Ultralevel Assembly of Micron-scale Components

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

Modern mechanical assembly techniques are currently used to manufacture integrated hybrid electronic structures and composite materials. Limitations such as the trade-off between precision and speed in these systems and the inadvertent development of static charge on dielectric surfaces limit the feasible component size to hundreds of microns. Faster motion results in misplacement due to increased vibration. Static charge causes parts to be moved from the desired location in an uncontrolled manner. Self-assembly techniques have been used to assemble composite materials on the micron or nanometer scale, but are limited to close-packed structures. The current drive in the microelectronics industry toward increased integration and decreasing component size, and the development of micron scale composite materials require new assembly techniques. This research project seeks to develop techniques for such ultralevel assembly. Ultralevel assembly refers to the surface mount of discrete micron and submicron scale components directly on active substrates such as silicon chips. The proposed method is a hybrid assembly process, utilizing electrostatic and electrophoretic forces in conjunction with light pressure to guide, or even "fly" components into position. This sort of hybrid assembly process is also promising for the development of composite materials made up of micron scale particles arranged in non-close-packed arrays. The proposed method for utilizing electrostatic forces to aid in assembly is based on controlling the local surface charge density on the substrate and component. A corona discharge device will be used to deposit a uniform surface charge on the component, and a charge of opposite polarity onto the substrate target area. The Coulombic force between the component and the oppositely charged target area will attract the component to the target. A corona discharge device utilizes a point electrode at high voltage over a planar ground to cause local ionization of the surrounding gas. The ionized gas molecules are accelerated toward the ground, and deposited on a dielectric surface. Electrophoretic positioning in an electrolyte solution will be used to place parts smaller than 10 micrometers in diameter. The surfaces of the components will adopt a charge in an electrolyte due to the specific absorption of potential determining ions. Small patterned electrodes on the substrate surface will be used to create an electric field and attract the charged parts to the substrate surface. The accuracy of the proposed process will be dictated by the highly controlled Coulombic forces and radiation pressure and not by the positioning errors and vibration of the mechanical placement system. The simultaneous use of these forces will allow the efficient assembly of discreet components and will introduce the exciting possibility of forming new composite materials on the micron scale. %%% Electrophoretic deposition of particulate coatings with no control over microstructure has been used industrially for many years. This research project seeks to use this technique to place micro-components in a specific location on a substrate surface. The use of a focused laser beam in addition to these Coulombic forces will allow more accurate control over the position and orientation of the component. The application of such non-contact techniques offers the potential for vast improvements over traditional mechanical assembly. This technique might have broad impacts in the microelectronics industry. ***