"System in package technology" - design for manufacture challenges

Purpose – To present key challenges associated with the evolution of system-in-package technologies and present technical work in reliability modeling and embedded test that contributes to these challenges. Design/methodology/approach – Key challenges have been identified from the electronics and integrated MEMS industrial sectors. Solutions to optimising the reliability of a typical assembly process and reducing the cost of production test have been studied through simulation and modelling studies based on technology data released by NXP and in collaboration with EDA tool vendors Coventor and Flomerics. Findings – Characterised models that deliver special and material dependent reliability data that can be used to optimize robustness of SiP assemblies together with results that indicate relative contributions of various structural variables. An initial analytical model for solder ball reliability and a solution for embedding a low cost test for a capacitive RF-MEMS switch identified as an SiP component presenting a key test challenge. Research limitations/implications – Results will contribute to the further development of NXP wafer level system-in-package technology. Limitations are that feedback on the implementation of recommendations and the physical characterisation of the embedded test solution. Originality/value – Both the methodology and associated studies on the structural reliability of an industrial SiP technology are unique. The analytical model for solder ball life is new as is the embedded test solution for the RF-MEMS switch.

Group technology approach to the open shop scheduling problem with batch setup times

This paper studies the problem of scheduling jobs in a two-machine open shop to minimize the makespan. Jobs are grouped into batches and are processed without preemption. A batch setup time on each machine is required before the first job is processed, and when a machine switches from processing a job in some batch to a job of another batch. For this NP-hard problem, we propose a linear-time heuristic algorithm that creates a group technology schedule, in which no batch is split into sub-batches. We demonstrate that our heuristic is a -approximation algorithm. Moreover, we show that no group technology algorithm can guarantee a worst-case performance ratio less than 5/4.

The recovery mechanism of platinum group metals from catalytic converters in spent automotive exhaust systems

The recovery of platinum group metals (PGMs) from catalytic converters of spent exhaust systems is considered in this paper. To be cost-effective, recovery processes must be well over 90% efficient and so the optimisation of their operation is vital. Effective optimisation requires a sound understanding of the operation and the underlying process mechanisms. This paper focuses on pyrometallurgical recovery operations used and typified by the Johnson–Matthey process. Analysis of this process reveals that it cannot be simply explained by the gravity model that is normally assumed. The analysis reveals that the affinity of PGM particles for the melted collector metal is a key factor in the behaviour of the process. A rational explanation of the key issues that govern the process behaviour is proposed and shown to be consistent with available operational data. The results generated would be applicable to other similar processes.

Collector-metal behaviour in the recovery of platinum-group metals from catalytic converters

A commercial pyrometallurgical process for the extraction of platinum-group metals (PGM) from a feedstock slag was analysed with the use of a model based on computational fluid dynamics. The results of the modelling indicate that recovery depends on the behaviour of the collector phase. A possible method is proposed for estimation of the rate at which PGM particles in slag are absorbed into an iron collector droplet that falls through it. Nanoscale modelling techniques (for particle migration or capture) are combined with a diffusion-controlled mass-transfer model to determine the iron collector droplet size needed for >95% PGM recovery in a typical process bath (70 mm deep) in a realistic time-scale (<1 h). The results show that an iron droplet having a diameter in the range 0.1–0.3 mm gives good recovery (>90%) within a reasonable time. This finding is compatible with published experimental data. Pyrometallurgical processes similar to that investigated should be applicable to other types of waste that contain low levels of potentially valuable metals.

Woman-centred care

Changes over the past decade have emphasised the individual service user and their relationship with the health service. Within the maternity services this has been interpreted as woman-centred care a result of key initiatives; the Winterton Report (House of Commons, 1992. Maternity Services. Second Report of the Health Committee (Winterton Report), Vol. 1. HMSO, London) and Changing Childbirth (DoH, 1993a, Changing childbirth: reports of the expert maternity group parts 1 & 2. HMSO, London). Changing Childbirth outlined key principles of the maternity services and the need for the woman (and her partner, if she wishes) to be the focus of care. The key principles are choice, continuity and control. High quality care depends on the recognition of individuals as having unique needs which continues to be reflected within contemporary policy documents (DoH, 1997, The new NHS: modern and dependable. HMSO, London). This paper presents findings related to the provision of woman-centred care from a national research and development study. The study design incorporated (i): a national survey which was undertaken with midwives, midwife supervisors and doctors; and (ii): in-depth case studies in which information was obtained through interviews with midwives, midwife supervisors, educators, managers, doctors and mothers. Midwives, at all levels, are involved in changing maternity service provision and adapting to new systems of care which aim to increase continuity of care and carer for the woman. The researchers sought to understand how woman-centred care was interpreted and experienced in practice. The findings have been used to identify the continuing educational needs of midwives, and to develop an open learning educational package to meet identified need. The curriculum was designed to enhance the move towards the provision of a more integrated woman-centred service.

Mathematical modelling: a laser soldering process for an optoelectronics butterfly package

For sensitive optoelectronic components, traditional soldering techniques cannot be used because of their inherent sensitivity to thermal stresses. One such component is the Optoelectronic Butterfly Package which houses a laser diode chip aligned to a fibre-optic cable. Even sub-micron misalignment of the fibre optic and laser diode chip can significantly reduce the performance of the device. The high cost of each unit requires that the number of damaged components, via the laser soldering process, are kept to a minimum. Mathematical modelling is undertaken to better understand the laser soldering process and to optimize operational parameters such as solder paste volume, copper pad dimensions, laser solder times for each joint, laser intensity and absorption coefficient. Validation of the model against experimental data will be completed, and will lead to an optimization of the assembly process, through an iterative modelling cycle. This will ultimately reduce costs, improve the process development time and increase consistency in the laser soldering process.

