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 battery's packaging foil. The interconnections should be printed before filling the battery to avoid the decomposition of the electrolyte which happens at 80 °C.