat treatment that affects different regions of the copper sheet differently, allowing ease of manufacture in the bulk while maintaining deformation resistance at the critical bonding interface.
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 approach effectively suppresses deformation of the copper member and destruction of the active metal nitride layer when ultrasonic waves are applied, maintaining excellent bonding reliability in the copper/ceramic bonded body and insulated circuit substrate.
Implementation Method 1
diffusing Mg in the copper member to refine the crystal grains
Implementation Method 2
when ultrasonic waves are applied
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
A copper/ceramic bonded body of the present invention is formed by bonding a copper member, which is formed of copper or a copper alloy, and a ceramic member, in which a ratio D1/D0 is 0.60 or less, D0 being an average crystal grain size of the entire copper member, D1 being an average crystal grain size of the copper member at a position 50 µm from a bonding surface with the ceramic member, D0 and D1 being obtained by observing a cross-section of the copper member along a laminating direction.