BSHM meetings: BMS History of Mathematics Splinter Group

Introduction to abstracts from papers given at BMS History of Mathematics Splinter Group, held 17 April 2007, in Swansea.

Computational approach for reliable and robust system-in-package design

A computational modelling approach integrated with optimisation and statistical methods that can aid the development of reliable and robust electronic packages and systems is presented. The design for reliability methodology is demonstrated for the design of a SiP structure. In this study the focus is on the procedure for representing the uncertainties in the package design parameters, their impact on reliability and robustness of the package design and how these can be included in the design optimisation modelling framework. The analysis of thermo-mechanical behaviour of the package is conducted using non-linear transient finite element simulations. Key system responses of interest, the fatigue life-time of the lead-free solder interconnects and warpage of the package, are predicted and used subsequently for design purposes. The design tasks are to identify the optimal SiP designs by varying several package input parameters so that the reliability and the robustness of the package are improved and in the same time specified performance criteria are also satisfied

Reliability based design optimisation for system-in-package

This paper discusses a reliability based optimisation modelling approach demonstrated for the design of a SiP structure integrated by stacking dies one upon the other. In this investigation the focus is on the strategy for handling the uncertainties in the package design inputs and their implementation into the design optimisation modelling framework. The analysis of fhermo-mechanical behaviour of the package is utilised to predict the fatigue life-time of the lead-free board level solder interconnects and warpage of the package under thermal cycling. The SiP characterisation is obtained through the exploitation of Reduced Order Models (ROM) constructed using high fidelity analysis and Design of Experiments (DoE) methods. The design task is to identify the optimal SiP design specification by varying several package input parameters so that a specified target reliability of the solder joints is achieved and in the same time design requirements and package performance criteria are met

Microwave curing for high density package

Summary form only given. Currently the vast majority of adhesive materials in electronic products are bonded using convection heating or infra-red as well as UV-curing. These thermal processing steps can take several hours to perform, slowing throughput and contributing a significant portion of the cost of manufacturing. With the demand for lighter, faster, and smaller electronic devices, there is a need for innovative material processing techniques and control methodologies. The increasing demand for smaller and cheaper devices pose engineering challenges in designing a curing systems that minimize the time required between the curing of devices in a production line, allowing access to the components during curing for alignment and testing. Microwave radiation exhibits several favorable characteristics and over the past few years has attracted increased academic and industrial attention as an alternative solution to curing of flip-chip underfills, bumps, glob top and potting cure, structural bonding, die attach, wafer processing, opto-electronics assembly as well as RF-ID tag bonding. Microwave energy fundamentally accelerates the cure kinetics of polymer adhesives. It provides a route to focus heat into the polymer materials penetrating the substrates that typically remain transparent. Therefore microwave energy can be used to minimise the temperature increase in the surrounding materials. The short path between the energy source and the cured material ensures a rapid heating rate and an overall low thermal budget. In this keynote talk, we will review the principles of microwave curing of materials for high density packing. Emphasis will be placed on recent advances within ongoing research in the UK on the realization of "open-oven" cavities, tailored to address existing challenges. Open-ovens do not require positioning of the device into the cavity through a movable door, hence being more suitable for fully automated processing. Further potential advantages of op- - en-oven curing include the possibility for simultaneous fine placement and curing of the device into a larger assembly. These capabilities promise productivity gains by combining assembly, placement and bonding into a single processing step. Moreover, the proposed design allows for selective heating within a large substrate, which can be useful particularly when the latter includes parts sensitive to increased temperatures.

Design for reliability for wafer level system in package

This paper discusses the Design for Reliability modelling of several System-in-Package (SiP) structures developed by NXP and advanced on the basis of Wafer Level Packaging (WLP). Two different types of Wafer Level SiP (WLSiP) are presented and discussed. The main focus is on the modelling approach that has been adopted to investigate and analyse the board level reliability of the presented SiP configurations. Thermo-mechanical non-linear Finite Element Analysis (FEA) is used to analyse the effect of various package design parameters on the reliability of the structures and to identify design trends towards package optimisation. FEA is used also to gain knowledge on moulded wafer shrinkage and related issues during the wafer level fabrication. The paper provides a brief outline and demonstration of a design methodology for reliability driven design optimisation of SiP. The study emphasises the advantages of applying the methodology to address complex design problems where several requirements may exist and uncertainties and interactions between parameters in the design are common.

Horsham Properties Group Ltd v Clark: possession - mortgagee's right or discretionary remedy?

Comments on the Chancery Division decision in Horsham Properties Group Ltd v Clark on whether a mortgagee's exercise of its contractual right, on the mortgagor falling into arrears, to appoint receivers such that the property could be sold and possession obtained without triggering the court's discretionary powers pursuant to the Administration of Justice Act 1970 s.36 infringed the mortgagor's rights under the European Convention on Human Rights 1950 Protocol 1 art.1. Considers the implications of proposed reforms recasting the mortgagee's right to possession as a discretionary remedy. [From Legal Journals Index]