Power modules are utilized for electric power control and play a key role in efficient energy conversion. One of the reliability problems in power modules is the wire-liftoff, in which an aluminum wire delaminates from a silicon chip. The wire-liftoff phenomenon is a thermal fatigue failure caused by repeated temperature cycles during the operation of power modules. According to an experimental study, the wire-liftoff lifetime decreases with increase in the maximum junction temperature of a temperature cycle, Tmax, then levels off above 200°C of Tmax. Such a saturation phenomenon of the wire-liftoff lifetime is main concern of the present study. We select the nonlinear fracture mechanics parameter T*-integral range, as a physical quantity describing the wire-liftoff lifetime. The T*-integral range, ΔT*, is only one fracture mechanics parameter that can be applied to thermal fatigue under a cyclic thermo-elastic-plastic creep condition. We perform nonlinear finite element analyses of a power module to calculate the ΔT* based on the mathematical expression of ΔT* for various temperature cycles. As a result, the ΔT* obtained from the exact method based on the mathematical expression of ΔT* is expected to be utilized for quantitative estimation of wire-liftoff lifetime in a wide temperature range of low to high temperatures.

This paper presents a power-cycling degradation monitoring method of an IGBT module with a VCE(sat) sensing circuit and junction temperature prediction by a three-dimensional structure model. A chopper circuit was introduced to provide a continuous-current-conducting operation of the IGBT module. The VCE(sat) sensing circuit with a low-cost IoT platform “Leafony” was utilized to monitor the junction temperature of an IGBT chip, which transferred the measured signal as digital data, and thus obtained a higher noise immunity than an analog-based circuit. The junction temperature of IGBT chip in the power module was analyzed from the dissipated power of IGBT and the transient thermal impedance between the chips and the ambient. This analysis is effective not only to observe the degradation but also to estimate the thermal resistance. Comparing the temperature profile between experiment and prediction provides health condition of the IGBT model. Predicted thermal profiles agreed with measured ones with 10 % increase of thermal resistance, which was degraded by a power cycle tester. From these results, the proposed monitoring method is effective to detect the progress of power cycle degradation.

Generally, hard ceramic carbide particles, such as B4C and TiC, are angulated, and particle size control below the micrometer scale is difficult owing to their hardness. However, submicrom-eter particles (SMPs) with spherical shape can be experimentally fabricated, even for hard carbides, via instantaneous pulsed laser heating of raw particles dispersed in a liquid (pulsed laser melting in liquid). The spherical shape of the particles is important for mechanical applications as it can directly transfer the mechanical force without any loss from one side to the other. To evaluate the potential of such particles for mechanical applications, SMPs were compressed on various sub-strates using a diamond tip in a scanning electron microscope. The mechanical behaviors of SMPs were then examined from the obtained load–displacement curves. Particles were fractured on hard substrates, such as SiC, and fracture strength was estimated to be in the GPa range, which is larger than their corresponding bulk bending strength and is 10%–40% of their ideal strength, as calculated using the density-functional theory. Contrarily, particles can be embedded into soft substrates, such as Si and Al, and the local hardness of the substrate can be estimated from the load–displacement curves as a nanoscale Brinell hardness measurement.

This paper evaluates the insulation capability of a gate-insulating layer used in organic thin-film transistors (OTFTs) under mechanical loading. For this evaluation, a novel specimen structure which has a “semiconductor-less” structure is proposed; in the proposed structure, the semiconductor layer is removed from the conventional OTFT structure. The evaluation results demonstrate that the insulation capability of the gate-insulating layer is deteriorated starting from 1.0~1.5% strain of the specimen. Additionally, the degradation of the insulation capability is saturated around the yield stress (3.0~4.0% strain) of the specimen substrate (PEN). The evaluation results of the leakage current represent that the leakage path is the source-gate-drain electrode via the gate electrode. The laser-microscope observation results show that the plastic deformation (mechanical damage) is observed in the insulation layer in the degradation range of the insulation capability.

