SAW Filter Protective Layer Structure for Flip-Chip Stress Relief

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Solution Overview

Problem

Existing surface acoustic wave filters face degradation due to stress concentration at the end portions of the protective layer during flip-chip mounting, leading to potential damage, oxidation, and corrosion, which complicates the mounting process and affects filter characteristics.

Innovation Solution

The electronic device features a protective layer with a design where the distance between the piezoelectric substrate and the protective layer surface varies, with the second portion being inclined and having a convex surface, reducing stress concentration and increasing the rigidity of the protective layer, thereby minimizing damage and maintaining filter characteristics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If the protective layer has a uniform thickness design, 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 fabrication simplicityVSAvoidprotective layer integrity during mounting

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The protective layer is designed with different thicknesses at different locations: a first thickness in the central region and a smaller second thickness at the end portions. This local variation in thickness distributes stress during flip-chip mounting, preventing stress concentration at the ends while maintaining manufacturing feasibility through standard deposition processes.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The protective layer incorporates a curved surface at the end portions instead of sharp edges, creating a gradual transition in thickness. This curvature reduces stress concentration by eliminating abrupt geometric discontinuities, thereby preventing damage during mounting operations while maintaining a relatively simple fabrication process.

Inventive Principle:

Principle #14Spheroidality (Curvature)

2Strength

If the protective layer is made thicker to increase rigidity, then damage during mounting is reduced, but stress concentration and oxidation at end portions increases

Engineering Contradiction:

Improveprotective layer rigidityVSAvoidoxidation and corrosion at end portions

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The protective layer provides adequate thickness in the central region to ensure rigidity and protect internal structures, while reducing thickness at the end portions to minimize stress concentration and exposure to oxidizing environments. This localized thickness variation simultaneously achieves both protection and reduced susceptibility to oxidation.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The curved surface at the end portions reduces the surface area exposed to oxygen and moisture compared to a flat extended surface, thereby decreasing oxidation and corrosion while maintaining structural integrity through the curved geometry's inherent stress distribution properties.

Inventive Principle:

Principle #14Spheroidality (Curvature)

3Reliability

If the protective layer has a complex variable thickness design, then stress distribution is improved, but the manufacturing process becomes complicated

Engineering Contradiction:

Improvestress distribution uniformityVSAvoidprotective layer structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The protective layer implements a simple two-region thickness variation (central region with first thickness, end portions with second thickness) rather than complex continuous variation. This simplified local differentiation achieves effective stress distribution while remaining compatible with standard semiconductor fabrication processes.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The curved surface at the end portions provides a smooth, continuous transition in thickness that can be achieved through conventional deposition and planarization techniques, avoiding the need for complex multi-step manufacturing processes while effectively distributing stress.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Data Source

PatentUS11791797B2Electronic device and module including the same

Publication Date: 2023.10.17 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.