LTCC technology is based on sintering of multi-layered thick-film sheets (50-250 µm) or so-called green tapes, which are screen-printed with thick-film pastes such as conductors, resistors, etc. The terms low temperature and co-fired originate from the relatively low sintering temperatures (<900°C) compared to conventional ceramics and simultaneous firing of tapes together with screen-printed thick-film material, respectively. These characteristics are achieved by improving the tapes’ properties and adopting the physical and chemical thick-film properties to that of tape, whilst retaining their functional properties. Evidently, mastering the technology requires fundamental understanding of the compatibility issues between the tape and the pastes and the effect of processing conditions on this relation. In this perspective, this paper aims to point the origin and extent of chemical and physical interactions between co-fired materials and explain the use of carbon-black sacrificial paste to fabricate 3-D micro-fluidic devices without sagging of the channel walls.