Circuit Board Assembly Research Articles

A Multi-Objective Optimization Approach for Multi-Head Beam-Type Placement Machines

This paper addresses a highly challenging scheduling problem in the field of printed circuit board (PCB) assembly systems using Surface Mounting Devices (SMD). After describing some challenging optimization sub-problems relating to the heads of multi-head surface mounting placement machines, we formulate an integrated multi-objective mathematical model considering of two main sub-problems simultaneously. The proposed model is a mixed integer nonlinear programming one which is very complex to be solved optimally. Therefore, it is first converted into a linearized model and then solved using an efficient multi-objective approach, i.e., the augmented epsilon constraint method. An illustrative example is also provided to show the usefulness and applicability of the proposed model and solution method.

Pb-free v/s Tin-Lead Reliability Comparison for Telecom/High Reliability Applications

With the European Union's (EU's) RoHS directives coming into force in July 2006 for consumer electronics products, the transition to lead-free (Pb-free) solder has occurred at a rapid pace. This push has driven many OEM suppliers/manufacturers to adopt Pb-free solder and End of Life many of their conventional Tin-Lead (Sn-Pb) components. This has forced telecom or high reliability applications to adopt Pb-free solder compositions with many reliability anomalies unanswered. While there have been many studies published on long term reliability of Pb-free solder joints at the component level, there have been few studies focused on the time zero reliability of the joints at the printed circuit board assembly (PCBA) level. The goal of this study is to help the OEM suppliers and their customers (like service providers) to come up with a common PCBA test methodology that will help identify and weed out early, marginal manufacturing and design defects that would crop up due to transition to the Pb-free solder. A normalized reliability data comparison and impact of the test on Pb-free and Tin-Lead solder alloys using test vehicles is presented in this study. The sequential PCBA level evaluation methodology involves a series of tests that include Thermal Aging, Mechanical Shock, Vibration, Functional test over elevated temperature and Destructive Analysis (Dye & Pry and Cross-sectional analysis) . The solder joint reliability comparisons for different components are presented against this methodology using different PCBA constructions (test vehicles).

Dynamic properties analysis and test of SMT printed circuit board assembly

In this paper, a SMT-PCB assembly is manufactured with different packaging forms and material parameters. A finite element model is established for analysing the basic dynamic property of the sample based on some simplified treatments in the modelling. In the meantime, the experimental test is developed to test the dynamic response of the SMT-PCB assembly. The comparison between the experimental test and simulation can illustrate the validity of the test and of the modelling method. It builds a basis for future investigation such as fatigue life estimation and structural optimisation for improving the working characteristics. Finally, some suggestions on how to optimise the chip layout and improve its reliability also are discussed.

A heuristic model and software development for SMT line balancing: a case study

Printed circuit board assembly (PCBA) is the major portion of manufacturing processes of electronic manufacturing services (EMS) industry, where surface mounting technology (SMT) has become the primary assembly method. Two series-connected SMT placement machines in a SMT assembly line are often the bottlenecks due to the unevenly distributed workloads. This paper studies the line balancing of the SMT assembly line focusing on the workload distribution between the two placement machines. A heuristic approach is proposed to reduce the workload difference of the two machines without increasing the total machine setup time. A software, which can be used as an effective automation tool for a company, is then developed based on the heuristic model. This will increase the quality of the service that the company provides to its customers.

Modelling and analysis of dynamic capacity complexity in multi-stage production

The uncertainty associated with managing dynamic capacity problem is the main source of its complexity. This article presents a system dynamics approach to model and analyse operational complexity of dynamic capacity in multi-stage production. The unique feature of this approach is that it captures the stochastic nature of three main sources of complexity associated with dynamic capacity. These are the demand, internal manufacturing delay and capacity scalability delay. The developed model was demonstrated by an industrial case study of multi-stage printed circuit board assembly line. The analysis of simulation experiments showed that ignoring complexity sources can lead to wrong decisions concerning both scaling levels and backlog management decisions. In addition, a general trade-off between the controllability and complexity of the dynamic capacity was illustrated. Finally, comparative analysis of the effect of each of these sources on the complexity level revealed that internal delay has the highest impact on dynamic capacity efficiency. Guidelines and recommendations for better capacity management and reduction of its complexity are presented.

