Abstract: P-type Bi0.5Sb1.5Te3 compounds doped with 3wt% Te were fabricated by spark plasma sintering and their mechanical and thermoelectric properties were investigated. The sintered compounds with the bending strength of more than 50MPa and the figure-of-merit 2.9×10-3/K were obtained by controlling the mixing ratio of large powders (PL) and small powders (PS). Compared with the conventionally prepared single crystal thermoelectric materials, the bending strength was increased up to more than three times and the figure-of-merit Z was similar those of single crystals. It is expected that the mechanical properties could be improved by using hybrid powders without degradation of thermoelectric properties.
Abstract: The tests of 63Sn-37Pb under cyclic strain and stress were conducted to investigate the material’s time-dependent behavior. A damage-coupled viscoplastic model and its failure criterion are proposed. The prediction of the proposed viscoplastic model implies that the model can describe the cyclic strain and cyclic stress ratcheting behavior, and the fatigue lives very well.
Abstract: The use of anisotropically conductive adhesives (ACA) for the direct interconnection of flipped silicon chips to printed circuits (flip chip packaging), offers numerous advantages such as reduced thickness, improved environmental compatibility, lowered assembly process temperature, increased metallization options, cut downed cost, and decreased equipment needs. Despite numerous benefits, ACA film type packages bare several reliability problems. The most critical issue among them is their electrical performance deterioration upon consecutive thermal cycles attributed to gradual delamination growth through chip and adhesive film interface induced by CTE mismatch driven shear and peel stresses. In this study, warpage of the chip is monitored by real time moiré interferometer during –50oC to +125oC temperature range. Moreover, reduction in chip warpage due
to increase in delamination length is obtained as in function of thermal fatigue cycles. Finally, a new model to predict damage level of ACA package and remained life is proposed and developed.
Abstract: Cyclic bend test and drop test were carried out as a second level reliability test method in order to characterize the joint performance between electronic components and board. Two types of package substrates were used for the test. The one was NiAu plated, and the other one was organic solderability preservatives (OSP) finished. Drop test was done in accordance with JEDEC standard test method . Drop impact and duration time was 1,500G and 0.5ms, respectively. Cyclic bend test was performed with Amkor internal specification because there is no international standard for the test. The Amkor internal specification was edited based on the IPC/JEDEC specification . Board deflection and cyclic frequency was 3mm and 1Hz, respectively. NiAu substrate showed better mean life performance about by 30% in cyclic bend test. OSP substrate showed the same or better failure rate performance in drop test. Typical solder joint failures and intermetalic crack were found by failure analysis.
Abstract: A series of tensile tests at constant strain rate were conducted on tin-lead based solders with different Sn content under wide ranges of temperatures and strain rates. It was shown that the stress-strain relationships had strong temperature- and strain rate- dependence. The parameters of Anand model for four solders were determined. The four solders were 60Sn-40Pb, 40Sn-60Pb, 10Sn-90Pb and 5Sn-95Pb. Anand constitutive model was employed to simulate the stress-strain behaviors of the solders for the temperature range from 313K to 398K and the strain rate range from 0.001%sP -1 P to 2%sP -1 P. The results showed that Anand model can adequately predict the rate- and temperature- related constitutive behaviors at all test temperatures and strain rates.
Abstract: In this study, epoxy molded multi chip package was investigated and a highly reliable
structure against failure of copper trace on PCB substrate was proposed. Function failure caused by the pattern crack during component level thermal cycle test was considered. In-plane and out-of-plane movements of package during thermal loading were measured by moiré interferometry and shadow moiré. Measured data were compared with numerical analysis results. Two dimensional and three dimensional numerical analysis were performed considering visco-elastic material properties. Tensile stress in the core layer was analyzed quantitatively and qualitatively. Analysis showed that the reliability of pattern crack could be improved by decreasing the chip thickness and increasing the core thickness, and that the material property of die adhesive was important.
Abstract: The effects of different bonding parameters-temperature, pressure, curing time, bonding temperature ramp and post-processing on the adhesive strengths of Anisotropic Conductive Adhesive Film (ACF) interconnection were investigated. The test results showed the adhesive strength increased as the bonding temperature increase. The curing time had great influence on the adhesive strength of ACF joints. The adhesive strengths increased as the bonding pressure increasing, but decreased if the bonding pressure was over 0.25MPa. The effects of different Teflon thickness on the pressure header and post-processing on adhesive strengths performance of ACF joints were studied. It was shown that the 90o peeling strength became deteriorated as the Teflon thickness increase. Different post-processing conditions showed that the specimens kept in 120oC chamber for 30 minutes had the best performance of the ACF interconnection. The environmental experiments of the thermal cycling (-40 - 125oC) and the high temperature/humidity (85oC, 85%RH) aging were used to evaluate the reliability of the specimens with different bonding parameters. It was shown that the high temperature/humidity was the harshest condition to the ACF bonding. The optimum bonding parameters were determined to obtain better peeling strength.
Abstract: In order to investigate the hydrogen gas effect on non-propagation phenomena of a type 304 austenitic stainless steel, fatigue tests with in-situ observation using a Scanning Laser Microscope were performed in air, in 0.18MPa hydrogen gas and in 0.18MPa nitrogen gas. A nonpropagating crack was observed during the fatigue test in air. At almost the same stress level of non-propagating in air, non-propagating cracks were also observed in fatigue tests in hydrogen and in nitrogen. Stress level of the non-propagation is not sufficiently different in the three environments. However, the process up to non-propagation differs from each other, for example, the crack path and debris.
Abstract: The susceptibility to environmental embrittlement (EE) of automobile spring steels was investigated using six different steels. A SSRT test and TDS analysis were applied to specimens subjected to wet-dry cyclic corrosion tests in a NaCl solution. Experimental results revealed that the reduction in ductility after the corrosion tests was pronounced with increasing strength level. This degradation was closely associated with the resistance to pitting corrosion. Consequently, the hydrogen absorbed in steel and the corrosion pit as a geometric damage were responsible for the EE of spring steels. The hydrogen in rust layer had no significant influence on the EE.