MELTING TEMPERATURES AND THERMAL CONDUCTIVITIES OF POSSIBLE SUBSTRATES FOR THREE-DIMENSIONAL CONDUCTIVE INK JET PRINTING

摘要

The current research project originated from the manufacturing limitations of integrated circuits. In the near-term future, it will not be competitive to use automated machine or hand assembly processes to produce consumer products. It is our contention that such a conceptual process can be rendered obsolete for numerous consumer products. To achieve this, the investigators' goal in ongoing research is to deposit conductive materials onto a multitude of substrates and products using specialized continuous ink-jet (CIJ) print heads. Currently, electrical conducting materials to provide the equivalent traces of a PCB can be directly deposited on 2-D structural components. Research at the University of Pittsburgh also makes it possible to fabricate various electronic components by the same production process as the conductive elements. The focus of this paper, however, is on the thermodynamic and heat transfer properties of potential substrates that will make 3-D circuit printing possible. Three substrate materials were considered: Delrin, epoxy/glass composite, and Butter-Board. To overcome issues of curing temperature and component heat release, the melting/breakdown temperature and thermal conductivity value had to be found for each material. Oven curing tests were conducted over predetermined temperature intervals for 1"x1"x1" cubes of each substrate material. After each curing cycle, the test specimens were examined for discoloration, melting, and volume expansion. The results were then used to specify the design parameters for thermal conductivity testing. A firebrick test block was constructed, and repeatable conductivity tests were completed using a known heat output and experimentally determined temperatures. In comparing the three materials, it was discovered that epoxy/glass composite possesses the highest melting temperature, at between 275°C and 300°C, and a potentially good thermal conductivity of 0.653 W/m*K. Butter-Board, however, had the lowest of the thermal conductivity values of 0.416 W/m*K, but also exhibited a lower breakdown temperature. Of the three materials, the epoxy/glass composite is the most promising given the current curing temperature requirements of the thermally conductive inks. Future research directions could include investigation of the operational thermal conductivity of the chosen substrate materials, and a comparison of the experimental values with those predicted by finite element modeling.