Ultrasonic Bond Quality Check via Reflection Coefficient
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Solution Overview
Problem
Existing methods for controlling the quality of bonding between substrates, especially when they are made of the same material with very small surface roughness, are non-destructive but face challenges in measuring the echo signal, making it difficult to assess the adhesion energy accurately.
Innovation Solution
A method involving the emission of an ultrasonic excitation signal and measuring the return signal to calculate the spectral signal representative of the overall reflection coefficient, which includes detecting the frequency difference between resonance peaks to deduce the adhesion energy between substrates, allowing for non-destructive quality control even in cases with small interface roughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If mechanical stress is applied to separate substrates to measure adhesion energy, then adhesion energy can be estimated, but the method becomes destructive and cannot be used for all assemblies
Solution Approach 1:
The patent replaces the mechanical stress method with an ultrasonic vibration-based measurement system. An ultrasonic transducer applies high-frequency vibrations to the substrate assembly, and the reflection coefficient of these ultrasonic waves is measured. This substitution eliminates the need for mechanical separation while still providing adhesion energy information through the relationship between ultrasonic reflection characteristics and bonding quality.
Solution Approach 2:
The patent changes the measurement parameter from mechanical separation force to ultrasonic reflection coefficient. By measuring how ultrasonic waves reflect from the substrate interface rather than applying mechanical stress to separate substrates, the method provides non-destructive adhesion assessment. The reflection coefficient varies with bonding quality, enabling measurement without damaging the assembly.
2Reliability
If ultrasonic echo reflection is measured to assess bonding quality, then non-destructive measurement is achieved, but the echo signal becomes difficult or impossible to measure when substrates are identical with very small surface roughness
Solution Approach 1:
The patent introduces a coupling layer or uses the substrate itself as an intermediary to enhance the ultrasonic signal interaction with the bonding interface. By measuring the reflection coefficient of ultrasonic waves propagating through the substrate rather than directly at the interface, the method overcomes the difficulty of detecting weak echoes from smooth interfaces between identical materials.
Solution Approach 2:
The patent utilizes high-frequency mechanical vibrations (ultrasonic range) to induce detectable responses at the bonding interface. The ultrasonic vibrations create dynamic stress conditions that enhance the contrast in reflection coefficients between well-bonded and poorly-bonded interfaces, making the measurement feasible even when static surface roughness is very small.
3Measurement precision
If spectral analysis of ultrasonic echo is performed to characterize interface properties, then non-destructive interface characterization is achieved, but the method requires measurable echo which is not available for smooth interfaces between identical materials
Solution Approach 1:
The patent transitions from measuring direct interface echoes to measuring the reflection coefficient of ultrasonic waves that have propagated through the substrate thickness. This dimensional change in the measurement approach allows characterization of interface properties indirectly through bulk wave reflection, bypassing the limitation of direct echo measurement from smooth interfaces.
Solution Approach 2:
The patent replaces direct echo measurement with reflection coefficient measurement of transmitted ultrasonic waves. Instead of detecting the weak echo reflected directly from the interface, the system measures how ultrasonic waves reflected from the far side of the substrate are affected by the bonding quality, providing an alternative measurement pathway that works for smooth interfaces.
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
Enables effective non-destructive assessment of bonding quality between substrates with small surface roughness, providing accurate adhesion energy measurements and improving the precision of bonding evaluation.
Implementation Method 1
measuring, by means of said transducer, a return ultrasonic signal comprising at least one echo of the excitation signal on the rear face of the second substrate
Implementation Method 2
emitting an ultrasonic excitation signal in the direction of the assembly by means of an ultrasonic transducer
Data Source
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AI summary
The invention relates to a method for checking an assembly comprising first (W1) and second (W2) joined substrates, comprising the following steps: a) transmitting an ultrasonic excitation signal towards the assembly by means of an ultrasonic transducer (301) located on the front face (A1) side of the first substrate (W1); b) measuring, using the transducer (301), an ultrasonic feedback signal including at least one echo (EF) of the excitation signal on the rear face (B2) of the second substrate (W2); c) calculating, using a processing circuit (303), a spectral signal representative of the change in frequency of an overall reflection coefficient of the assembly, defined as the ratio between the feedback signal measured in step b) and the excitation signal; and d) deriving, from said spectral signal, information relating to the quality of the bond between the first (W1) and second (W2) substrates.