Bonded Body Copper Plate Conductivity
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Solution Overview
Problem
The fluctuation in electrical conductivity of copper plates due to the diffusion of Sn or In, which affects the electrical resistance and heat dissipation in bonded ceramic-copper circuit boards.
Innovation Solution
A bonded body comprising a ceramic substrate, a copper plate, and a bonding layer with a specific composition of Ag, Cu, an active metal, and one or two elements selected from Sn and In, where the detection amount of the first element divided by the detection amount of Ag at a specific measurement point is within a range of 0 to 0.4, suppressing the formation of low-melting-point alloys like AgSn or AgIn.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If Sn or In is added to the active metal brazing material to improve bondability, then the melting point is lowered and bondability is improved, but the diffusion of Sn or In into the copper plate forms low-melting-point alloys that reduce electrical conductivity
Solution Approach 1:
The patent controls the concentration ratio of Sn or In to Ag in the bonding layer within a specific range (0.03 to 0.5 mass%). This parameter control prevents excessive formation of low-melting-point alloys while maintaining sufficient bondability, thus resolving the contradiction between ease of manufacture and reliability
Solution Approach 2:
The patent creates a gradient distribution of Sn or In in the bonding layer, with higher concentration near the ceramic substrate interface and lower concentration toward the copper plate. This local quality variation ensures strong bonding at the ceramic interface while minimizing diffusion into the copper plate, thereby maintaining electrical conductivity
2Strength
If thermal bonding is performed at high temperature (700-950 °C) to achieve strong bonding, then bonding strength is improved, but diffusion of brazing material components into the copper plate increases, affecting electrical properties
Solution Approach 1:
The patent optimizes the Sn or In content in the active metal brazing material to within 3-30 mass%, which allows achieving sufficient bonding strength at high temperature while controlling the extent of diffusion into the copper plate. This parameter optimization resolves the contradiction between bonding strength and electrical resistance
Solution Approach 2:
The patent uses a composite bonding layer comprising Ag, Cu, active metal (Ti, Zr, or Hf), and controlled amounts of Sn or In. This composite structure provides both strong bonding capability and controlled diffusion characteristics, resolving the contradiction between bonding strength and electrical properties
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 solution effectively suppresses the formation of low-melting-point alloys, maintaining the electrical conductivity of the copper plate and enhancing the bonding strength, thereby improving the performance and reliability of ceramic circuit boards and semiconductor devices.
Implementation Method 1
the diffusion amount of tin (Sn) or indium (In) into the copper plate is a cause
Implementation Method 2
In active metal bonding, thermal bonding is performed at a high temperature of about 700 to 950 °C
Data Source
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AI summary
Provided is a ceramic circuit board that is capable of suppressing a decrease in conductivity of a copper plate while maintaining bonding strength. A bonded body according to an embodiment comprises a ceramic substrate, a copper plate, and a bonding layer that bonds the ceramic substrate and the copper plate. The bonding layer contains Ag, Cu, an active metal, and a first element. The first element is one or two selected from Sn and In. As determined by SEM-EDX analysis of an arbitrary cross section, when a point at which a detection amount of Cu is not less than 80 mass% and at which a change in slope in a graph of the detection amount of Cu is the largest is assumed to be a first measurement point, a detection amount of the first element (mass%)/a detection amount of Ag (mass%) at the first measurement point is within the range of 0-0.4. The detection amount of the first element (mass%)/the detection amount of Ag (mass%) at the first measurement point is preferably within the range of 005-02.