Laser Ultrasonic Inspection Research Articles

펄스 레이저와 CFPI를 이용한 이종금속 접촉부의 이물질 측정에 관한 연구

A laser ultrasonic inspection system is a non-contact inspection device which generates and measures ultrasonics by using laser beam. A laser ultrasonic inspection system provides a high measurement resolution because the ultrasonic signal generated by a pulse laser beam has a wide-band spectrum and the ultrasonic signal is measured from a small focused spot of a measuring laser beam. In this study, galvanic corrosion phenomenon was measured by non-destructive and non-contact method using the laser. The case of mixed foreign material on the part of corrosion was assumed and laser ultrasonic experiment was conducted. Ultrasonic was generated by pulse laser from the back side of the specimen and ultrasonic signal was acquired from the same location of the front side using continuous wave laser and Confocal Fabry-Perot Interferometer(CFPI). The characteristic of the ultrasonic signal of exist foreign material part was analyzed and the location and size of foreign material was measured.

The Present Development Situation of Laser Ultrasonic Nondestructive Testing Signal Processing System

Currently, laser ultrasonic nondestructive testing is the best application prospect of nondestructive testing methods. This paper expounds the mechanism and the qualitative analysis of the common defects of the laser ultrasonic inspection and introduces the application of matching pursuit algorithm guided wave testing technology in signal processing. This paper focuses on the laser ultrasonic detection system and analysis of the detected data using the finite element method.

Laser ultrasonic inspection for water transport through membrane in a PEM fuel cell

The performance of a proton exchange membrane fuel cell (PEMFC) was reported to be strongly influenced by water management. This work presents laser ultrasonic inspection for in-situ detection of water across the membrane electrode assembly (MEA). A laser induced grating or an alternative interdigitated piezoelectric fiber composite based acoustic wave transducer was placed on an extension of the flow field plate to launch fixed-wavelength plate waves propagating parallel to the flow channels. The acoustic waves passing through the flow channels underlain by the moist MEA were detected at the opposite end using knife-edge technique. The phase velocities of the acoustic guided waves do not change much between both moist and moist-free states. The insight of water transport could be gained through the excess attenuation of guided waves. The synthetic aperture focusing technique was utilized to establish clear B-mode images of water transport through the membrane.

Laser Ultrasonic Inspection of Solder Bumps in Flip-Chip Packages Using Virtual Chip Package as Reference

In flip-chip (FC) packages, the solder bumps are sandwiched between the silicon die and the substrate, making them no longer visible for usual visual inspection. An inspection system capable of evaluating the quality of the hidden solder bumps in FC packages has been developed. The system pulses a laser on the top surface of a chip package to generate ultrasonic waves in the package to excite structural vibrations which can then be measured using an interferometer. Since defective solder bumps cause changes in the transient vibration response of a test sample, quality of the test sample can be assessed by correlating its vibration responses to that of a known-good reference sample. The limitation to this method is the necessity to use a known-good reference chip package, which typically involves expensive testing using alternate methods. In this paper, the development of a method without the need of known-good reference samples is presented. This method, called hybrid reference method, uses a statistical approach to find the most similar packages and then average their time domain vibration signals to generate virtual time domain signals. These virtual signals are what we call hybrid reference signals and they are correlated back with the vibration signals from the sample under inspection to obtain a quality signature. Finally, defective and nondefective chip packages are separated by estimating a beta distribution that fits the quality signature histogram of the inspected packages, and then determining a critical threshold for an acceptable quality signature. This method was applied on two types of FC packages with no available pre-established known-good reference chip package. The results of this quality assessment were validated by comparison with electrical test and X-ray technique results.

Laser ultrasonic inspection, a new inspection technique and its effects on the integrity and surface properties of the metallic surfaces

Laser ultrasonic inspection (LUI) is the name given to the techniques in which a laser beam interacts with the surface of a test sample and replaces piezoelectric transducers for launching and probing elastic sound waves. When this wave returns to the surface, a separate laser interferometer detects the small resulting displacement. This technique is strictly non-contact and is therefore suitable for in-process inspection of parts while at high temperature or moving at high speed. In the field of non-destructive techniques (NDT), the association of laser generation with optical detection provides a completely remote inspection system. As this process involves hitting of high power laser beam on to the surface to be inspected and ablation of the superficial layer of the surface, one of the objections from the conventional oil and gas industry to LUI system is apprehension of potential damage or adverse effect on the surface property and integrity. This possible problem is seen as severe on pressurized pipes to the extent of being dangerous to the system. This work attempts to present a qualification methodology which was experimentally applied to known metallic samples and with standard LUI testing conditions. Binary image processing techniques have been used with hybrid filtering and statistical measurements to quantify the findings. A relational approach is used within the digital image processing domain to qualify the extent of metal loss that occurs during a prolonged exposure of the clean metallic surface to the laser beam. A comparative study has been done on Duplex steel (UNS S31803) and Carbon steel. Samples were studied for relative metal loss, possible changes in hardness and micro-structural anomalies (if any). A new qualification method has been developed using digital image processing to approximate the damage sustained by the exposure. The results are quite promising and alleviate many doubts that conventional NDT experts may have in connection with the LUI system, especially in the oil and gas scenarios.

