Mechanical problems of semiconductor devices are reviewed. The emphasis is placed on the problems relating to deformation and strength of the device component, which are incurred in the production process. The case examples describe single crystal growth, wafer processing, wafer bonding, interconnections and packaging. Thermal stress due to different thermal expansion among the materials which constitute devices plays an important part in the deformation and strength of the devices. The object of the problems is a miniature and multi-thin-layered material system which consists of different materials. Phase transition from liquid to solid often occurs in the constituent materials during device processing. Mechanical stress is mainly induced by temperature change in the manufacturing and operating processes. Interfacial strength among bonded dissimilar materials is crucial to device reliability. In conclusion, the characteristic factors common to the mechanical problems are summarized.

View full abstract

The cyclic stress-strain response and the test method-dependent characteristics of metallic materials were discussed from the viewpoint of such metallurgical factors as the motion of screw dislocations, the formation of strain-induced martensite and dynamic strain ageing. Furthermore, their low-cycle fatigue life was examined in terms of the total strain and the plastic strain, and the existence of a unified total strain-based life curve common to the various steel materials was suggested. The plastic strain-based low-cycle fatigue life was successfully estimated through surface crack growth analysis, which was made using the elastic-plastic fracture mechanics ; the inflection appearing in the logΔε_p-1ogN_f relationship of the high strength-low ductility materials as well as the Coffin-Manson law embodied in the ductile materials was satisfactorily described through the crack growth analysis. Finally, it was shown that the equivalent stress and plastic strains generated at the notch root were predominant factors in governing the crack initiation life of the grooved cylinder components.

View full abstract

A one-dimensional generalized thermoelasticity is presented based on Lord and Shulman's theory, which involves one relaxation time of the thermoelastic process. This theory has been developed in an attempt to eliminate the paradox of an infinite velocity of thermoelastic propagation inherent in the classical theory. The analytical object of this paper is an infinite body with a circular cylindrical hole. The boundary condition is that a constant heat flux is flowing into the infinite body from a circular cylindrical hole but the displacement at the hole is constrained. An approximate analysis for short periods of time is carried out because it is very difficult to obtain an exact solution. The numerical results of the effect of the relaxation time on displacement, temperature and stress distributions are shown.

View full abstract

When a solid sphere is subjected suddenly to a uniform temperature rise over its cross section, a stress wave occurs at the surface the moment thermal impact is applied. The stress wave at the surface proceeds radially inward to the center of the sphere. The wave may accumulate at the center and give rise to very large stress magnitudes, even though the initial thermal stress is relatively small. This phenomenon is called the stress-focusing effect. This paper analyzes the effects of these waves precisely using the ray theory. The numerical results give clear indications of a stress-focusing effect in spheres.

View full abstract

Two-dimensional impulsive stresses are analyzed, by the boundary element method with the Laplace transformation and the numerical inversion using the fast Fourier transformation. The condition of the stability between the length of the element and the time step is given by the analysis. The validity of the condition is confirmed by the numerical results. Under the consideration of this condition, the dynamic stress concentration factors of the circular hole, the elliptic hole and the elliptic notch in a strip are obtained from surface forces and tengential derivatives of surface displacements. It is shown that the dynamic stress concentrations are spproximately ten percent larger than the static ones.

View full abstract

As is well known, peculiar stress fields caused by surface flaws are exposed on the surface of engineering materials under working loads. Few studies applying thermoelastic effects whose thermograms are closely related to the isopachics on the surface have been made to estimate various surface flaws through nondestructive testing, although these effects are generally employed in stress analysis of engineering structures. The authors have extended the thermoelastic techniques, therefore, to find nondestructively semielliptical surface cracks with various axial ratios and inclination angles to the tensile axis, and have analyzed the isopachics over the surface using a finite element method for comparison with the thermal image. As a result of these studies, it has been verified that the dimensions of the surface cracks were successfully estimated through the temperature profiles of the thermograms.

View full abstract

The time history of the dynamic stress intensity factor is analyzed for a dynamic one-point bending test in which an edge-cracked specimen is impacted at the midspan without supports. A simple formula is derived for calculating the dynamic stress intensity factor with the specimen modeled as a cracked Euler-Bernoulli beam. Numerical examples are presented to demonstrate the practical applicability of the formula. It is shown that a reasonable accuracy is obtained by the present formula as compared with a finite element computation, and the CPU time is about 1% of the finite element method. Another numerical analysis is also performed for a steel 1PB specimen impacted by a falling cylinder. The contact force between the specimen and the impactor is estimated by applying Hertz's theory to the local deformation near the contact point. It is found that both ends of the 1PB specimen bounce up in an early stage and then the specimen flies off flexing vibrationally; the value of the dynamic stress intensity factor reaches its maximum at the instant when the specimen bends most sharply.

View full abstract

A constitutive law for elastic-plastic materials is presented on the assumption that the deviatoric stress increments affect plastic strain increments. By the use of weighing parameters, the law is expressed as an averaging rule of the usual plastic potential law (J₂-flow rule) and a rule which permits plastic strain increments to depend only on stress increments. The developed law allows the existence of a vertex on the yield surface. It can, however, be expressed formally in the same equation as the usual J₂-flow rule, which implies that it is applicable to such a solution scheme as the finite element method.

