Thermal deformation measurement of the solder joints in electronic packages using electron moiré method

In this paper, electron moiré method is used to measure the thermal deformation of electronic packages. In order to observe the electron moiré fringe, a holographic grid was replicated on the cross section of the BGA type package at 150°C. This grid was fabricated on a glass plate using a moving point holographic system, and was replicated to measured area at high temperature. Under SEM, the holographic grid(specimen grid) and a programmed electron beam scan(master grid) interfere and form electron moiré patterns. The shear strain measurement technique using electron moiré method is described. Using the electron moiré method, the shear strains in the different solder joints were measured and analysed. Some useful results were obtained.     

FATIGUE CRACK TIP STRAINS IN 7075-T6 ALUMINUM ALLOY

Abstract— The plastic enclave surrounding a fatigue crack in a 7075-T6 aluminum alloy specimen is studied using moiré interferometry. Two distinct plastic zones are identified from inspection of moiré interferometric fringe patterns. The sizes and shapes of the monotonic and the cyclic plastic zones are correlated with previous theoretical and experimental results. Live load strain distributions in the plastic enclave are computed from high sensitivity (0.417 micron per fringe) full-field in-plane displacement contour maps. Comparison with theoretical and experimental strain distributions are included.     

Deformation Data from Thermal Marking

Abstract: A novel experimental technique for strain measurement, named thermal moiré, and based on a combination of thermography and moiré concepts, is presented in this paper. The proposed technique essentially involves the temporary imprinting of a thermal pattern onto the surface of the object of interest as a substitute for conventional gratings, to remove the need for physical printing, etching or bonding. In materials with low diffusivity, the thermal pattern can be observed with an infrared camera and analysed using conventional techniques. Work on the development of suitable laboratory apparatus is described, and preliminary experimental results are presented to illustrate the feasibility of the method.     

Application of moiré technique in the stress analysis of cutting tools

Knowledge of the stress field in cutting tools is necessary for their strength evaluation. However, the experimental analysis of stresses in cutting tools during machining poses a number of problems in view of the steep stress gradient present. Photo-elasticity and the 'built-up tool' methods are the common techniques used for this purpose. In the present paper results on the stresses in cutting tools obtained during actual machining through the successful application of the transmitted moiré technique, are presented. In these experiments transparent epoxy tools carrying moiré gratings were used to machine commercial lead alloy at low speeds. The tool rake angle was varied. The effectiveness of moiré method, basically a displacement analysis technique, in providing useful data on tool stresses comparable with the other direct stress analysis techniques such as photo-elasticity is also discussed in the paper.     

High Temperature Gratings for the Moiré and Moiré Interferometry Methods and their Application to Deformation Measurement - A Review

Abstract: This paper gives a general review of the production of high temperature gratings and their application to deformation measurement. The fabrication techniques for gratings and deformation measurement methods using the gratings are discussed. The review is confined to in-plane moiré and moiré interferometry methods. Some typical applications in high temperature deformation measurement are briefly discussed.     

The use of strippable photographic film for moire grating production

Practical details are presented concerning the use of strippable film for the production of moiré gratings. Strippable film is produced primarily for application in graphic arts. The influence of the use of the film on the accuracy of measurement in the direct moiré method is discussed.     

A RAPID METHOD FOR CALCULATING THE TRANSVERSAL STRAIN IN THE MOIRE TECHNIQUE ALONG SECTIONS OF SYMMETRY

An approximate rapid method is described for calculating in the moiré technique the transversal strain directly from the longitudinal strain distribution across sections of symmetry. The method is based on evaluation of the load transmitted through the section and is corroborated by two examples.     

Thermal Properties Measurement of Micro-electromechanical System Sensors by Digital Moire Method

Abstract:  The thermal properties of a micro-electromechanical system sensor were analysed by a novel digital moiré method. A double-layer micro-cantilever sensor (60  μ m long, 10  μ m width and 2  μ m thick) was prepared by focused ion beam milling. A grating with frequency of 5000 lines mm⁻¹ was etched on the cantilever. The sensor was placed into a scanning electron microscope system with a high temperature device. The observation and recording of the thermal deformation of the grating were realised in real-time as the temperature rose from room temperature to 300 °C at intervals of 50 °C. Digital moiré was generated by interference of the deformed grating and a digital virtual grating. The thermal properties including strain distribution of the sensor and the linear expansion coefficient of polysilicon were accurately measured by the phase-shifted moiré patterns.     

Measurement of strain concentration factor of composites plate using moiré interferometry

In this paper, using a 1200 lines/mm replicated grating, the moiré interferometry method was applied to study the strain concentration factor of a carbon fibre composites plate with a central hole. The rules of strain concentration factors were determined under different loads.     

TRIAXIAL ANALYSIS OF THE "POKER-CHIP" TEST

Axial compression of thin circular discs made of plasticized epoxy resin was studied. The plane faces were cemented to platens rigid compared with the material of the discs so that the constraint due to cementing created in the discs a three-dimensional state of stress. The internal strain distribution was measured by the moiré method which yielded enough data for an evaluation of this state of stress. The influence of the aspect-ratio of diameter D to thickness t of the disc was investigated.     

