Development and optimization of a Low Temperature Co-fired Ceramic suspension for Mask-Image-Projection-based Stereolithography

Abstract

This dissertation has the main goal of developing ceramic materials for Mask-Image- Projection-based Stereolithography (MIP-SLA) technology, focused on electronic applications. To accomplish this aim, a low temperature co-fired ceramic (LTCC) material was selected, mainly used for radio frequency applications. Moreover, the proof of concept of AM technology hybridization and multi-materials printing is also demonstrated, opening the door to new researchers in the field of 3D-2D printing electronic devices, from both the material and technology perspectives.

To successfully achieve the main goal, the different steps of the whole process were successfully achieved, i.e, formulation of a LTCC photocurable suspension, its printability by MIP-SLA technology, and the post-thermal treatment of debinding and sintering.

The photocurable LTCC suspension consists of ceramic particles dispersed in a suitable photocurable resin, which must polymerize in the visible light range, trapping the ceramic particles. The challenge of the development and optimization of a LTCC photocurable suspension for MIP-SLA with the appropriate rheological and photocurable behavior is accomplished in this work.

The printed piece contains the polymeric part, which must be removed (debinding) and then sintered for the densification of the final ceramic piece. This is the most difficult and time- consuming step of the whole process. The so-called debinding is one of the most challenging steps of the SLA-based technology of ceramic materials. In this sense, a detailed study of the debinding process is carried out for a deeper understanding of the degradation of the resin during the thermal debinding. For this to happen, the optimization of the temperature rate and used atmosphere during the thermal treatment is also presented in this work. In fact, the analysis and understanding of thermal treatment parameters and their repercussion on the final results is the key to successfully achieving the main goal, which is to obtain final ceramic pieces without defects.

The limits of the MIP-SLA printing process are presented, analyzing the resolution, fidelity of pattern transfer, and accuracy of the printing process using the optimized LTCC suspension. The involved phenomena during the photopolymerization such as light scattering, non- uniformities of the light projection along the building platform and shrinkage during the polymerization, are analyzed and optimized for a fruitful printing process.

The greatest achievement of this work is the possibility of printing complex geometry with high resolution with a LTCC material, which has never been demonstrated before in the field of additive manufacturing. This is the beginning of new breakthroughs in multimaterial printing for electronic applications.

El objetivo principal de la tesis doctoral es el desarrollo y optimización de una suspensión cerámica fotocurable para la fabricación aditiva mediante la tecnología Mask-Image- Projection-Based Stereolithography (MIP-SLA), y la obtención de piezas cerámicas finales. Durante el proceso de impresión, el fotopolímero reacciona con la luz proyectada atrapando las partículas cerámicas en su matriz, lo cual posibilita la impresión de piezas cerámicas en verde (matriz polimérica y partículas cerámicas). Después del proceso de impresión es necesario eliminar la parte orgánica y realizar la sinterización de la pieza para la obtención de la pieza cerámica final. El material cerámico seleccionado para la formulación de la suspensión fotocurables ha sido un cerámico de baja temperatura de co-sinterización (Low Temperature Co-fired Ceramics, LTCC), para aplicaciones electrónicas.

Para el desarrollo de la suspensión fotocurable de LTCC se ha teniendo en cuenta su comportamiento reológico y sus propiedades de fotopolimerización adecuadas a la tecnología de impresión. Una vez optimizada la suspensión cerámica, se han analizado el proceso de impresión y se ha optimizado el ciclo térmico, tanto de la etapa de quemado del polímero (debinding) como del proceso de sinterización para la densificación de la pieza cerámica final.

Se ha logrado una formulación adecuada a la tecnología, la cual ha permitido la impresión de piezas en verde y posterior debinding y sinterizado de las piezas con geometrías complejas. Se demuestra también la posibilidad de impresión de piezas cerámicas con circuitos impresos de plata, lo cual abre camino para el desarrollo de la impresión híbrida de multimateriales.