One of the common reliability concern on most of power modules is a failure of its bonding. Stress, strain, and displacement fields around those bonding in power modules are required for highly-reliable design based on physically/mechanically based failure model. They can be accurately obtained from CAE tools such as finite element computer codes for stress analysis with mechanical properties of materials not only in the elastic region but also in the inelastic region. In this paper, for the reliability study of an aluminum bonding wire, an experimental study was performed to acquire its plastic and creep characteristics. The temperature-dependent constitutive equations for plastic and creep behavior of an aluminum wire are presented based on the isothermal tensile test data. These constitutive equations can be used at the temperatures ranging from 20 degrees C to 250 degrees C, and are useful for estimating fatigue life predictions of bonding wires, when we utilize the failure models based on the physical quantities such as the inelastic strain range, the inelastic strain energy density range, the nonlinear fracture mechanics parameter T* range and so on.

The J-integral range or the cyclic J-integral, Delta J, is frequently utilized to deal with the fatigue crack growth of ductile materials with large scale yielding. Delta J was originally defined as a line integral similar to the J-integral proposed by Rice. Many researchers correlated fatigue crack growth rate of ductile materials with Delta J defined by J(max) - J(min). Although it is theoretically shown that the latter definition of.J, that is, Delta J = J(max) - J(min), is not equivalent to the former defined by a line integral, why is the latter definition of.J utilized so frequently? This question is main concern of the present paper. To answer this question, we derive the expression of Delta J represented by a line integral for HRR singular fields, which govern the vicinity of a crack tip under large scale yielding, then formulate the difference between the.J represented by a line integral and Delta J = J(max) - J(min). We perform the error estimation for three-point bending specimens to clarify how accurately (J(max) - J(min)) predicts the Delta J-value, compared with the Delta J represented by a line integral, which is supposed to provide the exact Delta J-value. As a result, the Delta J-value calculated from (J(max) - J(min)) is identical to the Delta J-value calculated from a line integral in the case of the zero-tension cyclic loading conditions, and the deviation between the former and latter values is small under near zero-tension and large cyclic loading amplitude conditions. The use of the Delta J defined by (J(max) - J(min)) should be limited to the cases where near zero-tension and large cyclic loading amplitude conditions are satisfied.

A concept of three dimensional visual characterization is proposed here for the performance deterioration behavior of flexible electronic devices under bending deformation. Here the loading space is defined in a two dimensional manner with two axes. One is to indicate the severity of bending, starting from completely flat ending with ultimately loaded where the device is folded into half. The other is to indicate the number of loading cycles with specified levels of bending severity. By plotting the performance, whatever it is, in a three dimensional manner over the plane spanned with these two axes, its deterioration behavior is fully visualized quantitatively and entirely over the possible space of bending load. Feasibility of such a characterization is eventually demonstrated with silver nano-particle printed flexible wires. The experimental results are examined in detail from the view point of finding useful information for reliability improvement, i.e. promising contribution of the concept for further development of more robust flexible devices.

Power modules are utilized for electric power control and play a key role in efficient energy conversion. A structural reliability problem of wire bonding, wire-liftoff, in power modules becomes important at high-temperature operation. Wire-liftoff is a thermal fatigue phenomenon caused by thermal stress due to mismatch of coefficients of thermal expansion between a wire and a chip material. According to experimental studies, a saturation phenomenon of wire-liftoff lifetime was observed in power modules above the maximum junction temperature of 200 degrees C. In this paper, we examine the failure models for predicting wire-liftoff lifetime proposed in the previous studies and also propose a new failure model based on the nonlinear fracture mechanics parameter T*-integral range Delta T*. Among various failure models, the proposed model is the best to represent a saturation phenomenon of wire-liftoff lifetime. For practical use of the failure model based on Delta T*-integral range, we propose a simple calculation method of Delta T*-integral range that can be calculated by using the commercial finite element computer code such as Marc, Ansys, and so on.

Micro scale torsion test method was developed to investigate continuous deformation behavior around initial yield point of copper single crystal structure. Continuous load-displacement curve was obtained by torsion test because dislocation burst phenomenon was suppressed by stress gradient and torsion stress direction which parallel to the specimen surface. In case that new constitutive law was applied to the simulation, crystal plasticity parameter of copper could be evaluated by parameter fitting which using load-displacement curve of experiment and simulation. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd, All rights reserved.

