SAW Protective Cap Structure for Moisture-Resistant IDTs
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Solution Overview
Problem
Conventional surface acoustic wave devices using polyimide materials for protection suffer from reduced moisture resistance in high temperature or high humidity environments, leading to oxidation of interdigital transducers, which compromises their functionality.
Innovation Solution
A surface acoustic wave device and fabrication method that replaces polyimide materials with a conductive surrounding structure and cap layer, such as a solder or epoxy resin, to enhance moisture resistance and prevent oxidation, utilizing electroplating and reflow processes to form a protective metal or molded plastic structure around the interdigital transducers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If polyimide material is used for protective cap layer, then the device structure is simple and easy to manufacture, but moisture resistance deteriorates in high temperature or high humidity environment
Solution Approach 1:
The patent uses a composite protective structure combining solder material (such as tin or tin alloy) as the cap layer on the interdigital transducer, surrounded by a conductive structure (such as copper or electroplating material). This composite material approach provides superior moisture resistance compared to single-material polyimide, while maintaining manufacturability through established electroplating and soldering processes.
2Device complexity
If polyimide material is used for protective cap layer, then the fabrication process is simple, but oxidation protection is insufficient in high temperature or high humidity environment
Solution Approach 1:
The patent employs solder materials (such as tin or tin alloy) as the cap layer, which form protective oxide layers that prevent further oxidation of the underlying interdigital transducer. The conductive surrounding structure (copper or electroplating material) also provides oxidation protection. These materials create a protective environment around the sensitive IDT components, preventing harmful oxidation even in high temperature or humidity conditions.
3Device complexity
If conventional protective structure is used, then the structure is simple, but moisture penetration occurs leading to interdigital transducer oxidation
Solution Approach 1:
The patent implements a nested protective structure where the solder cap layer is positioned on top of the interdigital transducer, which is in turn surrounded by the conductive surrounding structure (copper or electroplating material). This multi-layer nested arrangement creates progressive barriers against moisture penetration, with each layer providing additional protection and ensuring that even if one layer is compromised, the underlying layers continue to protect the IDT.
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 proposed solution effectively prevents oxidation of interdigital transducers by improving moisture resistance, ensuring the reliable operation of surface acoustic wave devices in challenging environmental conditions.
Implementation Method 1
A conductive surrounding structure includes: a wall part, disposed on the substrate and surrounding the surface acoustic wave members; and a lateral layer part, disposed on the wall part. The lateral layer part has an opening above the surface acoustic wave members. A cap layer covers the lateral layer part and closes the opening.
Implementation Method 2
utilizing electroplating and reflow processes to form a protective metal or molded plastic structure around the interdigital transducers
Implementation Method 3
the cap layer is a reflow solder layer to close the opening of the lateral layer part
Data Source
AI summary
A surface acoustic wave (SAW) device including a substrate is provided. Multiple surface acoustic wave elements are disposed on the substrate. A conductive surrounding structure includes: a wall part, disposed on the substrate and surrounding the surface acoustic wave elements; and a lateral layer part, disposed on the wall part. The lateral layer part has an opening above the surface acoustic wave elements. A cap layer covers the lateral layer part and closes the opening.