AC-pulse modulated electrohydrodynamic jet printing and electroless copper deposition for conductive microscale patterning on flexible insulating substrates

Abstract

This paper presents a novel micro-manufacturing method for fabrication of electrical features and patterns on highly insulating substrates and flexible substrates based on high-resolution AC-pulse modulated electrohydrodynamic jet (e-jet) printing of silver nanoink as seed layer followed by electroless copper deposition. Traditional ink jet printing method is limited in printing resolution which is determined by dimension of printing nozzle and dimension of droplets. Traditional e-jet printing has the disadvantage of residual charge problem especially for highly insulating substrates which cannot dredge remained charge of printed droplets, resulting in distorted electrostatic field and low printing controllability. Meanwhile, for printing of liquid phase ink, feature resolution contradicts with the required thickness, which is a key factor of conductivity of printed patterns. In this paper, a novel ACmodulated e-jet printing technique is applied to neutralize charges on substrates by switching polarity of consequent droplets for direct printing of high-resolution conductive silver patterns on insulating substrates. Electroless copper deposition is introduced in the fabrication process to solve the thickness problem of the resulting features. Variables of fabrication process, including amplitude and frequency of AC-pulsed voltage, plotting speed, curing temperature, number of layers, concentration of solution for copper growth, were identified to achieve reliable and conductive printed patterns. Sub-20µm silver tracks with resistivity about 3.16 times of bulk silver were successfully fabricated. We demonstrated that ac-pulse modulated e-jet printing followed by electroless copper deposition can produce high resolution conductive patterns with improved thickness on insulating substrates and flexible substrates, which can be applied to direct printing and micro scale patterning for flexible electronics and wearable devices applications.

Direct Printing and Electrical Characterization of Conductive Micro-Silver Tracks by Alternating Current-Pulse Modulated Electrohydrodynamic Jet Printing

“…Detailed characterization of these parameters for droplet formation was presented in our earlier works in Refs. [42][43][44].…”

The study of electrohydrodynamic printing by numerical simulation

“…Direct writing techniques show their great potential in for fabrication of micro and nano-structures with low cost, simplified procedures, low-pollution [1]. Among the direct writing methods (Ink jet printing, fused deposition modeling, stereo lithography apparatus, etc.…”

Precise Electrohydrodynamic Direct-Write Micro-Droplets Based on a Designed Sinusoidal High-Voltage AC Power

“…The AC electric field can reduce the accumulation of the charges on the nozzle by neutralizing the electric polarity, which can help to suppress the charge repulsion interferences under the DC electric field and promote jet stability and deposition precision [13][14][15]. Under the AC electric field, the free charges reciprocate along the jet and the polarity of the electric field force on the jet changes periodically, then micro/nano droplets can be obtained at a corresponding frequency [16,17]. Wei et al [18] applied a new high-resolution AC-pulse modulated electrohydrodynamic (EHD) jet printing technology to obtain the drop-on-demand fabrication.…”