Active Brazing Thermal Expansion Matching for Pressure Sensors
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Solution Overview
Problem
Pressure sensors experience thermomechanical stresses due to differences in thermal expansion coefficients between the measuring membrane and the base body, leading to reduced measurement accuracy and hysteresis, especially in temperature-dependent measurements.
Innovation Solution
The use of active brazing alloys with specific compositions, such as Zr-Ni-Ti and Zr-Ni-Ti-Cu-Al, that match the thermal expansion coefficient of the ceramic bodies, and a method to determine the thermal expansion coefficient of the active brazing by measuring capacitance changes at different temperatures, ensuring a well-adapted thermal expansion coefficient for the active brazing in the soldered state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If active brazing is used to connect the measuring membrane and base body, then the mechanical strength and hermetic seal are improved, but thermomechanical stresses arise due to mismatched thermal expansion coefficients
Solution Approach 1:
The patent modifies the thermal expansion coefficient parameter of the active brazing alloy by adjusting its chemical composition (specific ratios of Zr, Ni, Ti, Cu, Al) to match the thermal expansion coefficient of the ceramic measuring membrane and base body. This parameter change eliminates the thermal expansion mismatch that causes thermomechanical stresses during temperature variations, while maintaining the strong mechanical connection and hermetic seal provided by active brazing.
Solution Approach 2:
The patent employs a composite active brazing alloy consisting of multiple elements (Zr, Ni, Ti, Cu, Al) in specific proportions. This composite material combines the benefits of strong adhesion to ceramics (from Zr, Ni, Ti) with tailored thermal expansion properties (achieved through Cu and Al additions), thereby resolving the contradiction between mechanical strength and thermal stress compatibility.
2Stress or pressure
If the thermal expansion coefficient of active brazing is adapted to match ceramic, then thermomechanical stresses are reduced, but the composition and selection of brazing material become more complex
Solution Approach 1:
The patent systematically adjusts the compositional parameters of the active brazing alloy to achieve the target thermal expansion coefficient. By varying the ratios of Zr, Ni, Ti, Cu, and Al, the patent optimizes the thermal expansion match with ceramic while maintaining adequate mechanical properties, thereby reducing thermomechanical stress without excessive complexity.
Solution Approach 2:
The patent applies different compositional formulations of active brazing alloy for different specific applications or regions within the pressure sensor assembly. This allows optimization of thermal expansion matching for each specific ceramic component (measuring membrane vs. base body) while maintaining overall system compatibility, managing complexity through localized material selection.
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 approach reduces thermomechanical stresses and improves measurement accuracy by minimizing the difference in thermal expansion coefficients between the active brazing and the ceramic bodies, resulting in more reliable and precise pressure sensor readings.
Implementation Method 1
active brazing, which has a thermal expansion coefficient adapted to the thermal expansion coefficient of the ceramic of the base body and measuring membrane
Implementation Method 2
the electrodes form a capacitor with a capacitance that depends on their electrode spacing, which is dependent on a temperature-dependent height of the active brazing, and whereby when carrying out the at least one measurement the capacitance of the capacitor is measured at at least two different temperatures
Data Source
Figure 1~2
AI summary
The invention relates to a pressure sensor with two bodies which are connected together by active brazing (7) produced by active brazing an active hard solder, in particular a measurement membrane (1), especially a ceramic measurement membrane (1), said measurement membrane being elastically deformable by applying pressure and being subjected to a pressure (p), and a base body (3), in particular a ceramic base body (3), which are connected by active brazing (7) connecting an outer edge of the measurement membrane (1), including a pressure chamber (5), to an outer edge of a front side of the base body (3) facing the measurement membrane (1). The measurement properties of the pressure sensor were improved in that the active brazing (7) has a thermal expansion coefficient which is dependent on the measurements of the active brazing (7) and the materials of the body, and is adapted to a thermal expansion coefficient of at least one body, in particular the measurement membrane (1).