Self-alignment Capability Research Articles

A novel micromachined shadow mask system with self-alignment and gap control capability

We present a novel micromachined shadow mask system, which is capable of accurate self-alignment and mask-substrate gap control. The shadow mask system consists of a silicon shadow mask and a silicon carrier wafer with pyramidal cavities fabricated with bulk micromachining. Self-alignment and gap control of the shadow mask and the fabrication substrate can readily be achieved by using matching pairs of pyramidal cavities and steel spheres placed between. The layer-to-layer alignment accuracy of the new shadow mask system has been experimentally characterized and verified using both optical and atomic force microscopic measurements. As an application of this new shadow mask system, an organic thin-film transistor (OTFT) using pentacene as the semiconductor layer has been successfully fabricated and tested.

Self-aligned spatial filtering using laser optical tweezers

We present an optical spatial filtering device that has been integrated into a microfluidic system and whose motion and alignment is controlled using a laser optical tweezer. The lithographically patterned micro-optical spatial filter device filters out higher frequency additive noise components by automatically aligning itself in three dimensions to the focus of the laser beam. This self-alignment capability is achieved through the attachment of a refractive optical element directly over the circular aperture or pinhole of the spatial filter. A discussion of two different spatial filter designs is presented along with experimental results that demonstrate the effectiveness of the self-aligned micro-optic spatial filter.

Resin Self-Alignment Processes for Self-Assembly Systems

We have demonstrated the self-alignment processes using surface tension of the resin material for the self-assembly systems. It has been known that the surface tension of the resin material is too low to achieve the self-alignment capability. This paper presents a fundamental concept and principles of resin self-alignment processes. The numerical analysis is conducted to enhance understandings of resin self-alignment behavior and the relationship between process-related parameters. It was proved that resin self-alignment is different from the oscillatory motion of solder self-alignment and shows overdamped motion by the experiment. We could achieve the precise alignment of less than 0.4 μm.

Dynamic modeling for resin self-alignment mechanism

A new self-alignment process using surface tension of resin material was developed to realize a low-temperature, fluxless, and cost-effective alternative alignment process for the future assembly of electronic and optoelectronic systems. In this new self-alignment process, we achieved self-alignment capability by using 3-dimensional pads to form the positioning boundary, and by mounting chips in the opposite direction. This process releases the force acted on liquid bumps, even when using resin material, which has been known not to possess self-alignment capability because of its low surface tension. As the viscosity of the resin material is considerably higher than that of the solders, the restoring force resulting from its low surface tension must be larger than the resistance force resulting from its high viscosity. In this paper, we propose a new passive alignment mechanism using the surface tension of a resin material and a comprehensive mathematical model in order to enhance understanding of the self-alignment behavior of resin. Moreover, we conducted a scaled-up experiment to calibrate and verify the model's accuracy. It has been proved that resin self-alignment behavior is totally different from the oscillatory motion of solder alignment. This shows that the motion is aperiodic, regardless of the initial conditions of the system, such as an overdamped system due to the low surface tension and high viscosity characteristics of resin material.

Effect of Viscosity of Liquid Resin on Resin Self-Alignment Capability

We developed highly precise self-alignment process using resin materials for next generation microelectromechanical systems (MEMS), micro-opto-electro-mechanical systems (MOEMS) and optoelectronic multichip modules (OE-MCMs) applications. Although liquid resins have a characteristic as low as one tenth of the surface tension of solder in general, self-alignment capability could be achieved by using 3-D pads for positioning boundary. In this research, we propose the novel passive alignment mechanism in order to enhance understanding of alignment motion. Moreover, the influence of viscosity on alignment motion and alignment accuracy is demonstrated by scaled-up experiment. We could achieve highly precise alignment accuracy less than 0.4 μm.

A method using V-grooves to monitor the thickness of silicon membrane with m resolution

This article presents a method capable of easily identifying the membrane thickness of micro-sensors by a V-groove depth ruler that has been made in advance on silicon wafers before sensor fabrication. The proposed method not only provides a viable alternative to other etch-stop techniques, but can also be used as an in situ tool for depth or thickness monitoring with micrometer resolution. Without p+ diffusion or an n-epitaxial layer on silicon substrates, the batch processing capability of silicon piezoresisitve micro-sensors can be preserved with V-grooves. Furthermore, the method proposed herein could also calibrate the etching rate of anisotropic etching solutions, check the uniformity of pressure sensors and offer guidelines on how to further improve the batch process of silicon bulk micro-machining. Moreover, a revised shape of V-groove depth ruler with self-alignment capability is also proposed herein.

Flip chip-bonded GaAs MMICs compatible with foundry manufacture

A foundry-compatible flip-chip bonding technology has been developed for gallium arsenide monolithic microwave integrated circuits (MMICs). Metallurgical interactions between lead-tin solder and gold-based circuitry were prevented by the inclusion of a pinhole-free metal barrier layer. The solder bonds were extremely reproducible and provided a self-alignment capability at the flip-chip bonding stage. Microwave measurements showed test components to have more uniform characteristics than their wire-bonded counterparts and MMIC amplifiers to have the same behaviour in flip-chip or wirebonded form. All the bonds on a chip were made in a single solder reflow operation, representing a considerable saving in assembly effort.

Dynamic behavior of SMT chip capacitors during solder reflow

A dynamic model of a SMT (surface mount technology) type 1206 chip capacitor is developed. The model is used to determine the effects of pad geometry, chip metallization and dimensions, amount of solder, and chip displacement on the ability of the chip to lift (tombstone) and to self-align itself during solder reflow. Both static and dynamic characterizations are shown. The model simulations show that the chip capacitor will begin to lift initially for some geometries, but tombstoning does not appear to be a problem. Thus, to help the self-alignment capabilities, the simulations show that system configurations with smaller pad lengths, smaller pad gaps, larger solder volume, and smaller metallization are best. These conclusions are confirmed when compared to existing recommendations based upon experimental tests. It is concluded that the model is a powerful tool that can be used to optimize these system parameters. >

Self-Alignment Systems for Heavily Loaded, Compliant, Hydrodynamic Air Bearings

Internal and external self-alignment system for compliant-foil journal bearings have been developed and tested at 35000 rpm in ambient air. These system have been shown to substantially improve the self-alignment capabilities of the compliant-foil bearings. The standard bearings with center-split bump have a misaligned capacity of 0.07 degrees at 55 kPa and 0.03 degrees at 83 kPa. Bearings with an internal self-alignment system were shown to have 0.15-degree misalignment capability at 55-kPa loading and 0.06 degrees at 90 kPa. A bearing with an external self-alignment system tolerated 0.43 degrees of misalignment at 69 kPa and 0.37 degrees at 110 kPa. Self-alignment capabilities of the bearings were improved at higher speed. Limited testing at 288°C showed that the temperature had no influence on the bearing performance. Presented at the 35th Annual Meeting in Anaheim, California, May 5–8, 1980