Ceramic Heater Terminal Bonding via Mo/AlN Intermediate Layer
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Solution Overview
Problem
Ceramic heaters face challenges in securely attaching power terminals due to poor wettability and significant thermal expansion differences between ceramic and metallic materials, leading to thermal stress and cracks.
Innovation Solution
The use of an intermediate layer of Mo/AlN or W/AlN between the resistive heating element and ceramic substrate, combined with an active brazing material, to reduce thermal stress and enhance mechanical strength, allowing for secure bonding of power terminals within recesses in the ceramic substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If power terminal is attached directly to ceramic substrate using conventional brazing methods, then bonding strength is achieved, but thermal stress causes cracks in ceramic substrate
Solution Approach 1:
An intermediate layer comprising Mo/AlN or W/AlN is introduced between the power terminal and ceramic substrate. This intermediate layer has a coefficient of thermal expansion that is intermediate between the ceramic substrate and metallic power terminal, thereby reducing thermal stress during heating and cooling cycles while maintaining strong bonding strength.
Solution Approach 2:
The intermediate layer is formed as a composite material combining metal (Mo or W) and ceramic (AlN) phases. This composite structure provides both mechanical strength for bonding and thermal expansion compatibility, solving the contradiction between bonding strength and crack prevention.
2Reliability
If non-heating zone is created for power terminal attachment, then thermal stress is avoided, but heater design flexibility and compactness are reduced
Solution Approach 1:
The intermediate layer enables power terminal attachment in heating zones by mediating the thermal expansion mismatch. This eliminates the need to create non-heating zones, thereby maintaining design flexibility and compactness while still preventing thermal stress-induced cracks.
3Strength
If active brazing alloy is used to secure power terminal in heating zone, then bonding is achieved, but thermal expansion incompatibility causes cracks
Solution Approach 1:
The Mo/AlN or W/AlN intermediate layer serves as a mediator between the active brazing alloy and the power terminal. Its intermediate thermal expansion coefficient bridges the gap between the brazing alloy and metallic terminal, preventing cracks while maintaining bonding strength in heating zones.
Solution Approach 2:
The intermediate layer's composite structure of metal and ceramic phases provides both the bonding capability needed for active brazing and the thermal expansion properties needed to prevent cracks during thermal cycling.
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 effectively reduces thermal stress and prevents cracks in the ceramic substrate, ensuring reliable and durable attachment of power terminals while accommodating thermal expansion differences.
Implementation Method 1
the difference in coefficient of thermal expansion between the ceramic material and the metallic material is significant and thus a bond between the ceramic material and the metallic material is difficult to maintain
Implementation Method 2
the active brazing material is heated under vacuum, thereby bonding the terminal to the intermediate layer
Implementation Method 3
the intermediate layer, the resistive heating element, and the ceramic substrate are sintered
Implementation Method 4
Heat generated by the resistive heating element can be rapidly transferred to a target object disposed proximate the ceramic substrate because of the excellent heat conductivity of ceramic materials
Data Source
AI summary
A method of securing a terminal to a ceramic heater is provided by the present disclosure. The ceramic heater includes a ceramic substrate and a resistive heating element, and the method includes exposing a portion of the resistive heating element, forming an intermediate layer on at least one of the portion of the resistive heating element and the ceramic substrate proximate the portion of the resistive heating element, the intermediate layer being selected from a group consisting of Mo/AlN and W/AlN, and bonding the terminal to the intermediate layer.