CMUT Transducer Insulation Layer and Flexible PCB Design
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Solution Overview
Problem
The existing capacitive micromachined ultrasonic transducers (CMUTs) face issues with electrical short-circuiting due to the flexible printed circuit board's conductive foil coming into contact with the substrate's side surface, leading to increased thickness of the protection film and distance between the acoustic lens and the chip, which deteriorates transmission and reception performance.
Innovation Solution
The solution involves a flexible printed circuit board without a coverlay in the region facing the substrate, with an insulation layer on the substrate surface facing the circuit board, ensuring electrical insulation and reducing the length of the circuit board that sticks out, allowing for a thinner protection film and closer acoustic lens mounting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a flexible printed circuit board with coverlay is used to connect the CMUT to external circuits, then electrical insulation is provided, but the circuit board sticks out from the chip surface, increasing the thickness of the protection film and the distance between the acoustic lens and the chip
Solution Approach 1:
The patent applies local quality by selectively removing the coverlay only from the region where the flexible printed circuit board contacts the substrate, while maintaining the coverlay in other regions for electrical insulation. This localized modification allows the circuit board to lie flush with the chip surface without compromising overall insulation, thereby reducing the protection film thickness requirement while maintaining electrical safety.
2Reliability
If a flexible printed circuit board with coverlay is used to connect the CMUT to external circuits, then electrical insulation is provided, but the distance between the acoustic lens and the chip increases, deteriorating transmission and reception performance
Solution Approach 1:
The patent removes the coverlay locally from the contact region between the flexible printed circuit board and the substrate, allowing the circuit board to sit flush with the chip surface. This enables the acoustic lens to be positioned closer to the chip, improving transmission and reception performance, while the coverlay remains in other areas to provide necessary electrical insulation.
3Ease of manufacture
If the conductive foil of the flexible printed circuit board contacts the substrate side surface, then electrical connection is achieved, but electrical short-circuiting occurs
Solution Approach 1:
The patent extracts (removes) the coverlay from the specific region where the flexible printed circuit board makes contact with the substrate. This extraction eliminates the electrical insulation barrier in the contact region, allowing direct electrical connection between the conductive foil and the substrate, thereby achieving reliable electrical connection without short-circuiting.
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 configuration enhances the transmission and reception performance of the capacitive transducer by preventing electrical short-circuiting and allowing for a more compact design with improved acoustic lens proximity.
Implementation Method 1
a DC voltage generating unit 301 is connected to the first electrode 102, and a predetermined DC voltage Va is applied to the first electrode 102. The second electrode 103 is connected to a transmitting and receiving circuit 302. The second electrode 103 has a fixed potential that is close to a GND potential. In this manner, a potential difference Vbias (=Va−0 V) occurs between the first and second electrodes. By controlling Va, the value of Vbias is made equal to a desired potential difference determined by the mechanical property of the cell
Implementation Method 2
If the transmitting and receiving circuit 302 applies an AC drive voltage to the second electrode 103, an AC electrostatic attraction force is generated between the first and second electrodes. Thus, the vibrating membrane 101 vibrates at a certain frequency to transmit an ultrasonic wave.
Implementation Method 3
upon receiving an ultrasonic wave, the vibrating membrane 101 vibrates. Thus, a small electric current flows in the second electrode 103 due to electrostatic induction. By measuring the value of the electric current using the transmitting and receiving circuit 302, a received signal can be retrieved.
Data Source
AI summary
A transducer includes an element disposed on a substrate, where the element includes an electrode, and a connection electrode electrically connected to the electrode of the element. A conductive portion disposed on an insulating film of a flexible print circuit board is electrically connected to the connection electrode. Part of the conductive portion is exposed so as to face a surface of the substrate having the element disposed thereon. An insulation layer is disposed on part of the surface of the substrate facing the flexible print circuit board.