Modeling and experiments on an isothermal fatigue test for solder joints

This paper investigates an isothermal fatigue test for solder joints developed at the NPL. The test specimen is a lap joint between two copper arms. During the test the displacement at the ends of the copper are controlled and the force measured. The modeling results in the paper show that the displacement across the solder joint is not equal to the displacement applied at the end of the specimen. This is due to deformation within the copper arms. A method is described to compensate for this difference. The strain distribution in the solder was determined by finite element analysis and compared to the distribution generated by a theoretical 'ideal' test which generates an almost pure shear mode in the solder. By using a damage-based constitutive law the shape of the crack generated in the specimen has been predicted for both the actual test and the ideal pure shear test. Results from the simulations are also compared with experimental data using SnAgCu solder.

Effects of solder reflow on the reliability of flip-chip on flex interconnections using anisotropic conductive adhesives

This work describes the work of an investigation of the effects of solder reflow process on the reliability of anisotropic conductive film (ACF) interconnection for flip-chip on flex (FCOF) applications. Experiments as well as computer modeling methods have been used. The results show that the contact resistance of ACF interconnections increases after the reflow and the magnitude of the increase is strongly correlated to the peak reflow temperature. In fact, nearly 40 percent of the joints are open when the peak reflow temperature is 260°C, while there is no opening when the peak temperature is 210°C. It is believed that the coefficient of thermal expansion (CTE) mismatch between the polymer particle and the adhesive matrix is the main cause of this contact degradation. To understand this phenomenon better, a three-dimensional (3-D) finite element (FE) model of an ACF joint has been analyzed in order to predict the stress distribution in the conductive particles, adhesive matrix and metal pads during the reflow process. The stress level at the interface between the particle and its surrounding materials is significant and it is the highest at the interface between the particle and the adhesive matrix.

On-line algorithms for single machine scheduling with family setup times

The paper considers an on-line single machine scheduling problem where the goal is to minimize the makespan. The jobs are partitioned into families and a setup is performed every time the machine starts processing a batch of jobs of the same family. The scheduler is aware of the number of families and knows the setup time of each family, although information about a job only becomes available when that job is released. We give a lower bound on the competitive ratio of any on-line algorithm. Moreover, for the case of two families, we provide an algorithm with a competitive ratio that achieves this lower bound. As the number of families increases, the lower bound approaches 2, and we give a simple algorithm with a competitive ratio of 2.

Assessing the performance of crack detection tests for solder joints

This paper presents both modelling and experimental test data to characterise the performance of four non-destructive tests. The focus is on determining the presence and rough magnitude of thermal fatigue cracks within the solder joints for a surface mount resistor on a strip of FR4 PCB. The tests all operate by applying mechanical loads to the PCB and monitoring the strain response at the top of the resistor. The modelling results show that of the four tests investigated, three are sensitive to the presence of a crack in the joint and its magnitude. Hence these tests show promise in being able to detect cracking caused by accelerated testing. The experimental data supports these results although more validation is required.

On Hamilton cycles in locally connected graphs with vertex degree constraints

It is shown that every connected, locally connected graph with the maximum vertex degree Δ(G)=5 and the minimum vertex degree δ(G)3 is fully cycle extendable. For Δ(G)4, all connected, locally connected graphs, including infinite ones, are explicitly described. The Hamilton Cycle problem for locally connected graphs with Δ(G)7 is shown to be NP-complete

Challenges in modelling biofluids in microchannels

This paper presents the challenges encountered in modelling biofluids in microchannels. In particular blood separation implemented in a T-microchannel device is analysed. Microfluids behave different from the counterparts in the microscale and a different approach has been adopted here to model them, which emphasize the roles of viscous forces, high shear rate performance and particle interaction in microscope. A T-microchannel design is numerically analysed by means of computational fluid dynamics (CFD) to investigate the effectiveness of blood separation based on the bifurcation law and other bio-physical effects. The simulation shows that the device can separate blood cells from plasma.

Influence of megasonic agitation on the electrodeposition of high aspect ratio blind vias

This paper presents preliminary studies in electroplating using megasonic agitation to avoid the formation of voids within high aspect ratio microvias that are used for the redistribution of interconnects in high density interconnection technology in printed circuit boards. Through this technique, uniform deposition of metal on the side walls of the vias is possible. High frequency acoustic streaming at megasonic frequencies enables the decrease of the Nernst diffusion layer down to the sub-micron range, allowing thereby conformal electrodeposition in deep grooves. This effect enables the normally convection free liquid near the surface to be agitated. Higher throughput and better control of the material properties of the deposits can be achieved for the manufacturing of embedded interconnections and metal-based MEMS. For optimal filling performance of the microvias, a full design of experiments (DOE) and a multi-physics numerical simulation have been conducted to analyse the influence of megasonic agitation on the plating quality of the microvias. Megasonic based deposition has been found to increase the deposition rate as well as improving the quality of the metal deposits.