Thermomechanical behaviour of environmentally benign Pb-free solders

<title/>Electronic packaging is a critical part of products such as computers, cellular phones, automotive components and other electronic devices. The package must be tailored to incorporate as many input/output interconnects as possible, in a limited amount of space. Until recently, most solder balls were made of a eutectic Pb-Sn alloy, because of its low melting point, excellent wetting characteristics and adequate creep and thermal fatigue strength. The potential health hazards associated with the toxicity of lead are significant. Given the widespread use of Pb-Sn solder in the manufacture and assembly of circuit boards, the development and reliability of new Pb-free solders is crucial for the successful substitution of these materials in the electronics industry. Pb-free solder alloys are complex materials with various important microstructural attributes. These include the nanoscale precipitates of Ag3Sn in Sn-Ag-Cu or Sn-Ag alloys, as well as Cu6Sn5 intermetallic formed at the interface between the solder and Cu metallisation. The mechanical behaviour of solder alloys is extremely important because solder joints must retain their mechanical integrity under a myriad of conditions such as creep, thermal fatigue, and mechanical shock and drop resistance. A significant amount of work has been carried out on the monotonic shear, creep and thermal fatigue resistance of these materials. An important new area of research is the mechanical shock and vibration fatigue behaviour of Pb-free solders. The developments in all these areas are critically examined in this paper.

X-Ray Image Reconstruction of Solder Joints by Using Several Algebraic Reconstruction Techniques

In this study, several Algebraic Reconstruction Technique (ART) algorithms are used to construct the 3 D sliced images from several transparent X-ray images. The speed and quality of image reconstruction are two important requirements when doing the inspection in a printed circuit board (PCB) assembly line. . To fulfill the requirements, several methodologies are discussed. The image qualities of regular ART method, binary ART method and Mixed ART method are developed and compared. The binary ART method uses the property of x-ray absorb rate of metal, silicon and other non- metal material are extremely different. The absorb rates of non-metal part are assumed to be zero and metal parts are assumed to be a single value. By using this method the quality of image reconstruction is improved. The mixed ART method is the combination of the tradition ART method and binary ART. Due to the X-ray sensor’s framing time, a method to improve the image reconstruction quality due to effect of X-ray sensor framing time is also discussed. Finally, the best solution algorithm is found to be mixed binary steering ART when consider the signal noise of X-ray detector.

Integrated component scheduling models for chip shooter machines

This paper focuses on minimizing printed circuit board (PCB) assembly time for a chip shooter machine, which has a movable feeder carrier holding components, a movable X–Y table carrying a PCB, and a rotary turret with multiple assembly heads. The assembly time of the machine depends on two inter-related optimization problems: the component sequencing problem and the feeder arrangement problem. Nevertheless, they were often regarded as two individual problems and solved separately. This paper proposes two complete mathematical models for the integrated problem of the machine. The models are verified by two commercial packages. Finally, a hybrid genetic algorithm previously developed by the authors is presented to solve the model. The algorithm not only generates the optimal solutions quickly for small-sized problems, but also outperforms the genetic algorithms developed by other researchers in terms of total assembly time.

Sensor fusion of phase measuring profilometry and stereo vision for three-dimensional inspection of electronic components assembled on printed circuit boards

Automatic optical inspection (AOI) for printed circuit board (PCB) assembly plays a very important role in modern electronics manufacturing industries. Well-developed inspection machines in each assembly process are required to ensure the manufacturing quality of the electronics products. However, generally almost all AOI machines are based on 2D image-analysis technology. In this paper, a 3D-measurement-method-based AOI system is proposed consisting of a phase shifting profilometer and a stereo vision system for assembled electronic components on a PCB after component mounting and the reflow process. In this system information from two visual systems is fused to extend the shape measurement range limited by 2pi phase ambiguity of the phase shifting profilometer, and finally to maintain fine measurement resolution and high accuracy of the phase shifting profilometer with the measurement range extended by the stereo vision. The main purpose is to overcome the low inspection reliability problem of 2D-based inspection machines by using 3D information of components. The 3D shape measurement results on PCB-mounted electronic components are shown and compared with results from contact and noncontact 3D measuring machines. Based on a series of experiments, the usefulness of the proposed sensor system and its fusion technique are discussed and analyzed in detail.

