Contactless Inspection Research Articles

State Detection of Bond Wires in IGBT Modules Using Eddy Current Pulsed Thermography

Insulated gate bipolar transistor (IGBT) modules are important safety critical components in electrical power systems. Bond wire lift-off, a plastic deformation between wire bond and adjacent layers of a device caused by repeated power/thermal cycles, is the most common failure mechanism in IGBT modules. For the early detection and characterization of such failures, it is important to constantly detect or monitor the health state of IGBT modules, and the state of bond wires in particular. This paper introduces eddy current pulsed thermography (ECPT), a nondestructive evaluation technique, for the state detection and characterization of bond wire lift-off in IGBT modules. After the introduction of the experimental ECPT system, numerical simulation work is reported. The presented simulations are based on the 3-D electromagnetic-thermal coupling finite-element method and analyze transient temperature distribution within the bond wires. This paper illustrates the thermal patterns of bond wires using inductive heating with different wire statuses (lifted-off or well bonded) under two excitation conditions: nonuniform and uniform magnetic field excitations. Experimental results show that uniform excitation of healthy bonding wires, using a Helmholtz coil, provides the same eddy currents on each, while different eddy currents are seen on faulty wires. Both experimental and numerical results show that ECPT can be used for the detection and characterization of bond wires in power semiconductors through the analysis of the transient heating patterns of the wires. The main impact of this paper is that it is the first time electromagnetic induction thermography, so-called ECPT, has been employed on power/electronic devices. Because of its capability of contactless inspection of multiple wires in a single pass, and as such it opens a wide field of investigation in power/electronic devices for failure detection, performance characterization, and health monitoring.

Basic examination of noncontact inspection in solid material by using high-intensity aerial ultrasonic waves and optical equipment

Recently, developments have improved methods employing aerial ultrasonic waves for contactless inspection of internal defects in materials such as metals, pipe walls, and fiber-reinforced plastics. Specially, this method is noncontact way differ from conventional ultrasonic inspection that is necessary to contact probe to object. We have developed a new method of aerial ultrasonic inspection that uses high-intensity aerial ultrasonic waves and optical equipments. That is, the object is excited in noncontact way using high-intensity aerial ultrasonic waves and the vibration velocity on the object surface is measured with a laser Doppler galvanometer at same time. We analysis the vibration information and detect defect in materials. We also developed a point-converging acoustic source with a stripe-mode vibration plate to generate the high-intensity aerial ultrasonic waves, an essential component of the method. While the sound source operates at a single resonance frequency, the generated ultrasonic wave has nonlinear acoustic characteristics and generates nonlinear higher harmonics at the focal point because the sound intensity increases by converging a sound wave. Under nonlinear ultrasonic irradiation, the object vibrates at the fundamental frequency and harmonic frequencies corresponding to the ultrasonic waves. Therefore, we also attempted to detect defect in materials for analyzing nonlinear vibration.

Evaluation of machined part surface roughness using image texture gradient factor

In mechanical manufacturing, the state of a machined part surface is very crucial, particularly in aeronautics, and as a result, great care must be exercised in its measurement. Over the past few years, many research studies have been carried out to mitigate the disadvantages (contact, off-line inspection, speed of limited measurement) inherent in the classic measurement of the roughness by contact with a stylus. The contribution of this paper is to demonstrate the feasibility of the contactless inspection of part surface roughness using an optical microscope. Unlike most works in the domain that use image average of grey level and the average cycle of the texture, a new image characteristic named the gradient factor of the image is defined and used to estimate the part roughness parameters. The effect of the vision system parameters on image quality is investigated then the statistical characteristics of the images best describing the machined surface are determined and used to estimate the roughness parameters. The study shows that several roughness parameters (Ra, Rq, Rv, Rt and Rz) can be estimated using only image-extracted features and models, without the need to know the machining parameters used to generate the surface. The results obtained with the vision system are comparable to those obtained with a stylus contact surface roughness measurement system, and could help in the online monitoring of the surface roughness.

Contactless Functionality Inspection of Flat-Panel-Display Pixels and Thin-Film Transistors by Capacitive Coupling

A fast and thorough detection of structural and functional defects of flat-panel displays, large-area image detectors, and printed electronics requires a contactless and flexible inspection technique. Moreover, to accelerate the development of new products and to increase yields, efficient device characterization including the analysis of single component functionality and testing under operating conditions is essential. In this contribution, a contactless inspection method solely based on capacitive coupling is used to analyze pixel and thin-film transistor (TFT) functionality of active-matrix liquid crystal and electrophoretic display backplanes. Employing a capacitively coupled sensor, the measurement of the evolution of the pixel electrode voltage during TFT operation (switching) yields display flicker and TFT parameters, such as TFT on- and off-currents, TFT threshold, and intrinsic capacitance. To confirm the measurement results, the pixel voltage was also measured with an active voltage probe brought into contact with the pixel electrodes under test.