Single-frequency pulsed laser oscillator and system for laser-ultrasonics

We present a new pulsed laser oscillator and system for the optical detection of ultrasound in materials. A single-frequency laser oscillator based on a pulse pumped Nd:YAG rod inside a ring cavity is proposed. The laser delivers single-frequency pulses of 35 W power. Pulse to pulse stability of the laser is obtained with a classical Pound–Drever–Hall method. Power of about 1 kW can be obtained when the second rod of a dual-rod pumping chamber is used as an amplifier. The performance of the system is then investigated with a GaAs photorefractive crystal-based two-wave mixing phase demodulator. In particular, the intensity noise of the laser can be made small enough to allow the detection limit to be set by the shot-noise of the laser. The coherence length of the laser is about 20 m, which makes it a versatile laser-ultrasonic inspection system operated with a two-wave mixing-based phase demodulator. A complete compact and affordable system is obtained when the second rod of the pumping chamber is used to operate a short pulse laser for the generation of ultrasound. Tests of this laser-ultrasonic system on metallic samples are presented.

501 レーザーを用いた無色透明材料の音速測定に関する研究

A pulse laser has been used to generate ultrasonic transients in samples of the laser ultrasonic nondestructive inspection. However, it is impossible to excite ultrasonic wave in transparent materials by a pulse laser. In this study, the surface of a transparent ceramic specimen is painted black in order to absorb the laser energy. As a result, heating by pulse laser, the specimen with a black surface band makes the pulse wave. By using the pulse wave, the sound speeds in a transparent ceramic specimen are measured. The experimental results were identical with the results by the ultrasonic pulse method.

Development of a Flexible Laser Ultrasonic Probe

Ultrasonics is a widely used nondestructive testing technique, which is often applied off-line for weld quality inspection. Laser ultrasonic (LU) inspection systems have the potential for on-line application, providing the means to identify unacceptable welds as they are formed. Because LU systems are non-contacting, they can be used for testing moving specimens or for operation in hazardous and/or high temperature environments. A highly versatile system can be created when an optical fiber delivery system is incorporated into the design. Introduction of a focusing objective increases the allowable working distance and permits stronger generation using material ablation as the generating mechanism. This paper describes the development of a laser ultrasonic probe using an optical fiber delivery system with a distal end, focusing objective. The optical fiber delivery system can be configured as a single fiber source, a linear array (fiber bundle) or a phased array. Results include experimentally obtained directivity patterns demonstrating ultrasonic generation using ablation sources. Thermoelastic source results are also included. This paper demonstrates the potential of the fiber tool and presents an overview of the weld control scheme.

Laser ultrasonic surface wave inspection of alumina ceramics of varying density

In this paper, the surface acoustic wave velocity results acquired from the inspection of specially manufactured and characterised alumina ceramic materials are presented. Ultrasonic velocity data of alumina-based ceramics in the range 60–100% theoretical density was generated utilising non-contacting laser-ultrasonic measurements based on laser generation and detection of surface acoustic waves with the objective of creating a routine technique for industrial advanced alumina inspection. With linear fitting the surface acoustic wave velocity data serves as a calibration graph for using laser ultrasonics for routine monitoring of alumina. A second laser ultrasonic technique based on the laser generation and foil transducer detection of surface acoustic waves was used to validate the surface acoustic wave velocities measured by the laser generation/detection technique.

Laser ultrasonic inspection of concrete structures. Phase 1 : Berger, H. Industrial Quality, Inc., Gaithersburg, Maryland (United States), PB93- 158194/GAR, 21 pp. (Jun. 1989)

Laser ultrasonic inspection of concrete structures. Phase 1 : Berger, H. Industrial Quality, Inc., Gaithersburg, Maryland (United States), PB93- 158194/GAR, 21 pp. (Jun. 1989)

53915 Laser ultrasonic inspection of honeycomb aircraft structures

53915 Laser ultrasonic inspection of honeycomb aircraft structures

VLSI Package Reliability

The challenge presented by advanced package development in the past five years has further accentuated the constant need for package quality and reliability monitoring through extensive laboratory testing and evaluation. As pin counts and chip geometries have continued to increase, there has been additional pressure from the military and commercial sectors to improve interconnect designs for packaged chips, including chips directly attached to the printed wiring board (PWB). One of the options employed has been tape automated bonding (TAB). However, this assembly technique also presents new standardisation, qualification and reliability problems. Therefore, at Rome Air Development Center (RADC), there is regular assessment (through in‐house failure analysis studies) of parts destined for military and space systems. In addition, Department of Defense (DoD) high tech development programmes, such as very high speed integrated circuits (VHSIC), have utilised all present screening methods for package evaluation, and have addressed the need for development of more definitive non‐destructive tests. To answer this need, two RADC contractual efforts were awarded on laser thermal and ultrasonic inspection techniques. Through these package evaluations, a number of potential reliability problems are identified and the results provided to the specific contractors for corrective action implementation. Typical problems uncovered are lid material and pin corrosion, damage to external components and adhesion problems between copper leads and polyimide supports, hermeticity failures, high moisture content in sealed packages and particle impact noise detection (PIND) test failures (internal particles). Further tests uncover bond strength failures, bond placement irregularities, voids in die attach material (potential heat dissipation problems), and die surface defects such as scratches and cracks. This presentation will review the specific package level physical test methods that are employed as a means of evaluating reliable package performance. Many of the tests, especially the environmental tests—e.g., salt atmosphere and moisture resistance—provide accelerated forms of anticipated conditions and are therefore applied as destructive tests to assess package quality and reliability in field use. In addition to a manufacturer's compliance with designated qualification procedures, the key to package quality lies in utilising good materials and well‐controlled assembly techniques. This practice, along with effective package screen tests, will ensure reliable operation of very large scale integration (VLSI) devices in severe military and commercial environment applications.