3D Integration and assembly of wireless sensor nodes for ‘green’ sensor networks

Integration and assembly of wireless sensor nodes within limited size and volume may not only reduce production cost, but also enable layout-free distribution of autonomous sensor nodes for environmental monitoring, energy consumption management, remote monitoring of civil infrastructure, as well as for biological and human health monitoring. Pursuit of the lowest power consumption of the wireless sensor nodes is another critical issue, which may allow us to use solar cell or other energy harvesting device as the power source, and then reduces the system installation difficulties and maintenance cost. Therefore, in this work, we have engaged in developing a practical applicable approach for flexible assembly of wireless sensor nodes with lowest possible size and lowest power consumption form both system block and physical interconnection points-of-view. A customized RF-transmitter IC (operation frequency: 315MHz) with universal interface to both digital sensors and analog sensors was developed to manage the power consumption of those sensors as well as to reduce the power consumption of data transmission. Buried bump interconnection technology (B2it^TM) with internal cavities for bare die IC chips and passive components was introduced for 3D integration and assembly of MEMS sensors, customized RF-transmitter IC, crystal oscillator, resistors, capacitors and other passive components. One of the world smallest wireless sensor nodes, 3.9 mm (W)×3.9 mm (D)×3.5 mm (T) (except for power source and antenna), was demonstrated for humidity and temperature monitoring. Power consumption of above sensor nodes was evaluated and compared with our previous prototype, in which a commercial available RF-transmitter IC was integrated for data transmission. The developed approach in this work is believed practically valuable as platform technologies for mass production of wireless sensor nodes as well as for ubiquitous applications of those sensor nodes in wireless sensor networks.