Local distributions of crystal orientation and residual stress of Cu lines (600 rim and 400 nm) in large-scale integrated circuit (LSI) interconnects are visualized by electron backscatter diffraction (EBSD). The crystal orientation distribution is random and texture is not observed. Bamboo grain boundary structures form with decreasing Cu line width. The Wilkinson EBSD method indicates that the residual elastic stress of a Cu line in an LSI interconnect is locally high at twin boundaries, grain boundaries, and the Cu/dielectric interface. The local distributions of residual elastic stress at these boundaries and the interface should induce preferential crack nucleation. (C) 2014 Elsevier B.V. All rights reserved.

A specimen size effect on the adhesion strength of Cu/insulation layer interface was studied by means of a new elastic-plastic finite element simulation technique. By considering the influence of the plastic zone at the interface crack tip, the adhesion strength appeared almost independent of the specimen size. Since the Cu crystals were far smaller than the specimen dimensions and thus no significant difference should be expected in adhesion strength, it is speculated that an accurate estimation of the plastic zone is essential for micro-scale specimen evaluation. (C) 2014 Elsevier Ltd. All rights reserved.

Local adhesion strength of the interface between Cu line and SiN cap layer in a Cu damascene interconnect structure of LSI has a significant fluctuation when evaluated with in-plane dimensions of 1 x 1 mu m specimens, which was 4.78 +/- 1.63 J/m(2). The reproducibility of the evaluation technique was investigated by evaluating the strength of the Cu/SiN interface for the specimens fabricated on a plate of Cu single crystal, where the interface strength was measured as 0.62 +/- 0.02 J/m(2). The relative standard deviation of interface strength distribution in LSI interconnect structure was 34% which was more than ten times larger than the value 2.5% for the specimens fabricated on the plate of Cu single crystal. The significant fluctuation of interface strength was induced clearly not by the random error of the evaluation technique, but by the inhomogeneous grain structure of Cu line with various crystal orientations and grain boundaries. By means of elastic-plastic interface crack extension simulations, it was revealed that the difference in the amount of energy dissipated in plastic deformation of Cu layer mainly leads to a significant fluctuation of the apparent strength. Plastic deformation of Cu layer plays a dominant role on the local strength of interface Cu/SiN in LSI interconnects. (C) 2014 Elsevier B.V. All rights reserved,

Local adhesion strength of the interface composed of a single copper grain and SiN insulation layer was evaluated by using subgrain-scale specimens fabricated on a damascene interconnect structure. Crystallographic information was also surveyed at the fracture sites of the specimens in view of possible correlations between the strength and the crystal orientation of copper. Evaluated strength distributed on the crystal orientation map with a wide range of scatter, which indicates that copper crystal orientation plays an important role on adhesion strength. In addition, the relationship between the evaluated adhesion strength and the crystal orientation of copper grain suggests the significant contribution of the energy to be dissipated to plastic deformation. The result of this fundamental evaluation supports the possible variation of local interface adhesion strength in damascene interconnects which consist of polycrystalline copper and the insulation layer. (C) 2014 Elsevier B.V. All rights reserved.

The local interfacial strength is a key factor in designing and fabricating advanced three-dimensional large-scale integration interconnect structures. In this paper, both local fracture tests and three-dimensional elastic-plastic crack propagation analysis for a 10 mu m x 10 mu m specimen were performed, and the local interfacial adhesion between a Cu interconnect and a SiN cap layer were evaluated. The three-dimensional elastic-plastic crack propagation simulation was developed to evaluate the interfacial adhesion that eliminated the effect of progressive plastic dissipation energy during crack propagation. The results show that the average interfacial adhesion for Cu/SiN is 4.46 +/- 0.17 J/m(2). The crack propagation behavior and fracture pattern depend on the interfacial adhesion, and these differences are due to the plastic yielding of the side edge of the specimen. The critical interfacial adhesion for the onset of shear fracture is 4.92 J/m(2), which is the upper bound of the interfacial adhesion evaluation for the 10 mu m x 10 mu m specimen. (C) 2012 Elsevier Ltd. All rights reserved.

