Influence of Photo-initiator concentration on photoactivation of composites prepared with LTCC and silver powders for DLP based 3D printing and their characterization

Abstract

DLP (Digital Light Processing) based 3D (three dimensional) printing had been a widely used additive manufacturing technique with its broad aspects in rapid prototyping, packaging, biomedical applications, PCB etc due to its high resolution and reliability. Since, drive for miniaturization in electronic industry had been increasing; the need of additive manufacturing becomes better and reliable solution for fabrication of electronic device. In this study, we attempt to adopt LTCC (Low Temperature co-fired ceramic) technology with DLP based additive manufacturing machine to reduce lead time, running cost and investment cost while increasing production volume to levels suited for SMEs. This work reports our 3D Printing trials with composites using LTCC/dielectric and silver powder. Initial trials using the commercially available resins showed residue after firing the package which indicates its unsuitability for electronic packaging applications. Hence, the new resin was formulated by varying the Photo-initiator 2,4,6 -trimethyl benzoyl diphenyl phosphine oxide (TPO) Concentration. Photoresist was prepared by mixing the Photo-initiator (1 to 3wt %), Surfactant (2.5wt %) and diacrylate based monomer (96.5 -94.5wt%) in planetary mixer and the composition was optimised. Curing parameters for the unloaded resin such as exposure time, Intensity etc were varied accordingly and optimised. The photoresist and the printed samples were analysed for their viscosity, optical inspection, NMR, FTIR. Printing trials were done by preparing composites with Dielectric (LTCC) and conducting material (Silver) using above prepared photopolymer in 50:50 ratio. Effect of variation in the exposure time and intensity on the loading of functional material for curing has also been studied. Printed patterns were then sintered at about 875°C with standard LTCC firing cycle. No residue was observed after the sintering cycle. Trials using composites with different material were also tried. Characterisation of these composites and printed packages are reported. For 50% loading of functional material shrinkage of about 29% was observed. Effect of solid loading on shrinkage of sintered sample were also studied and reported.