Jao-Hwa Kuang

Dynamic characteristics of shaped micro-actuators solved using the differential quadrature method

This study examined the dynamic characteristics of nonlinear electrostatic pull-in behavior for shaped actuators in micro-electro-mechanical systems (MEMS). The natural frequencies of a fixed–fixed shaped beam vibrating around its statically deflected position were calculated using the differential quadrature method (DQM). The proposed model included the nonlinear interaction between the curved electrostatic field force and the shaped micro-beam, as well as the mid-plane stretching, axial residual stress and electrical field fringing effect. Very good agreement existed between the results simulated using the proposed model and the measured data. This work also investigated the micro-beam and electrode shape effect on the natural frequencies of the actuator system. Analytical results indicate that the variation in the micro-beam and the electrode shapes might not only influence the electrostatic field distribution but also significantly alter the dynamic characteristics of the micro-actuator. Analytical results demonstrate that the shaped micro-beam with curved electrode can increase the working voltage range approximately six times compared to the rectangular micro-beam and flat electrode.

Failure Mechanisms Associated With Lens Shape of High-Power LED Modules in Aging Test

High-power light-emitting diode (LED) modules encapsulated with different lens shapes after a thermal-aging test were studied experimentally and numerically. Samples from different manufacturers were aged at 80degC, 100degC, and 120degC under a constant driving voltage of 3.2 V. The results showed that the LED modules encapsulated with a hemispherical-shaped plastic lens exhibited a better lifetime due to better thermal dissipation than those with cylindrical-or elliptical-shaped plastic lenses. Results also showed that the optical power of the LED modules increased after removing the plastic lens because degradation of the lens material decreased the amount of light. The key module package-related failure modes under thermal-aging were identified as the degradation of the plastic lens and lens material. A finite-element method (FEM) simulation showed that thermal and major principle stress distributions of the high-power LED modules were dependent on aging temperature. Both experimental and FEM simulated results clearly indicated that a uniformly thermal dissipation to minimize the thermal effect along the thermal path from the LED chip to the plastic lens is essential to extend the operating life of high-power LED modules.

The Effect of Tooth Wear on the Vibration Spectrum of a Spur Gear Pair

In this paper, the effect of tooth wear on the vibration spectrum variation of a rotating spur gear pair is studied. In order to approximate the dynamic characteristics of an engaging spur gear pair, the load sharing alternation, position dependent mesh stiffness, damping factor and friction coefficient are considered in the mathematical model. The wear prediction model proposed by Flodin et al. is used to simulate the tooth profile wear process. The variation of the vibration spectra introduced from the interaction between the sliding wear and the dynamic load is simulated and analyzed. Numerical results indicate that the dynamic load histogram of an engaging spur gear pair may change greatly with the tooth wear. This finding implies that the variation of the gear vibration spectrum might be used to monitor the tooth wear of an engaging spur gear pair.

Post-weld-shift in dual-in-line laser package

The post-weld-shift (PWS) effect in laser welding for a dual-in-line package (DIP) with fiber pigtail to semiconductor laser connection has been studied experimentally and numerically. Experimental results show that the PWS of an optical component welded by a dual-beam laser system deforms and the welded component rotates counterclockwise as the difference of the energies between two laser beams increases. This indicates that the PWS in laser packaging can be minimized by properly controlling the laser beam-to-beam energy balance. A thermal-plasticity coupled finite-element model (FEM) has been also carried out on the analysis of the effect of PWS in laser packaging. Numerical results show that a PWS in the DIP may be introduced from an unbalanced distribution of residual stresses introduced from the solidification shrinkage. A satisfactory agreement between the experimental results and FEM calculations suggests that the FEM may provide an effective method for predicting the PWS in laser welding technique for optoelectronic packaging.

Contact stress variations near the insulated rail joints

Abstract The effect of an insulated rail joint (IRJ) on the contact stress variation near wheel-rail contact zones was simulated by employing three-dimensional finite element models. Three linear elastic IRJ materials, i.e. epoxy-fibreglass, polytetrafluoroethylene (PTFE) and Nylon-66, were investigated. Contact elements were used to simulate the interaction between the wheel and rail contact points. Numerical results showed that the presence of IRJ might significantly affect the wheel-rail contact stress distributions. Results also indicated that the traditional Hertzian contact theory is no longer available to predict the contact stress distribution around the rail joints.

Decay Mechanisms of Radiation Pattern and Optical Spectrum of High-Power LED Modules in Aging Test

Decay of radiation pattern and optical spectrum of high-power LED modules fabricated by different manufacturers after a thermal-aging test were investigated experimentally and numerically. Samples were aged at 65degC, 85degC, and 95degC under a constant current of 350 mA. The results showed that the radiation pattern of the LED modules at the two view angles of plusmn(45deg ~ 75deg) decreased more than the other angles as aging time increased. This was due to the reduction of optical power from corner shape of lens. Due to the degradation of lens material after thermal aging, the center wavelength of the LED spectrum shifted 5 nm. Furthermore, the radius curvature of plastic lens was observed to have 6-70 mum contraction as aging times increased. The key module package related to the decrease of power density, the change of radiation pattern, and the shift of optical spectrum in high-power LED modules under thermal aging were due to the degradation of lens material and lens structure. Both experimental and simulated results clearly indicated that improving the lens structure and lens material is essential to extend the operating life of the high-power LED modules. This study may provide practical LED package guidelines in low-cost consumer applications.

