Inertial Sensor Substrate Warping Control

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Solution Overview

Problem

Inertial sensors using silicon MEMS technology face challenges in accurately detecting inertia due to substrate warping caused by adhesive expansion and contraction with temperature changes, and issues with sensor element installation accuracy.

Innovation Solution

The inertial sensor employs a base substrate with specific lateral surfaces bonded to the package using different adhesives, where the second and third adhesives have lower coefficients of linear expansion and higher moduli of elasticity than the first adhesive, and are applied to intersecting surfaces to create tensile stress and restrain substrate warping.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If the sensor element is bonded to the package only via the bottom surface of the base substrate, then the bonding process is simple, but the base substrate warps due to adhesive expansion and contraction caused by temperature changes, reducing detection accuracy

Engineering Contradiction:

Improvebonding process simplicityVSAvoiddetection accuracy

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The bonding process is segmented into three separate bonding operations: bottom surface bonding with first adhesive, first lateral surface bonding with second adhesive, and second lateral surface bonding with third adhesive. This segmentation allows each adhesive to be optimized for its specific function while collectively preventing substrate warping.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different adhesives with different properties are applied to different locations of the base substrate. The first adhesive (silicone or polyimide) is used for bottom bonding, while the second and third adhesives (epoxy) are used for lateral surface bonding. This local quality differentiation addresses the warping issue at specific locations without compromising overall detection accuracy.

Inventive Principle:

Principle #3Local quality

2Ease of manufacture

If the sensor element is bonded to the lateral surface of the package only via the lateral surface of the base substrate, then the bonding process is simplified, but the accuracy of the installation position of the sensor element to the package drops

Engineering Contradiction:

Improvebonding process simplicityVSAvoidinstallation position accuracy

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The bonding approach transitions from two-dimensional (bottom surface only) or single-lateral-surface bonding to three-dimensional multi-surface bonding. By bonding the bottom surface and two lateral surfaces simultaneously, the sensor element achieves precise positioning in multiple spatial dimensions, improving installation accuracy while maintaining manufacturing feasibility.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Device complexity

If a single adhesive is used for bonding the base substrate to the package, then the manufacturing process is simple, but the base substrate warps due to thermal expansion and contraction of the adhesive

Engineering Contradiction:

Improveadhesive configuration complexityVSAvoidsubstrate stability

Core Design Contradiction:

Device complexityVSStability of the object's composition

Solution Approach 1:

The bonding system uses a composite adhesive configuration combining three different adhesives: first adhesive (silicone or polyimide) for bottom bonding, and second and third adhesives (epoxy) for lateral surface bonding. This composite approach leverages the complementary properties of different adhesives to achieve both flexibility and dimensional stability, preventing substrate warping while managing device complexity.

Inventive Principle:

Principle #40Composite materials

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 configuration improves the accuracy of sensor installation and reduces substrate warping, enabling precise detection of inertia by mitigating the effects of temperature-induced adhesive expansion and contraction.

Implementation Method 1

the base substrate warps due to at least one of expansion and contraction of the adhesive caused by a change in the ambient temperature

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

the second adhesive and the third adhesive have a lower coefficient of linear expansion than the first adhesive... the second adhesive and the third adhesive have a higher modulus of elasticity than the first adhesive

Methodology Applied

Scientific EffectTensile stress: Tension

Data Source

PatentUS11268977B2Inertial sensor, electronic apparatus, and vehicle

Publication Date: 2022.03.08 SEIKO EPSON CORP

AI summary

An inertial sensor includes: a sensor unit; a base substrate having the sensor unit arranged at one surface thereof and having a first lateral surface and a second lateral surface; a package accommodating the sensor unit and the base substrate and having an inner bottom surface, a first inner wall surface, and a second inner wall surface; a first adhesive bonding together an other surface of the base substrate and an inner bottom surface of the package; a second adhesive bonding together the first inner wall surface of the package and the first lateral surface; and a third adhesive bonding together the second inner wall surface of the package and the second lateral surface.