Metal-Ceramic Substrate With Soft Intermediate Layer
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Solution Overview
Problem
Conventional metal-ceramic substrates lack improved mechanical, thermal, and electrical properties, particularly in terms of flexural and breaking strength, thermal stability, and electric field resistance, especially under changing temperatures.
Innovation Solution
A metal-ceramic substrate comprising at least two ceramic layers separated by an intermediate metal layer with high adhesive strength and Brinell hardness less than 75, fabricated using DCB bonding or active soldering, enhancing mechanical and thermal properties while maintaining electrical integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a single ceramic layer is used, then the structure is simple, but the flexural and breaking strength are insufficient
Solution Approach 1:
The substrate is divided into multiple ceramic layers (at least two) separated by an intermediate metal layer, rather than using a single thick ceramic layer. This segmentation increases the overall flexural and breaking strength by distributing mechanical stresses across multiple layers and interfaces, while maintaining a manageable structural complexity through the use of a standardized intermediate layer.
2Strength
If metal layers are used to bond ceramic layers, then the adhesive strength increases, but the thermal stability decreases due to hardness
Solution Approach 1:
The metal of the intermediate layer is specifically selected or treated to have a Brinell hardness of less than 75, which is a critical parameter change. This reduced hardness allows the metal to provide high adhesive strength (greater than 10N/mm) to the ceramic layers while simultaneously maintaining thermal stability by accommodating thermal expansion differences without creating rigid constraints that would lead to cracking under temperature changes.
3Strength
If the metal layer has high hardness for strength, then the adhesive strength increases, but cracks occur in ceramic layers under temperature changes
Solution Approach 1:
The intermediate metal layer with Brinell hardness less than 75 serves as a cushioning layer that absorbs and accommodates thermal expansion stresses before they can propagate into the ceramic layers. This pre-cushioning effect prevents cracks from forming in the ceramic layers during temperature changes, while still maintaining the necessary adhesive strength through the metal-ceramic bonding interfaces.
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 substrate exhibits significantly increased flexural and breaking strength by a factor of 1.5 and electric strength by a factor of 1.4 compared to single ceramic layers, with improved thermal stability and resistance to temperature changes, preventing cracks and maintaining electrical integrity.
Implementation Method 1
a bond is produced at a temperature of ca. 800-1000° C. between a metal foil, for example a copper foil, and a ceramic substrate, for example aluminum-nitride ceramic, using a hard solder, which in addition to a main component such as copper, silver and/or gold also contains an active metal. This active metal is at least one element of the group Hf, Ti, Zr, Nb, Ce, creates a bond between the solder and the ceramic through a chemical reaction, while the bond between the solder and the metal is a metallic hard solder bond.
Implementation Method 2
the bond between the solder and the metal is a metallic hard solder bond
Implementation Method 3
to prevent damage or cracks in the respective adjacent ceramic layer, especially in the case of strains due to changing temperatures, the metal of the inner metal layer has a Brinell hardness of less than 75, preferably a Brinell hardness of less than 40
Data Source
AI summary
A metal-ceramic substrate for electrical circuits or modules includes at least one first outer metal layer forming one first surface side of the metal-ceramic substrate and at least one second outer metal layer forming one second surface side of the metal-ceramic substrate. The outer metal layers are bonded respectively by two-dimensional bonding with the surface sides of a plate-like substrate body.