Wiring Electrode Multilayer Structure for SAW Device
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Solution Overview
Problem
Existing surface acoustic wave devices face challenges in reducing size while maintaining electrode properties and ensuring reliable plating film adhesion, particularly due to laser irradiation effects on Al film electrodes, which can lead to corrosion and adhesion failures.
Innovation Solution
A multilayer structure comprising a refractory metal layer with a melting point of 900°C or higher, a diffusion preventive film, and an Al or Al-alloy film is used for the wiring electrodes, with a Pt film as the refractory metal layer to prevent property alteration and corrosion, and a manufacturing method involving laser-formed through-holes for conductive layer filling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a through-hole is formed in the support layer by laser irradiation and an under bump metal layer is filled in the through-hole, then size reduction is realized, but the Al film may experience altered properties due to laser beam irradiation and plating film adhesion becomes difficult
Solution Approach 1:
The wiring electrode is divided into multiple functional layers: the Al film layer for electrical connection, the natural oxide film layer for adhesion promotion, and the barrier metal layer for laser resistance. This segmentation allows each layer to perform its specific function without interfering with others, solving the contradiction between size reduction and plating adhesion
Solution Approach 2:
The natural oxide film is allowed to form on the Al film surface before laser irradiation and plating processes. This preliminary formation of the oxide film ensures that when the under bump metal layer is later filled into the through-hole, it can adhere properly to the oxide film surface, preventing adhesion failures
2Reliability
If the Al film is used as wiring electrode connected to IDT electrodes, then electrical connection is achieved, but the Al film properties are altered by laser beam irradiation causing corrosion
Solution Approach 1:
The natural oxide film acts as an intermediary layer between the Al film and the laser beam. It absorbs and dissipates the laser energy, preventing direct damage to the Al film while still allowing electrical functionality. This intermediary layer protects the Al film from laser-induced corrosion
Solution Approach 2:
The wiring electrode structure is designed as a composite of multiple materials: Al for electrical conductivity, natural oxide for laser protection and adhesion, and barrier metal for additional thermal and chemical resistance. This composite structure combines the advantages of different materials to overcome their individual weaknesses
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 ensures reliable electrical connections and prevents property alteration of wiring electrodes, enhancing adhesion and corrosion resistance, thus improving the reliability and size reduction of surface acoustic wave devices.
Implementation Method 1
the through-holes are holes penetrating through the insulating member and formed by irradiation of a laser beam
Data Source
AI summary
In an elastic wave device, IDT electrodes on a piezoelectric substrate are electrically connected to wiring electrodes. A support member covers at least portions of the wiring electrodes. Through-holes in the support member expose upper surfaces of the wiring electrodes and have conductive layers filled therein. The wiring electrodes each have a multilayer structure in which a refractory metal film having a melting point of 900° C. or higher, a diffusion preventive film, and an Al or Al-alloy film are laminated successively from the upper surface side.