Yi-Ming Jen

Biaxial fatigue crack initiation life prediction of solid cylindrical specimens with transverse circular holes

Multiaxial fatigue crack initiation lives of solid cylindrical specimens with transverse circular holes were investigated. Neubers rule and the finite element approach were both used to obtain the local stresses and strains of the hole. Neubers rule applied for the hole in this study failed to estimate the local stress state under combined push-pull and torsional fatigue loading. Several prediction models for multiaxial fatigue lives were used to examine the experimental results with the assistance of the local strain approach through the finite element analysis in this study. It was found that the maximum stress on the hole edge was uniaxial, and all models gave good predicted results by using only push-pull fatigue data of smooth specimens.

Finite element based fatigue life estimation of the solder joints with effect of intermetallic compound growth

Abstract This paper develops an analysis procedure to study the effects of intermetallic compound (IMC) growth on the fatigue life of 63Sn–37Pb (lead-rich)/96.5Sn–3.5Ag (lead-free) solder balls for flip-chip plastic ball grid array packages under thermal cycling test conditions. In this analysis procedure, the thickness of the IMC increased with the number of thermal cycles, and was determined using the growth rate equation. A series of non-linear finite element analyses was conducted to simulate the stress/strain history at the critical locations of the solder balls with various IMC thicknesses in thermal cycling tests. The simulated stress/strain results were then employed in a fatigue life prediction model to determine the relationship between the predicted fatigue life of the solder ball and the IMC thickness. Based on the concept of continuous damage accumulation and incorporated with the linear damage rule, this study defines the damage of each thermal cycle as the reciprocal of the predicted fatigue life of the solder joints with the corresponding IMC thickness. The final fatigue failure of the solder ball was determined as the number of cycles corresponding to the cumulative damage equal to unity. Results show that the solder joint fatigue life decreased as the IMC thickness increased. Moreover, the predicted thermal fatigue life of lead-rich solders based on the effects of IMC growth is apparently smaller than that without considering the IMC growth in the reliability analysis. Results also show that the influence of the IMC thickness on the fatigue life prediction of the lead-free solder joint can be ignored.

Fatigue characterization of acid-treated carbon nanotube/epoxy composites

This study investigates how the acid treatment of multi-walled carbon nanotubes affects the fatigue behavior of carbon nanotube/epoxy composites. Nanocomposites with 0.5 and 1.0u2009wt% acid-treated carbon nanotubes display slightly and significantly stronger fatigue strength than those with equal-content as-received carbon nanotubes, respectively. However, excessive addition of carbon nanotubes fails to increase the fatigue resistance of epoxy resins, owing to carbon nanotube agglomeration. Furthermore, the fatigue strength of nanocomposites depend on the ultimate strength rather than the carbon nanotube contents or treatments. Furthermore, how carbon nanotube contents and related treatments influence the fatigue strength of the nanocomposites is elucidated by examining the fractographs of the specimens.

Effect of Size of Lid-Substrate Adhesive on Reliability of Solder Balls in Thermally Enhanced Flip Chip PBGA Packages

Six design cases of lid-substrate adhesive with various combinations of widths and heights were analyzed to investigate how the size of the adhesive affects the reliability of the solder balls of thermally enhanced flip chip plastic ball grid array (FC-PBGA) packages in thermal cycling tests. Analysis results were compared with data on the reliability of conventional FC-PBGA packages. Thermal-mechanical behavior was simulated by the finite element (FE) method and the eutectic solder was assumed to exhibit elastic-viscoplastic behavior. The temperature-dependent nonlinear stress/strain relationship of the adhesive was experimentally determined and used in the FE analysis. Darveauxs model was employed to obtain the predicted fatigue life of the solder ball. Simulation results reveal that the fatigue life of the solder balls in thermally enhanced FC-PBGA packages is much shorter than that in conventional FC-PBGA packages, and the life of solder balls increases with both the width and the height of the adhesive. However, the effect of the width of the adhesive on the reliability of the solder ball is stronger than that of the height. Moreover, increasing either the width or the height reduces the plastic strain in the adhesive at critical locations, indicating that the reliability of the adhesive can be improved by its size. The predicted results of the life of solder balls for some selected studied packages are also compared with experimental data from thermal cycling tests in the paper