Cohesive-Zone Explicit Submodeling for Shock Life-Prediction in Electronics

Modeling transient-dynamics of electronic assemblies is a multiscale problem requiring methodologies which allow the capture of layer dimensions of solder interconnects, pads, and chip-level interconnects simultaneously with assembly architecture and rigid-body motion. Computational effort needed to attain fine mesh to model chip interconnects while capturing the system-level dynamic behavior is challenging. Product-level testing depends heavily on experimental methods and is influenced by various factors such as the drop height, orientation of drop, and variations in product design. Modeling and simulation of integrated circuit (IC) packages are very efficient tools for design analysis and optimization. Previously, various modeling approaches have been pursued to predict the transient dynamics of electronics assemblies assuming symmetry of the electronic assemblies. In this paper, modeling approaches to predict the solder joint reliability in electronic assemblies subjected to high mechanical shocks have been developed. Two modeling approaches are proposed in this paper to enable life prediction under both symmetric and anti-symmetric transient-deformation. In the first approach, drop simulations of printed circuit board assemblies in various orientations have been carried out using beam-shell modeling methodologies without any assumptions of symmetry. This approach enables the prediction of full-field stress-strain distribution in the system over the entire drop event. Transient dynamic behavior of the board assemblies in free and JEDEC drop has been measured using high-speed strain and displacement measurements. Relative displacement and strain histories predicted by modeling have been correlated with experimental data. Failure data obtained by solder joint array tensile tests on ball grid array packages is used as a failure proxy to predict the failure in solder interconnections modeled using Timoshenko beam elements in the global model. In the second approach, cohesive elements have been incorporated in the local model at the solder joint-copper pad interface at both the printed circuit board (PCB) and package side. The constitutive response of the cohesive elements was based on a traction-separation behavior derived from fracture mechanics. Damage initiation and evolution criteria are specified to ensure progressive degradation of the material stiffness leading to cohesive element failure. Use of cohesive zone modeling (CZM) enabled the detection of dynamic crack initiation and propagation leading to intermetallic compound (IMC) brittle failure in PCB assemblies subject to drop impact. Data on solder interconnect failure has been obtained under free-drop and JEDEC-drop test.

The optimisation of the single surface mount device placement machine in printed circuit board assembly: a survey

This article surveys research on the single surface mount device (SMD) placement machine optimisation problem. We classify the optimisation problem into five sub-problems: feeder setup, component placement sequencing, nozzle optimisation, component retrieval plan and motion control; and analyse issues relevant to each of these. One of the aims of this article is to provide guidance to other researchers and gain a deeper understanding of the various optimisation issues that arise in this domain. This could lead to the design of improved heuristics, which are more appropriate to the real-world scheduling problem of the SMD placement machine.

Estimating printed circuit board assembly times using neural networks

Several production planning tasks in the printed circuit board (PCB) assembly industry involve the estimation of the component placement times for different PCB types and placement machines. This kind of task may be, for example, the scheduling of jobs or line balancing for single or multiple jobs. The simplest approach to time estimation is to let the production time be a linear function of the number of components to be placed. To achieve more accurate results, the model should include more parameters (e.g. the number of different component types, the number of different component shapes, the dimensions of the PCBs, etc.). In this study we train multilayer neural networks to approximate the assembly times of two different types of assembly machines based on several parameter combinations. It turns out that conventional learning methods are prone to overfitting when the number of hidden units of the network is large in relation to the number of training cases. To avoid this and complicated training and testing, we use Bayesian regularisation to achieve efficient learning and good accuracy automatically.

