Moire Interferometer Research Articles

An Experimental and Computational Study on Moisture Induced Epoxy Swelling in Non-hermetic Optoelectronic Packages

Moisture induced epoxy swelling is a potential failure mechanism in nonhermetic packages. Epoxy materials used in the package absorb moisture and swell in a relatively humid environment. This will result in hygroscopic stresses in the material that can eventually lead to failure. The coefficient of hygroscopic swelling (CHS) is a material property that characterizes moisture induced swelling in the material. It is defined as the ratio of hygroscopic strain to the moisture concentration in the material. Prior research investigated the measurement of CHS experimentally using techniques such as thermo mechanical analysis (TMA) (Ardebili et al., 2003, “Hygroscopic Swelling and Sorption Characteristics of Epoxy Molding Compounds Used in Electronic Packaging,” IEEE Trans. Compon. Packag. Technol., 26(1), pp. 206–214; Mckague et al., 1978, “Swelling and Glass Transition Relations for epoxy Matrix Material in Humid Environments,” J. Appl. Polym. Sci., 22, pp. 1643–1654.), Moiré interferometry (Han et al., 2003, “Measurement of the Hygroscopic Swelling Coefficient in Mold Compounds Using Moire Interferometer Experimental Techniques,” IEEE Trans. Compon. Packag. Technol., 27(4), pp. 40–44), and digital image correlation (DIC) (Park and Zhang, 2007, “Investigation of Hygroscopic swelling of Polymers in Freezing Temperature,” ASME International Mechanical Engineering Congress and Exposition). Some of these studies recommended investigation of improved measurement techniques, while others made some procedural assumptions that may not be applicable for all materials. One of the goals of this study was to investigate an improved technique for CHS measurement and helps to better understand the various factors that affect the measurement. The DIC technique was used to measure the moisture swelling of the epoxy material considered for use in the package. Moisture loss during the measurement results in a change in moisture concentration in the sample. While it may be thought that the moisture loss during the DIC scan can be assumed negligible due to the short test time compared with other methods, this assumption did not hold well for the current epoxy material. The ramp rate chosen for the test affects the moisture loss. It introduces a level of nonuniformity in temperature and moisture distribution in the sample. A suitable value that takes into account both of these effects was determined. The moisture loss measured during the DIC scan was accounted for in the CHS computation. In addition to this, the temperature and concentration dependence of the CHS was determined. Results indicated that the temperature and concentration effects are small for the current test material within the test temperature range. The moisture loss found during the DIC measurement leads to a nonuniform moisture distribution in the sample. This was characterized by using experimental and computational methods and the effect on the measurement was determined.

Automatic Full Strain Field Moiré Interferometry Measurement with Nano-scale Resolution

Moire Interferometry (MI) theoretically can provide real-time full strain field measurements in dynamic environment. So it’s extensively used in reliability analysis of electronic packaging. Due to the nature of specimen preparations procedure, the optical noise is usually too strong so that an accurate phase-based information processing is not possible. In this paper, a 164 nm/pixel spatial resolution Moire Interferometer with automated full strain field calculation is proposed. Provided by two-level zooming system, the high spatial resolution increase the signal intensity and eliminate some optical noise which allows accurate full strain field map generated automatically by the combination of phase shifting technique and continuous wavelet transform (CWT). Furthermore, the calculation procedure of CWT proposed here does not require unwrapping and differentiation, which avoid the possible numerical noise introduced in these two steps. In the proposed system, pixel by pixel in-plane strain tensors will be calculate from the intensity map of interferograms using phase-based method. The resulting strain tensor can be used to model constitutive relationship or compare with finite element analysis results. A thermal experiment on BGA packaging is used to demonstrate the advantages of the proposed new design.

