Quality Mapping of Offset Lithographic Printed Antenna Substrates and Electrodes by Millimeter-Wave Imaging

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.

Towards in-situ quality control of conductive printable electronics: a review of possible pathways

“…Even with a 3 mm spatial resolution of the detector, it was possible to identify conductive and non-conductive areas. This approach introduces the possibility of simultaneously obtaining dielectric and spatial information on samples [117,118].…”

“…Zhang et al [117] inspected the surface uniformity of printed inks using THz imaging and the system resolution. Figures 29(a areas, which correspond to silver electrodes and PET, respectively.…”

“…Characteristics AODE [96] LED [102] Non-linear OM [71] THz imaging [117] ECT [93,104] ST [106,107] THz-TDS [83,114] SAXS [99] Thickness extension of this capability is the implementation of artificial intelligence (AI) assistance, in particular, machine learning algorithms (MLAs) that can selflearn a production process by comparing the results obtained with a defined threshold for electrical performance and/or defect size. This type of machine learning has already been used in a similar way for pass and fail cases [122].…”

Terahertz Characterization of Lead-Free Dielectrics for Different Applications

“…Compared with conventional Fourier transform infrared spectroscopy (FTIR), which offers amplitude information only, coherent-based THz instruments have many advantages as they can offer both amplitude and phase information simultaneously. From the measured spectra, the complex refractive index, complex permittivity, permeability, and electrical conductivity can be extracted. , …”

“…From the measured spectra, the complex refractive index, complex permittivity, permeability, and electrical conductivity can be extracted. 6,7 There are many different methods for performing THz coherent spectroscopy, such as a vector network analyzer, 8 a quantum cascade laser, 9 a backward wave oscillator, 10 and a free-electron laser. The most widely and conveniently used broad-band coherent system is THz time-domain spectroscopy (THz-TDS), which has been intensively studied and upgraded since the early 1980s.…”