Acoustic Wave Device Support Recesses for Thermal Stress
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Solution Overview
Problem
Acoustic wave devices with wafer level package (WLP) structures face thermal stress issues due to the larger thermal expansion coefficient of the support compared to the piezoelectric substrate, leading to potential damage from concentrated thermal stress.
Innovation Solution
Incorporating recesses on the support's surface, particularly closer to the piezoelectric substrate, to disperse thermal stress effectively, reducing the likelihood of damage by distributing stress across a wider area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a support with larger thermal expansion coefficient than the piezoelectric substrate is used in a WLP-structure acoustic wave device, then the support can be provided with easier manufacturing and material availability, but the support deforms by greater amount with temperature changes causing large thermal stress that may damage the piezoelectric substrate
Solution Approach 1:
The support is designed with non-uniform thickness, creating regions of different mechanical properties. The first region has greater thickness to provide structural stability and reduce thermal stress, while the second region has lesser thickness to accommodate deformation. This local variation in thickness allows the support to manage thermal expansion differences without transmitting excessive stress to the piezoelectric substrate.
Solution Approach 2:
The support is divided into two distinct regions with different thickness characteristics. This segmentation allows each region to serve different functions: the first region handles overall structural support and stress distribution, while the second region allows for controlled deformation. The division into regions enables the support to reconcile the conflicting requirements of manufacturing ease and substrate protection.
2Device complexity
If the support is made with uniform thickness for simplicity, then the manufacturing process is simplified, but stress concentrates at specific points during thermal cycling causing potential damage to the piezoelectric body
Solution Approach 1:
Instead of uniform thickness, the support employs local quality variation through non-uniform thickness distribution. The first region with greater thickness provides enhanced stress distribution capability, while the second region with lesser thickness reduces overall complexity. This approach improves strength and stress distribution without requiring complex multi-component structures.
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 reduces thermal stress on the piezoelectric substrate, minimizing the risk of damage and enhancing the durability of the acoustic wave device.
Implementation Method 1
the support has a larger thermal expansion coefficient than the piezoelectric substrate, and therefore, the support tends to deform by a greater amount than the piezoelectric substrate with changes in temperature. Therefore, a large thermal stress may act on the piezoelectric substrate
Data Source
AI summary
An acoustic wave device includes a piezoelectric substrate, an IDT electrode provided on the piezoelectric substrate, a support provided on the piezoelectric substrate so as to surround the IDT electrode, and a cover provided on the support. The support has a larger thermal expansion coefficient than the piezoelectric substrate. The IDT electrode is provided in a hollow space that is surrounded by the piezoelectric substrate, the support, and the cover. The support includes an inner surface on a side of the hollow space, and an outer surface on a side opposite to the inner surface, and the support includes a recess provided in at least one of the inner and outer surfaces.