Risk mitigation framework for a robust design process

The increasing complexity of new manufacturing processes and the continuously growing range of fabrication options mean that critical decisions about the insertion of new technologies must be made as early as possible in the design process. Mitigating the technology risks under limited knowledge is a key factor and major requirement to secure a successful development of the new technologies. In order to address this challenge, a risk mitigation methodology that incorporates both qualitative and quantitative analysis is required. This paper outlines the methodology being developed under a major UK grand challenge project - 3D-Mintegration. The main focus is on identifying the risks through identification of the product key characteristics using a product breakdown approach. The assessment of the identified risks uses quantification and prioritisation techniques to evaluate and rank the risks. Traditional statistical process control based on process capability and six sigma concepts are applied to measure the process capability as a result of the risks that have been identified. This paper also details a numerical approach that can be used to undertake risk analysis. This methodology is based on computational framework where modelling and statistical techniques are integrated. Also, an example of modeling and simulation technique is given using focused ion beam which is among the investigated in the project manufacturing processes.

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.

Design, modeling and characterization of a microinductor for future DC-DC power converters

Experimental, analytical and simulated data are presented in this article to assess the performance of electrodeposited nickel-iron within a novel solenoid microinductor. A design flowchart highlights the primary design principles when developing a microscale magnetic component for DC-DC power converters. Thermal modeling is used to predict the operational conditions that generate undesirable thermal generation within the component. Operating at 0.5MHz, the microinductor achieves an efficiency and power density of 78% and 7.8 W/cm3, respectively.

Integrated reliability and prognostics prediction methodology for power electronic modules

The article consists of a PowerPoint presentation on integrated reliability and prognostics prediction methodology for power electronic modules. The areas discussed include: power electronics flagship; design for reliability; IGBT module; design for manufacture; power module components; reliability prediction techniques; failure based reliability; etc.

Multilevel refinement for combinatorial optimisation: boosting metaheuristic performance

The multilevel paradigm as applied to combinatorial optimisation problems is a simple one, which at its most basic involves recursive coarsening to create a hierarchy of approximations to the original problem. An initial solution is found, usually at the coarsest level, and then iteratively refined at each level, coarsest to finest, typically by using some kind of heuristic optimisation algorithm (either a problem-specific local search scheme or a metaheuristic). Solution extension (or projection) operators can transfer the solution from one level to another. As a general solution strategy, the multilevel paradigm has been in use for many years and has been applied to many problem areas (for example multigrid techniques can be viewed as a prime example of the paradigm). Overview papers such as [] attest to its efficacy. However, with the exception of the graph partitioning problem, multilevel techniques have not been widely applied to combinatorial problems and in this chapter we discuss recent developments. In this chapter we survey the use of multilevel combinatorial techniques and consider their ability to boost the performance of (meta)heuristic optimisation algorithms.

Multilevel approaches applied to the capacitated clustering problem

This paper presents two multilevel refinement algorithms for the capacitated clustering problem. Multilevel refinement is a collaborative technique capable of significantly aiding the solution process for optimisation problems. The central methodologies of the technique are filtering solutions from the search space and reducing the level of problem detail to be considered at each level of the solution process. The first multilevel algorithm uses a simple tabu search while the other executes a standard local search procedure. Both algorithms demonstrate that the multilevel technique is capable of aiding the solution process for this combinatorial optimisation problem.

Approximation results for flow shop scheduling problems with machine availability constraints

This paper considers two-machine flow shop scheduling problems with machine availability constraints. When the processing of a job is interrupted by an unavailability period of a machine, we consider both the resumable scenario in which the processing can be resumed when the machine next becomes available, and the semi-resumable scenario in which some portion of the processing is repeated but the job is otherwise resumable. For the problem with several non-availability intervals on the first machine under the resumable scenario, we present a fast (3/2)-approximation algorithm. For the problem with one non-availability interval under the semi-resumable scenario, a polynomial-time approximation scheme is developed.

Megasonic agitation for enhanced electrodeposition of copper

In this paper we propose an agitation method based on megasonic acoustic streaming to overcome the limitations in plating rate and uniformity of the metal deposits during the electroplating process. Megasonic agitation at a frequency of 1 MHz allows the reduction of the thickness of the Nernst diffusion layer to less than 600 nm. Two applications that demonstrate the benefits of megasonic acoustic streaming are presented: the formation of uniform ultra-fine pitch flip-chip bumps and the metallisation of high aspect ratio microvias. For the latter application, a multi-physics based numerical simulation is implemented to describe the hydrodynamics introduced by the acoustic waves as they travel inside the deep microvias.