Researchers at South Korea’s Daegu Gyeongbuk Institute of Science and Technology (DGIST) have developed a specialised ultrasonic sensor capable of imaging microscopic cracks, air voids and other internal defects in semiconductor components without cutting or damaging them.
The research team, led by Professor Jang Jin-ho from DGIST’s Department of Electrical Engineering and Computer Science, developed a “threaded-lens focused ultrasonic sensor” designed to improve image clarity by reducing internal acoustic noise. The technology could support non-destructive testing (NDT) of power semiconductors used in electric vehicles and aerospace systems, where component reliability is critical.
Threaded Lens Design Reduces Acoustic Noise
Conventional ultrasonic sensors can struggle to resolve fine internal structures because ultrasonic waves reflected repeatedly within the lens generate noise that obscures image details. Increasing sensor size to address this limitation can also be difficult in industrial inspection environments with restricted installation space.
To overcome this challenge, the DGIST team introduced densely spaced, angled grooves along the side of the ultrasonic lens. Inspired by sound-absorbing structures used in anechoic chambers, the threaded grooves scatter reflected waves in multiple directions rather than allowing them to converge at a single point.
The design reduces noise generated by internal reflections while maintaining the sensor’s overall dimensions and core components. This approach could improve imaging performance without requiring a complete redesign of existing sensor assemblies.
Optimising the Sensor for High-Resolution Inspection
Computer simulations identified a thread height of 500 micrometres and an inclination angle of 30 degrees as optimal design conditions, balancing acoustic noise suppression with manufacturing practicality.
When tested on an automotive power semiconductor module, the sensor successfully imaged internal structures that conventional sensors had struggled to distinguish because of acoustic noise. These included metal wires approximately one-quarter the width of a human hair and small air bubbles.
According to the research team, the resulting image clarity was comparable to that achieved using computed tomography (CT), highlighting the technology’s potential for detailed internal inspection of semiconductor components.
Potential Applications in Semiconductor NDT
Power semiconductors used in electric vehicles and aerospace systems must withstand demanding electrical and thermal conditions. Microscopic cracks, voids and other internal defects can compromise component performance and reliability, making accurate inspection important during manufacturing and quality assurance.
The threaded-lens sensor could support the detection of voids, delamination and micro-cracks within multilayer semiconductor packages. Potential applications also include high-resolution acoustic microscopy and medical ultrasonic sensors.
The technology retains existing piezoelectric components and assembly processes, requiring additional machining of the lens’s side surface. This design approach may simplify integration into industrial inspection systems compared with solutions that require substantial equipment modifications.
Further Validation Before Commercialisation
Despite the promising results, additional work is required before the technology can be deployed widely. The threaded geometry must be optimised for different ultrasonic frequencies and lens materials, while integration with automated, high-speed inspection equipment will require further validation.
The research team estimates that commercialisation could be approximately two years away. It plans to expand testing of real-world manufacturing defects through joint research with semiconductor manufacturers.
“The significance of this work lies in solving what has long been the biggest challenge for industrial ultrasonic sensors — internal lens noise — through a simple geometric modification,” said Professor Jang Jin-ho. “Going forward, we will expand verification of real-world process defects through joint research with semiconductor manufacturers and accelerate the development of next-generation non-destructive inspection systems.”
DGIST postdoctoral researcher Kang Seong-hu and integrated master’s-doctoral student Park Hyeon-gyu served as co-first authors of the study. The findings were published in NDT & E International, a peer-reviewed journal specialising in non-destructive testing.
Reference: https://mbiz.heraldcorp.com/article/10917290
