Super Inkjet Printed Redistribution Layer for a MEMS Device
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Printed electronics (PE) is a novel area of electronics manufacturing where functional inks and suitable ink deposition devices, such as inkjet or roll-to-roll equipment, are used to create electrically functional features. A lion’s share of current applications are in the field of low-cost, large-area electronics where the printing technologies have a significant advantage over the conventional methods due to faster processing speed and higher process flexibility. Since this has been seen as the holy grail of printed electronics, little research has been done on the field of small-area applications such as microelectronics packaging. However, with recent developments in high resolution printing, this application area should be within the reach of printing technologies as well. The main purpose of this study is to find out if the production methods developed for printed electronics could be used in the packaging of microelectromechanical systems (MEMS). Specifically, the aim is to print a high density redistribution layer (RDL) of a MEMS device package with a state of the art electrohydrodynamic (EHD) inkjet printer. By using inkjet technology instead of the current method, electrochemical plating, the costs and environmental impact of the fabrication process could be reduced significantly. This is based on the fact that inkjet printing is an additive and electrochemical plating a subtractive manufacturing method. Subtracting material leads to larger amount of wasted resources and additionally, the chemicals used to etch the copper plating are environmentally unfriendly. Additive nature of the inkjet technology increases the flexibility of production process by making the prototyping easier and enabling shorter exchange-of-die times. Applicability of EHD printing in RDL manufacturing is demonstrated by printing high density interdigital and meander structures. The secondary purpose of the thesis is to gain knowledge about operation of an EHD printer. Since this is a new development in the field of printed electronics, the existing literature is quite limited. Therefore, in addition to short literature study, statistical tools are used to look for significant parameters affecting the printing process. This analysis results in statistical models which relate the printing parameters to conductor width, thickness and sheet resistance.