Thin alumina wafer fabrication by vat photopolymerisation based additive manufacturing

Abstract

In VAT Photopolymerization (VP), a ceramic slurry is cured layer by layer under light (200–760 nm) to fabricate ceramic parts from a 3D CAD model. Lithography-based Ceramic Manufacturing (LCM) a VP process presents a significant advancement over traditional tape-casting methods in the production of thin ceramic substrates. While tape casting is limited in its ability to produce substrates in a single step, with thickness in the range of 100s of microns, typically necessitating the lamination of multiple tapes to achieve greater thicknesses. LCM overcomes this limitation, and it offers precise control over layer thicknesses, ranging from 10 to 100 microns, and is capable of directly printing substrates in the range of several hundred microns. This capability not only streamlines the manufacturing process but also ensures more consistent quality and greater flexibility in substrate thickness, making LCM a superior technique for producing thin ceramic substrates. However, the main challenge in LCM is to make these substrates without any warpage. This study aims to nail down the root cause of the warpage by employing various characterization techniques (including FTIR, nano-indentation, SEM and TGA), and by identifying factors that contribute to the warpage. It is observed that layer-wise fabrication leads to a curing gradient owing to the multiple exposures of already cured layers, causing the final layers to cure less than the initial ones. Due to this, mechanical properties such as hardness and modulus are significantly different for the initial and final layers. In thin parts (<300 microns), a significant proportion of under-cured layers contribute to pronounced warpage. To make a warpage-free substrate, a post-curing strategy is proposed and examined. It is concluded that 80 % of the warpage can be reduced by the proposed post-curing method.