Flip-Chip SAW Band Reject Filter With Low-Loss Resonator Interconnects
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Solution Overview
Problem
Conventional surface acoustic wave (SAW) band reject filters are large and expensive due to the need for high Q factors in modern wireless communication standards, which require steep transition bands and are not efficiently implemented using conventional components like air cavity filters.
Innovation Solution
A compact low-loss SAW band reject filter design using flip chip assembly technology, where three SAW resonators are connected via electrode bars on a substrate, reducing the size of the die and minimizing excessive loss and parasitic inductance by placing electrode bars on the substrate rather than the die.
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 large in size and expensive
Solution Approach 1:
The patent replaces conventional mechanical air cavity filters with surface acoustic wave (SAW) resonators that use acoustic wave propagation on piezoelectric substrates. This substitution enables high Q factors and steep transition bands while achieving compact filter sizes, as SAW resonators can be integrated on small die areas unlike bulky air cavity structures
Solution Approach 2:
The patent changes the fundamental operating parameters by using high Q SAW resonators with specific frequency characteristics to achieve the required transition band steepness. By selecting resonators with appropriate Q factors and arranging them in specific topologies (series and parallel combinations), the filter achieves sharp rejection characteristics without requiring large physical dimensions
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 larger
Solution Approach 1:
The patent divides the filter into multiple separate SAW resonator modules (at least three resonators) that can be independently designed and manufactured. Each resonator operates at a specific frequency and Q level, and they are combined through electrode bars to achieve the overall steep transition band response. This segmentation allows optimization of individual resonator sizes while achieving the required overall filter performance
Solution Approach 2:
The patent transitions from planar resonator layouts to a three-dimensional flip-chip assembly architecture. By stacking resonators vertically and using z-axis bonding, the design achieves compact horizontal footprints despite the larger vertical dimensions required for high Q resonators. The electrode bars extend in multiple dimensions to connect resonators efficiently
3Reliability
If long connecting bus bars are used to connect SAW resonators on a large die, then the resonators can be electrically connected, but excessive loss and parasitic inductance are introduced
Solution Approach 1:
The patent extracts the connecting function from the die substrate itself and implements it through separate electrode bars that are specifically designed for minimal loss. These electrode bars are made from low-resistance materials and are optimally routed to minimize length and parasitic effects, separating the connection function from the resonator structure
Solution Approach 2:
Instead of connecting resonators through long bus bars on the die surface, the patent inverts the connection approach by using vertical z-axis connections through bonding pads and solder bumps. This reverses the traditional planar connection topology, allowing resonators to be connected through the thickness of the die assembly rather than across the die surface, thereby minimizing connection length and 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
The design achieves a compact, low-loss SAW band reject filter with reduced size and cost, enabling smaller and more efficient RF front ends for wireless communication equipment.
Implementation Method 1
surface acoustic wave, SAW, band reject filters
Implementation Method 2
SAW resonators can be used to implement band pass filters and band reject filters
Implementation Method 3
The solder balls may be a good conducting metal such as tin, aluminum, copper, silver or gold, or a combination of conducting metals
Data Source
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AI summary
A method and system for providing a surface acoustic wave band reject filter are disclosed. According to one aspect, a surface acoustic wave band reject filter (34) includes a substrate (24) having electrode bars and bonding pads (36) formed on the substrate (24). The filter (34) further includes at least one die (26) having a side facing the substrate (24). A plurality of surface acoustic wave resonators (10) are formed on the at least one die (26) formed on the substrate (24). Solder balls (22) formed on a side of the at least one die (26) facing the substrate (24) are positioned to engage bonding pads on the substrate. The plurality of surface acoustic wave resonators (10) collectively exhibit a band reject filter response.