A novel scheme for the evaluation of interface adhesion energy was examined by a detailed numerical simulation of interface crack extension. The effects of crystal orientation on the Cu/SiN interface adhesion strength of LSI was evaluated using the finite element method. Crack extension simulation was conducted with a model of the actual specimen used for the interface fracture test. The characteristics of elastic-plastic deformation, which changes significantly depending on crystal orientation, were taken into account in the model. With this scheme, the effect of orientation of single crystals on the maximum load P-max was investigated under the condition of a constant bonding energy of the interface at the beginning of unstable crack propagation during the fracture test. The values of P-max obtained with a number of different crystal orientations ranged over 179-311 mu N. The result indicates that the crack propagates more easily in the case that slip deformation of Cu near the interface starts with a low stress, as in the case of the (111) surface. It implies that the apparent interface adhesion strength represented by the load required to debond the interface strongly depends on Cu crystal orientation, because the amount of energy used for plastic deformation of the Cu crystal changes with crystal orientation near the interface. (C) 2013 The Japan Society of Applied Physics

A new technique for the evaluation of local interface adhesion energy was applied to the interface between Cu and cap layer in a Cu damascene interconnect structure, which consists of both the interfacial fracture test and the finite-element simulation. After specimens in-plane dimensions of 1×1 μm, 5×5 μm and 10×10 μm fractured by focused ion beam (FIB), the interfacial fracture test was implemented by a novel system with nano-indenter in FIB-SEM dual-beam microscope.With the maximum load measured during the fracture test employed in an elastic-plastic simulation, interface adhesion energy was evaluated and almost equal among all types of specimens. On the other hand, the variation of the evaluated interface adhesion energy tends to be larger with the decreasing specimen size. With the result of electron backscattering diffraction analysis for Cu lines whose average grain size were 400nm diameter, it is suggested that local interface strength significantly varies depending on local grain distribution in a Cu interconnect structure. © 2013 The Japan Society of Mechanical Engineers.

Numerical methods like the finite element (FE) method are often used to evaluate the reliability of electronic packages. However, the accuracy of non-linear numerical analyses should be confirmed by experimental measurements. In this study, we evaluated the strain distribution in flip chip (FC) packages with multi-layered printed circuit boards (PCBs) by combining the digital image correlation method (DICM) and the non-linear FE method, considering the viscoelasticity of resins and the elastoplasticity and creep of solder alloy. Four types of FC package consisting of two types of buildup (BU) resin and two types of underfill (UF) resin were evaluated. The distributions of strain on the cutting sections of FC packages were measured using the DICM with microphotographs obtained by a confocal laser scanning microscope (CLSM). The strain measurements showed that the UF resin with the low coefficient of thermal expansion (CTE) reduced thermal strain around a solder bump, and the BU resin with the low CTE reduced the strain concentration along the interface between a Si chip and a solder bump. We performed the non-linear FE analyses while taking into account the viscoelastic Poisson's ratio of the UF resin and the constant instantaneous Poisson's ratio. The result of the FE analyses with the constant instantaneous Poisson's ratio did not correspond with the strain measurements using the DICM. The normal strain in a solder bump was less than that obtained by the measurement, and the direction of a shear strain band in a solder bump was different from that measured using the DICM. On the other hand, the FE analyses considering the viscoelastic Poisson's ratio showed good agreement with the strain measurements using the DICM. The strain measurement using the DICM improved the accuracy of the non-linear FE analysis of microelectronic packages effectively. (C) 2012 Elsevier Ltd. All rights reserved.

The adhesion strength distribution at the interface between damascene copper lines and the cap layers covering the lines was explored. A novel system composed of a dual-beam SEM/FIB equipped with a nanoindenter and an EBSD camera enabled successful evaluation with a resolution of the order of 300 nm, which is the scale of crystal grains. The adhesion strength was found to scatter in a range spanning roughly half to double the average value. Although no clear correlation was observed with the geometry of the copper line, the impact of the copper grain structure beneath the specimens was rather distinct, where the adhesion strength of specimens with grain boundary junctions observed on their footprints was significantly lower than that of specimens without junctions. This result suggests that the microscopic structure of deposited materials may strongly influence the strength of adhesion to neighboring layers. Therefore, the evaluation of local adhesion is important from an engineering point of view as a means for avoiding unexpected fractures at possible weak points and assessing the mechanical reliability of the layered systems. (C) 2012 Elsevier B.V. All rights reserved.

