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In this work, the printing and sintering characteristics of pattern area and via-hole section were investigated. To analyze the printing characteristics depending on the rheology of ink, Cu micro/Ag nano-hybrid inks (Cu/Ag hybrid inks) were prepared by varying the amount of epoxy, and the fabricated inks were printed on via-hole formed substrates. The printed Cu/Ag hybrid ink films were subsequently sintered by an intense pulsed light (IPL) sintering method. Various IPL sintering parameters including irradiation energy and pulse number were employed to enhance the sintering characteristics of pattern area and via-hole section. The sintered Cu/Ag hybrid ink films were characterized using scanning electron microscopy and X-ray photoelectron spectroscopy. The detailed sintering mechanism of Cu/Ag hybrid ink inside the via-hole section was monitored in real-time by in situ resistance monitoring. As a result, the Cu/Ag hybrid ink with the optimal ratio of epoxy content (0.56 wt%) showed good printability of pattern area and via-hole section. In addition, the proposed multi-pulse IPL sintering conditions (irradiation energy: 7 J/cm2, pulse duration: 1 ms, off-time: 9 ms, pulse number: 20) exhibited low resistivity (pattern area: 5.12 μΩ cm, via-hole section: 7.79 μΩ cm) and a 5B adhesion strength level. • Cu micro/Ag nano-hybrid inks were printed and intense pulsed light (IPL) sintered. • Ink contents were optimized for printing of pattern area and via-hole section. • Multi-pulse IPL sintering was introduced to improve sintering characteristics. • Optimally IPL sintered case exhibited superior sintering characteristics. [ABSTRACT FROM AUTHOR]

Abstract In this work, intense pulsed light (IPL) sintering process was investigated with vacuum stretching and heating of the polymer substrate for warpage free printed electronics circuit. The IPL irradiation energy and substrate heating temperature were optimized to obtain high electrical conductivity, high adhesion strength, and little warpage of printed Cu electrodes pattern on the polyimide (PI) substrate. Scanning electron microscopy and x-ray diffraction were conducted to characterize microstructure and transformation crystal phase of the IPL sintered Cu nanoparticle (NP)/microparticle (MP)-ink film. The resistivity of IPL sintered Cu NP/MP-ink films was measured using the four-point probe method and profilometer. In order to monitor IPL sintering process, in-situ resistance and temperature monitoring of Cu NP/MP-ink were conducted. Also, a transient heat transfer analysis was performed using finite-element analysis software to predict temperature gradients of Cu NP/MP-ink and polymer substrate during IPL light sintering process. As a result, the optimal IPL light sintered Cu NP/MP-ink film (vacuum applied, 150 °C heating, and irradiation energy: 3.5 J/cm2) had a low resistivity 6.94 μΩ·cm and 5 B level of adhesion strength with almost no warpage of PI substrate. Highlights • Cu nano/micro particle (NP/MP)-ink was intense pulsed light (IPL) sintered. • We employed the substrate vacuum holding and heating during IPL sintering. • 3.5 J/cm2 with 150 °C heating was determined as optimum conditions. • The sintered Cu NP/MP-ink showed the lowest resistivity with 5B adhesion level. • The Cu NP/MP-ink was sintered with almost no warpage of polymer substrate. [ABSTRACT FROM AUTHOR]

Abstract In this study, the effect of rheological properties of Cu nano/micro (NP/MP)-inks with various amounts of dispersant on the print-ability and sinter-ability for flash light sintering was investigated. The rheological properties such as viscosity, viscoelasticity and thixotropic index of Cu NP/MP-inks were measured using a rheometer. The fabricated Cu NP/MP-inks were printed on polyimide substrate using a screen printing method. The 3D profile of printed Cu NP/MP-ink pattern was measured using surface profiler. In order to sinter the printed Cu NP/MP-inks, flash light sintering technique was employed. The flash light irradiation conditions (pulse power, pulse number, on-time, and off-time) were optimized to obtain the high sintering characteristic of Cu NP/MP-inks. In order to characterize the microstructures and transformation crystal phase of the sintered Cu NP/MP-inks, scanning electron microscopy, focused ion-beam and X-ray diffraction analysis were performed. From the results, the optimal sintered Cu NP/MP-ink film had a 6.16 μΩ·cm resistivity and 5B level of adhesion strength. Highlights • We investigated the effect of dispersant on print-ability and sinter-ability. • 2.6 wt% of dispersant enhanced the printing uniformity and aspect ratio. • Enhanced print-ability improved the flash light sinter-ability. • The sintered Cu film showed the low resistivity and high adhesion strength. [ABSTRACT FROM AUTHOR]

Transparent conducting electrodes (TCEs) are fabricated through the flash light sintering of reverse-offset printed Ag mesh patterns. Interestingly, the narrower printing lines require a higher flash light energy to obtain an equivalent sheet resistance even if the same Ag nanoparticle ink is used. The microstructural development of sintered Ag nanoparticles is also retarded with the decrease of line width after the same flash light sintering. The temperature calculation in the Ag mesh patterns clearly reveals that heat dissipation is affected by the print dimension. To improve the performance of Ag mesh TCEs with 3 μm wide lines, a preheating step comprised of multi-pulses is inserted before a main flash light sintering. The multi-pulsed flash light sintering is effective in decreasing the sample temperature and in removing the substrate damages or microstructural defects. As a result, the flash light-sintered Ag mesh TCEs shows a sheet resistance of 27 Ω/□ and an optical transmittance of 84.7% including an optical transmittance of substrate. [ABSTRACT FROM AUTHOR]

A copper complex ion ink (including copper nanoparticles, a copper precursor and a silane coupling agent) was synthesized to enhance the adhesion between the copper pattern and a polyimide (PI) substrate. Oxygen plasma treatment was performed on the polyimide substrate to initiate a chemical reaction between the complex ion ink and the polyimide. Then, a two-step flash light sintering method (consisting of preheating and main sintering) was used to sinter the copper complex ion ink. The copper complex ion patterns were characterized as a function of the weight fraction of silane coupling agent using scanning electron microscopy (SEM), a four-point probe method and adhesion testing. In addition, a bending fatigue test was performed to evaluate the reliability of the conductive copper pattern under cyclic bending. The copper pattern fabricated with copper complex ion ink containing 3 wt% silane coupling agent exhibited the highest adhesion level (5B), the lowest resistivity (7.6 μΩ·cm) and a low resistance change (18%) after the bending fatigue test. The two-step sintering method used to enhance the adhesion between the copper complex ion ink and polyimide substrate was also studied using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). [ABSTRACT FROM AUTHOR]