H. S. Choy

Enhanced redshift of the optical band gap in Sn-doped ZnO free standing films using the sol-gel method

The optical band gap in free standing transparent zinc oxide (ZnO) films using the sol?gel method was studied. The effect of Sn doping on grain size, vibrational structure and on the optical properties of ZnO films was investigated. Contrary to the common observation, the optical band gap of Sn-doped ZnO is red-shifted from 3.38 to 3.18?eV as the doping weight percentage is increased to 3%. The redshift of the optical band gap is due to the deep states in the band gap, and a change of ~0.2?eV can only be observed when a substrate is not used. This study illustrates that removal of interaction between film boundaries and substrate is essential for developing effective band gap-tunable ZnO thin films.

Multiresponse Optimization of Surface Plasma Treatment Using Taguchi Method

Emerging plasma treatment on printed circuit boards has many applications from desmearing to micro/nanomanipulating of surface chemistry. However, the methodology to predict their mechanism behaviors and quantify their process performance is hampered by the fact that each plasma treatment response is very sensitive to a small change in a technologic parameter, undesirably causing detrimental effect on the overall response. This study thus uses Taguchis parameter design to identify the essential technologic parameters affecting the plasma treatment performance. The factor combinations for process performance optimization are observed to be intrinsically distinct for different polymer substrates. The optimal level correlation between responses and control factors is established by means of signal-to-noise (S/N) ratio. The analysis of variance is employed to identify the priority of factor influence. Finally, both predicted and experimental results are compared to determine the efficacy of using the proposed methodology to optimize the surface plasma treatment process.

Thermal performance and placement design of LED array package on PCB

This paper reports the thermal performance of a high-brightness light-emitting diode (LED) array package with a novel placement method on a metal core printed circuit board (MCPCB). The precise heat transfer analysis and modeling using computational fluid dynamics (CFD) were performed according to the practical working conditions of the LED array. The surface temperatures of the LEDs having the developed placement method were monitored and compared with that of LEDs using a conventional placement method. Emphasis was placed upon investigating how the radiant flux, efficacy, and uniformity of illuminance changed in accordance with the method. Thermal distribution of a commercial LED product having 36 high-brightness LEDs using the developed placement method is compared to that of the LED product having the original design. Results suggested that the new placement method could lower the individual LED surface temperature by rearranging the thermal distribution of the LED array. As a result, the overall heat dissipating capability of the LED array to the PCB and hence LED efficacy was improved.

The effect of plasma etching process on rigid flex substrate for electronic packaging application

The demand for high-speed signal transmission circuits triggers the use of polymer substrates having the superiorly mechanical and electrical reliability properties. Foremost among them, rigid-flex polymer substrates are being used in the printed circuit board (PCB) of electronic packaging technologies by utilizing their property compatible with device miniaturization and packaging integration. Modifying the polymer interfacial property further before subsequent processing, plasma treatment is employed to adjust the physical and chemical changes of the surface and subsurface. One special issue of plasma-induced change is the surface roughness (hydrophobic or hydrophilic) depending on every detail of process cycle conditions. Thus, it is difficult to be precisely controlled so as to deliver the desirable outcome. This study employs Taguchi experimental method to find the parameter critical to plasma etching particularly on rigid flex substrate. In contrast to the traditional use of atomic force microscopy (AFM) and/or scanning electron microscopy (SEM) to characterize the surface roughness morphology and thus deduce the optimal process conditions. It adopts a set of standard orthogonal arrays to determine parameters configuration and analysis results. These kinds of arrays use a small number of experimental runs but obtain maximum information and have high reproducibility and reliability. Taguchi method provides the experimenter with a systematic and efficient approach for conducting experiments to determine near optimum parameter settings for performance and cost.