Inkjet Printing of Thick-Film Resistors

Abstract

The integration of passive components directly into circuit board is an efficient alternative to surface mounted devices. Inkjet printing is the emerging technology for the deposition of a variety of particles and therefore for digital fabrication of microelectronic circuits. Resistors are one of the most frequently required passive components in electronic circuits. In LTCC-technology the integration and additionally the embedding of resistors promises new applications. Integrated resistors are usually screen printed. Inkjet printing has several advantages to compete seriously with screen printing as production method. This study investigates the possibilities and reliability of inkjet printing of thick-film resistors. In a first step, different resistive compositions are characterised towards compatibility with a commercial inkjet print head. The reliability and long term stability in drop formation are fundamental for production process. Further on, the interaction between ink and substrate has to be taken into account to reach the desired morphology. In a second step, the advantages of using inkjet for printing resistors are shown. A measure of ink amount is introduced for exact dosing of the ink. Afterwards, compositions with a wide resistivity range are printed with different print heads. The printed resistors are further passed alternatively through a post-fire or through a co-fire process. The effect of variations in particle composition and ink amount are characterized towards the change in electrical behaviour. Further, the influences of printing conditions on morphology and resistivity are discussed.