Shuichi Tani

Stress Concentration and Surface Roughness Effect on Strength of Polycrystalline Silicon Structure

In order to clarify the stress concentration and surface roughness effect on strength of the polycrystalline silicon (poly-Si) structure, bending tests of poly-Si microcantilever beam specimen and surface roughness measurement is performed. The bending test results are analyzed by means of maximum stress at the notch root calculated by FEM models, and it is found that this approach cannot describe the test results. Therefore, modified approach is taken into account by use of two parameters that are the maximum stress and area where stress is larger than 50% of the maximum stress, which indicates stress extension around the position of maximum stress representatively. By this two parameters approach, the test results are explained quantitatively and a strength design chart for stress concentration area of the poly-Si structure is obtained. On the other hand, relationship between strength and surface roughness are confirmed and useful information for the process quality control are obtained.Copyright

Two-dimensional Thermal Stress Analysis using X-FEM

Conventional FEM requires that the boundary of the element just matches the crack line to perform stress analyses of structures containing cracks in the field of fracture mechanics. These modeling processes are rather complicated and cannot be performed easily even if the automatic mesh generation technique is utilized. Recently, Belytschko et al. proposed the extended finite element method (X-FEM) based on the concept of partition of unity, and applied this method to the evaluation of the stress intensity factors and perfoming the crack extension simulation. The X-FEM can be used to simplify the modeling of continua containing several cracks and hence perform effective stress analyses related to fracture mechanics. This paper describes the two-dimensional thermal stress analysis of structures containing cracks. Stress intensity factors having mixed modes coupled with modeI and modeII are evaluated by MI-integral method in conjunction with XFEM. This method is examined in numerical examples of elastic and thermo elastic analyses. The numerical results show that X-FEM is an effective method for performing thermal stress analyses and evaluating stress intensity factors.

EVALUATION OF FATIGUE DAMAGE IN SOLDER JOINTS OF ELECTRONIC DEVICES

ABSTRACT This paper proposes the evaluation method of fatigue damage (fatigue crack length) in solder joints of electronic devices. The fatigue damage is evaluated by means of the residual strength obtained by the peeling test of cracked solder joint after mechanical fatigue test. The observation of fracture surface of solder joints are carried out by scanning electron microscope (SEM) in order to investigate the relationship between the residual strength and fatigue crack length. Moreover, the residual strength of cracked solder joints is estimated by the finite element analysis. The test and analysis are carried out for the surface mount IC packages. It is found that the fatigue damage in solder joints can be evaluated by the peeling test and the finite element analysis is available for the estimation of the residual strength.