Hyun Sup Lee

A novel low temperature bonding technique for plastic substrates using X-ray irradiation

The present study proposes a new low temperature bonding technique for two plastic substrates using deep X-ray irradiation. The deep X-ray irradiation causes the decrease of molecular weight of PMMA, which in turn decreases the glass transition temperature (T/sub g/). Lowered T/sub g/ on the surface of two PMMA sheets makes bonding possible at low temperature. The present study also offers a tool to predict the decrease of T/sub g/ based on the relationship between X-ray dose and molecular weight. Bonding experiments are conducted at various bonding temperatures near the desired T/sub g/. Then, the bonding strength is measured by means of a tensile test machine (MTS system). The bonding is found to be successfully achieved when the bonding temperature is 8/spl sim/15/spl deg/C higher than the desired T/sub g/. The bonding strength is about 0.96 MPa.

Birefringence distribution in V-grooved optical parts by hot embossing process

For micro-optical products, hot embossing process seems to have more merits because of small thermal cycle that improves optical and mechanical properties and low material flow that reduces the internal residual stress. This study investigates the effects of processing conditions on the birefringence distribution, directly affecting optical quality, in V-grooved optical products. A hot embossing machine was designed and manufactured. Dimensional accuracy and low birefringence are strongly required with respect to the replication accuracy and optical quality.

Microlens Fabrication by the Modified LIGA Process and Hot Embossing Process

Microlens and microlens arrays is realized using a novel fabrication technology based on the exposure of a resist, usually PMMA, to deep X-rays and subsequent thermal treatment. The fabrication technology is very simple and produces microlenses and microlens arrays with good surface roughness (less than 1 nm). The molecular weight and glass transition temperature of PMMA is reduced when it is irradiated with deep X-rays. The microlenses were produced through the effects of volume change, surface tension, and reflow during thermal treatment of irradiated PMMA. Microlenses were produced with diameters ranging from 30 to 1500 μm. Moreover, fabrication of the microlens through the hot embossing process is studied based upon a microlens mold insert fabricated by the modified LIGA process. A hot embossing machine is designed and manufactured. The hot embossing process follows steps of heating a mold to desired temperature, embossing a mold insert on substrate, cooling the mold to deembossing temperature, and deembossing.Copyright