Multiphysics simulation of microwave curing in micro-electronics packaging applications

Purpose – This paper aims to present an open-ended microwave curing system for microelectronics components and a numerical analysis framework for virtual testing and prototyping of the system, enabling design of physical prototypes to be optimized, expediting the development process. Design/methodology/approach – An open-ended microwave oven system able to enhance the cure process for thermosetting polymer materials utilised in microelectronics applications is presented. The system is designed to be mounted on a precision placement machine enabling curing of individual components on a circuit board. The design of the system allows the heating pattern and heating rate to be carefully controlled optimising cure rate and cure quality. A multi-physics analysis approach has been adopted to form a numerical model capable of capturing the complex coupling that exists between physical processes. Electromagnetic analysis has been performed using a Yee finite-difference time-domain scheme, while an unstructured finite volume method has been utilized to perform thermophysical analysis. The two solvers are coupled using a sampling-based cross-mapping algorithm. Findings – The numerical results obtained demonstrate that the numerical model is able to obtain solutions for distribution of temperature, rate of cure, degree of cure and thermally induced stresses within an idealised polymer load heated by the proposed microwave system. Research limitations/implications – The work is limited by the absence of experimentally derived material property data and comparative experimental results. However, the model demonstrates that the proposed microwave system would seem to be a feasible method of expediting the cure rate of polymer materials. Originality/value – The findings of this paper will help to provide an understanding of the behaviour of thermosetting polymer materials during microwave cure processing.

Investigating the impact of exit availability on egress time using computer based evacuation simulation

This paper examines the influence of exit availability on evacuation time for a narrow body aircraft under certification trial conditions using computer simulation. A narrow body aircraft which has previously passed the certification trial is used as the test configuration. While maintaining the certification requirement of 50% of the available exits, six different exit configurations are examined. These include the standard certification configuration (one exit from each exit pair) and five other exit configurations based on commonly occurring exit combinations found in accidents. These configurations are based on data derived from the AASK database and the evacuation simulations are performed using the airEXODUS evacuation simulation software. The results show that the certification practice of using half the available exits predominately down one side of the aircraft is neither statistically relevant nor challenging. For the aircraft cabin layout examined, the exit configuration used in certification trial produces the shortest egress times. Furthermore, three of the six exit combinations investigated result in predicted egress times in excess of 90 seconds, suggesting that the aircraft would not satisfy the certification requirement under these conditions.

Predicting the likely impact of aircraft post crash fire on aircraft evacuation using fire and evacuation simulation

The SMARTFIRE Computational Fluid Dynamics (CFD) fire field model has successfully reproduced the observed characteristics including measured temperatures, species concentrations and time to flashover for a post-crash fire experiment conducted by the FAA within their C-133 cabin test facility. In this test only one exit was open in order to provide ventilation for the developing cabin fire. In real post-crash fires, many exits are likely to be open as passangers attempt to evacuate. In this paper, the likely impacts on evacuation of a post-crash fire in which various exiting combinations are available are investigated. The fire scenario, investigated using the SMARTFIRE software, is based on the C-133 experiment but with a fully furnished cabin and with four different exit availability options. The fire data is imported into the airEXODUS evacuation simulation software and the resulting evacuations examined. The combined fire and evacuation analysis reveals that even though the aircraft configuration is predicted to comfortably satisfy the evacuation certification requirement, when fire is included, a number of casualties result, even from the certification compliant exit configuration.

Numerical simulation of microwave thawing using a coupled solver approach

Thawing of a frozen food product in a domestic microwave oven is numerically simulated using a coupled solver approach. The approach consists of a dedicated electromagnetic FDTD solver and a closely coupled UFVM multi-physics package. Two overlapping numerical meshes are defined; the food material and container were meshed for heat transfer and phase change solution, whilst the microwave oven cavity and waveguide were meshed for the microwave irradiation. The two solution domains were linked using a cross-mapping routine. This approach allowed the rotation of the food load to be captured. Power densities obtained on the structured FDTD mesh were interpolated onto the UFVM mesh for each timestep/turntable position. The UFVM solver utilised the power density data to advance the temperature and phase distribution solution. The temperature-dependant dielectric and thermo-physical properties of the food load were updated prior to revising the electromagnetic solution. Changes in thermal/electric properties associated with the phase transition were fully accounted for as well as heat losses from product to cavity. Two scenarios were investigated: a centric and eccentric placement on the turntable. Developing temperature fields predicted by the numerical solution are validated against experimentally obtained data. Presented results indicate the feasibility of fully coupled simulations of the microwave heating of a frozen product. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Approximating the evacuation of the World Trade Center North Tower using computer simulation

This article concerns an investigation of the full scale evacuation of a building with a configuration similar to that of the World Trade Center (WTC) North Tower using computer simulation. A range of evacuation scenarios is explored in order to better understand the evacuation of the WTC on 11 September 2001. The analysis makes use of response time data derived from a study of published WTC survivor accounts. Geometric details of the building are obtained from architects' plans while the total building population used in the scenarios is based on estimates produced by the National Institute of Standards and Technology formal investigation into the evacuation. This paper attempts to approximate the events of 11 September 2001 and pursue several `what if' questions concerning the evacuation. In particular, the study explores the likely outcome had a single staircase survived intact from top to bottom. More generally, this paper explores issues associated with the practical limits of building size that can be expected to be efficiently evacuated using stairs alone.

On efficient data integrity and data origin authentication for wireless sensor networks utilising block cipher design techniques

Analysis of the generic attacks and countermeasures for block cipher based message authentication code algorithms (MAC) in sensor applications is undertaken; the conclusions are used in the design of two new MAC constructs Quicker Block Chaining MAC1 (QBC-MAC1) and Quicker Block Chaining MAC2 (QBC-MAC2). Using software simulation we show that our new constructs point to improvements in usage of CPU instruction clock cycle and energy requirement when benchmarked against the de facto Cipher Block Chaining MAC (CBC-MAC) based construct used in the TinySec security protocol for wireless sensor networks.

Optimising vessel layout using human factors simulation

Evaluating ship layout for human factors (HF) issues using simulation software such as maritimeEXODUS can be a long and complex process. The analysis requires the identification of relevant evaluation scenarios; encompassing evacuation and normal operations; the development of appropriate measures which can be used to gauge the performance of crew and vessel and finally; the interpretation of considerable simulation data. In this paper we present a systematic and transparent methodology for assessing the HF performance of ship design which is both discriminating and diagnostic.

Investigating the impact of aircraft exit availability on egress time using computer simulation

This paper examines the influence of exit availability on evacuation time for narrow body aircraft under certification trial conditions using computer simulation. A narrow body aircraft which has previously passed the certification trial is used as the test configuration. While maintaining the certification requirement of 50% of the available exits, six different configurations are examined. These include the standard certification and five other exit configurations based on commonly occurring exit combinations found in accidents. These configurations are based on data derived from the AASK database and the evacuation simulations are performed using the airEXODUS evacuation software. The results show that the certification practise of using half of the available exits predominately down one side of the aircraft is neither statistically relevant nor challenging. For the aircraft cabin layout examined, the exit configuration used in certification trial produces the shortest egress times. Furthermore, three of the six exit combinations investigated result in predicted egress times in excess of 90 seconds, suggesting that the aircraft would not satisfy the certification requirement under these conditions.