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.