Review of the technology and reliability issues arising as optical interconnects migrate onto the circuit board

Light has the greatest information carrying potential of all the perceivable interconnect mediums; consequently, optical fiber interconnects rapidly replaced copper in telecommunications networks, providing bandwidth capacity far in excess of its predecessors. As a result the modern telecommunications infrastructure has evolved into a global mesh of optical networks with VCSEL’s (Vertical Cavity Surface Emitting Lasers) dominating the short-link markets, predominately due to their low-cost. This cost benefit of VCSELs has allowed optical interconnects to again replace bandwidth limited copper as bottlenecks appear on VSR (Very Short Reach) interconnects between co-located equipment inside the CO (Central-Office). Spurred by the successful deployment in the VSR domain and in response to both intra-board backplane applications and inter-board requirements to extend the bandwidth between IC’s (Integrated Circuits), current research is migrating optical links toward board level USR (Ultra Short Reach) interconnects. Whilst reconfigurable Free Space Optical Interconnect (FSOI) are an option, they are complicated by precise line-of-sight alignment conditions hence benefits exist in developing guided wave technologies, which have been classified into three generations. First and second generation technologies are based upon optical fibers and are both capable of providing a suitable platform for intra-board applications. However, to allow component assembly, an integral requirement for inter-board applications, 3rd generation Opto-Electrical Circuit Boards (OECB’s) containing embedded waveguides are desirable. Currently, the greatest challenge preventing the deployment of OECB’s is achieving the out-of-plane coupling to SMT devices. With the most suitable low-cost platform being to integrate the optics into the OECB manufacturing process, several research avenues are being explored although none to date have demonstrated sufficient coupling performance. Once in place, the OECB assemblies will generate new reliability issues such as assembly configurations, manufacturing tolerances, and hermetic requirements that will also require development before total off-chip photonic interconnection can truly be achieved

Modelling and prototyping the conceptual design of 3D CMM micro-probe

This paper details the prototyping of a novel three axial micro probe based on utilisation of piezoelectric sensors and actuators for true three dimensional metrology and measurements at micro- and nanometre scale. Computational mechanics is used first to model and simulate the performance of the conceptual design of the micro-probe. Piezoelectric analysis is conducted to understand performance of three different materials - silicon, glassy carbon, and nickel - and the effect of load parameters (amplitude, frequency, phase angle) on the magnitude of vibrations. Simulations are also used to compare several design options for layout of the lead zirconium titanate (PZT) sensors and to identify the most feasible from fabrication point of view design. The material options for the realisation of the device have been also tested. Direct laser machining was selected as the primary means of production. It is found that a Yb MOPA based fiber laser was capable of providing the necessary precision on glassy carbon (GC), although machining trials on Si and Ni were less successful due to residual thermal effects.To provide the active and sensing elements on the flexures of the probe, PZT thick films are developed and deposited at low temperatures (Lt720 degC) allowing a high quality functional ceramic to be directly integrated with selected materials. Characterisation of the materials has shown that the film has a homogenous and small pore microstructure.