Recessed Substrate Design for SAW Devices
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Solution Overview
Problem
Conventional substrates with electrode lands for signal-side and ground terminals suffer from stray capacitance, which affects filter characteristics in surface acoustic wave devices, and increasing distance or reducing land area to mitigate this either enlarges the device or compromises bonding strength.
Innovation Solution
A substrate design with a recessed portion on one main surface and a second main surface connected via through-holes, featuring first and second electrode lands of different sizes and potentials, where the second electrode lands are outside the recessed portion and have a larger area to enhance bonding strength and reduce stray capacitance, using ceramics with controlled shrinkage during firing to maintain substrate integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the distance between electrode lands is increased to decrease stray capacitance, then the stray capacitance is reduced, but the size of the surface acoustic wave device increases
Solution Approach 1:
The patent introduces a recessed portion that creates a vertical dimension (depth) to separate electrode lands. By placing one electrode land at the bottom of the recessed portion and another on the surface, the design utilizes the third dimension (depth) to achieve spatial separation without increasing the horizontal footprint of the device.
Solution Approach 2:
The recessed portion creates a nested structure where one electrode land is positioned within a depression formed in the substrate, while another electrode land sits on the outer surface. This nesting arrangement allows compact positioning of electrodes with different potentials in a vertically stacked configuration.
2Object-affected harmful factors
If the area of each electrode land is decreased to decrease stray capacitance, then the stray capacitance is reduced, but the bonding strength provided by bumps decreases
Solution Approach 1:
The patent applies different area sizes to different electrode lands based on their functional requirements. The first electrode land (at bottom of recessed portion) has a smaller area optimized for reducing stray capacitance, while the second electrode land (on outer surface) has a larger area optimized for providing sufficient bonding strength for bump connections.
Data Source
AI summary
A substrate includes a substrate main body that includes a first main surface and a second main surface facing the first main surface. First electrode lands are disposed inside a recessed portion of the first main surface of the substrate main body. Second electrode lands are disposed in a region outside the recessed portion. The first electrode land and the second electrode land are connected to different electric potentials.