Process and production planning for circuit board assembly

Process planning output can be post-processed into criteria for job scheduling decisions in printed circuit board assembly using surface-mount technology (SMT). Artificial intelligence-based techniques used in computerized planning and scheduling systems in other industries can be extended to printed circuit board operations. These techniques include blackboard architectures, object-oriented programming systems, and nonmonotonic reasoning systems. These techniques were used to demonstrate a unique architecture of blackboard systems that communicate via object-oriented messages to arrive at a shop-floor process plan and production schedule. The methodology was specialized to the assembly of printed circuit boards using surface-mounted components in a high-variety/low-volume product mix. The assembly facility was represented as a hierarchical object of product, process, and organizational knowledge. The system of working heuristics was integrated within a prototype environment with the practitioners that assisted in its development. The end result is a good working methodology for system development, implementation, and maintenance by knowledge worker involvement.     

Combined effects of linear and angular errors in pc board assembly

Automated printed circuit board assembly is a complex process where accuracy is a critical issue. This paper discusses the quantitative effects of linear and angular errors present in such a system on the successful assembly of through-hole components that have been properly registered. Both additive and statistical error compounding methods are illustrated. Mathematical models developed in this study can be used to determine the relative effects of critical system parameters and tolerances on proper insertion of the component into the pc board. Optimal design and control specifications can therefore be obtained for an efficient and successful assembly system.     

Workload planning in small lot printed circuit board assembly

The problem of workload planning in small lot printed circuit board (PCB) assembly concerns the determination of the daily mix of production orders to be released into the production system. When switching from one production order (board type) to another, a considerable set-up time is incurred based on the number of component feeders to be replaced in the component magazine of the assembly machines. To support the order-mix decision faced by a major electronics manufacturer, two versions of a linear programming model are developed. The models differ primarily in their degree of aggregation and their computational effort. In order to reduce the aggregational error incurred, a fuzzy approach is developed to estimate the number of component set-ups at automatic SMD placement machines. Our numerical investigation reveals that sufficiently accurate solutions may be obtained from a highly aggregate fuzzy LP-model and this is achieved with considerably less computational effort than with a more detailed LP-model. We also demonstrate the potential suitability of the fuzzy LP-model for implementation within an interactive decision support system.     

Solderability and its measurement

The ease with which molten solder wets and spreads on the appropriate metallic surfaces of electronic component assemblies during the manufacturing process is referred to broadly as the solderability of the component or printed circuit board. Two needs are evident: a traceable solderability measurement method giving reproducible data that predict process performance, and an agreed level of solderability which, for a given manufacturing process, will deliver an acceptably robust solder joint. This paper describes briefly present understanding of the mechanisms that govern solderability and the measurement methods most likely to prove acceptable to the electronics assembly industry     

Mechanism to minimise the assembly time with feeder assignment for a multi-headed gantry and high-speed SMT machine

This paper proposes the development of a mechanism to minimise the assembly time for a multi-headed gantry and high-speed surface mounting technology machine by determining the component assignment to feeder slots. Since a gantry moves long distances in order to pick components, place them on the board and then return them to the feeder slots, we classified the overall assembly time according to the different movements of a gantry. The overall assembly time is then minimised by presenting a new heuristic for the feeder assignment, consisting of Nearest Component Allocation (NCA) and Globally Updated Assignment (GUA). NCA contains information about how each component type locates closely to others on the board. Using the solution from NCA, the component distance function calculates the most representative distance between component types. Then, GUA is applied to improve the NCA solution. The experiments consist of several printed circuit boards with numbers of component types and points to be placed. Highlights of this paper are that: a classification of the gantry movements is proposed based on the average speed; a heuristic NCA-GUA for feeder assignment is developed by considering the placements on the board; the computational time is greatly reduced by NCA-GUA without degrading the solution quality; and a decision process for nozzle assignment is proposed to minimise the overall assembly time. The results show how NCA and GUA affect the final results, and how this mechanism leads to better performance than a genetic algorithms or 2-opt swap search. This comparison proves that our method provides competitive and effective solutions in terms of minimising the overall assembly time.     

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.     

