Protective Layer Geometry for Stress-Resistant SAW Modules

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Solution Overview

Problem

Existing electronic devices, such as surface acoustic wave filters, face degradation in characteristics due to stress concentration at the end portions of the protective layer during flip-chip mounting, leading to potential damage, oxidation, and corrosion.

Innovation Solution

The electronic device includes a piezoelectric substrate with a protective layer having a specific geometry, where the distance between the substrate and the protective layer surface varies, with the greatest distance at one end and shortest at the other, and the end portions of the protective layer are curved convexly, reducing stress concentration and potential damage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If the protective layer has a uniform thickness, then the manufacturing process is simple, but stress concentration occurs at the end portions during flip-chip mounting causing damage and degradation

Engineering Contradiction:

Improveprotective layer fabricationVSAvoidprotective layer integrity

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The protective layer is designed with non-uniform thickness, being thickest at the end portions and thinnest at the center. This local variation in thickness provides enhanced stress resistance at the end portions where stress concentration occurs during flip-chip mounting, while maintaining adequate coverage and protection throughout the structure.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The thickness parameter of the protective layer is deliberately varied across different locations. By changing the thickness parameter from uniform to graduated (thickest at ends, thinnest at center), the design optimizes stress distribution and prevents damage at critical end portions during mounting operations.

Inventive Principle:

Principle #35Parameter changes

2Strength

If the protective layer is made thicker overall, then damage resistance improves, but stress concentration at end portions increases during mounting

Engineering Contradiction:

Improveprotective layer damage resistanceVSAvoidstress concentration at end portions

Core Design Contradiction:

StrengthVSStress or pressure

Solution Approach 1:

Rather than uniformly increasing thickness, the design applies local quality by making the protective layer thickest at the end portions where stress concentration occurs during flip-chip mounting. This localized thickness enhancement provides targeted stress resistance without the need for overall thickness increase throughout the entire layer.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The protective layer features a curved surface profile with a convex shape, being thickest at the end portions and thinnest at the center. This curvature design naturally distributes stress more evenly during mounting, preventing stress concentration at the end portions while maintaining adequate protection.

Inventive Principle:

Principle #14Spheroidality (Curvature)

3Reliability

If the end portions of the protective layer are made convex, then stress concentration is reduced during mounting, but the manufacturing precision requirements increase

Engineering Contradiction:

Improvestress distribution during mountingVSAvoidprotective layer geometry control

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The protective layer is designed with a convex curved surface profile where the end portions are thickest and the center is thinnest. This curvature geometry naturally reduces stress concentration during flip-chip mounting by distributing forces more evenly across the bonding interface, improving reliability without requiring complex manufacturing processes.

Inventive Principle:

Principle #14Spheroidality (Curvature)

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 reduces the potential for damage to the protective layer and associated electrodes, thereby minimizing degradation in filter characteristics and simplifying the mounting process by relaxing coplanarity requirements.

Implementation Method 1

surface acoustic wave resonator device which includes interdigitated electrodes on a piezoelectric substrate

Methodology Applied

Scientific EffectSurface acoustic wave: Surface Acoustic Wave

Data Source

PatentUS12278616B2Electronic device and module including the same

Publication Date: 2025.04.15 MURATA MFG CO LTD

AI summary

An electronic device includes an insulation material layer provided on a first main surface of a piezoelectric substrate and surrounding a functional element, and a protective layer provided on the insulation material layer. The piezoelectric substrate and the insulation material layer define a hollow portion accommodating the functional element. The protective layer includes a first portion above the hollow portion, a second portion adjacent to the first portion at one end of the second portion, and a third portion adjacent to the second portion at another end of the second portion. A distance between the first main surface and a surface of the protective layer in the thickness direction is greatest at a location where the second portion is adjacent to or in a vicinity of the first portion, and the distance is shortest at a location where the second portion is adjacent to or in a vicinity of the third portion.