Precise deposition of molten microdrops: the physics of digital microfabrication

Abstract Objects, materials or components may be built up by precise deposition of molten microdrops under controlled thermal conditions. This provides a means of ‘digital microfabrication’, or fabrication of 3D objects microdrop by microdrop under complete computer control much in the same way as 2D hard copy is obtained by ink-jet printing. In this paper we present a study of some basic modes of precise deposition and solidification of molten microdrops. The conditions required for controlled deposition are discussed, and experimental results and theoretical analyses are given for various basic deposition modes. These include columnar (i. e. drop-on-drop) deposition at both low and high frequencies, sweep deposition of continuous beads on flat surfaces, and repeated sweep deposition for buildup of larger objects or materials. The theory provides a means for generalizing our particular experimental results, which were obtained with hard waxes, to other melts. An important parameter in the theory is the solidification angle, that is, the apparent contact angle of the solidified melt. Our study indicates that in microscale deposition this angle appears under some conditions to be a property of the melt material, the target material and the characteristic temperatures involved, independent of the spreading dynamics.