Twyman-Green Interferometry Research Articles

Investigation of Thermomechanical Behaviors of Flip Chip BGA Packages During Manufacturing Process and Thermal Cycling

The purpose of this study is to investigate the thermomechanical behaviors of flip chip ball grid array packages during reflow process, underfilling, underfill curing, and under thermal cycling tests (TCT). The emphasis is placed on the deformations and stress state (especially for die stresses) of the packages. The real-time Twyman-Green interferometry is used for measuring the out-of-plane thermal deformations of the specimen subjected to thermal loadings before and after underfilling. A finite element method (FEM) and an available theoretical solution have been employed to validate experimental observations and provided stress results. The TCT has been carried out, and its result indicates that the die-cracking failure dominates the life of thermal reliability. The full-field deformation data shows that the thermomechanical behavior of the packages before underfilling is creep-governed due to solder joint creep, but becomes, after underfilling, more or less creep-independent and acts as a three-layer structure with zero stress at underfill-curing temperature. However, it is also shown that no warpage status (or free-stress state) for the package could shift from the underfill-curing temperature to the glass transition temperature (T/sub g/) of the underfill material, once the package goes through solder reflow in which the temperature is usually higher than the T/sub g/ of underfill material. For the stress analyses, the FEM model and the corrected Suhir solution validated by experimental results present the deformations and stress state of the packages under the TCT. It is suggested that the adequate die/substrate thickness ratio can reduce the die stress significantly and, as a result, increase the life of the TCT. In addition, the die cracking in the packages during the TCT could be also eliminated by using a lower Tg underfill material which allows the tensile-compressive cycling loads at the critical point during the TCT, instead of higher tensile-lower compressive or purely high tensile loads.

Evaluation of micromechanical properties of buckled SiO xN y-loaded membranes by combining the Twyman–Green interferometry with nanoindentation and point-wise deflection technique

In view of applications in MOEMS technology, an interferometric technique has been developed for determination of micromechanical properties of PECVD-deposited SiO x N y thin films. By combining the Twyman–Green interferometry with nanoindentation technique, an original “point-wise” deflection method is proposed, particularly appropriated to measure the residual stress in the case of silicon membranes compressively prestressed by SiO x N y deposition. For such SiO x N y membranes, operating at the first mode of buckling, the nonindentation permits the extraction of Young's modulus and interferometry measures the out-of-plan displacements, respectively. The proposed point-wise deflection technique combines both the interferometric and Young's modulus data, giving the access to the distribution of residual stress versus the optical quality of SiO x N y films. The residual stress is monitored as a function of the refractive index of SiO x N y , establishing the relationship between the optical and micromechanical properties of deposited thin films. High measuring accuracy and resolution have been demonstrated, allowing measurements to be used to enhance PECVD process control

High sensitivity moiré interferometry and incremental hole-drilling method for residual stress measurement

The theoretical development of a combined method of moiré interferometry, Twyman–Green interferometry and incremental hole-drilling method is presented. The relationship between the three-dimensional surface displacements produced by introducing a blind hole and the corresponding residual stress is established by employing the existing theoretical solution containing a set of undetermined coefficients. The in-plane surface displacements U x and U y and out of plane surface displacement U z produced by the relaxation of residual stresses are obtained from moiré interferometry and Twyman–Green interferometry respectively. The accuracy of the method and the experimental procedure to determine the signs of residual stresses are described. A typical examp1e is presented.

227 モアレ干渉法とトワイマン・グリーン干渉法併用による三次元表面変形計測システムの構築(OS6-6 ハイブリッド計測)(OS6 実験力学の新展開)

227 モアレ干渉法とトワイマン・グリーン干渉法併用による三次元表面変形計測システムの構築(OS6-6 ハイブリッド計測)(OS6 実験力学の新展開)

Study of Surface Residual Stress by Three-Dimensional Displacement Data at a Single Point in Hole Drilling Method

A method combining moire´ interferometry, Twyman–Green interferometry, and blind hole drilling method is proposed for simple and accurate determination of residual stress. The relationship between the three-dimensional surface displacements produced by introducing a blind hole and the corresponding residual stress is established by employing the Fourier expansion solution containing a set of undetermined coefficients. The coefficients are calibrated by 3D finite element method. The surface in-plane displacements Ux,Uy, and the out-of-plane displacement Uz produced by the relaxation of residual stress are measured by moire´ interferometry and Twyman–Green interferometry, respectively, after the hole-drilling procedure. The complete three-dimensional displacement data at any single point around the hole can be used for residual stress determination. The accuracy of the method is analyzed and the experimental procedure is described to determine the sign of residual stresses. As an implementation of the method, a shot peening residual stress problem is studied. [S0094-4289(00)00802-1]

