Inkjet Printing as Technology for In-Situ Blending of Thick-Film Resistor Inks

Abstract

The integration of passive components directly into circuit boards is an efficient alternative to surface mounted devices. Digital printing methods are more and more emerging technologies for the fabrication of microelectronic circuits. Inkjet printing is a technology for the deposition of a variety of particles with the unique selling proposition of in-situ ink blending. 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 opportunities of in-situ blending in inkjet printing of thick-film resistors. In a first step, the different options of ink blending are analyzed theoretically. In order to have a basis for further calculations five compositions with a wide resistivity range are printed purely. Afterwards the printed resistors are passed through a post-fire process and the electrical properties are recorded. Reliability and long term stability in drop formation are fundamental for production process. In a second step, the different options of ink blending are analyzed. The five compositions are blended to four combinations of neighbouring inks and are printed and blended with two inkjet printheads. The effect of blending is characterized towards the change in electrical behaviour and the different blending techniques are compared. Additionally, the opportunity of layer thickness variations is investigated and its influence is analyzed. Further, the influences of printing conditions on morphology and resistivity are discussed.