Direct Thermocouple Bonding to Ceramic Substrates
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Solution Overview
Problem
Conventional methods for securing thermocouples to ceramic heaters result in delayed temperature response due to the thermocouple measuring the temperature of a metal sheath rather than the ceramic substrate, leading to inaccurate measurements and potential 'overshooting' during rapid temperature changes.
Innovation Solution
Directly bonding the thermocouple junction to the ceramic substrate using active or ordinary brazing materials, either by applying the material to the substrate, placing the junction on it, and heating in a vacuum chamber, or using a metallized layer with the brazing material to ensure a strong and stable bond.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal sheath is used to secure the thermocouple to the ceramic substrate, then the thermocouple is mechanically attached and secured, but the temperature measurement is delayed and inaccurate due to the sheath's thermal mass
Solution Approach 1:
The patent removes the metal sheath from the thermocouple assembly, extracting the source of thermal delay. The thermocouple wires are directly bonded to the ceramic substrate without the intermediate sheath structure, eliminating the thermal mass that caused measurement delays while maintaining mechanical security through direct bonding.
Solution Approach 2:
The patent introduces a bonding material as an intermediary between the thermocouple junction and the ceramic substrate. This bonding material enables direct thermal coupling and mechanical attachment simultaneously, allowing the thermocouple to measure substrate temperature directly without the thermal delay of a metal sheath.
2Ease of operation
If a metal sheath is used to secure the thermocouple, then mechanical attachment is achieved, but temperature overshooting occurs during rapid ramping due to delayed response
Solution Approach 1:
The patent extracts the metal sheath that caused the response delay, allowing the thermocouple to respond instantaneously to temperature changes. This enables precise temperature control during rapid ramping operations without overshooting, while mechanical attachment is maintained through direct bonding to the substrate.
Solution Approach 2:
The patent applies bonding material to the ceramic substrate surface before attaching the thermocouple junction. This preliminary action ensures proper thermal and mechanical coupling is established before operation, enabling accurate temperature measurement and control from the start of the heating process.
3Strength
If conventional bonding methods are used between ceramic and metal, then mechanical attachment is achieved, but the bond is difficult to maintain at high temperature due to poor wettability and thermal expansion mismatch
Solution Approach 1:
The patent changes the bonding parameters by using a bonding material specifically formulated for high-temperature ceramic-to-ceramic or ceramic-to-metal bonding. This bonding material has matched thermal expansion properties and maintains wettability at elevated temperatures, enabling strong bonds that remain stable during high-temperature operation.
Solution Approach 2:
The patent employs a composite bonding material that combines properties suitable for bonding to both ceramic substrates and thermocouple wires. This composite material addresses the wettability and thermal expansion mismatch issues by incorporating materials that are compatible with both substrates, ensuring strong and stable bonds at high temperatures.
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 allows for accurate and instantaneous temperature measurement of the ceramic substrate, reducing the risk of overshooting and maintaining stability at elevated temperatures, thereby improving control over the heating process.
Implementation Method 1
applying an active brazing material onto the surface of the ceramic heater substrate; heating the active brazing material in a vacuum chamber; maintaining the active brazing material at a predetermined temperature and time in the vacuum chamber
Implementation Method 2
a resistive heating element either embedded within or secured to an exterior surface of the ceramic substrate. Heat generated by the resistive heating element can be rapidly transferred to a target object
Implementation Method 3
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
Methods of securing a thermocouple to a ceramic substrate are provided. The thermocouple includes a pair of wires that define a junction, and the method comprises directly bonding the junction of the thermocouple to the ceramic substrate. In one form, the junction is directly bonded using an active brazing material.