Flip-Chip SAW Band Reject Filter Layout for Low-Loss Miniaturization
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Solution Overview
Problem
Conventional surface acoustic wave (SAW) band reject filters are large and costly due to the need for high Q values, which are not efficiently achieved with conventional components, making them unsuitable for modern wireless communication equipment requiring compact and low-loss designs.
Innovation Solution
The implementation of SAW band reject filters using flip chip assembly technology with electrode bars formed on the substrate, reducing the size of the die and minimizing loss and parasitic inductance by placing SAW resonators closer together and using shorter electrode bars.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional components such as air cavity filters are used to implement high Q band reject filters, then the filter achieves steep transition bands, but the filter becomes undesirably large in size and expensive
Solution Approach 1:
The patent replaces conventional mechanical air cavity filters with surface acoustic wave (SAW) resonators that utilize acoustic wave propagation on a piezoelectric substrate. This substitution enables high Q values and steep transition bands while achieving compact filter dimensions suitable for modern wireless equipment
Solution Approach 2:
The patent changes the fundamental operating parameters by using SAW resonators with specific electromechanical coupling coefficients and acoustic wave propagation characteristics. By controlling the reflector finger spacing to be less than one-half of the acoustic wavelength and using specific interdigital transducer configurations, the filter achieves high Q values in a compact form factor
2Manufacturing precision
If SAW resonators with high Q are used for band reject filter design, then steep transition bands are achieved, but the resonator dimensions become much bigger requiring huge die and long connecting bus bars that introduce excessive loss and parasitic inductance
Solution Approach 1:
The patent repositions the SAW resonators vertically on the die surface rather than spreading them out horizontally. By stacking resonators in multiple layers or utilizing the vertical dimension of the die, the design achieves compact horizontal footprint while maintaining short inter-resonator connection lengths, thereby reducing parasitic inductance and insertion loss
Solution Approach 2:
The patent merges the functions of multiple SAW resonators into a compact integrated structure where resonators are closely spaced and interconnected with minimal parasitic elements. The connecting bus bars are integrated directly into the resonator structure rather than being separate external connections, reducing overall loss
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 approach enables the creation of compact, low-loss SAW band reject filters that are more suitable for modern wireless communication equipment, reducing the overall size and cost while maintaining high Q values.
Implementation Method 1
Surface acoustic wave, SAW, devices have been used to implement miniature band pass filters
Implementation Method 2
SAW resonators can be used to implement band pass filters and band reject filters
Implementation Method 3
inter-digital transducer, IDT, interlaced fingers electrically connected by two IDT bus bars
Data Source
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AI summary
A surface acoustic wave band reject filter (34) implemented as a flip chip assembly is presented. The surface acoustic wave band reject filter (34) comprises a substrate (24) including electrode bars (20) and bonding pads (36) formed on the substrate (24), and at least one die (26) having a side facing the substrate (24), a plurality of surface acoustic wave resonators (10) being formed on the at least one die (26), the at least one die (26) being mounted on the substrate (24), solder balls (22) in contact with the side of the at least one die (26) facing the substrate (24), the solder balls (22) being positioned to be in electrical contact with the electrode bars (20) and bonding pads (36) on the substrate (24), the plurality of surface acoustic wave resonators (10) being connected by the electrode bars (20) and bonding pads (36) via the solder balls (22) and collectively exhibiting a band reject filter response. According to a first arrangement, a first three of the plurality of the surface acoustic wave resonators (10) are arranged so that two of the plurality of surface acoustic wave resonators (10) are electrically in series, and a third surface acoustic wave resonator (10) is electrically in parallel to and between the two of the plurality of surface acoustic wave resonators (10). According to a second arrangement, a first three of the plurality of surface acoustic wave resonators (10) are arranged such that a first two surface acoustic wave resonators (10) are electrically in parallel, and a third surface acoustic wave resonator (10) is electrically intervening between the first two surface acoustic wave resonators (10).