Ultrasonic Transducer Acoustic Stack Manufacturing Without Dicing
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Solution Overview
Problem
The manufacturing process of ultrasonic transducers is complicated by the need to dice the acoustic stack for electrical and acoustic isolation, which can result in poor performance due to non-uniform sputter plating and thermal stress caused by elevated temperatures, leading to issues like low capacitance.
Innovation Solution
A method involving a piezoelectric ceramic layer with ceramic posts extending above non-conductive material, plasma etching to level the posts with the epoxy, and sputter plating at reduced temperatures to ensure uniform coating and reduce thermal stress, followed by forming electrodes and providing electrical isolation without dicing the acoustic stack.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the sputter plating process is performed at elevated temperatures (about 120°C), then the plating process can be completed, but the epoxy expands unrestrained causing non-uniform coating and thermal stress that damages the thin plating
Solution Approach 1:
The patent changes the temperature parameter of the sputter plating process from the conventional 120°C to a reduced temperature range (room temperature or below), thereby eliminating thermal expansion of the epoxy and preventing plating damage while maintaining coating quality
Solution Approach 2:
The patent applies a preliminary action by adjusting the ceramic posts to protrude above the epoxy surface before plating, creating a configuration that prevents epoxy expansion from damaging the plating during the subsequent low-temperature sputter process
2Ease of manufacture
If the ceramic posts are depressed below the epoxy surface, then the lamination process can be completed, but the sputter plating process cannot provide uniform coating along the perpendicular surfaces
Solution Approach 1:
The patent inverts the conventional arrangement by making the ceramic posts protrude above the epoxy surface rather than being depressed below it, which enables uniform sputter plating coverage while still allowing lamination to proceed
3Reliability
If dicing is performed to separate transducer elements, then electrical and acoustic isolation is achieved, but the manufacturing process becomes complicated and time-consuming
Solution Approach 1:
The patent performs preliminary action by forming isolation trenches and filling them with non-conductive material during the lamination process itself, achieving electrical and acoustic isolation before final assembly, thereby eliminating the need for subsequent dicing operations
Solution Approach 2:
The patent merges the isolation structure formation with the lamination process by integrating trench formation and non-conductive material deposition into the same manufacturing step, thereby achieving both structural assembly and electrical isolation simultaneously
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 simplifies the manufacturing process, enhances the uniformity of the plating, reduces thermal stress, and improves the reliability of the piezoelectric ceramic layer by maintaining the ceramic posts at the same level as the epoxy, resulting in better adhesion and performance.
Implementation Method 1
During operation, an electrical waveform pulse is applied to the electrodes of the piezoelectric ceramic, causing a mechanical change in ceramic dimension and generating an acoustic wave
Implementation Method 2
when an acoustic wave reflected from the material under inspection contacts the surface of the piezoelectric ceramic, it generates a voltage difference across the electrodes that is detected as a receive signal
Implementation Method 3
Portions of the surfaces of the piezoelectric ceramics are metal coated (with a sputter plating process), forming electrodes (signal and ground)
Implementation Method 4
plasma etching to level the posts with the epoxy
Data Source
AI summary
An acoustic stack for ultrasonic transducers comprising a backing block, flexible printed circuit board, piezoelectric ceramic layer, and acoustic matching layer. The various components of the acoustic stack are bonded together using an adhesive material and high pressure in a lamination process. The piezoelectric ceramic layer is manufactured to provide electrical and acoustic isolation without the need for dicing through multiple layers of the acoustic stack. A flex circuit provides the necessary electrical connections to the electrically isolated electrodes of the piezoelectric ceramic layer.