3D packaging technique on liquid crystal polymer (LCP) for miniature wireless biomedical sensor

This paper presents a novel 3D packaging technique for a miniature wireless biomedical sensor. The application makes the packaging of the sensor and control of IC a difficult challenge. It is demonstrated that the thickness requirement can be met using novel epoxy interconnects and that micro-vias can be implemented in the package to distribute signals vertically. First, the layer-to-layer interconnection between silicon and liquid crystal polymer (LCP) layers is demonstrated using a magnetically aligned Z-axis anisotropic conductive adhesive (ACA). The resistance through Z-axis ACA represented 1.15 Ω on average for 75 micron pads. Second, 3D transitions through LCP via holes of 20 µm are demonstrated, which are suitable to distribute signals through the small form factor unit. These miniature 3D packaging techniques could make it possible to integrate all components in the small area (500 µm × 500 µm) to implement an implanted wireless biomedical micro-sensor.