Force Sensor Low-Temperature Substrate Joining
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Solution Overview
Problem
In existing force sensors, residual stress from substrate joining can cause distortion, leading to shifts in output zero points and increased variation in bridge circuit outputs due to differences in thermal expansion coefficients, reducing yield.
Innovation Solution
Joining the sensor substrate and base substrate at a lower temperature than 250°C, using a sensor-side support with a closed inner peripheral edge and positioning sensor-side electrically connecting portions along the periphery to prevent resin entry and reduce stress, while using metal joint layers for low-temperature metal joining.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If substrate joining is performed at high temperature (300-400°C) to ensure proper bonding, then joining strength is improved, but residual stress increases causing substrate distortion
Solution Approach 1:
The patent changes the temperature parameter from conventional high temperature (300-400°C) to low temperature (room temperature or slightly elevated), fundamentally altering the joining process to avoid thermal expansion differences that cause distortion while maintaining adequate bonding strength through extended processing time or optimized joining pressure
Solution Approach 2:
The patent performs preliminary positioning and alignment of the sensor substrate and base substrate before joining, ensuring precise registration of electrode pads and connecting portions. This preliminary action prevents misalignment that could exacerbate distortion effects during joining
2Reliability
If multiple joining operations (substrate joining and electrode pad joining) are performed separately, then connection reliability is improved, but manufacturing complexity increases
Solution Approach 1:
The patent merges the substrate joining operation with the electrode pad joining operation into a single integrated process step. By designing the electrode pads and connecting portions to be joined simultaneously through the same low-temperature joining process, the patent reduces manufacturing complexity while maintaining connection reliability through unified process control
Solution Approach 2:
The joining process is designed to serve multiple functions simultaneously: it bonds the sensor substrate to the base substrate, connects the electrode pads to the connecting portions, and seals the assembly. This multi-functional approach reduces the number of separate operations needed while ensuring consistent results across all joining points
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 decreases residual stress, stabilizes the sensor substrate, and improves yield by preventing distortion and maintaining sensor sensitivity.
Implementation Method 1
a sensor substrate 10 provided with a plurality of piezoresistance elements 13, in which an electrical resistance of each piezoresistance element 13 changes in accordance with an amount of displacement of a displacement portion 11
Implementation Method 2
using metal joint layers for low-temperature metal joining
Data Source
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AI summary
Provided are a force sensor and a method of manufacturing the force sensor in which distortion of substrates due to residual stress after joining of substrates can be decreased, and with which the yield can be improved. A sensor substrate includes a plurality of piezoresistance elements. The electrical resistance of each piezoresistance element changes in accordance with an amount of displacement of a displacement portion displaced by an external load applied through a pressure receiving unit. A base substrate supports the sensor substrate. The sensor substrate and the base substrate each include a support supporting the displacement portion such that the displacement portion can be displaced and a plurality of electrically connecting portions electrically connected to the plurality of piezoresistance elements. The supports of the sensor and base substrates are joined to each other and the plurality of electrically connecting portions of the sensor and base substrates are joined to each other. Furthermore, in each of the sensor and base substrates, either the support or the plurality of electrically connecting portions or both extend to the periphery of the sensor substrate or the base substrate.