Thick film pastes for nitride ceramics for high power applications

摘要

Aluminum and silicon nitride ceramics show high potent as substrate materials for thick film- / hybridapplications in the field of power electronics and microwave technology. A main advantage of AlN is its veryhigh thermal conductivity. Si_3N_4 has also a thermal conductivity comparable to AlN but higher thermal shockresistance and fracture toughness. Nevertheless, the use of Si_3N_4 in power electronic packages or heaterapplications is not achieved due to the lack of suitable connection technology such as thick film pastes. The mainchallenge for the respective pastes is the adhesion on the substrate. The low thermal expansion (CTE) of about2.8 ppm/K of Si_3N_4 and material interactions with the thick film components must be considered in the pastedevelopment. Therefore, new glasses and glass-ceramic composites are required.Reason development was performed towards AgPd based thick film heater pastes for Si_3N_4., The pastes consistsof AgPd in a 1:1 ratio, an inorganic filler and a glass phase adapted to the CTE of Si_3N_4. By variation of thecontent of inorganic filler and glass content three pastes with a sheet resistivity of 0.1 ohm/sq, 0.8 ohm/sq, and7.9 ohm/sq and temperature coefficient of the resistance (TCR) between -100 and 100 ppm/K were developed.The performance of heater films prepared from these pastes under electric pulse load was studied. An electricalpower of up to 85 W can be applied without a significant change of the resistivity (ΔR/R) of 0.1%. As referencecomparable investigations on AlN were performed with adapted pastes. The film structures were analyzed inFESEM studies.