Surface Acoustic Wave Device Bonding and Plating Integration
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Solution Overview
Problem
Conventional surface acoustic wave devices are bulky due to the need for a package, stacked part, and lid, and suffer from thermal stress and poor connections caused by differences in linear expansion coefficients between the piezoelectric element and the package when using bumps for connection.
Innovation Solution
A manufacturing method involving a first substrate with an interdigital transducer and electrode pad, bonded to a smaller second substrate with an external terminal and castellation, using a bonding layer and electrolytic plating to connect the electrode pad to the castellation, eliminating the need for bumps and integrating the second substrate as both a lid and package.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bumps are used to connect the piezoelectric element to the package substrate, then electrical connection is achieved, but thermal stress and poor connections occur due to difference in linear expansion coefficients
Solution Approach 1:
The patent changes the connection method from mechanical bumps to a bonding process using a bonding layer formed by screen printing or similar techniques. This process change eliminates the need for high-temperature bump formation and subsequent reflow, thereby reducing thermal stress caused by differential expansion between the piezoelectric element and package substrate.
Solution Approach 2:
The patent introduces a bonding layer as an intermediary material between the piezoelectric element and the package substrate. This bonding layer serves as a compliant interface that accommodates differential thermal expansion, reducing stress transmission while maintaining reliable electrical and mechanical connection.
2Reliability
If a package, stacked part, and lid are used to enclose the piezoelectric element, then hermetic sealing is achieved, but the device size increases
Solution Approach 1:
The patent merges the functions of the package substrate, stacked part, and lid into a single integrated package substrate structure. The package substrate itself is designed with raised regions that provide both structural support and hermetic sealing, eliminating the need for separate stacked parts and lids, thereby reducing overall device size while maintaining protection of the piezoelectric element.
Solution Approach 2:
The package substrate is designed to perform multiple functions simultaneously: it provides mechanical support, electrical connection through external terminals, hermetic sealing through its raised structure, and structural enclosure. This multi-functionality eliminates the need for separate components, achieving compact device design without compromising reliability.
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 method enables the creation of a compact, low-profile surface acoustic wave device with high bonding reliability, reducing thermal stress and improving connection quality.
Implementation Method 1
bonding the second substrate to the first substrate by the bonding layer by pressing the second substrate against the first substrate at a fixed heating temperature
Implementation Method 2
the plating layer 23 is grown by an electrolytic plating method subsequent to mounting the second substrate to the first substrate
Data Source
AI summary
To provide a manufacturing method for a surface acoustic wave device, which makes it possible to easily and reliably connect a piezoelectric element to a substrate having an external connection terminal, and a surface acoustic wave device capable of being made smaller using this manufacturing method. A surface acoustic wave device, having a first substrate which has a interdigital transducer and an electrode pad on one side; and a second substrate which has an external terminal, and a castellation formed on the side connected to the external terminal, wherein the surface of the second substrate opposite the surface on which the external terminal is formed is bonded by a bonding layer to the electrode pad, the first substrate is larger in size than the second substrate, and a part of the electrode pad, which extends outwardly of the second substrate, is connected to the castellation by a plating layer.