Silicon MEMS Sensor Sealing Structure to Minimize Lid Cracks
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Solution Overview
Problem
Existing sealing methods for MEMS packages, such as those using laser irradiation to melt and seal through holes, risk inducing cracks due to thermal stress from differing thermal expansion coefficients between the sealing material and the lid portion.
Innovation Solution
A physical quantity sensor design that includes a movable body accommodated in a space between a base body and a lid body, where the space is sealed with a melt portion formed by melting a through hole in the lid body, and the lid body and melt portion contain silicon, with the melt portion having a continuous curved surface with unevenness to manage residual stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If laser light is radiated to melt and seal the through hole, then the sealing effect is improved, but thermal stress and crack risk increase due to different thermal expansion coefficients
Solution Approach 1:
The patent changes the geometric parameters of the through hole to a specific aspect ratio (depth/diameter between 0.5-2.0) and introduces a curved surface with unevenness at the bottom, which modifies the melting and solidification behavior during laser sealing. This parameter optimization reduces thermal stress concentration while maintaining effective sealing.
Solution Approach 2:
The patent introduces a curved surface with unevenness at the bottom of the through hole instead of a flat surface. This curvature design distributes the thermal stress more evenly during laser melting and sealing, preventing stress concentration that would lead to cracks in the lid body.
2Reliability
If the through hole is melted and sealed, then the space sealing is achieved, but residual stress remains in the vicinity of the through hole
Solution Approach 1:
The curved surface with unevenness at the bottom of the through hole creates a gradual transition zone during melting and solidification. This curvature prevents abrupt stress changes and distributes residual stress more uniformly in the sealing region, reducing the risk of stress-induced cracking.
Solution Approach 2:
By optimizing the aspect ratio of the through hole (depth/diameter between 0.5-2.0) and introducing curved surface features, the patent controls the melting and solidification process to minimize residual stress while maintaining sealing integrity.
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
The solution effectively seals the space while minimizing the occurrence of cracks, ensuring the reliability and stability of the physical quantity sensor and its applications, such as in inertial measurement units.
Implementation Method 1
irradiating the through hole and the recess portion with laser light to melt the through hole and the recess portion and seal the space
Implementation Method 2
a periphery of the through hole is melted, and thus the through hole is closed
Data Source
AI summary
Provided is a physical quantity sensor including: a movable body; a base body; and a lid body, in which the movable body is accommodated in a space between the base body and the lid body, the space is sealed with a melt portion obtained by melting a through hole provided in the lid body, the lid body and the melt portion contain silicon, and the melt portion has a continuous curved surface having unevenness.