Metal-Ceramic Substrate Joining with Silver-Free Active Solder
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Solution Overview
Problem
Existing methods for producing metal-ceramic substrates, such as direct copper bonding and solder-based techniques, face challenges including high temperature requirements and limitations to specific ceramic types, as well as suboptimal thermal and current conductivity, particularly when using solder materials with metals having melting points above or below 700°C and active metals.
Innovation Solution
A method involving a stack of ceramic, metal foil, and solder material with a metal having a melting point of at least 700°C, a metal with a melting point below 700°C, and an active metal, where the solder material is heated to form an integral bond between the ceramic and metal foil, optimizing conductivity without altering the connecting layer composition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder material containing silver is used to connect metal foil to ceramic body, then reliable connection is achieved, but silver migration problems occur and thermal/conductivity is limited
Solution Approach 1:
The patent removes silver from the solder material composition entirely, extracting the problematic element that causes migration while maintaining the connection function through alternative metal compositions containing copper, tin, and active metals
Solution Approach 2:
The patent changes the chemical composition parameters of the solder material by replacing silver-based alloys with silver-free formulations containing copper (60-90 wt%), tin (5-30 wt%), and active metals (0.1-5 wt%), fundamentally altering the material properties to eliminate migration while improving conductivity
2Reliability
If connecting layer composition is varied to improve thermal and current conductivity, then conductivity increases, but manufacturing complexity and cost increase
Solution Approach 1:
The patent optimizes the compositional parameters within a fixed formulation range (copper 60-90%, tin 5-30%, active metal 0.1-5%) to achieve high conductivity while maintaining manufacturing simplicity, avoiding the need for complex multi-layer or gradient structures
Solution Approach 2:
The patent creates a composite solder material combining copper (for conductivity), tin (for low melting point and wetting), and active metals (for ceramic bonding), achieving superior thermal and electrical conductivity while maintaining ease of manufacture through a single homogeneous layer
3Strength
If high temperature processing is used in DCB method, then copper foil bonds to ceramic body, but temperatures must be maintained below copper melting point limiting process flexibility
Solution Approach 1:
The patent changes the bonding mechanism by using low-melting-point tin (melting point 232°C) instead of copper oxide bonding, enabling effective connection at temperatures below 300°C rather than requiring 700-1000°C, thus expanding process flexibility
Solution Approach 2:
The patent utilizes the phase transition of tin from solid to liquid at 232°C to enable wetting and bonding of the metal foil to ceramic surface, allowing connection at temperatures well below copper melting point through controlled melting and solidification of the tin component
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 method enhances the thermal and current conductivity of metal-ceramic substrates while maintaining a given connecting layer composition, reducing silver migration and improving material properties, resulting in a more cost-effective and efficient production process.
Implementation Method 1
the solder material is heated to form an integral bond between the ceramic and metal foil
Implementation Method 2
a solder-based techniques... the copper compound melts and wets the surface of the ceramic body to form a stable, integral bond
Implementation Method 3
The role of the active metal is to react with the ceramic material and thus to enable a connection of the ceramic material to the remaining solder to form a reaction layer
Data Source
AI summary
The invention relates to a method for producing a metal-ceramic substrate and to a furnace suitable for carrying out the method. With the method, a metal-ceramic substrate with increased thermal and current conductivity can be obtained. The method comprises the steps of providing a stack containing a ceramic body, a metal foil, and a solder material in contact with the ceramic body and the metal foil, the solder material comprising a metal having a melting point of at least 700° C., a metal having a melting point of less than 700° C., and an active metal, and heating the stack, the stack passing through a heating zone for heating.