Hot gas stream application in micro-bonding technique

Abstract

ABSTRACT This paper presents a new concept for bonding micro-parts with dimensions in the range of 50 µm to 300 µm. Two different kinds of adhesives - polyurethane adhesive foil and hot melt glue - were applied to a basic substrate by different techniques. The focused and concentrated hot gas stream softened glue which had been applied in a solid state. Micro-parts were then embossed in the softened glue, or covered and shielded by it. In this way, a rigid and compact bond was obtained after cooling. For the positioning of micro- parts (optical fibers), it has been necessary to manufacture adequate V-grooves. Finite el ement analyses using the ANSYS TM program package were perfor med in order to evaluate parameters which govern the heat transfer to the adhesive and substrate respectively. Experimental results are in good agreement with results obtained by the numerical simulations. The advantages of this new approach are small system size, low capital costs, simple usage, applicability to many material combinations, easy integration into existing production lines, etc. Keywords: micro-bonding, hot gas stream, adhesives, V-grooves 1. INTRODUCTION New technological trends dictate needs for smaller and constantly more complex micro-systems. The only acceptable respond to these needs are hybrid micro-o pto-e lectrom echanical systems (MOEMS). Hybrid MOEMS consist of micro-components with different functions (mechanic, electronic, optical, fluidic, etc.), often made of different materials in different processes. Micro-components must be combined in such a way as to allow their operation without hindrances. Because of this, assembly and packaging play very impor tant role in the MO EMS production chain. On the other side, it is well known that assembly and packaging comprise a considerable 80% of total production costs [1]. This fact leaves a lot of room for various improvements, especially with regard to bonding. The bonding process with an intermediate layer of adhesive will be described in this paper. Although the main function of adhesives is bonding different layers together, in the literature, some other applications are mentioned. In micro-optical systems, optical fibers or even micro-lenses can be made of adhesives and in flip chip configurations, electrically conductive adhesives are used to form electrical connections between components [2]. In micro-fluidic systems, J. Simon, et al. have described th e use of room-temperature-curing UV epoxy adhesive as micro-gaskets in an array of liquid-filled micro-relays [3]. The mostly used adhesives in MEMS fall into the group of UV-curable adhesives. The curing time of UV-cured adhesive is usually between a few seconds and a few hours, depending on the chemical properties of the adhesive and its function. It is possible to cure the UV-adhesives at the room temperature, but this process takes a long time (at least 24 hours). Using a hot gas stream for softening or melting an adhesive is a well-known principle in the macro-world, implemented mainly for joining thermoplastics. In the research presented in this paper, this concept is employed for joining micro-components into complex a nd sophisticate structures. For example, optical fibers have been positioned into mechanically machined V-grooves an d firmly adhered to a basic substrate.