3D Printing of structures with embedded circuit boards using novel holographic optics

摘要

This work describes the fabrication of silver paste conductive tracks using laser direct writing technology, where the substrate is also generated by a laser melting process using low density polyethylene (LDPE). This has enabled the direct writing of 3D small circuit boards with discrete electronic components included into the writing process. The conventional laser plastic sintering technology mainly uses Nylon-12, which generates a non-functional product with high porosity. Nylon and LDPE are fun dament ally insulators and as such don't conduct the heat generated from focused beam well into the substrate. Therefore these materials have traditionally formed sintered powders products. The step forward reported here is to reverse engineer the correct heat flux distribution to predict the correct melt flow conditions. Meanwhile, some researchers have also undertaken laser curing of conductive pastes/inks cases with the Gaussian beam and they exhibit an obvious laser — induced degradation in the central region because of the nature of Gaussian beam. In this project, the laser beam is reconstructed by Holographic Optical Elements (HOE) to a desirable beam shape; with the aid of a self-designed Computational fluid dynamics (CFD) model which describes the workpiece conditions at different input beam shapes. The LDPE substrate is made from powder form, to enable a layer-by-layer additive manufacturing process. The silver paste is then deposited on it, which is followed by selective laser scanning. After curing the mechanical properties of the substrate, the resistivity of the conductive track are measured. Surface profilometer and Field emission gun scanning electron microscopy (FEG-SEM) are selected to investigate the product topography and microstructure, respectively. Comparisons between the HOE modified laser beam and standard Gaussian beam are made in both modelling and experimental parts. The results indicates that by using the designed beams, one can cont- ol the profile of the heat affected zone and make consolidated plastic of a useful engin eering nature; meanwhile, the flow in side the paste is stable when it is cured upon the correct energy distribution, therefore the electrical resistivity is reduced.