Shadow-Free Moire Interferometer with Dual Projection for In-Line Inspection of Light Emitting Diodes

In small-sized liquid crystal display markets, small light-emitting diodes (LEDs) are generally used for the illumination part of backlight units. For their uniform light-emitting, the volumetric size control of each pocket is crucial to the LED manufacturing process because the pocket fills with the transparent encapsulating material which plays a role in focusing the emitted light ray from the LED chip and protecting the LED wafer chip and wire-bonding. A special three-dimensional vision system is presented for volumetric inspection of the LED pocket with concave shape. Conventional measurement techniques of measuring the LED pocket easily produce noisy results due to the shadow problem-induced geometric configuration of the imaging part and pattern projecting part. In order to prevent this effect, the proposed sensor system utilizes a dual projection system. By using two measurement results acquired from pattern projections switching with different incident angles, shadow-free results can be acquired. In this article, we will describe the sensor system's principle and the sensor fusion algorithm combining two measurement results efficiently. A series of experiments is conducted to verify the performance of this proposed system. The measurements results show very satisfactory inspection performance and they are discussed in depth.

Thermal Fatigue Life Prediction of ACF Bonding Flip Chip Packaging

The use of flip-chip technology has many advantages over other approaches for high-density electronic packaging. ACF (anisotropic conductive film) is one of the major flip-chip technologies, which has short chip-to-chip interconnection length, high productivity, and miniaturization of package. In this study, thermal fatigue life of ACF bonding flip-chip package has been predicted. Elastic and thermal properties of ACF were measured by using DMA and TMA. Temperature dependent nonlinear bi-thermal analysis was conducted and the result was compared with Moire interferometer result to verify FEM results. Calculated displacement field was well matched with experimental result. Thermal fatigue analysis was also conducted. The maximum shear strain occurs at the outmost located bump. Shear stress-strain curve was obtained to calculate fatigue life. Fatigue model for electronic adhesives was used to predict thermal fatigue life of ACF bonding flip-chip packaging. Approximately, 700 cycles have been expected under current conditions (JEDEC standard No. 22-A104)

3908 位相シフト画像の同時撮影によるモアレ干渉縞の位相解析(S17-2 光学的手法,S17 実験力学における最近の展開)

This paper describes a new simultaneous phase stepping method for moire interferometry. Conventional phase-stepping methods are widely accepted but the measured data are vulnerable to disturbances such as air fluctuations, temperature changes, vibrations and so on during the interferogram recording. To overcome this, a unique camera having a micro-retarder array on a CCD is used for observing interferograms. The specific structure makes it possible to calculate polarization states. Using this camera in a moire interferometer, the distribution of in-plane displacements is obtainable from a single image.

New three-dimensional displacement measurement system: modified four-beam moire´ interferometer–Twyman/Green

An MMI-T/G system composed of a modified four-beam moire interferometer (MMI) and a Twyman/Green (T/G) interferometer is developed. The MMI-T/G can measure 3-D displacement fringe patterns with a single loading on the specimen. In the MMI-T/G system, one incident laser beam is diffracted into multiple beams by the cross-line grating on the specimen, where the ±1 order diffractive beams are redirected back to the specimen by flat mirrors, then rediffracted by the specimen grating onto the CCD, generating the in-plane displacement fringe pattern; the zero-order diffractive beam interferes with a reference beam of the T/G, generating the out-of-plane displacement fringe pattern. Details of the derivation of the fringe-governing equations are given based on the wavefront interference theory. The fringe-governing equations so obtained are comparable with those derived previously based the Doppler frequency shift theory and conventional moire interferometry. The in-plane displacement sensitivity of the new system can be shown to be twice of that of a normal moire interferometer. The optical setup has the advantages of structure novelty, flexibility, and high fringe contrast. Experiments are carried out to validate the derived governing equations, and clear thermodeformation fringe patterns of an electronic package are shown.

