Novel Three-Dimensional Packaging Approaches Using Magnetically Aligned Anisotropic Conductive Adhesive for Microwave Applications

Upon the application of a magnetic field, ferromagnetic particles will self-align along the field lines of the applied field. Rods are thus formed that can grow until they are stopped by a substrate after application of a material and at the angle of the applied field. The dynamic growth of the columns is beneficial for implementing packages with complicated three-dimensional system integration. The growth of the rods, internal to the material, has the ability to adapt to the gap between pads or even an angle between the substrates. In this work, we demonstrate these advantages by showing multilayer interconnects as well as angled connections for three-dimensional vertical chip stacking concepts. Four layers of silicon on top of each other were integrated with multilayer interconnects and the RF performance is demonstrated. In addition, we implemented a novel three-dimensional packaging structure for a horizontal-to-vertical plane transition, with the performance evaluated for a variety of angles. Consequently, the Z-axis anisotropic conductive adhesive is shown to be a suitable solution to implement advanced three-dimensional integrated microwave applications.