Ceramic Circuit Substrate Brazing with Carbon Fiber Composite
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Solution Overview
Problem
Ceramic circuit substrates face issues with low mechanical strength and heat cycle resistance, particularly in high-load and high-thermal-stress applications, such as motor vehicles and electric railways, due to thermal expansion coefficient differences between ceramic and metal components, leading to bonding strength and thermal resistance inefficiencies.
Innovation Solution
A ceramic circuit substrate is developed with a silver-copper brazing material layer containing 0.3-7.5 parts by mass of carbon fibers and 1.0-9.0 parts by mass of active metals like titanium, zirconium, or hafnium, which approximates the thermal expansion coefficient of the ceramic substrate, enhancing bonding strength and heat dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If aluminum nitride substrates are used for high thermal conductivity, then thermal dissipation performance is improved, but mechanical strength and toughness deteriorate
Solution Approach 1:
The patent uses silicon nitride substrate as a composite ceramic material that combines both thermal conductivity and mechanical strength properties, overcoming the limitation of aluminum nitride which has high thermal conductivity but low mechanical strength. The silicon nitride substrate integrates multiple desirable properties in a single material system.
Solution Approach 2:
The patent changes the material parameter from aluminum nitride to silicon nitride, fundamentally altering the material properties to achieve both high thermal conductivity and high mechanical strength simultaneously, rather than having to trade off between these properties.
2Temperature
If thick metal plates are used to improve heat dissipation, then thermal management is improved, but thermal stress from thermal expansion coefficient differences increases
Solution Approach 1:
The patent introduces a brazing material layer as an intermediary between the silicon nitride substrate and metal plates. This brazing layer acts as a stress buffer that accommodates thermal expansion coefficient differences, reducing thermal stress while maintaining effective heat dissipation pathways.
Solution Approach 2:
The patent modifies the brazing material composition by adding carbon fibers and specific active metals to change its mechanical and thermal properties, enabling it to serve as an effective stress-buffering intermediary that reduces thermal stress transmission.
3Ease of manufacture
If conventional brazing materials are used for bonding, then bonding process is simple, but bonding strength and heat cycle resistance deteriorate
Solution Approach 1:
The patent creates a composite brazing material combining silver or copper base metal with carbon fibers and active metals. This composite structure provides both strong bonding capability and excellent heat cycle resistance, maintaining simplicity while dramatically improving reliability.
Solution Approach 2:
The patent changes the compositional parameters of the brazing material by incorporating specific ratios of carbon fibers (0.03-5 wt%) and active metals (1-20 wt%), which fundamentally improves the material's performance in terms of bonding strength and thermal stress resistance.
4Reliability
If carbon powder is added to brazing material to improve heat cycle resistance, then heat cycle properties are improved, but thermal conductivity deteriorates
Solution Approach 1:
The patent uses carbon fibers instead of carbon powder in the brazing material composite. The fibrous structure provides heat cycle resistance through crack bridging and stress distribution while maintaining thermal conductivity pathways, overcoming the limitation of carbon powder which blocks heat flow.
Solution Approach 2:
The patent applies carbon fibers with specific aspect ratios and distributions within the brazing material matrix, creating local structural qualities that provide mechanical reinforcement and stress buffering without significantly impeding overall thermal conduction pathways.
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 solution achieves a crack rate of less than 1% in 2,000 heat cycle tests, improving heat cycle resistance and operational reliability while maintaining high bonding characteristics.
Implementation Method 1
a silver-copper brazing material layer... which approximates the thermal expansion coefficient of the ceramic substrate, enhancing bonding strength
Implementation Method 2
silver-copper brazing material layer containing 0.3-7.5 parts by mass of carbon fibers and 1.0-9.0 parts by mass of active metals... enhancing bonding strength and heat dissipation
Implementation Method 3
Ti, which is an active metal, covalently bonds with N of the nitride ceramic substrate to form TiN (titanium nitride), and a bonding layer is formed with this TiN
Data Source
AI summary
It is an object of the present invention to obtain a ceramic circuit substrate having high bonding strength, excellent heat cycle resistance, enhanced reliability of operation as an electronic device, and excellent heat dissipation properties. The present invention provides a ceramic circuit substrate in which metal plates, particularly copper plates, and both main surfaces of a ceramic substrate are bonded vial silver-copper brazing material layers. The silver-copper brazing material layers are formed from a silver-copper brazing material including i) 0.3-7.5 parts by mass of carbon fibers, and ii) 1.0-9.0 parts by mass of at least one active metal selected from titanium, zirconium, hafnium, niobium, tantalum, vanadium, and tin; with respect to iii) a total of 100 parts by mass of a) 75-98 parts by mass of silver powder and b) 2-25 parts by mass of copper powder. The carbon fibers having an average length of 15-400 μm, an average diameter of 5-25 μm and an average aspect ratio of 3-28.