Ceramic-Metal Diffusion Bonding for Thermistor Peeling
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Solution Overview
Problem
Conventional electronic components, such as thick film thermistors, face issues with the lower electrode peeling off from the alumina substrate due to differences in crystal structure and melt temperature, leading to poor diffusion bonding.
Innovation Solution
Incorporating a ceramic layer diffusion-bonded to the substrate and a metal layer, where the ceramic layer acts as a buffer, allowing for strong bonding between the substrate and the metal layer, preventing peeling and ensuring sufficient conductivity without the need for glass additives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conductor paste is applied onto a fired alumina substrate and then subjected to firing to form a lower electrode, then the lower electrode can be formed on the substrate, but the lower electrode is easily peeled from the alumina substrate due to poor diffusion bonding
Solution Approach 1:
A ceramic layer is introduced as an intermediary between the alumina substrate and the lower electrode. This ceramic layer has a crystal structure and melt temperature that facilitate diffusion bonding, acting as a mediator that enables strong bonding between the substrate and electrode despite their incompatible properties.
Solution Approach 2:
The patent employs a composite structure consisting of the alumina substrate, the ceramic layer with specific crystal structure, and the lower electrode. This composite material approach allows each layer to contribute its advantageous properties, with the ceramic layer providing the necessary diffusion bonding capability.
2Strength
If a ceramic layer is introduced between the substrate and metal layer, then bonding strength is improved and peeling is prevented, but the device structure becomes more complex
Solution Approach 1:
The bonding interface is segmented into multiple functional layers: the alumina substrate, the intermediate ceramic layer with specific crystal structure, and the lower electrode. This segmentation allows each layer to perform its specific function optimally while maintaining overall structural integrity.
Solution Approach 2:
The patent changes the crystal structure parameter of the intermediate layer to match compatible properties between the alumina substrate and metal electrode. By adjusting this critical parameter, diffusion bonding is enabled without requiring complex additional structures or processes.
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 ceramic layer effectively reduces interdiffusion and maintains the temperature characteristics of the thermistor, enabling a smaller, more reliable electronic component with improved bonding strength and conductivity.
Implementation Method 1
a ceramic layer including a ceramic material and diffusion-bonded to the substrate; a metal layer including a first principal surface and a second principal surface opposed to the first principal surface, with the first principal surface diffusion-bonded to the ceramic layer
Data Source
AI summary
An electronic component in which a metal layer is unlikely to be peeled from a substrate includes an insulating ceramic substrate, a ceramic layer diffusion-bonded to the substrate, a metal layer including a first principal surface and a second principal surface opposed to the first principal surface, with the first principal surface diffusion-bonded to the ceramic layer, and a characteristic layer diffusion-bonded to the second principal surface of the metal layer and prepared from a ceramic material, wherein the characteristic layer varies in resistance value with respect to ambient temperature or applied voltage.