An Optical Interferometry System for Measuring Three-Dimensional Displacements

The system is a combination of a Moire interferometer (which measures the displacement in the plane of a sample) and a Twyman–Green interferometer used for measurements in the perpendicular plane. The diffraction grating that is applied to the sampleis also used as a beam splitter. As a result, the system is simple in design and easy to adjust, and its sensitivity is higher than that of a two-grating Moire interferometer by a factor of two. The fringe pattern is distinguished by its high contrast and spatial resolution. The system has been tested in measuring the three-dimensional thermal deformation of microelectronic devices.

이방성 전도 필름을 이용한 플립칩 패키지의 열피로 수명 예측 및 강건 설계

The use of flip-chip technology has many advantages over other approaches for high-density electronic packaging. ACF (anisotropic conductive film) is one of the major flip-chip technologies, which has short chip-to-chip interconnection length, high productivity, and miniaturization of package. In this study, thermal fatigue life of ACF bonding flip-chip package has been predicted. Elastic and thermal properties of ACF were measured by using DMA and TMA. Temperature dependent nonlinear bi-thermal analysis was conducted and the result was compared with Moire interferometer experiment. Calculated displacement field was well matched with experimental result. Thermal fatigue analysis was also conducted. The maximum shear strain occurs at the outmost located bump. Shear stress-strain curve was obtained to calculate fatigue life. Fatigue model for electronic adhesives was used to predict thermal fatigue life of ACF bonding flip-chip packaging. DOE (Design of Experiment) technique was used to find important design factors. The results show that PCB CTE (Coefficient of Thermal Expansion) and elastic modulus of ACF material are important material parameters. And as important design parameters, chip width, bump pitch and bump width were chose. 2nd DOE was conducted to obtain RSM equation for the choose 3 design parameter. The coefficient of determination (R2) for the calculated RSM equation is 0.99934. Optimum design is conducted using the RSM equation. MMFD (Modified Method for Feasible Direction) algorithm is used to optimum design. The optimum value for chip width, bump pitch and bump width were 7.87mm, 430~m, and 78~m, respectively. Approximately, 1400 cycles have been expected under optimum conditions. Reliability analysis was conducted to find out guideline for control range of design parameter. Sigma value was calculated with changing standard deviation of design variable. To acquire 6 sigma level thermal fatigue reliability, the Std. Deviation of design parameter should be controlled within 3% of average value.

201 レーザーモアレ干渉法を用いたセラミックス/金属接合界面角部における特異場の解析

Characteristics of singular field around interface edge between ceramic and soft metal interlayer around the corner and the mid region of the jointed beam were investigated experimentally and theoretically. Displacement fields around the interface edge were measured using laser moire interferometer displacement anlysis technique. The measured singular field around elastic/elastic-plastic interface edge was compared with theoretical results (elastic/linear hardening material interface edge prediction and elastic/power law hardening material interface edge prediction). The controlling factors for the singular field around elastic/elastic-plastic interface edge were proposed and its validity was examined. The influence of hardening properties of interlayers on the controlling factors were investigated experimentally and theoretically.

Characterization of short duration stress pulses generated by impacting laminated carbon-fiber/epoxy composites with magnetic flyer plates

Short duration stress pulses are of particular interest in determining the interfacial crack tip instability criteria for the dynamic fracture behavior of laminated carbon-fiber/epoxy composites. However, the heterogeneous architectures of laminated composites can alter the characteristics of a stress pulse as it propagates toward a crack tip. This makes it difficult to use standard dynamic testing techniques for characterizing these materials, since these techniques assume the characteristics of the stress pulse do not change as a result of propagation and can therefore be unambiguously determined from impact conditions. This paper presents a novel experimental technique that has been developed for characterizing short duration stress pulse propagation in laminated composite materials. In this technique, a dynamic moire interferometer is used to capture fringe patterns corresponding to displacement fields associated with short duration stress pulses that were generated by impacting 0° and 90°/0°/90° carbon-fiber/epoxy composites with a magnetic flyer plate. Appropriate dynamic testing conditions for capturing high fidelity fringe patterns were determined using the recently developed dynamic moire fringe contrast factor. The effects of the composite architecture on the propagation of short duration stress pulses observed with the dynamic moire interferometer were confirmed by transient dynamic finite element analysis. From comparisons of experimental and numerical data, it was determined that the impact conditions for the magnetic flyer plate and laminated composite will not necessarily be planar, which has a significant effect on the intensity and duration of the propagating stress pulse.

