Differential Pad Placement Design of a Capacitive Coupling-Based Stacked Die Package

Stacked die package using capacitive-based chip-to-chip signaling offers low energy-per-bit costs and high I/O density. Many previously published works on capacitive proximity I/O have focused on mechanical methods for accurate chip alignment. This paper explores design considerations to address stacked die structures with differential signaling chip-to-chip communication based on capacitive coupling. The signal and noise properties of capacitively coupled channels are studied using a 3-D electromagnetic field solver to extract mixed-mode scattering parameters of the differential signal pads. We present side differential and corner differential arrangements and compare their ability to reject noise. We then formulate a functional data analysis approach for assessing the signal transmission quality. Our results indicate that the differential transmitter and receiver pads arrangement and placement can significantly affect the interaction between a channel and its nearest neighbors. The preferred choice for I/O pad placement design depends on the placement arrangements and the overlap ratio of the differential I/O pads.