Inkjet printed large-area flexible circuits: a simple methodology for optimizing the printing quality

Abstract

In this work, a simple methodology was developed to enhance the patterning resolution of inkjet printing, involving process optimization as well as substrate modification and treatment. The line width of the inkjet-printed silver lines was successfully reduced to 1/3 of the original value using this methodology. Large-area flexible circuits with delicate patterns and good morphology were thus fabricated. The resultant flexible circuits showed excellent electrical conductivity as low as 4.5 Ω/□ and strong tolerance to mechanical bending. The simple methodology is also applicable to substrates with various wettability, which suggests a general strategy to enhance the printing quality of inkjet printing for manufacturing high-performance large-area flexible electronics.

Laser‐Induced Forward Transfer: A Digital Approach for Printing Devices on Regular Paper

“…On the one hand, we can notice how the multiple‐printing approach leads to a dramatic drop in sheet resistance from around 500–700 mΩ □ −1 at a thickness of 2 µm to 25 mΩ □ −1 at a thickness of 8 µm. These values are much smaller than those commonly obtained via IJP (0.2–4.5 Ω □ −1 ), [ 5,6,46–48 ] and of the same order as those typical of SP, where sheet resistances of 15–70 mΩ □ −1 are usually achieved. [ 5,44–46 ] On the other hand, as the number of prints increases, the points gather along the same trend with no apparent difference between substrates.…”

“…Although lines at 30 µJ were narrower than those at 40 µJ, we considered that printing at 40 µJ was more convenient; 30 µJ is a pulse energy close to the transfer threshold, which can easily result in irregularities and defects due to the typical instabilities of lasers, as it is clear from the neck apparent in the line printed at 30 µJ on c‐paper (red arrow in Figure 2a). The line widths obtained in those optimum conditions, around 200 µm, are larger than the minimum features typical of IJP, [ 6,48,54 ] but of the same order as the ones achieved with SP. [ 44,45 ] This makes these results acceptable in a broad range of applications.…”

“…The thickness and sheet resistance of the lines (2.3 µm and 550 mΩ □ −1 , respectively) are substantially better than those typically obtained with IJP (around 0.3–1.0 µm and 1 Ω □ −1 ). [ 6,48,58 ] Nonetheless, comparing them with the high aspect‐ratio and highly conductive lines characteristic of SP technology, lines are still thin and resistive. [ 5,44–46 ] From the obtained sheet resistance, resistivity is estimated to be around 130 µΩ cm, clearly above the nominal value (≈37.5 µΩ cm).…”

“…[ 4 ] Nowadays, though, PE is aiming for flexible devices and those PCBs are being replaced by polymeric substrates such as polyethylene terephthalate polyethylene naphthalate, or polyimide. [ 5–7 ] These plastic substrates fulfill many of the PE advantages since they are organic, low‐cost, and light‐weight, besides being flexible. However, in the last years paper, a substrate widely used in the graphics industry has been investigated as a potential alternative for PE.…”

“…[ 19,20 ] These rheological properties are compatible with high solid contents, and in the case of conductive inks, they can result in the fabrication of interconnects with sheet resistances as low as 50 mΩ □ −1 , [ 5,44–46 ] much lower than those resulting from IJP (around 1 Ω □ −1 ). [ 5,6,46–48 ] All of this makes LIFT an interesting candidate as the digital alternative aimed at in the preceding paragraph.…”