Electrical Performance Characterization of an Inkjet-Printed Flexible Circuit in a Mobile Application

Consumer electronic devices tend to become ever smaller and lighter, and one way to reduce their size and weight is to use flexible circuit boards in, e.g., mobile phones, cameras, and laptop computers. Usually, flexible circuits are used in a device body to reduce device size and weight, to place a circuit on a nonflat surface, or to add a movable property in the device structure. Flexible circuits can be wrapped around the device body in a stationary application or to provide a hinge or a joint between moving parts in a dynamic application. There are many reasons for seeking new manufacturing technologies; to produce flexible circuits with cost-efficient materials, environmental values, and fewer manufacturing steps being some of the preferred ones. Inkjet printing is an emerging technology for manufacturing flexible electronics and the number of materials that can be deposited by inkjet is constantly expanding. Fabricating printed circuit boards by inkjet technology differs from the common manufacturing methods in some ways. Because inkjet technology is an additive process, minimal amounts of material is wasted during fabrication, and as no material is taken away, all deposited material goes to create a circuit. In large-scale manufacturing, this could have a positive environmental impact. In addition, digital control of the printing process enables easy and fast modification of circuit board layout files, which is beneficial for prototyping and small-volume manufacturing. This paper focuses on the applicability of inkjet technology for manufacturing flexible circuits. As a demonstrator device, we use a flexible circuit working as a user interface module in a mobile phone, and we report on its design and fabrication and the testing and measurement of its electrical performance. Comparison of electromagnetic compatibility/electrostatic discharge and antenna tests of the original flexible circuit and the inkjet-printed prototype shows that the electrical performance of the inkjet-printed circuit is similar or close to that of the original product.