Development and characterisation of ultra thin autonomous modules for ambient system applications using 3D packaging techniques

The work presented in this paper represents two strands of the work of the ambient system team at NMRC to produce ultraminiature sensor modules (K. Delaney et al, Proc. 40th IMAPS Nordic Conf., pp. 13-21, 2003). These modules with an ultimate target size of <1 mm³ are needed for the implementation of future ad-hoc networks for ambient systems. Ambient systems stem from convergence of three key technologies: ubiquitous computing, ubiquitous communication and intelligent user friendly interfaces. On convergence, humans will be surrounded by intelligent interfaces, supported by computing and networking technology which is everywhere, embedded in everyday objects such as furniture, clothes, vehicles, and smart materials. The work done for the realisation of the 1 mm³ autonomous sensor module is following a technology roadmap developed by NMRC. The work is carried out in different phases: in the first phase a 25 mm cube fabricated as 3D stackable modular PCB is being reported (J. Barton et al, UbiComp 2002, and ICEWES 2002). The current module is a 1 cm cube, combining a microcontroller, PLD, accelerometer, light dependant resistors and coloured LEDs with the aim of creating modular wireless computational unit (J. Barton et al, Proc. 53rd Electron. Comp. and Tech. Conf., 2003). This paper details the assembly, characterisation and reliability issues of this module while work done to realise a very thin multi layer flexible substrate for a 5 mm cube is presented.