Ultrasonic Wire Bonding Force Sensor With Driver Force Cancellation
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Solution Overview
Problem
Conventional ultrasonic wire bonding devices experience a delay in detecting bonding forces due to the location of the force sensor, compromising the accuracy of bonding force measurements during wire bonding operations.
Innovation Solution
A force sensor with a piezoelectric sensing element is integrated into the ultrasonic transducer, featuring a novel arrangement of electrodes on opposing surfaces of its portions, which cancels out driving forces from the piezoelectric driver stack, allowing for more accurate measurement of bonding forces by amplifying the contact detection signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the force sensor is located far away from the wire bonding tool, then the device structure is simplified, but the measurement precision deteriorates due to detection delay
Solution Approach 1:
The force sensor is merged with the ultrasonic transducer by integrating the piezoelectric sensing element into the bond head assembly. This combination allows the force sensor to be positioned close to the wire bonding tool, enabling real-time detection of bonding forces without compromising device structure simplicity.
Solution Approach 2:
The piezoelectric sensing element acts as an intermediary between the bonding interface and the measurement system. It directly senses the bonding forces at the source and converts them into electrical signals, eliminating the detection delay that would occur with distant sensors.
2Device complexity
If a conventional force sensor is used, then the device structure is simple, but the bonding force measurement accuracy deteriorates due to driving force interference
Solution Approach 1:
The piezoelectric sensing element uses an asymmetric electrode configuration where opposite surfaces have opposite polarity arrangements. This asymmetry creates differential measurement capability that cancels out the driving forces from the piezoelectric driver stack while preserving the bonding force signal.
Solution Approach 2:
The driving forces from the piezoelectric driver stack, which normally interfere with measurement, are converted into a beneficial effect. The opposite polarity arrangement causes these driving forces to produce equal and opposite signals that cancel each other out, while the bonding force produces a differential signal that is amplified.
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 enables precise and accurate monitoring of bonding forces during wire bonding operations by reducing interference from driving forces, enhancing the overall measurement accuracy.
Implementation Method 1
a piezoelectric sensing element mounted in an ultrasonic transducer of an ultrasonic wire bonding device
Implementation Method 2
outputs of the piezoelectric sensing element caused by driving forces from a piezoelectric driver stack for driving the ultrasonic transducer to vibrate
Data Source
AI summary
A force sensor for determining a bonding force during wire bonding operations includes: a piezoelectric sensing element mounted in an ultrasonic transducer of an ultrasonic wire bonding device, the piezoelectric sensing element including a first portion and a second portion, and first and second opposing surfaces, wherein the first surface of the first portion has a positive electrode and the second surface of the first portion has a negative electrode respectively, and the first surface of the second portion has a negative electrode and the second surface of the second portion has a positive electrode respectively.