Copper Pillar Bumps on Acoustic Wave Components

In this study, we give an evolutional overview of packaging solutions for acoustic wave components, for the last two decades. Nowadays, acoustic wave components are essential for mobile data communication. Due to the need of a cavity above the micro-acoustic structures and steadily increasing requirements on electrical performance and size reduction, packaging has experienced a rapid progress. To achieve further miniaturization of acoustic wave components, we present a manufacturing method for the replacement of solder balls by copper pillar bumps as interconnects on one of the thinnest commercially available package, namely, TFAP™ (Thin Film Acoustic Package) of RF360. The round copper pillar bumps consist of copper, nickel and a tin cap. Spin coating and photolithography followed by electroplating is used to create copper pillar bumps on wafer level. Resist and seed layer are removed in a batch process. The tin is reflowed in formic acid atmosphere to form the solder cap. First copper pillars are cut with focused ion beam to examine the cross section with a scanning electron microscope.