Ashok Sridhar

Inkjet-printing- and electroless-plating- based fabrication of RF circuit structures on high-frequency substrates

In this paper, a method to fabricate radio frequency (RF) circuit structures is described. This method involves inkjet printing of a silver nanoparticle-based ink on a functional substrate material to create the seed track (i.e., the seed layer), onto which copper is subsequently deposited by an electroless plating method, to obtain the desired thickness and conductivity of the RF structures. This process combination was validated by fabricating an S-band filter on a high-frequency substrate and comparing the RF performance of this filter with that of a filter fabricated using the conventional lithography-based method. The adhesion of the circuit structures to the substrate was qualitatively ascertained by the scotch tape test method. The performance of the inkjet-printed–electroless-plated filter was comparable to that of the conventional filter, thus proving the suitability of this novel method for practical RF applications.

Reliable Inkjet-Printed Interconnections on Foil-Type Li-Ion Batteries

Shapeable rechargeable Li-ion batteries are a good option for the power source of system-in-package devices; nevertheless, their size and temperature limitations are a constraint during the fabrication process. Inkjet-printed interconnections on top of the battery are proposed in order to reduce the size and costs of wireless sensor network devices that require the use of Li-ion batteries. The reliability of such interconnections under high-humidity and elevated-temperature conditions is characterized in terms of electrical and adhesion properties; the micro- and macrostructures of the ink are observed in detail. Two silver inks are used to print the interconnections. The resistivity values of printed structures are in the range of 8.6-47.6 μΩ·cm, and all of them pass the reliability tests. The adhesion characteristics are good for Ink A; however, Ink B presents failures under high-humidity conditions. For a good adhesion, a plasma treatment should be performed prior to printing. The electrical performance of the interconnections is not affected by high-humidity and high-temperature conditions. Furthermore, there is no indication of silver migration. It is recommended that the curing temperature of the ink is kept low (<; 155°C) in order to avoid cracks in the ink structure and damages to the batterys packaging foil. The interconnections should be printed before filling the battery to avoid the decomposition of the electrolyte which happens at 80 °C.

Performance of inkjet-printed structures on different substrate materials under high humidity and elevated temperature conditions

Inkjet printing is widely being researched as enabling technology for printed electronics; however, there are scarce publications concerning the reliability of inkjet-printed structures on different substrates. The reliability of such structures under high humidity and high temperature conditions is treated in this work. To do so, the adhesion and resistivity of printed structures on PET, Rogers, PI and FR-4 materials are studied before and after a moisture resistance test. The samples present average resistivity values in the range of 12–106 μΩ-cm and only one specimen of the Rogers sample fails the reliability test. The Rogers sample presents perfect adhesion characteristics, the adhesion can be improved for the rest of the samples, especially for the PI sample. The general performance of inkjet-printed structures on different substrate materials is good.