Papers by Author: Jeng Shen Huang

Abstract: The debris re-adhering on the machining surface will affect the workpiece precision in EDM; therefore, the main purpose of this research is to study the re-sticky phenomenon of the powder metallurgy (PMM) in EDM. PMM with different melting points from 1450oC to 3410oC were used as EDM materials, the copper and the tungsten were chosen as the electrodes. The polarity in EDM was depended on the pole of the electrode. For observing the re-sticky position of the debris, the electrode was set no rotation or with 200 rpm rotational speed in EDM. The results showed that the melting point of PMM did not exceed 3000oC (PMM did not contain tungsten); the debris of PMM would not re-stick on the working surface no matter what polarity was used in EDM. However, only negative polarity can cause the re-adhesive effect when the melting point of PMM exceeded 3000oC. The debris would re-stick on any machining position when the electrode was not rotated in EDM. However, the debris would adhere on the central of the working area with 200 rpm rotational speed of the electrode.

Abstract: Generally, impact and shock to portable electronic products can cause significant functional and physical damage in the form of internal component failure or package-to-board interconnection breakage. Therefore, this paper provides a dynamic simulation of shock impact to investigate the internal stress and strains of a printed circuit board (PCB) with ball grid array (BGA) chipset. The tin balls will be simulated with a minimum element size as 0.0536 mm in LS-DYNA finite element software. The corresponding strains of dynamic analysis on PCB board will be compared with those of the experimental measurements using the strain gauge. Finally, the model established has values of peak strain and impact duration close to those measured in the actual shock test. The comparison results of the experimental and numerical strain show that the smallest difference is 0.70%. Furthermore, we also investigate the signal curves of experimental error source on the accelerometer and strain gauge. The measurement results show that the capabilities of the repetition and stability both the input signals and output signals are excellent. This result provides researchers in relevant fields with an excellent example and model for further study of PCB with BGA chipsets.

Abstract: Using TracePro® Monte-Carlo ray-tracing simulations, this paper investigates the improved light extraction efficiency (LEE) obtained by patterning the surface and/or substrate of GaN LEDs with unique three-dimensional micro-cavity patterns. The simulations commence by considering the case of a sapphire-based GaN LED. The effects on the LEE of the micro-cavity dimensions, the absorption coefficient of the active layer, the point source location, and the chip dimensions are systematically examined. Subsequently, the LEE performance of the sapphire-based GaN LED is compared with that of a thin-GaN LED for various surface texturing strategies. In general, the results show that patterning either the surface or the substrate of the LED structure provides an effective improvement in the LEE of both the sapphire-based GaN LED and the thin- GaN LED. For both LED structures, the maximum LEE enhancement is obtained by patterning both the upper surface of the LED and the substrate surface. However, the simulation results indicate that the improvement obtained in the LEE is the result primarily of pattering the upper surface of the LED.