Acoustic Wave Device Support Layer Thermal Stress
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Solution Overview
Problem
The existing flip-chip packaging method for acoustic wave devices faces stress issues due to the large linear thermal expansion coefficient of piezoelectric substrates, which can lead to bump failure as the substrate shrinks, causing warpage and increased stress on the bumps.
Innovation Solution
Incorporating a support layer with a lower linear thermal expansion coefficient than the piezoelectric substrate, embedded in the periphery or recessed portions of the substrate, to reduce stress on the bumps by inhibiting substrate shrinkage and warpage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a piezoelectric substrate with a large linear thermal expansion coefficient is used for the acoustic wave device, then the substrate can be manufactured with standard piezoelectric materials, but the substrate shrinks during cooling after bump formation, causing warpage and increased stress on the bumps that may lead to bump failure
Solution Approach 1:
The patent introduces a support layer with specifically controlled thermal expansion parameters (linear thermal expansion coefficient of 5×10^-6 to 15×10^-6 /°C) to change the overall thermal expansion behavior of the substrate structure, reducing the stress on bumps during temperature changes
Solution Approach 2:
The patent creates a composite structure by combining the piezoelectric substrate with a support layer having different material properties (lower linear thermal expansion coefficient). This composite structure compensates for the high thermal expansion of the piezoelectric material, reducing stress on the bumps during thermal cycling
2Stability of the object's composition
If the piezoelectric substrate is allowed to shrink freely with thermal expansion, then the substrate maintains its natural dimensional changes, but this causes warpage that increases stress on the bumps and reduces device reliability
Solution Approach 1:
The support layer is designed with specific physical parameters (thickness ratio of 10-100% of substrate thickness, linear thermal expansion coefficient of 5×10^-6 to 15×10^-6 /°C) to control and stabilize the dimensional changes of the overall substrate structure during thermal cycling
Solution Approach 2:
The support layer acts as a counterbalancing element that compensates for the dimensional instability and warpage of the piezoelectric substrate during thermal expansion and contraction, maintaining overall structural stability and preventing bump failure
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 embedded support layer effectively reduces stress on the bumps, enhancing the reliability of the acoustic wave device by minimizing the impact of thermal expansion mismatch between substrates.
Implementation Method 1
a support layer that is located in at least a part of a periphery of the first substrate, is in contact with a side surface of the first substrate, and has a less linear thermal expansion coefficient than the first substrate
Data Source
AI summary
An acoustic wave device includes: a first substrate made of a piezoelectric material; an acoustic wave element located on the first substrate; a bump located on the first substrate; a second substrate located on the first substrate through the bump, the second substrate facing the first substrate across an air gap; and a support layer that is located in at least a part of a periphery of the first substrate, is in contact with a side surface of the first substrate, and has a less linear thermal expansion coefficient than the first substrate.