The importance of a correct alignment in contactless inspection of additive manufactured parts

Nowadays products having complex freeform custom-made shapes can be fabricated without any tool by means of additive manufacturing processes. Additive manufactured parts must be inspected for quality to verify that they meet dimensional and geometrical specifications among other requirements just as any other product. Contactless inspection carried out with optical 3D scanners is preferred to traditional pointwise measurements because of the higher amount of data retrieved in short times. A key step of the contactless inspection process is the definition of the part reference frame for the alignment of scan data. This paper considers different 3-2-1 alignments and analyze their influence on the inspection results, putting in evidence that an inattentive or inaccurate definition of the part reference frame can lead to incorrect evaluations of real part deviations.

Contactless inspection of electrically isolated electronic components of planar electronic devices by capacitive coupling

During the early steps of the production process, printed electronic circuits and devices such as flat panel displays and detector panels consist of a large number of electrically isolated components. Detection and thus inspection of isolated electronic parts by capacitive coupling only becomes possible if an appropriate sensor design is chosen. Therefore, the dependence of sensor performance on sensor design was analyzed by means of finite element simulations based on the nonmatching grid approach. A clear detection of individual components is achieved if the sensor imposes a non-uniform potential distribution along the boundary surface of the substrate that carries the electronic components. Sensor resolution can drastically be increased by shielding specific sensor electrode areas or employing an additional shielding encompassing the sensor electrode. From the analysis of the simulation results, design rules for sensor electrode and shielding geometry are deduced. Finally, the performances of a sensor obeying to the deduced design rules and a currently employed sensor are compared with regard to directly electrically accessible components.

Contactless inspection of castings: analysis of alignment procedures

In foundry industries as well as in many other sectors, inspection practice has been facing a gradual revolution through the introduction and development of optical scanners in recent years. The main advantage of contactless quality control is that the external geometry of the cast tool or cast part can be completely inspected in short times by retrieving the coordinates of hundreds of thousands of points. The role and importance of the alignment operation in part inspection is undeniable since any error leads to an unreliable inspection of the part. Therefore, the definition of part reference systems on scan data for computer aided inspection is a crucial operation. The aims of this paper are to highlight this issue and to point out how an improper procedure for part alignment can lead to an incorrect evaluation of real part deviations, especially when the accuracy of the scan data is low.

Contactless Inspection of Flat-Panel Displays and Detector Panels by Capacitive Coupling

As the variety and application areas of planar electronic devices such as flat-panel displays (FPDs) and detector panels increase, flexible inspection methods are becoming more and more important. In this paper, a contactless inspection technique exploiting the capacitive coupling between probe electrodes and the conductive parts of the devices is presented. Measuring principle and setup, as well as sensor chip design, are illustrated and discussed in detail. To evaluate the performance of the system, inspection results of FPD backplanes and X-ray detector panels are compared with the optical images of the inspected areas. Various typical panel defects and defect conglomerations are resolved and can be unambiguously distinguished. Moreover, a precise classification of the detected defects is obtained. Finally, the detectability of device defects beyond the shown examples and the application to thin-film-transistor parameter extraction is discussed.

Contactless inspection of planar electronic devices by capacitive coupling: Development of a model describing the sensor signal and its impact on signal post-processing

With regard to a contactless inspection method for planar electronic devices, a model to derive the signal of the employed sensors has been developed. The measurement technique is exclusively based on capacitive coupling and, for instance, applied to the inspection of flat panel displays (FPDs) and printed electronics. To analyze the sensor signals, to evaluate the sensor performance, and to advance signal post-processing, a model of the capacitive coupling is essential. Focussing on configurations of conductor tracks arranged in parallel, the model approach is explained and illustrated in detail. Finite element (FE) simulations and measurements are used to derive the model parameters, to validate the model approach, and to evaluate the model performance. Possible applications to signal post-processing are discussed. As an example, the model is used to reconstruct the voltages applied to individual tracks of a configuration from the sensor signal. Furthermore, the model is extended to configurations of two-dimensionally arranged conductor tracks.