OBSERVING REAL-TIME THERMAL DEFORMATIONS IN ELECTRONIC PACKAGING

A robust scheme of moire interferometry for real-time observation of thermal deformations was developed. It was implemented with a convection-type heating/cooling environmental chamber, which produced rapid temperature control. Vibrations caused by the environmental chamber were circumvented by rigid links that connected the specimen to the moire interferometer rather than supporting the specimen by the chamber. The result was exceptionally stable fringes. The system was utilized to document temperature-dependent behavior of a PBGA package assembly.

Single-grid moiré interferometer

A moire interferometer is described which uses only one grid rather than the more normal two. The instrument is useful in line imaging applications where the object must be well separated from the optics, such as in production environments. Depth resolution can be changed simply by replacing the moire grid, which does not require system re-alignment. The design equations for the system are derived and the design process is described. An example instrument has been assembled and performance results are presented.

A new moiré interferometer for measuring in-plane displacement

This paper proposes a new moire interferometer to be used for determining in-plane displacement of a body deformed with small strains and small surface slopes. With this interferometer, the grating not only diffracts the incoming beam but also rediffracts the two first orders, each of which is reflected by a mirror, back into the path of the incoming beam. The two rediffracted beams are then directed to the viewer to generate an interference fringe pattern that depends only on the in-plane displacement. Theoretical analysis of this new interferometer is presented. It was determined that the sensivity of the interferometer is twice that of conventional interferometers, and the slightly warped beam wave front coming from the laser source does not affect the measurement result. An experiment was performed by adopting the proposed and conventional interferometers to determine the displacement of a specimen grating. The results confirm the advantages of using this new interferometer.

High-magnification moiré interferometer for crack tip analysis of steels

A high-magnification moire interferometer, particularly suitable for near-tip field analysis in cracked materials, is described. It has a submillimeter field of view, a high-resolution image sensor (1.4 million pixels), X-Y-Z translation stage and an optical fiber light delivery system. These features enable the microscope head to observe the crack tip while the specimen is loaded in a standard tensile test machine. Automated fringe pattern analysis, using temporal phase shifting and spatial phase unwrapping, enables thex ory displacement component to be measured and the corresponding in-plane strain component computed. The displacement placement accuracy is better than 40 nm, and the effective strain gage dimension is ∼ 25 μm. Furthermore, the interferometer has a built-in white light microscope that allows the observation of the specimen granular microstructure in exact registration with the displacement field. The interferometer has hence been employed to investigate the near-tip fields of a precracked stainless steel specimen under load. The influence of the grain boundaries on the measured displacement fields was relatively minor. The near-tip strain field shows a significant asymmetrical behavior despite pure mode lloading conditions.

A study of the mixed-mode interfacial fracture toughness of adhesive joints using a multiaxial fatigue tester

In this paper, a new technique is introduced for the control of the far field and mixed-mode crack tip of a single lap shear specimen with a crack along the interface. An investigation has been conducted to use one single lap shear specimen to obtain a series of values of interfacial fracture toughness as a function of the mixed-mode phase angle. The interfacial fracture behavior of the single lap shear specimen subjected to multiaxial concentrated line loads was investigated using a unique six-axis submicron tester coupled with a high density laser moire interferometer. The six-axis submicron tester was used to provide the displacement-controlled multiaxial concentrated line loads, whereas the moire interferometry technique was used to monitor the crack length during the test. In addition, a finite element technique was simultaneously used to determine the near crack tip displacement fields of the single lap shear specimen. The interfacial fracture toughness and phase angle were computed by using these near tip displacement variables through the analytical energy release rate and phase angle expressions derived by the authors. The results show that the facilities and methodology used in the current study can indeed be proved to possess the ability to control the far field and the mixed-mode conditions at crack tip, and to efficiently perform the mixed-mode fracture test.

