Surface Acoustic Wave Filter ESD Protection via Multilayer Wiring
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Solution Overview
Problem
Surface acoustic wave filters have low electrostatic discharge (ESD) resistance due to narrow electrode finger pitch, and while dummy electrode fingers can increase ESD resistance, they are prone to breakdown, reducing the effectiveness of surge charge protection.
Innovation Solution
A filter device with a multilayered substrate and long wirings that connect signal terminals to outer terminals, using solder or gold bumps to enhance ESD resistance by ensuring surge charges are attenuated before reaching IDT electrodes, and incorporating a CSP or WLP package structure to increase wiring lengths and reduce the risk of short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pitch of electrode fingers of IDT electrodes is made narrow, then the filter device achieves better filtering performance, but ESD resistance becomes low
Solution Approach 1:
The patent introduces an intermediary protection structure consisting of dummy electrode fingers and surge charge reception electrodes positioned between the IDT electrodes and external signal terminals. These intermediary elements intercept and dissipate surge charges before they can reach the sensitive IDT electrodes, thereby protecting the narrow-pitch electrode structure from ESD damage while maintaining its filtering performance
Solution Approach 2:
The patent implements beforehand cushioning by providing dummy electrode fingers and surge charge reception electrodes that are specifically designed to absorb and dissipate electrostatic discharge energy before it can reach the IDT electrodes. This protective structure is pre-positioned to cushion against potential ESD events, ensuring the narrow-pitch IDT electrodes remain protected while maintaining filtering functionality
2Reliability
If dummy electrode fingers are added to increase ESD resistance, then protection against surge charge is improved, but the dummy electrode fingers are prone to breakdown when surge charge enters once
Solution Approach 1:
The patent introduces an intermediary protection structure consisting of dummy electrode fingers and surge charge reception electrodes positioned between the IDT electrodes and external signal terminals. These intermediary elements intercept and dissipate surge charges before they can reach the sensitive IDT electrodes, thereby protecting the narrow-pitch electrode structure from ESD damage while maintaining its filtering performance
Solution Approach 2:
The patent implements beforehand cushioning by providing dummy electrode fingers and surge charge reception electrodes that are specifically designed to absorb and dissipate electrostatic discharge energy before it can reach the IDT electrodes. This protective structure is pre-positioned to cushion against potential ESD events, ensuring the narrow-pitch IDT electrodes remain protected while maintaining filtering functionality
3Reliability
If wiring length is increased to improve ESD resistance, then surge charge attenuation is enhanced, but device complexity increases
Solution Approach 1:
The patent utilizes the substrate's thickness dimension by routing wirings through internal layers and using via holes to connect different levels. This three-dimensional wiring approach effectively increases the wiring length for surge charge attenuation without increasing the planar footprint, thereby enhancing ESD resistance while maintaining a compact device structure
Solution Approach 2:
The patent embeds multiple wiring layers and via holes within the substrate structure, creating a nested configuration where wirings are routed through internal layers. This nesting approach allows the wirings to be longer for better surge charge attenuation while keeping the overall device structure compact and manageable, reducing the apparent complexity despite the increased wiring length
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 effectively increases ESD resistance in surface acoustic wave filters by ensuring sufficient wiring lengths to attenuate surge charges, thereby improving the protection against electrostatic discharges and reducing the risk of short circuits.
Implementation Method 1
the first and second signal terminals of the first and second filters are respectively joined to the first and second signal electrode pads with bumps. In a filter device according to a preferred embodiment of the present invention, the bumps are solder bumps.
Data Source
AI summary
A filter device includes a first filter chip including a first signal terminal and a second filter chip including a second signal terminal that are mounted above a package substrate including a substrate main body. First and second signal electrode pads are provided on a first main surface of the package substrate and are respectively joined to the first and second signal terminals. First and second outer terminals are provided on a second main surface of the substrate main body. The first and second signal electrode pads and the first and second outer terminals are connected to each other with first and second wirings, respectively. The second outer terminal is located at the first signal electrode pad side and the first outer terminal is located at the second signal electrode pad side when seen from above.