Ceramic-Copper Bonding Layer Composition for Faster Thermal Joining
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Solution Overview
Problem
The existing methods for bonding a ceramic substrate and a copper plate, such as those used in circuit boards, face challenges with mass productivity due to the need for vacuum processing and slow batch processing times, which limit the heating and cooling rates and result in long processing times.
Innovation Solution
A bonded body comprising a ceramic substrate, a copper plate, and a bonding layer containing Ag, Cu, Ti, and one or two selected from Sn and In, where a Ti alloy exists at the bonding boundary with a concentration of at least 30% over 30 μm, enhancing the bonding strength and suppressing the diffusion of Ag, Sn, and In into the copper plate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If vacuum thermal bonding is performed using Ti-containing brazing material, then bonding strength between ceramic substrate and copper plate is improved, but processing time increases significantly due to batch processing requirements
Solution Approach 1:
The invention changes the chemical composition parameters of the brazing material by adding Sn and/or In elements to the Ti-Ag-Cu system. This compositional modification enables the material to achieve adequate bonding strength without requiring vacuum conditions, allowing atmospheric pressure bonding processes that can be performed continuously, thus resolving the contradiction between bonding strength and productivity
Solution Approach 2:
The invention eliminates the requirement for vacuum (inert environment) by formulating a brazing material that can bond effectively in atmospheric conditions. The addition of Sn and/or In creates a eutectic system that melts and flows readily at bonding temperatures, forming strong bonds without needing vacuum protection, thereby enabling continuous processing and improving productivity
2Reliability
If slow heating and cooling rates are used in batch processing, then bonding quality is maintained, but processing time increases to over 24 hours per batch
Solution Approach 1:
The invention utilizes phase transition characteristics of the Ti-Ag-Cu-Sn-In brazing material, specifically the eutectic melting point around 780°C. The material undergoes controlled solid-liquid phase transition during bonding, allowing rapid heating and cooling while maintaining bonding quality. The phase transition enables the material to flow and fill gaps quickly during melting, then solidify rapidly upon cooling, reducing total processing time while ensuring reliable bonds
3Strength
If Ti is used as active metal for bonding, then bonding strength is enhanced, but Ti nitriding or oxidation occurs before bonding, requiring vacuum processing
Solution Approach 1:
The invention creates a composite brazing material system combining Ti, Ag, Cu, Sn, and In elements. The Ti component provides active metal bonding capability for strong adhesion to ceramic substrates, while Ag and Cu provide ductility and electrical conductivity, and Sn/In lower the melting point. This composite formulation allows the material to function effectively in atmospheric conditions without vacuum, eliminating the need for complex vacuum bonding apparatus while maintaining enhanced bonding 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 proposed solution enables faster bonding processes with increased heating and cooling rates, improving mass productivity while maintaining strong bonding strength and reducing the diffusion of elements that could adversely affect the copper plate.
Implementation Method 1
a Ti alloy of Ti and at least one selected from Ag, Cu, Sn, and In existing at a bonding boundary between the copper plate and the bonding layer
Implementation Method 2
thermal bonding is performed under a pressure of not less than 1×10−3 Pa during the bonding
Data Source
AI summary
A bonded body includes a ceramic substrate, a copper plate, and a bonding layer provided on at least one surface of the ceramic substrate and bonding the ceramic substrate and the copper plate, in which the bonding layer contains Ag, Cu, Ti, and a first element being one or two selected from Sn and In, a Ti alloy of Ti and at least one selected from Ag, Cu, Sn, and In existing at a bonding boundary between the copper plate and the bonding layer, and the Ti alloy existing over not less than 30% per a length of 30 μm at the bonding boundary.