Abstract
Offset lithographic printed flexible antenna substrate boards and electrodes have attracted much attention recently due to the boost of flexible electronics. Unmanned quality inspection of these printed substrate boards and electrodes demands high-speed, large-scale and nondestructive methods, which is highly desired for manufacturing industries. The work here demonstrates two kinds of millimeter (mm)-wave imaging technologies for the quality (surface uniformity and functionality parameters) inspection of printed silver substrates and electrodes on paper and thin polyethylene film, respectively. One technology is a mm-wave line scanner system and the other is a terahertz-time domain spectroscopy-based charge-coupled device (CCD) imaging system. The former shows the ability of detecting transmitted mm-wave amplitude signals only; its detection is fast in a second time scale and the system shows great potential for the inspection of large-area printed surface uniformity. The latter technology achieves high spatial resolution images of up to hundreds of micrometers at the cost of increased inspection time, in a time scale of tens of seconds. With the exception of absorption rate information, the latter technology offers additional phase information, which can be used to work out 2D permittivity distribution. Moreover, its uniformity is vital for the antenna performance. Additionally, the results demonstrate that compression rolling treatment significantly improves the uniformity of printed silver surfaces and enhances the substrate’s permittivity values.
Highlights
In recent years, flexible and stretchable electronics based on modern printing technologies have developed at an unprecedented rate and are involved in various applications, such as antennas for wearable wireless communications [1,2] and bio-molecular monitors [3]
Inspired by the work of Arapov et al [25], in which rolling compression was used to improve the conductivity of printed binder-based graphene inks, one of the printed silver samples on Teslin style paper substrates was compressed by a mini roller mill at room temperature and the other was not
The images acquired from the 100 GHz line scanner are shown in Figure 4, where the 33 × 67 pixels
Summary
Flexible and stretchable electronics based on modern printing technologies have developed at an unprecedented rate and are involved in various applications, such as antennas for wearable wireless communications [1,2] and bio-molecular monitors [3]. At the heart of this technology trend, flexible substrate boards and electrodes are vital components for the design and performance of such antennas. Offset lithographic printing is an established high-volume, high-speed printing technique and it has been developed to pattern a wide range of conductive materials on diverse substrates, such as flexible papers and polymers, to realize low-cost, large-area and multifunctional electronic performances [4,5,6,7,8]. It is essential for manufacturers to Electronics 2019, 8, 674; doi:10.3390/electronics8060674 www.mdpi.com/journal/electronics
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