Papers by Author: Sum Huan Ng

Abstract: This study aims to investigate laser welding process for the bonding of micro-fluidic devices. PMMA was selected for the investigation. The devices consist of an opaque substrate with micro-channels and a transparent cover. The welding process was optimized according to laser power, welding speed and clamping pressure. The cross-sectional analysis, flow and pressure tests, as well as the lap-shear test were conducted on the samples welded with the optimized process parameters. The results show that the laser welding can meet the requirements for bonding the plastic micro-fluidic devices.

Abstract: Recently, material removal utilising electrokinetic phenomenon was proposed as an alternative to create material removal at the nanometric level [1]. The concept of the introduced material removal process is to impinge particles contained in the slurry, under the influence of hydrodynamic and electrokinetic effects, onto the workpiece with a predetermined velocity to create material removal on the surface. The material removal process proved to be feasible where the material removal rate was reported to be in the range of a few hundred nm/hr with a surface roughness of a few nm (RMS). This paper aims to look into the effect of the electrochemical dissolution on the material removal process since high voltages are involved during the material removal process. During the experimental study, electrochemical dissolution was observed and it contributed a certain proportion of the material removal process. However, the main material removal mechanism still relies on the mechanical action of the abrasive particles on the surface of the workpiece to create material removal during the process.

Abstract: With the demand for precise nanometric material removal with minimal defects, several non-contact ultraprecision machining techniques were developed over recent decades. The electrokinetic material removal technique [1] is one such method that allows material to be removed without any physical contact between the tool and the workpiece. In this work, the influence of the slurry mixture on the material removal rate for the electrokinetic material removal process is studied. During the process, it was observed experimentally that the mixture of the slurry affected the material removal rate. The parameters varied in the slurry mixture experiments were the size and concentration of the particles. Explanations for the behaviour of the material removal rate were also suggested during the study to further understand the electrokinetic material removal technique.

Abstract: The sealing of microchannels is a key step in the fabrication of microfluidic devices and thermal bonding is a common technique used. Here, major manufacturing issues and considerations in thermal bonding are investigated, including bonding quality and microchannel deformations. Flatness of substrate is extremely crucial to the uniformity in bonding. While increased bonding pressure helps to overcome problems related to surface topography and to enhance bond strength, its significant impact on geometrical changes of microchannel due to viscoelastic effect should also be taken into consideration.

Abstract: This paper describes a mechanical mechanism of chemical mechanical polishing (CMP) and the model is applied to the polishing of silicon substrates by polyurethane pads and slurries containing fumed silica as is typically done in the manufacture of integrated circuits. The model utilizes the concept that the polishing pad surface contains asperities that support the normal load on the wafer, and that friction and hydrodynamic forces influence wear. The interfacial fluid pressure can significantly influence the normal pressures on the wafers and its effects modify the wear rate predictions.