Postweld-shift-induced fiber alignment shifts in laser-welded laser module packages: experiments and simulations

The fiber alignment shifts induced by the postweld shift (PWS) in laser-welded transistor outline (TO)-Can-type laser module packages were studied experimentally and numerically. The PWS-induced fiber alignment shifts were quantitatively determined by four geometrical parameters, namely: 1) the lateral shift (r); 2) the position angle (/spl alpha/); 3) the swing angle (/spl theta/); and 4) the tilt angle (/spl psi/). The measured coupling powers in laser module packages before welding, after welding, and after a welding compensation clearly confirmed with the measured fiber alignment shifts determined by the dominant parameters of the r and /spl alpha/ that the fiber shifts due to the PWS could be realigned back closer to their original optimum position after applying a welding compensation, and, hence, the coupling power loss due to the PWS could be regained. A coupled thermal-elastoplasticity model of finite-element-method (FEM) analysis was performed to evaluate the effects of PWS on fiber alignment shifts in laser module packages. The measured fiber alignment shifts determined by the dominant parameters of the r and /spl alpha/ were in good agreement with the numerical calculation of the FEM analysis. In this study, the combination of the experimental and numerical results have significantly provided a practical design guideline for fabricating reliable laser-welded TO-Can-type laser module packages with a high yield and high performance for use in low-cost lightwave transmission systems.

A novel fiber alignment shift measurement and correction technique in laser-welded laser module packaging

A novel measurement and correction technique employing an ultra-high-precision laser displacement meter (LDM) with a 20-nm resolution to probe the postweld-shift (PWS)-induced fiber alignment shifts in laser-welded laser module packaging is presented. The results show that the direction and magnitude of the fiber alignment shifts induced by the PWS in laser-welded laser module packaging can be quantitatively determined by four parameters: the lateral position (r), the position angle (/spl alpha/), the swing angle (/spl theta/), and the tilt angle (/spl psi/). Further studies show that the deformation of the lateral shift and the position angle are the dominant mechanisms that determine the fiber alignment shifts induced by the PWS. This clearly indicates that the PWS can be quantitatively corrected timely by applying a single weld spot on the negative lateral shift and the position angle to compensate for the fiber alignment shifts. In comparison with previous studies of the PWS correction by a qualitatively estimated technique, this LDM technique has significantly provided an important tool for quantitative measurement and correction to the effect of the PWS on the fiber alignment shifts in laser-welded laser module packaging. Therefore, the reliable laser modules with high yield and high performance used in low-cost lightwave transmission systems may be developed and fabricated.

Fiber alignment shift formation mechanisms of fiber-solder-ferrule joints in laser module packaging

The fiber alignment shifts of fiber-solder-ferrule (FSF) joints in laser module packaging under temperature cycle testing using PbSn and AuSn solders are studied experimentally and numerically. The measured results showed that the fiber shifts of FSP joints with the hard AuSn solder exhibited shifts two times less than that with the soft PbSn solder. This suggests that the hard solder may be more suitable for FSF assembly than the soft solder. The results also showed that fiber shifts increased as the temperature cycle number and the initial fiber eccentric offset increased. The experimental measurements of fiber shifts were in good agreement with the numerical calculations of the finite-element method analysis. The major fiber shift formation mechanisms of FSF joints in temperature cycling may come from the localized plastic solder yielding introduced by the local thermal stress variation, the redistribution of the residual stresses, and the stress relaxation of the creep deformation within the solder. Furthermore, the stress relaxation of creep deformation in solder with either 21% (PbSn solder) or 5% (AuSn solder) may have significant influence on the fiber shifts. This study has provided an optimum approach for reduction of the fiber alignment shift of FSF joints in laser module packaging under temperature cycle testing, which is to solder the fiber near to the center of the ferrule and to select the AuSn hard solder.

Effect of temperature cycling on joint strength of PbSn and AuSn solders in laser packages

The effect of temperature cycle testing on the joint strength of PbSn and AuSn solders in laser diode packages has been studied experimentally and numerically. Experimental results showed that the joint strength increased as the temperature cycle number increased initially, and then became steady after 400 cycles. The joint strengths of PbSn and AuSn solders increased about 40% to 20% after undergoing 500 temperature cycles, respectively. A finite-element method (FEM) analysis was performed on the calculation of joint strength variation of PbSn and AuSn solders in temperature cycling tests. The coupled thermal-elasticity-plasticity model was employed in the solidification and residual stresses calculation. Simulation results were in good agreement with the experimental measurements that the solder joint strength increased as the temperature cycle increased. Numerical results indicate that the increasing solder joint strength comes from the redistribution of the residual stresses within the solder during temperature cycling tests. The local yielding and the creep effects on the low melting temperature solders will make uniform the residual stresses distribution introduced in the solidification process and increasing the solder joint strength as the temperature cycle number increased. The result suggests that the FEM is an effective method for analyzing and predicting the solder joint strength in laser diode packages.