The fracture behavior of a crack in an adhesive joint is important to investigate the integrity of adhesive structures. It is well known that the fracture toughness of a crack in an adhesive joint using ductile adhesive depends on the bond thickness. However, the mechanism of the dependence has not yet been elucidated. In the present study, we measured the fracture toughness of adhesive joints consisted of aluminum and rubber modified epoxy resin under mode I loading. The distributions of strain around a crack tip were measured using a micro-video-scope and the digital image correlation method (DICM). The measured distributions of strains were compared with that estimated using the finite element method (FEM) in conjunction with Gurson's model. The fracture toughness of adhesive joints used in this study decreased with the decrease of the bond thickness. According to the measurement and analyses, it is estimated that the stress and damage around a crack tip in a thinner adhesive layer were more increased by the higher constraint effect of adherends.

An effective strain measurement system for small region in electronic packages using digital image correlation method (DICM) was developed. The accuracy of measurement using the DICM was affected by the distortion of captured images. An error correction method using a piezo-stage was proposed to improve the accuracy of the DICM. The measured distribution of thermal strain in a print circuit board accurately correlated to the macroscopic warpage measured by a laser displacement meter. It proved the accuracy of the measured strain. The distributions of thermal strain in chip embedded print circuit boards were measured using the DICM. The measured distributions of strain qualitatively corresponded with those calculated by the finite element method.

It is difficult to characterize the local thermal properties of metal. In addition, local electric/thermal resistance due to lattice difects become a hube problem in fine semiconductor building. There is a strong correlation between those electrical and thermal properties. In this study, we have developed an evaluation method using an equivalent circuit network model. By considering the local electrical resistance proportional to the interatomic distance, the mechanical response and crystal orientation dependence of the electrical resistance were evaluated. Although there remains a problem with accuracy, the possibility as a simple method for evaluating local electrical characteristics has been shown. In order to control the lattice defects that affect the local characteristics, we conducted electrical resistance measurement under electrical/thermal stress, stress analysis, and simulated experiments, and investigated the mechanical anisotropic annealing method in the presence of gaps.

Copper interconnect systems of semiconductor devices has a risk of mechanical fracture along with the trend of further integration and miniaturization, because of many weak interfaces stacked to compose multilayered copper/dielectric systems. In order to estimate the fracture risk of the semiconductor products, not only the values of those adhesion strengths but also the information of the existing defect that can possibly initiate the interfacial fracture are essential. In this research, both the adhesion strength and the stochastic distribution of defect size at copper/dielectric interface that can be regarded as an equivalent crack were estimated. The crack extension behavior during the thermal load test as the same as a semiconductor process, shows good agreement with the developed model based on the fracture strength dependent on the microstructure of metal interconnect.

In this research, the diversity of fracture strength for the metal/insulator interface in semiconductor interconnects was investigated. Single crystalline copper and the interface structure consists of single crystalline copper and insulation layers were subjected to microscale mechanical test under scanning electron microscopy in order to evaluate the plasticity of single crystal copper and Cu/SiN interface strength quantitatively. Considering the obtained results, the surface energy of Cu/SiN interface strongly depends on the crystal plane orientation of Cu crystal facing to SiN layer. In addition, the diversity of resistance for Cu/SiN interface fracture is magnified by both the anisotropy of plasticity due to copper crystallinity and above-mentioned the diversity of Cu/SiN surface energy.

Copper interconnect systems of semiconductor devices has a risk of mechanical fracture along with the trend of further integration and miniaturization, because of many weak interfaces stacked to compose multilayered copper/dielectric systems. In order to improve mechanical reliability of the semiconductor products, those interface strengths were evaluated. In the case of polycrystalline copper structure, the evaluated strength of copper/SiN interface distributed with larger scatter than single crystalline copper structure. This result suggests that the microstructure of copper plays an important role on local interface strength. In addition, in-situ crystal orientation observation during the fracture test was performed. The obtained result demonstrated that the interface fracture accompanied the local plastic deformation of copper near the Cu/SiN interface depending on the microstructure.