Development of Reciprocating Inkjet System for Printed Electronic Devices

Abstract

Reciprocating inkjet system (RIS) is an additive manufacturing technology in which drops are formed on a substrate by extruding liquid ink from ink chamber via the reciprocating movement of a micro needle. Depending on the diameter of the micro needle, RIS is capable of a small amount drop (approx. 1 pl) with a wide range of viscosity (1~300,000mPa.s) levels, unlike a piezoelectric inkjet printing which can perform only 1-15mPa.s. Also, RIS is capable of printing inks with various drop sizes (10µm to 1000µm). This wide range of printable ink viscosity is attributed to both the mechanical extrusion mechanism adopted in the method, and the size controllability associated with the micro-needle diameter. Furthermore, the printing frequency of RIS is typically limited to 1-20 Hz which is considerably lower than that of conventional inkjet printing, (1-10kHz) because the micro needle must move in a reciprocating manner through mechanical movement. Although the slow frequency is at times problematic for some applications, the controllability of the high-resolution drop sizes is beneficial in applications such as the repair of open circuits, solder paste dropping for interconnections and all kinds of substrates. This paper, therefore, focuses on the development of RIS wherein printing process parameters (needle diameter, needle moving velocity, distance from substrate, and reciprocating frequency of inkjet head) are optimized. Moreover, the RIS is utilized to print fine conductive patterns on a flexible polyethylene terephthalate (PET) substrate for the fabrication of printed sensor which are analyzed by optical characterization. The results are then documented and discussed along with the conclusions drawn.