Stacked Acoustic Wave Filter Package for CTE Mismatch Bonding

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Solution Overview

Problem

Combining bulk acoustic wave (BAW) and surface acoustic wave (SAW) resonators or filters in a single package results in an undesirably bulky structure due to their different coefficients of thermal expansion (CTE), which can cause damage during the bonding process.

Innovation Solution

Introduce indentations on the substrate with higher CTE to accommodate stress and strain induced by the CTE mismatch, using transient liquid phase (TLP) bonding, and form a hermetic cavity to reduce rigidity and prevent structural damage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If BAW and SAW resonators are combined in a single package, then device performance is improved, but the package structure becomes bulky and rigid

Engineering Contradiction:

Improvedevice performanceVSAvoidpackage size

Core Design Contradiction:

ReliabilityVSVolume of moving object

Solution Approach 1:

The patent places the SAW resonator package inside the BAW resonator package, creating a nested configuration where the SAW package is positioned within the cavity of the BAW package. This nesting approach allows both resonator types to coexist in a compact arrangement, reducing the overall package volume while maintaining individual resonator functionality and improving device performance.

Inventive Principle:

Principle #7Nested doll (Nesting)

2Reliability

If substrates with different CTE are bonded together, then combined package is achieved, but stress and strain cause structural damage

Engineering Contradiction:

Improvebonding integrityVSAvoidstress and strain

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent introduces a compliant layer between the BAW and SAW substrates before bonding. This compliant layer is specifically designed to accommodate the coefficient of thermal expansion (CTE) mismatch between the two substrates, absorbing stress and strain that would otherwise cause structural damage during the bonding process or subsequent thermal cycling, thereby ensuring bonding integrity.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The patent modifies the mechanical properties of the bonding interface by introducing a compliant layer with specific elasticity characteristics. This changes the parameter of rigidity at the bonding interface, allowing it to be more flexible and better suited for accommodating thermal expansion differences, thus preventing stress-induced damage while maintaining reliable bonding.

Inventive Principle:

Principle #35Parameter changes

3Strength

If rigid substrate bonding is used, then strong mechanical connection is achieved, but CTE mismatch causes damage

Engineering Contradiction:

Improvebonding strengthVSAvoidstructural integrity

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The patent changes the mechanical parameter of the bonding interface by introducing a compliant layer with intermediate rigidity between the two rigid substrates. This creates a gradient in mechanical properties, allowing the bonding structure to maintain overall strength while the compliant layer specifically absorbs thermal stress, thereby preserving structural integrity despite CTE mismatch.

Inventive Principle:

Principle #35Parameter changes

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 method reduces the risk of structural damage during bonding, allowing for a compact combined BAW and SAW package with improved performance and reliability.

Implementation Method 1

at least one material comprising the first substrate and at least one material comprising the substrate may have different coefficients of thermal expansion

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

the step of bonding (106) the first substrate and second substrate may comprise performing transient liquid phase (TLP) bonding technique on the bonding elements

Methodology Applied

Scientific EffectTransient liquid phase bonding:

Data Source

PatentUS12407315B2Stacked filter package having multiple types of acoustic wave devices

Publication Date: 2025.09.02 SKYWORKS SOLUTIONS INC

AI summary

A stacked filter package is disclosed. The stacked filter package can include a first acoustic wave device having a first device type. The first acoustic wave device includes a first substrate having a first coefficient of thermal expansion. The stacked filter package can include a second acoustic wave device having a second device type different from the first device type. The second acoustic wave device includes a second substrate having a second coefficient of thermal expansion. The second coefficient of thermal expansion is at least double the first coefficient of thermal expansion. The stacked filter package can include a bonding structure between the first and second substrates. The bonding structure couples the first and second substrate.