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The creation of hole, cavity or channel structures in low-temperature cofired ceramics (LTCCs), using different sacrificial volume materials (SVMs) was tested. The main functionality of the SVMs should be: easy application into the holes; protection of holes during lamination; uninhibited lamination between layers; and, during firing should burn out before the pores of the LTCCs close, to leave the empty holes clear of any residue. Five different materials were tested—hydroxyethyl cellulose (HEC) 2 wt%, HEC 5 wt%, agar-agar, gelatin, and commercial carbon paste—and compared to a reference sample where no SVMs were used. In all cases, lamination parameters were minimised in order to preserve the tested hole structures. Matrixes with holes ranging from 158 to 268 µm, with pitches of 573 µm in a green state, were tested. The agar-agar caused ceramic deformation as a result of thermal burst during firing and the lamination between the layers was compromised. The carbon paste was difficult to handle, requiring extra equipment for hole filling and incomplete filling of the larger holes. Traces of carbon paste were left as a landing pad on top of the holes, inhibiting lamination at these areas. The gelatin and the 2 wt% and 5 wt% hydroxyethylcellulose (HEC 2 wt% and HEC 5 wt%) filled all holes completely, and also worked as adhesive-assisted lamination (AAL) materials with excellent lamination between layers. Excellent lamination was also observed in the no-SVM case. Thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) analyses established that, for all SVMs tested, the remaining residue is negligible after firing. As a result, the HEC 2 wt% material was considered ideal for use as an SVM.
Bibliographical noteThis research was funded by The Royal Society, grant number IES\R1\191236 and The APC was funded by MDPI. The laser equipment was funded by Brest Metropole “Fonds de Concours à la Recherche”, by the Finistère department council’s program “Aide aux Programmes de Recherche Emergants” and by Carnot Research funds. The laser equipment used in this work was co-funded by Brest Metropole FCR program, the department of Finistère in their AAPR program, and the Carnot program.
The authors would like to thank two student groups for preparing this work and proposing materials eligible for testing. Julian Kopp and Ali Alkhathami worked on a bibliographical survey and Joanne Khater, Romain Tessier and Mohammed Ez-Zerraq performed preliminary testing of SVM materials. We would also like to thank Philippe Elies at Plateforme d’Imagerie et de Mesures en Microscopie—UFR des Sciences and Techniques at Université de Bretagne Occidentale for performing the SEM-EDX analysis and Bronagh Miller for letting Douglas perform the TGA.
- carbon paste;
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