Ceramic Pressure Sensor Joint Layout for Thermal Stress Relief
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Solution Overview
Problem
The joining of components to brittle materials like ceramics using solder or braze often results in stress issues due to differing thermal expansion coefficients, leading to potential cracking and joint failure, particularly in applications like micro-electromechanical systems (MEMS) where thermal expansion differences between metal and ceramic layers cause stress concentration at the interface.
Innovation Solution
The solution involves relocating the metallization termination point away from the interface area between the metal and ceramic components, with the metallization layer extending beyond the joint area to reduce stress concentration, and using a thinner solder or braze layer to minimize thermal expansion-induced stress, thereby reducing the risk of cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If solder or braze is used to join metal components to ceramic materials, then the joint strength is improved, but stress concentration occurs at the metallization termination point due to thermal expansion mismatch
Solution Approach 1:
The metallization layer is extended from a two-dimensional interface layer into the third dimension by adding an overhang portion that extends beyond the ceramic substrate edge. This dimensional extension allows the metallization termination point to be positioned away from the high-stress joint interface, reducing stress concentration while maintaining joint strength.
Solution Approach 2:
The metallization structure is segmented into distinct functional portions: a base layer on the ceramic substrate for bonding, and an overhang portion extending beyond the substrate edge. This segmentation separates the bonding function from the electrical connection function, allowing the termination point to be located in a low-stress region while maintaining strong joint bonding.
2Area of stationary object
If the metallization termination point is located at the interface area between metal and ceramic, then the joint area is maximized, but crack formation is more likely due to stress concentration
Solution Approach 1:
The overhang portion of the metallization layer acts as an intermediary structure that bridges the ceramic substrate and the external electrical connection. By extending the metallization beyond the ceramic edge, it creates a transition zone that distributes stress away from the critical interface area, preventing crack formation while maintaining adequate joint area.
3Strength
If a thick solder or braze layer is used to ensure adequate bonding, then the joint strength is improved, but thermal expansion-induced stress is increased
Solution Approach 1:
The thickness parameter of the solder or braze layer is optimized to achieve adequate bonding strength while minimizing thermal expansion stress. By controlling the layer thickness within specific ranges, the joint maintains sufficient strength without excessive stress accumulation 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 approach effectively reduces stress at the metallization termination point, enhancing the reliability of the joint by minimizing the risk of crack formation and failure, particularly in applications where thermal expansion mismatches are significant.
Implementation Method 1
Typically, a metal layer is deposited on the brittle material using a suitable process, such as vapor deposition
Implementation Method 2
Differences in coefficients of thermal expansion can give rise to stresses that can damage the joint or otherwise shorten its lifetime
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
A method of joining a brittle material (460) to a component (490) is provided. The method includes depositing a metallization layer (220) on a surface of the brittle material (460). A layer of joining material is applied between the brittle material (460) and the component (490), such that the component (490) and the brittle material (460) define an interface area. The metallization layer (220) and the joining material layer extends beyond the interface area.