Impact of sensor design on the contactless inspection of planar electronic devices by capacitive coupling

The impact of sensor design on the inspection of planar electronic devices by capacitive coupling is investigated. To allow for the inspection of electrically isolated conductive parts of devices, such as partly processed flat panel displays or printed electronic circuits, new sensor designs have been developed and are evaluated with the help of finite element simulations. The analysis of the simulation results shows that a clear detection of the conductive parts is achieved if the sensor geometry enforces a non-uniform electrical field distribution in the range of the sensor area. By studying the capacitive coupling to the individual parts of the sensors, design rules for sensor electrode and shielding geometry are deduced.

Modelling the capacitive coupling of sensors applied to the contactless inspection of planar electronics

A model aimed to describe the capacitance between probe electrodes and the conductive parts of planar electronic devices is presented. The probe electrodes are the constitutive part of a sensor chip used in an inspection system which is exclusively based on capacitive coupling and employed for the inspection of devices such as flat panel displays and printed electronic circuits. Finite element (FE) simulations of the sensor signal are used to determine the model parameters and to verify the obtained results. The capacitive coupling for arbitrary configurations of parallel arranged conductor tracks and various distances between the tracks and the sensor chip is reproduced by the model. Absolute values of the capacitance with deviations below 5% can be obtained.

Contactless nondestructive inspection method and measuring system for the thermophysical characteristics of materials, with adaptive compensation for heat loss

A new method with loss compensation is proposed for contactless measurements of thermal conductivity and heat capacity. A microprocessor unit for implementing the method is described in detail.

Microelectronic test structures for rapid automated contactless inline defect inspection

Simple but unique and space-saving microelectronic test structures were designed to afford automated inline contactless defect inspection in a Scanning Electron Microscope (SEM)-voltage contrast (VC) mode for rapid electrical defect-monitoring, along with in situ defect-isolation and characterization capabilities. Such an automated inspection can support accelerated yield learning through increased defect-learning cycles, particularly on the sub-0.25-/spl mu/m-rule designs, as defects below optical resolution become significant. The system is also capable of the traditional visual inspection in the high-energy secondary-electron emission mode, affording the accurate determination of the "transfer coefficients" between the optical inspection results and the electrical faults from the SEM-VC inspection, needed for any foreign-material or contamination-to-yield model with high correlation or at a high confidence level.

Contactless rapid inspection of the corrosion state of underground pipelines

Contactless rapid inspection of the corrosion state of underground pipelines

Inspection of transparent polymers by photothermal detection of ultraviolet-laser generated thermal waves

The concept of photothermal wave imaging has been adapted to the nondestructive inspection of transparent polymeric samples by specific generation of thermal waves. Utilization of light sources according to the absorption properties of the material secured pure surface heating which is necessary for sensible measurements. Thickness profiles of thin films made of poly(ethylene terephthalate), which are transparent in the visible spectrum, could be measured using a pulsed KrF laser. Examples for the nondestructive inspection of complex textile samples such as coated fabrics are presented.The photothermal analysis (PTA) of optically generated thermal waves is a powerful tool for nondestructive, contactless inspection and evaluation of intrinsic properties of a sample.1,2 The method has been used for the observation of dynamic processes in adhesives, for the inspection of coatings on metal and of carbon fiber composites. A modulated light source, e.g., a chopped HeNe- or Ar+ laser, is used for local, modulated heating at the sample’s surface resulting in a time- and space-dependent temperature modulation which propagates through the material. In the case of a homogeneous layer heated only in a small volume at the surface the solution of the heat diffusion equation gives a heavily damped thermal wave T(x,y,z;t). In a one-dimensional model3 only the direction z perpendicular to the surface is considered and we obtain

Diagnosing the binder content in impregnated reinforcement material by using the results of contactless ultrasound inspection

1. The content of binder can be diagnosed from the change of the characteristics of reflecting ultrasound by impregnated reinforcement on condition that the method of impregnation entails a reduction of the volume of the pores that are open to the movement of the air flow. 2. In the diagnostics of the content of binder with the same type of reinforcement, the inspected characteristic may be the ratio of the amplitudes of the signals reflected by the impregnated and the dry reinforcement. 3. When ultrasound tests are carried out directly during the winding of products, the accuracy of the diagnostics can be substantially improved by using ultrasound signals measured on solid rigid reference specimens, in addition to the signals measured on impregnated and dry reinforcement, and also by taking into account the changes of the background signal.