High-Speed Cyclic Bend Tests and Board-Level Drop Tests for Evaluating the Robustness of Solder Joints in Printed Circuit Board Assemblies

This paper presents a comprehensive study of the resistance of solder joints to failure when subjected to strain rates that simulate the conditions of drop impact experienced by a portable electronic product. Two test methods are used in this study: the board-level drop-shock test (BLDST) and the board-level high-speed cyclic bend test (HSCBT). The performance of (i) 12 material combinations consisting of six solder alloys and two pad finishes, and (ii) 11 manufacturing variations covering three vendors, two finishes, three immersion gold thicknesses, and three thermal aging conditions were investigated using these two test methods. Correlations between the two test methods were performed. Quantitative correlation and sensitivity coefficients for the failure modes and the measured characteristic parameters—number of drops to failure for BLDST and number of cycles to failure for HSCBT—were evaluated. Finally, the potential of HSCBT as a test method for material selection and for bridging board-level and product-level tests was demonstrated through generation of board strain versus number of cycles to failure (S–N) curves of solder joints for six material systems, four bending frequencies, and two test temperatures.

A novel general approach to evaluating the PCBA for components with different membership function

The logistic support of high tech industry all emphasize that reliability design start, one must fully considers its life cycle. The reliability analysis and prediction are the main work objectives. The purpose is to ensure that the system (product) can achieve its designed functions under specific operating conditions. However, the incomplete failure data and different fault probability density function of the system elementary event also increase the difficulty of reliability design and calculation. It cannot be fully solved by traditional probability reliability. Therefore, a more general and efficient algorithm to assess the system reliability is needed. This paper proposed speculation by experts’ opinions according to incomplete information condition. It reasonably gives different fault membership function of possibility of failure distribution under different bottom event. It also applies fault-tree analysis, α-cut of vague set, and interval arithmetic operations of vague set to obtain fault interval and reliability interval of the system. Moreover, this paper also modifies Tanaka et al.’s fuzzy fault-tree definition and extended the new usage to fit different membership function of vague fault-tree. Then, find out the critical elementary event that affects the reliability of the system, which could be used for managerial decision-making, and as the bases to future system maintenance strategy. In numerical verification, a malfunction of printed circuit board assembly (PCBA) is presented as a numerical example. The result of the proposed method is compared with the listing approaches of reliability analysis methods.

Multiobjective Evolutionary Decision Support for Design–Supplier–Manufacturing Planning

Product development in modern enterprises usually involves collaboration among designers, suppliers, contract manufacturers to achieve efficiency and rapid response to changing markets. Product-development cost, lead time, and reliability are very critical elements in addition to functional features. However, it becomes increasingly challenging to obtain an optimal decision with respect to these multiple criteria as the number of involved entities increases in modern product developments. There is a clear need for planning tools to support effective decision making in this domain. The availability of efficient and accurate multiobjective optimization (MOO) algorithms becomes critical in such a decision support tool. This paper poses the product development as a multiobjective assignment problem in the context of printed circuit board assembly (PCBA) industry. We describe a new class of MOO algorithm based on the principles of differential evolution (DE). The multiobjective DE (MODE) algorithm is shown to approach Pareto-optimal solutions in a wide class of problems with better performance than the nondominated sorting genetic algorithm II from the literature, providing a practical tool for product-development decision support. A decision support system based on the object-oriented design methodology is described in this paper with the MODE as the core search engine. Experimental study of this decision support system is conducted using two real-world PCBA designs. We demonstrate the effectiveness of this proposed MODE algorithm and some use cases of such decision support system on facilitating decision makers' tradeoff analysis.

Optimizing PCB assembly for family setup strategy

PurposeThe purpose of this paper is to investigate the optimization for a placement machine in printed circuit board (PCB) assembly when family setup strategy is adopted.Design/methodology/approachA complete mathematical model is developed for the integrated problem to optimize feeder arrangement and component placement sequences so as to minimize the makespan for a set of PCB batches. Owing to the complexity of the problem, a specific genetic algorithm (GA) is proposed.FindingsThe established model is able to find the minimal makespan for a set of PCB batches through determining the feeder arrangement and placement sequences. However, exact solutions to the problem are not practical due to the complexity. Experimental tests show that the proposed GA can solve the problem both effectively and efficiently.Research limitations/implicationsWhen a placement machine is set up for production of a set of PCB batches, the feeder arrangement of the machine together with the component placement sequencing for each PCB type should be solved simultaneously so as to minimize the overall makespan.Practical implicationsThe paper investigates the optimization for PCB assembly with family setup strategy, which is adopted by many PCB manufacturers for reducing both setup costs and human errors.Originality/valueThe paper investigates the feeder arrangement and placement sequencing problems when family setup strategy is adopted, which has not been studied in the literature.

