Shear Force Microscopy for Sub-Surface Void Detection in Electronics

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Solution Overview

Problem

Current non-destructive characterization techniques, such as confocal scanning acoustic microscopy, have limited resolution and depth of penetration, failing to effectively detect sub-surface defects in power electronics modules, which can lead to assembly failures due to thermomechanical stresses and defects like cracks or voids.

Innovation Solution

A method using a scanning probe with a dither and receiver to emit ultrasonic waves and measure shear force amplitudes, creating approach curves to detect sub-surface voids by determining the slope of these curves, and employing machine learning to determine the optimum frequency for defect detection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If confocal scanning acoustic microscopy is used to detect defects, then the detection capability is improved, but the spatial resolution is limited by the diameter of the acoustic beam

Engineering Contradiction:

Improvedefect detection capabilityVSAvoidspatial resolution

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent replaces conventional acoustic wave propagation through the sample with a scanning probe microscopy technique that uses a vibrating cantilever probe. This substitution allows measurement of acoustic properties at the nanoscale without being limited by the diffraction limit of acoustic beams, achieving spatial resolution beyond what is possible with traditional C-SAM.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If scanning probe microscopy is integrated with acoustic waves to increase spatial resolution, then the spatial resolution is improved, but the depth of penetration is limited to near-field distance

Engineering Contradiction:

Improvespatial resolutionVSAvoiddepth of penetration

Core Design Contradiction:

Measurement precisionVSLength of stationary object

Solution Approach 1:

The patent measures shear force amplitude as a function of probe-to-sample distance, creating an approach curve that provides depth information. By analyzing how the shear force signal changes with distance, the system can detect sub-surface defects at depths beyond the traditional near-field limit, effectively adding a distance dimension to the measurement.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Measurement precision

If the probe is moved closer to the sample to increase measurement sensitivity, then the detection sensitivity is improved, but the probe may contact and damage the sample

Engineering Contradiction:

Improvedetection sensitivityVSAvoidsample damage risk

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent performs preliminary measurements at multiple distances to construct an approach curve before making final defect determination. This allows the system to identify the optimal measurement distance that provides sufficient sensitivity while maintaining a safe distance from the sample surface, preventing contact and potential damage.

Inventive Principle:

Principle #10Preliminary action

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 method enhances the detection of sub-surface voids in power electronics modules, improving the ability to identify defects before they cause assembly failures, with increased spatial resolution and depth penetration compared to existing techniques.

Implementation Method 1

emitting an ultrasonic wave from the probe towards the sample, measuring a shear force amplitude of a reflection of the ultrasonic wave at the probe

Methodology Applied

Scientific EffectUltrasonic wave reflection: Reflection

Implementation Method 2

measuring a shear force amplitude of a reflection of the ultrasonic wave at the probe as the probe moves towards the sample

Methodology Applied

Scientific EffectShear force measurement: Shear Stress

Implementation Method 3

the depth of penetration of acoustic waves (near-field distance) is generally limited to between 10 nm-1 μm

Methodology Applied

Scientific EffectAcoustic wave penetration: Acoustic Microscopy

Data Source

PatentUS11193913B2Methods and systems to detect sub-surface defects in electronics modules using shear force microscopy

Publication Date: 2021.12.07 THE OHIO STATES UNIV

AI summary

A method of detecting sub-surface voids in a sample comprises positioning a probe adjacent to a first point on the sample, emitting an ultrasonic wave from the probe towards the sample, moving the probe towards the sample, measuring a shear force amplitude of a reflection of the ultrasonic wave at the probe as the probe moves towards the sample, creating an approach curve by plotting the measured shear force amplitude of the reflection of the ultrasonic wave as a function of a distance between the probe and the sample, and determining whether a sub-surface void exists at the first point on the sample based on a slope of the approach curve.