Real-time correction of movement errors of a machine axis by multiple null-balancing using Twyman-Green interferometry

This paper presents a real-time correction method for the geometric movement errors of a translatory precision machine axis. The method utilizes the optical principle of Twyman-Green interferometry with two plane mirrors to detect one translatory and two rotational errors of the machine axis simultaneously. The errors measured are instantly suppressed by activating piezoelectric actuators using a null-balancing feedback control algorithm of multi-input and multi-output while the machine axis is moving. Experimental results demonstrate that movement errors can be controlled less than 10 nm for vertical straightness, 0.1 arcs for pitch, and 0.06 arcs for roll for a total distance of 50 mm by adopting the method proposed.

An interpretation of Twyman-Green interferograms from static and dynamic fracture experiments

The application of a Twyman—Green interferometer to measurements in static and dynamic fracture mechanics is described. Twyman—Green interferometry shows the absence of a dominant singular field in the out-of-plane deformation in the vicinity of a crack. For relatively brittle fracture and except near the crack flanks, the spatial gradient of the out-of-plane displacement for a quasi-statically propagating crack is well predicted by elastostatic simulations. In addition, this method has been employed to elucidate certain transient features involving cracks propagating at large fractions of the material wave speeds. The free surface out-of-plane deformation surrounding a constant velocity dynamically propagating crack in a plate is compared with the equivalent elastostatic case. It appears that the dynamic deformation may not be obtained from the static deformation simply by a Prandtl—Glauert mapping as might be suggested by the solution for the equivalent two-dimensional generalized plane stress problem. Alternatively, the general character of the three-dimensional dynamic surface deformation may be approximately fitted by a Doppler mapping of the static deformation when scaled by the crack to plate wave speed ratio.

Fringe pattern analysis by a phase-shifting method using Fourier transform

The interference fringes obtained by optical methods such as holographic interterometry and Twyman-Green interferometry are analyzed using image processing. To perform accurate and automated analysis, phase analysis methods have been recently developed. The Fourer transform moire and grid methods (FTMGM) and the phase-stepping method (PSM) are popular techniques to analyze phase distribution. However the FTMGM has noticeable error at the edges of the image if the data at both edges are not continuous. The PSM has large error if the brightness has noise. A new phase analysis method is proposed to erase these errors. This method can be performed using 3-D image processing. A 3-D (<i>x</i>,<i>y</i>,α) image is formed of many sequential phase-shifted 2-D (<i>x</i>,<i>y</i>) images, where a is the shifted phase value. By performing the a-directional Fourier transform on this 3-D image, the accurate phase distribution of the fringe pattern is obtained. An example applied to Twyman-Green interferometry is shown.

Three-Dimensional Effects Near a Crack Tip in a Ductile Three-Point Bend Specimen: Part II—An Experimental Investigation Using Interferometry and Caustics

An experimental investigation is undertaken to assess three-dimensional effects near a crack front in a ductile three-point bend specimen. The possibility of using the optical method of caustics for the measurement of the J-integral in the presence of large-scale yielding and three-dimensional fields is also investigated. Experiments using the optical methods of caustics by reflection and Twyman-Green interferometry are performed simultaneously on either side of the test specimen. The load and load-point displacement are also measured. The experimental results are compared with very good agreement to the results of a finite element simulation of the experiment. The caustics experiments are used to obtain a calibration relation between the value of the J-integral and the caustic diameter for load levels up to fracture initiation. It is proposed that such a calibration be used in dynamic fracture initiation experiments for the measurement of the time history of the dynamic J-integral.

Twyman–Green interferometry for semi-quantitative analysis of homogeneity and nonlinearity of a mixing crystal

Application of Twyman–Green interferometry is extended to achieve semi-quantitative assessment of optical qualities of a nonlinear crystal. Interferograms of a proustite crystal are analyzed and effects of crystal imperfections on the conversion efficiency of a parametric upconversion system are evaluated.

Twyman-Green interferometry for measurement of stresses in thin film on optically flat silicon substrates : C. M. Drum, Rev. Scient. Instrum.40 (6), (1969), p. 833

Twyman-Green interferometry for measurement of stresses in thin film on optically flat silicon substrates : C. M. Drum, Rev. Scient. Instrum.40 (6), (1969), p. 833

Twyman-Green Interferometry for Measurements of Stresses in Thin Films on Optically Flat Silicon Substrates

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