Experimental and numerical analysis of BGA lead-free solder joint reliability under board-level drop impact

Board-level solder joint reliability is very critical for handheld electronic products during drop impact. In this study, board-level drop test and finite element method (FEM) are adopted to investigate failure modes and failure mechanisms of lead-free solder joint under drop impact. In order to make all ball grid array (BGA) packages on the same test board subject to the uniform stress and strain level during drop impact, a test board in round shape is designed to conduct drop tests. During these drop tests, the round printed circuit board assembly (PCBA) is suffered from a specified half-sine acceleration pulse. The dynamic responses of the PCBA under drop impact loading are measured by strain gauges and accelerometers. Locations of the failed solder joints and failure modes are examined by the dye penetration test and cross section test. While in simulation, FEM in ABAQUS software is used to study transient dynamic responses. The peeling stress which is considered as the dominant factor affecting the solder joint reliability is used to identify location of the failed solder joints. Simulation results show very good correlation with experiment measurement in terms of acceleration response and strain histories in actual drop test. Solder joint failure mechanisms are analyzed based on observation of cross section of packages and dye and pry as well. Crack occurred at intermetallic composite (IMC) interface on the package side with some brittle features. The position of maximum peeling stress in finite element analysis (FEA) coincides with the crack position in the cross section of a failed package, which validated our FEA. The analysis approach combining experiment with simulation is helpful to understand and improve solder joint reliability.

Tri-Layer Structures Subjected to Combined Temperature and Mechanical Loadings

Thermal stress has been a concern in electronic packaging for decades. More recently, mechanical bending of printed circuit board (PCB) assembly has attracted increased interest due to the drop impact failure of interconnects in mobile products. Analytical solutions are available in the literatures for a PCB assembly modeled as a tri-layer structure, consisting of IC components, PCBs, and an interconnect layer, subjected to either thermal stress or mechanical bending, but there are no known reports for combined loadings. This paper presents a comprehensive treatment for a PCB assembly subjected to combined temperature and mechanical loadings, taking into account the axial, shear, and flexural deformation of the interconnects. Solutions are provided for two types of interconnect layer: one in which the interconnect layer is made of a continuous element such as adhesive, and another in which the interconnect layer is made of discrete elements such as solder joints. The solutions were successfully validated with finite-element analysis, and design analyses were performed for both types of interconnect layers.

A scheduling problem for PCB assembly: a case with multiple lines

A production scheduling problem for printed circuit board (PCB) assembly with multiple lines is addressed. The investigated problem is to schedule a set of PCB assembly jobs with different ready times and due dates on multiple assembly lines, with the objective to minimize the sum of total weighted tardiness of jobs and weighted makespan. The feature that each job can be completed by different lines with different process times makes the problem a special type of unrelated parallel-machine scheduling problem (PMSP) with special constraints and a unique objective. A mixed-integer linear programming model for the problem is established and verified through solving some small-sized problem instances to optimality. In order to solve the real-world problems, a steady-state genetic algorithm with an improved replacement strategy is proposed. Experimental tests and a case study are conducted to examine the usefulness and effectiveness of the approach.

Comparison of Inelastic Behaviors of Lead-Free and Sn—Pb Solder Joints

In this study, finite element analysis is used to investigate the inelastic behaviors of lead-free solders, 96.5Sn—3.5Ag and 95.5Sn—3.9Ag—0.6Cu, and classical 63Sn—37Pb solder-bumped wafer level chip scale package (WLCSP) on printed circuit board (PCB) assemblies subjected to four different temperature cycle tests. The behaviors of equivalent strain range and strain energy density at the outmost corner solder joint adjoining to the upper pad are examined. It is found that: (1) the 95.5Sn—3.9Ag—0.6Cu solder has the best performance on the effect of plastic behavior among these three solder alloys, but it accumulates more plastic strain while the number of temperature cycling increased; (2) the 96.5Sn—3.5Ag solder alloy can sustain more creep than others; (3) the difference exists between using the equivalent total strain range and the strain energy density, respectively, to assess the thermo-mechanical behaviors of the solder-bumped WLCSP on PCB assemblies.