Hydrogen-enhanced dislocation emission, motion and nucleation of hydrogen-induced cracking for steel

The change in dislocation configuration ahead of a loaded crack tip before and after charging with hydrogen wasin situ investigated in TEM using a special constant deflection loading device. The results showed that hydrogen could facilitate dislocation emission, multiplication and motion. The change in displacement field ahead of a loaded notch tip for a bulk specimen before and after charging with hydrogen wasin situ measured by the laser moire interferometer technique. The results showed that hydrogen could enlarge the plastic zone and increase the plastic strain. Thein situ observation in TEM showed that when hydrogen-enhanced dislocation emission and motion reached a critical condition, a nanocrack of hydrogen-induced cracking (HIC) would nucleate in the dislocation-free zone (DFZ) or at the main crack tip. The reasons for hydrogen-enhanced dislocation emission, multiplication and motion, and the mechanisms of nucleation of HIC have been discussed.

Temperature Measurement of Natural Convective Field Using Moire Interferometry.

Optical interferometers, such as the Mach-Zehnder interferometer, have often been used to measure the temperature of transparent fluids. In this paper, we utilize a Moire interferometer in which a conventional interferometer is combined with the Moire technique. By applying a fringe scanning technique to this Moire interferometer, a new fringe analytical system is obtained and the fringe analysis is automated with the aid of a personal computer. The temperature field of the air around a vertical heated plate under natural convection is measured and compared with the theoretical solution. The temperature measured using this system is in good agreement with the theoretical one. It is verified that this optical system is applicable for measuring the temperature of transparent fluids.

Displacement of the gerbil tympanic membrane under static pressure variations measured with a real-time differential moire interferometer

It is thought that chronic middle ear disease ultimately causes changes in the stiffness and elasticity of the tympanic membrane, but it is unknown whether such changes occur early in the course of the disease. In order to analyze mechanical changes in different parts of the tympanic membrane, a full field moire interferometry technique was utilized to measure the shape and real-time displacement in response to positive and negative pressure gradients applied across the tympanic membrane. The measurements were performed on fresh isolated temporal bones from the Mongolian gerbil. In order to gain sufficient visual access to the pars tensa for the moire measurements, the tympanic bulla was opened, the tensor tympani muscle and the incudo-stapedial joint were cut, and part of the medial wall of the tympanic cavity was removed. The malleus and incus and their ligaments were kept intact. The specimens were kept continuously humidified with an evaporator or in a humid chamber, since otherwise the tympanic membrane dries out in a few minutes when its medial surface is exposed. This desiccation reduces the elasticity and cause shrinkage which results in a reduction of the height of the cone constituted by the pars tensa. Profiles of the tympanic membrane at rest and under different pressure conditions were extracted from the moire interferograms. The tympanic membrane and ossicular complex exhibit a hysteresis effect as differences in the displacement patterns under identical pressure gradients during the loading and the unloading phase; a residual displacement of the pars tensa was for instance seen after the pressure gradient across the tympanic membrane was eliminated.

Phase stepping in projected-fringe fibre-based moiré interferometry

An optical fibre based moire interferometer for surface shape measurement is described. The technique uses an optical fibre interferometer to project interference fringes and is readily phase stepped without mechanical movement of components.

Comparison and combined operation of a moire deflectometer, Fizeau interferometer, and schlieren device

We demonstrate an instrument which enables the combined operation of a moire deflectometer, Fizeau interferometer, and schlieren device. By using each mode separately, it is possible to compare the three methods, and by combined operation, to benefit from the advantages of each method.