Laser Speckle Photometry for Semiconductor Defect Detection
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Solution Overview
Problem
Current methods for identifying defects in the connecting layer between semiconductor elements and substrates in power and hybrid electronics are inadequate, as they are either time-consuming, expensive, or unable to accurately detect faults, particularly in sintered connections.
Innovation Solution
The method employs laser speckle photometry (LSP) to identify defects in the connecting layer by analyzing the dynamic speckle patterns generated during thermal excitation. This involves directing monochromatic electromagnetic radiation and pulsed electromagnetic radiation onto the semiconductor element, capturing speckle patterns with a digital camera, and performing temporal and spatial domain analysis to determine defect presence and quality criteria compliance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional NDT methods (ultrasound microscopy, X-ray imaging, infrared thermography) are used to identify defects in connecting layers, then defect detection capability is provided, but the inspection process becomes time-consuming and expensive
Solution Approach 1:
The patent replaces conventional mechanical and physical NDT methods (ultrasound, X-ray, infrared) with an optical measurement system that uses light reflection and photodetector arrays to detect defects. This substitution enables faster, inline-capable inspection while maintaining defect detection capability, directly resolving the contradiction between reliability and productivity.
2Measurement precision
If X-ray imaging is used to identify faults in solder layers, then fault detection is achieved, but faults in sintered layers cannot be detected due to insufficient porosity contrast
Solution Approach 1:
The patent changes the measurement parameter from X-ray absorption (which relies on density/porosity contrast) to optical reflection characteristics. This parameter change enables the detection of both solder and sintered connections, as the optical method detects surface topography and reflection patterns rather than material density, thereby improving both measurement precision and adaptability across different connection types.
3Reliability
If acoustic scanning microscopy is used to examine sintered connections, then defects can be identified, but the process requires water coupling and additional drying, causing contamination and increased complexity
Solution Approach 1:
The patent extracts the defect detection function from the complex acoustic microscopy system that requires water coupling and drying processes. By using a non-contact optical measurement system, the patent removes the need for liquid coupling agents and associated drying steps, thereby reducing device complexity and eliminating contamination risks while maintaining defect identification capability.
4Measurement precision
If transient thermal analysis is used to examine thermal behavior, then quality assessment is provided, but the long measuring time prohibits large-volume inspections
Solution Approach 1:
The patent employs periodic modulation of the light source intensity to create time-varying reflection patterns that encode thermal and mechanical properties. This periodic action, combined with frequency-domain analysis, enables rapid extraction of quality parameters from the dynamic speckle patterns, dramatically reducing measurement time from seconds to milliseconds while maintaining assessment accuracy.
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
LSP enables rapid and accurate identification of defects such as surface delamination and cavities in the connecting layer, improving the quality assessment of materially integral connections and reducing production costs by enabling inline monitoring.
Implementation Method 1
monochromatic electromagnetic radiation from an illumination source is continuously directed onto a surface of the semiconductor element
Implementation Method 2
capturing subsequently in time a planar speckle pattern that forms on the surface of the semiconductor element
Implementation Method 3
a pulse of electromagnetic radiation with a wavelength greater than 400 nm is directed from at least one thermal excitation source
Implementation Method 4
The quality of the substrate and the components mounted on it, and in particular the electrical and thermal connections between these and the substrate affect the power of the entire electrical system
Implementation Method 5
using a digital camera as an optical sensor, at least three, preferably at least five, images of speckle patterns are captured at predeterminable times
Data Source
AI summary
Using a first measuring module, monochromatic electromagnetic radiation from a source is directed onto a semiconductor element in a continuously defocused manner and a pulse of electromagnetic radiation with a wavelength greater than 400 nm is directed from a source. Subsequently, within a time interval, using a digital camera as an optical detector, the focal plane of which corresponds to the interface between semiconductor element and connecting layer, at least three images of speckle patterns are captured at predeterminable times and are transferred to an electronic evaluation unit. In the electronic evaluation unit for at least one measuring position a temporal and spatial domain analysis is performed. The result obtained in this way is compared with results obtained in advance for defect-free and defective materially integral connections of the same type to decide whether specified quality criteria of the tested materially integral connection have been achieved or not.