View full abstract

A simple method for analysis of uniform-strength shape is newly proposed. In this paper, the most fundamental case of a static elastic body is considered. The idea of the present method came from the growth behavior of living organisms by which they changed their own shapes to adapt themselves to the mechanical living environment. The scheme consists of the iteration of the two analytical steps : (1) conventional elastic analysis for evaluation of stress distribution, and (2) incremental growth analysis using a constitutive equation of growth. In the latter step, a shape is deformed with an incremental bulk strain which is generated according to an objective stress indicating strength of the material. Two examples of a cantilever beam under top shear loading and a column under top compressive loading and gravity are analyzed to show the effectiveness of the proposed method.

View full abstract

Personal-computer-based software which enables us to quantitatively analyze the facet size of cleavage failures in Charpy impact tests by reconstucting the three-dimensional shapes of fracture surfaces was developed. This specially developed software was based on a computer image processing and pattern recognition technique consisting of two parts: one to reconstruct the three-dimensional fracture surface topography from a stereo pair of scanning electron micrographs, and the other to determine facet boundaries from the topography. By using this software, it became possible to measure the facet sizes quickly and with sufficient precision.

View full abstract

This paper is concerned with the ductile-brittle transition behavior of steels under mode II loading. Mode II fracture tests were carried out on center-cracked thin-sheet specimens of HT 50 and S 20 C. Test temperature was changed from room temperature to -196°C. From mode II tests, it was found that the fracture appearance changed with temperature as follows : (i) in the region T < T_B, a cleavage crack initiates and extends, (ii) in the region T > T_D, a ductile crack initiates and extends, and (iii) in the region T_B ≤ T ≤ T_D, a ductile crack initiates and then extends as a brittle cleavage crack. The transition curve under mode II loading was shifted to lower temperature than that under the mode I loading condition. The direction of the cleavage crack was about 64°inclined to the precrack. The direction of the ductile crack coincided with that of the precrack.

View full abstract

The mixed-mode fracture criterion of modes I and II of soda-lime glass was investigated using inclined indentation surface flaws in four-point bending. In order to examine the effect of mode II on the extension of cracks, specimens with inclined surface flaws oriented at an angle of 45°with respect to the outer fiber tensile stress direction were fractured under hydrostatic pressure of up to about 100 MPa. The obtained catastrophic fracture paths were noncoplanar with the initial flaw plane. The values of the critical stress intensity factors, K_IC and K_IIC, were obtained with the ratio K_IIC/K_IC=1.06 observed. The experimental plots of K_IvsK_II were compared with the existing theories. A strain energy density fracture criterion best described the mixed-mode fracture.

View full abstract

To analyze the stress concentration factor, stress distributions and fracture mechanics under forces in composite or concrete structures by photoelastic experiments, it is necessary to develop photoelastic-model materials. An orthotropic photoelastic-model material for transparent-type photoelastic devices was developed in this study ; it is called a copper fiber epoxy composite (abbreviated as C.F.E.C.). It was found that the C.F.E.C. developed in this study satisfies the property requirements of a photoelastic-model material, C.F.E.C. has the complete properties of a composite material. It is thought that it will be possible to apply C.F.E.C. to both medical engineering for modeling biological tissue and to the aerospace industry as an orthotropic photoelastic material.

View full abstract

A scanning laser acoustic microscope, SLAM, is applied to measure velocities of sound and to evaluate elastic constants of ceramics. The method of measuring sound velocity is based on spectral interferometry utilizing the interference fringes for a sample and for a reference material. In this study, a suitable sample holder is made to excite the ultrasonic waves to the desired mode, i.e., the longitudinal or the transverse mode, within the sample. Young's modulus, shear modulus, and Poisson's ratio of partially stabilized zirconia ceramics are evaluated from the measured velocities of sound. Then tensile tests are performed on the same sample and the elastic constants are measured. The elastic constants evaluated by SLAM are in agreement with those obtained by the tensile tests within a deviation of about l0 %. The method described here is useful for small specimens of the ceramic materials.

View full abstract

On the basis of linear beam theory, the static behavior of a pipe string designed for mining manganese nodules is formulated as a singularly perturbed boundary-value problem. This problem is analyzed by the method of matched asymptotic expansions and Galerkin's method. Static pipe deflections and bending moments are evaluated for the practical range of the towing speed of a ship. The pipe deflections obtained by Galerkin's method agree well with those obtained by the method of matched asymptotic expansions. However, it is found that Galerkin's method with the beam function is not effective in evaluating bending moments of the pipe string.

View full abstract

In order to develop deep wells in corrosive conditions, premium connections with high tensile strength and sealing performance are necessary. As for the high tensile strength, jump-out tensile failure, by which the tensile strength and the elongation of connections are decreased, should be prevented. The mechanical behavior and preventive conditions of the jump-out tensile failure are investigated through the failure analysis of connections with varied box-end profiles and thread length. Incomplete pin threads are necessary to prevent the jump-out tensile failure, in addition to the negative load flank angle thread for maintaining the engagement of the threads and the incomplete thread length for ensuring the shearing resistance. The rigidity of the box-end increased by a longer incomplete thread length and an unthreaded ring added to a box-end can help prevent the jump-out tensile failure by decreasing the deformation of the threads and the expansion of the box.

View full abstract