Effect of temperature on fatigue strength of carbon nanotube/epoxy composites

The monotonic and fatigue tensile strengths of acid-treated carbon nanotube/epoxy composites with various carbon nanotube contents were experimentally studied at −25℃, 0℃, 25℃, and 40℃. Experimental results reveal that the monotonic and fatigue strengths of the nanocomposites decreased as the temperature increased. The temperature-dependent S-N curves of the nanocomposites with various carbon nanotube contents were experimentally determined. The fatigue strength exponents in the power laws that described the S-N curves were independent of the carbon nanotube content and the testing temperature, and the reciprocals of the fatigue strength coefficients were related to the testing temperature according to the Arrhenius model. Nanocomposites with higher monotonic strength had a lower pre-exponential factor and activation energy. The epoxy-based nanocomposites presented obvious cyclic softening and dynamic creep characteristics in the fatigue tests conducted at 40℃. However, adding carbon nanotubes in the epoxy can diminish these phenomena significantly. The fracture surfaces demonstrated that the length of the pull-out carbon nanotubes increased with the testing temperature, indicating that a high temperature weakened the adhesion strength between the carbon nanotube surfaces and the polymer matrix.

Static and Fatigue Strengths of Carbon Nanotube/Epoxy Composites under Hygrothermal Environments

This study experimentally analyzed the hygrothermal effect on the static and fatigue strengths of acid-treated multi-walled carbon nanotubes (CNTs)/epoxy composites. The nanocomposite specimens with various CNT contents (0., 0.5, and 1.0 wt.%) were statically and fatigue-tested under three different hygrothermal conditions (25 °C/60% RH, 25° C/85% RH, and 40 °C/85% RH) to investigate the influences of hygrothermal conditions and CNT contents on the tensile static and fatigue strengths of the studied nanocomposites. The results show that the static and fatigue strengths decreased slightly at 25 °C/85% RH environments compared with those tested under the 25 °C/60% RH condition. However, the static and fatigue strengths of the studied nanocomposites decreased substantially under the 40 °C/85% RH condition. The combined temperature and humidity environments weaken the interfacial adhesion between the CNT surfaces and the epoxy matrix. Moreover, the experimental results show that the addition of 0.5 wt.% of carbon nanotubes improved the static and fatigue strengths considerably under the same hygrothermal environments. However, when an excessive amount of CNTs was used (1.0 wt.%), the nanocomposite exhibited the lowest strengths compared with the specimens with 0 and 0.5 wt.% CNTs. The stress concentration effect caused by the CNT aggregates was detrimental to the static and fatigue strengths of the studied nanocomposites.

Effect of Lid Materials on the Solder Ball Reliability of Thermally Enhanced Flip-Chip Plastic Ball Grid Array Packages

This research studied the thermal fatigue life for eutectic solder balls of thermally enhanced flip-chip plastic ball grid array (FC-PBGA) packages with different lid materials under thermal cycling tests. Three FC-PBGA packages with different lid materials, i.e., Al, AlSiC, and Cu, were utilized to examine the lid material effect on solder ball reliability. The cyclic stress/strain behavior for the packages was estimated by using the nonlinear finite element method. The eutectic solder was assumed to be elastic-plastic-creep. The stable stress/strain results obtained from FEM analysis were utilized to predict the thermal fatigue life of solder balls by using the Coffin-Manson prediction model. Simulation results showed that the fatigue life of the FC-PBGA package with a Cu lid was much shorter than FC-PBGA packages with other lid materials. The relatively shorter fatigue life for the FC-PBGA package with a Cu lid was due to the complex constrained behavior caused by the thermal mismatch between the lid, substrate and the printed circuit board. The difference was insignificant in the fatigue lives between the package with an Al lid and the conventional package.

Time and temperature dependent mechanical characterization of polymer-based materials in electronic packaging application

The thermo-mechanical testing of high performance polyimide films Type HPP-ST supplied by Dupont/spl reg/ is preceded under different strain rate and temperature environments. The stress-strain behavior of materials is simulated with constitutive framework, and the dependence of Youngs modulus on temperature and strain rate is reported. In view of the uncertainty of the Youngs modulus determination, the specimens were tested with unloading-reloading to verify the test results. Constant strain rate uniaxial tensile test and long-term creep test at various temperatures are preceded to characterize the time-temperature-dependent mechanical property precisely. Cyclic loading test was also performed on the specimen to investigate cyclic stress-strain behaviors. There is no research definitely related in the past, therefore the research is expected to enhance the finite-element-modeling accuracy and characterize the material properties.