Curvature contours of flexed plates by a multiple illumination moiré shearing interferometer

A new moiré method is proposed to map partial slope, partial curvature and twist curvature contours of laterally loaded specularly reflecting plate models. Converging HeNe laser light is diffracted by a lens plane cross grating, different combinations of orders are selectively permitted through the Fourier transform plane and collimated to illuminate the plate model. This technique eliminates the difficulties involved in Fourier filtering in the imaging optics, thereby extending the reflection moiré' interferomelry to general plate structures and loading. The slope contours are obtained still by double exposure.     

A single exposure reflection moiré interferometric technique for complete curvature analysis of bent plates

Most known moiré methods need to be repeated three times for getting curvature information in three different in plane directions, for the complete analysis. To overcome this difficulty, a new single exposure moiré interferometric technique is proposed that maps completely partial curvature contours in three different directions of laterally loaded specularly reflecting plate models. Converging HeNe laser light is diffracted by a lens plane cross grating. The 00, + 10 and the +01 diffraction orders are permitted through the Fourier transform (FT) plane and collimated to illuminate the plate model. The reflected light from the loaded model records the model with the inherent deformed interferometric cross grating superimposed on it. A posteriori Fourier filtering of the developed recording (moirégram) gives partial curvature contours pertaining to three different in plane directions from which the principal curvatures and the principal directions are obtained. Also, this technique, being a single exposure technique, has the potential for complete bending analysis of plates subjected to lateral impact loading and destructive loading applications, where the repeatability of the event may not be possible.     

TRIANGULAR AND v 2 GRATINGS FOR THE MOIRÉ TECHNIQUE

Methods for constructing two new types of grating for the moiré technique are described, their use is illustrated in application to a simple beam, and the range of measurable strains is established. In certain circumstances the use of these gratings presents a means of accurate analysis without recourse to elaborate equipment.     

The measurement of deformation of a bridge by moiré photography and photogrammetry

Optical techniques offer advantages over mechanical methods for displacement measurement. A comparative study has been made between photogrammetry and moiré photography during a destructive test applied to a bridge. The first provided accurate values for point displacements whereas the second revealed the whole field movements and indicated the region of eventual failure.     

On the Industrial Applications of Moiré and Fringe Projection Techniques

Abstract: This paper describes a set of tools and procedures based on the moiré and fringe projection techniques, which were developed to suit the requirements of real industrial situations. Particular attention was paid to flexibility, robustness and reliability, ease of use and calibration, and cost efficiency. Three case studies are being discussed in the paper. The first case describes a prototype shadow moiré instrument, which was developed for the detection of surface defects such as barely visible impact damage or corrosion inside lap-joints, during maintenance inspections of aeronautical structures. The second case presents a portable instrument based on the fringe projection technique for the automatic, full-field measurement of the shape and deformation of an arbitrary object. The system has applications ranging from deformation measurement of bioprostheses to correction of shape effects in the photoelastic analysis of complex aerospace components. Finally, a portable instrument was developed for the measurement of the location, orientation, shape and deformation of an arbitrary object, by combining the fringe projection technique with the laser spot technique for distance measurement. The system was used to assist in the integration of non-destructive evaluation techniques throughout the life cycle of an aircraft.     

STENCIL METHODS FOR PREPARING MOIRE GRIDS

Three methods are described for depositing moiré grids on specimens by means of thin metal meshes produced by electroforming. The methods involve printing, electro-etching, vacuum deposition, with the mesh used as a stencil, and they are capable of accurately reproducing grids with line densities of 2000 lines/in (80 lines/mm) and of giving good contrast.     

A hybrid experimental/computational approach to the assessment of crack growth criteria in composite laminates

While a number of criteria have been proposed for predicting the onset of crack growth in composite laminae, there has hitherto been no accepted method of assessing the value of alternative proposals. This study integrates the use of computational modelling, along with moiré interferometry for the quantitative mapping of near crack tip deformation fields. The moiré method was used to validate the computational model. It was then possible to use the computational model on its own to predict crack tip behaviour in more detail than could be done with the optical system alone.
This study chose one crack growth criterion - the normal stress ratio - to demonstrate the assessment routine. The value of the normal stress ratio (NSR) was calculated as a function of the ply angle to the loading direction. In order to obtain sensitive predictions of crack growth direction, it was desirable to proceed by analysing the crack tip behaviour down to radial distances from the crack tip of a few tens of microns. By a suitable choice of elements around the crack tip, the finite element model was able to predict values of the NSR down to a radius of 80 times10^-3 mm around the crack tip.     

Relative assessment of full field experimental stress analysis techniques

There is an array of full field experimental stress analysis techniques available to aid the designer or the engineer investigating service failures. This note reviews currently available methods (i.e. photoelasticity, moiré, laser holography, brittle lacquer and SPATE) and assesses their relative merits in practical applications.     

Applicability of Optical Geometric Differentiation for Time-average Geometric Moiré

Abstract:  Optical experimental method for analysis of derivatives of dynamic displacements from patterns of time-average moiré fringes is proposed in this paper. Derived analytical relationships for one-dimensional optical model are validated for two-dimensional elastic structures performing in-plane vibrations. The fact that digital image filtering techniques are normally required for the identification of time-averaged super-fringes does not lessen the practical value of the proposed method.