Inkjet printing is a promising technique for printed micro-electronics due to low cost, customizability and compatibility with large-area, flexible substrates. However, printed line shapes can suffer from bulges at the start of lines and at corner points in 2D line patterns. The printed pattern can be multiple times wider than the designed linewidth. This can severely impact manufacturing accuracy and achievable circuit density. Bulging can be difficult to prevent without changing the ink-substrate-system, the drying conditions or the circuit design, all of which can be undesirable. Here, we demonstrate a novel printing methodology that solves this issue by changing the order in which drops are placed on the substrate. The pattern is split up into segments of three drops where the central drop is printed last. This symmetric printing prevents the unwanted ink flow that causes bulging. Larger bulge-free patterns are created by successively connecting segments. Line formation in both traditional linear printing and our novel segmented and symmetric printing was analyzed to understand and optimize results. The printing of X-, T-, and L-shapes is considerably improved compared with the traditional linear printing methodology.
printing is becoming increasingly prevalent in the manufacturing of goods for different applications. Many of these applications will benefit from the integration of electronics into 3D-printed structures. In this study, we report a fabrication method to convert 3D-printed polyetherimide (PEI) into graphene by exposing it to a scanned laser beam. This laser-induced graphene (LIG) is not only conductive but also has a large gauge factor for mechanical strain sensing. We have achieved a sheet resistance of 0.30 Ω/sq which is 50 times lower than that of previous reports on 3D-printed PEI/PC sheets and the lowest LIG sheet resistance value reported to date on any polymer substrate. This is achieved due to three main factors: large thickness of LIG on a 3D-printed object, maximization of the laser energy per unit area, and improved LIG morphology on 3Dprinted PEI compared with that on commercial PEI.
Printed electronics is an alternative manufacturing paradigm for low-cost and large-area microelectronic devices and systems. Metal nanoparticle (MNP) inks are favorable to print conductors due to their high electrical conductivity. As-printed MNP ink requires sintering to become electrically conductive. High-quality MNP conductors require monitoring and optimization of the sintering process. Traditionally, electrical conductivity is measured to monitor the different sintering stages. This requires destructive probing or fabrication of dedicated test structures, which is challenging for in-line monitoring of high-volume manufacturing. Here, we demonstrate that frequency-domain thermoreflectance (FDTR), an optical pump-probe technique, can be used for process monitoring. Conductive features are inkjet printed with a silver nanoparticle ink. Intense pulsed light (IPL) sintering is used rather than traditional thermal sintering due to its capability of millisecond sintering. Thermal conductivity of IPL sintered features is measured using FDTR, where a frequency-modulated heat flux is applied with a pump laser and the obtained thermal phase of the probe laser is fitted to a thermal model. Thermal conductivity measured from FDTR agrees well with thermal conductivity calculated using Wiedemann-Franz Law from electrical conductivity measurements. By appropriately choosing six FDTR pump frequencies with the highest sensitivity and taking all the selected frequency-vs-phase data points at once, we can measure thermal conductivity in 12 s, a fraction of the traditional measurement time. In this way, the measurement time decreases considerably, and thermoreflectance becomes a suitable characterization technique for high-throughput manufacturing. A Monte Carlo-based prediction was performed to observe the effect of shorter measurement time on phase noise, and a much faster measurement configuration is proposed with an acceptable uncertainty in measurement. Our results demonstrate a simple approach for high-speed non-contact characterization of metal nanoparticle conductors with the combination of high-speed printing and high-speed sintering for low-cost electronics manufacturing.
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