Efficient operation methods for a component placement machine using the patterns on printed circuit boards

Operation of a PCB assembler is complicated to optimise since it requires simultaneous consideration of a component's rack assignment and component mounting sequencing. However, most previous researches considered the constraints separately on the optimisation process. Two different methods using special features on printed circuit boards are developed and presented in this research. Based on results from field surveys, it is found that identical components are positioned closely with each other or identical single boards are repeatedly printed on one big board to enlarge up to a proper size to be assembled in the machine. These patterns are adapted on the design of assembly methods to increase productivity. Simulation models are constructed using Visual C++ for performance evaluation purposes of the developed heuristics.     

Designing printed circuit stators for brushless permanent magnet motors

Progress in a number of areas of technology has made printed circuit motors a serious contender for many applications. Modern cost effective neodymium magnets have allowed compact motor designs. Multi-layer circuit board production techniques have made the production of printed circuit coils cheaper and easier. However, in spite of the growing importance of printed circuit brushless motors, there is a lack of analytical tools to assist with their design. Geometrical analysis has been used to allow the plotting of printed circuit tracks to be carried out more systematically. The track plotting procedures have been linked with the finite element method to predict rotational electromotive force (EMF) waveforms. Six prototype motors were built and they were used to experimentally validate the method of predicting EMF waveforms. A general design algorithm is presented based on the suggested track plotting procedure and the EMF prediction technique.     

Optimization of the assignment of circuit cards to assembly lines in electronics assembly

Process planning is an important and integral function for ensuring efficient operations in printed circuit card assembly systems. This paper presents a new approach for solving the circuit card to assembly line assignment problem to minimize assembly time. This problem occurs frequently in process planning for electronic assembly systems and involves considering other interelated process planning problems. The line assignment problem is formulated as a large-scale mixed-integer programming problem and then solved using problem decomposition along with the branch-and-bound algorithm. Techniques for improving the solution time are discussed, and the solution approach is demonstrated using industry representative data sets from Lucent Technologies. For the data sets considered, the solution approach provides solutions within 3% of optimal in approximately 6 min of computation time on a Sun UltraSparc 2 Workstation. The solution approach developed for addressing the line assignment problem can serve as a useful decision-support tool by offering significant opportunities to improve the productivity and throughput of the assembly lines with improved process plans. The approach also allows planning engineers to respond faster to changes in production requirements. This research will be of interest to researchers in printed circuit card assembly systems and to practitioners in both original equipment manufacturing and contract assembly firms.     

Simulation-based performance analysis and optimization of electronics assembly equipment

Due to the high degree of automation in modern printed circuit board (PCB) assembly, production planning and scheduling in this industry relies heavily on the accuracy of the underlying models of the automated machinery. In this paper, the derivation of such mathematical models is exemplified for one of the most wide-spread machine types (the so-called chip shooter). Moreover, a simulation system for practical use in the electronics assembly is presented which incorporates various types of assembly machines. It serves as a tactical production planning aid as well as a test field for the analysis of the kinematic processes of PCB assembly machines. Such simulation, tailored to the specifics of a production environment, gives reliable estimates of the achievable production volume. Considerable deviations between the performance figures provided by the machine supplier and the actual result can thus be explained, and potential assembly system configurations be compared by drawing on reliable measures. Since the equipment is modelled at a level which takes precise account of its specific kinematics, a detailed analysis of the operations of the individual machine can also be performed revealing potential bottlenecks in its design. These insights are used to optimize machine design and control. Methods based on graph theory as well as on modern numerical search algorithms have been developed for the latter purpose. They lead to considerable performance improvements.     

Integrated methodology for board assignment and component allocation in printed circuit board assembly

An approach to minimize makespan for assigning boards to production lines is described. Because of sequence-dependent set-up times, board assignment and component allocation have to be performed concurrently. An integrated methodology is developed to obtain a solution to these two problems. The methodology consists of seven phases: printed circuit board grouping, family decomposition, subfamily sequencing, Keep Tool Needed Soonest (KTNS) procedure, component set-up determination, component allocation and board assignment. Application of the methodology to industrial problems demonstrates that it can solve large-scale problems efficiently. In addition, the effect of two key parameters, feeder capacity and threshold value, on the performance of the solution procedure was examined. The results indicate that feeder capacity has an impact on total workload imbalance but not on the global makespan. Threshold value, a measure of effectiveness of joining a component type to a component group for a printed circuit board family, has a significant effect on the global makespan. The interactions of threshold value, and variations in printed circuit board requirement and component usage also affect global makespan.     

Board sequencing and component loading problem for a single machine in PCB assembly planning

Most current research sequentially solves the board sequencing and component-loading problem for a single machine in printed circuit board (PCB) assembly. The board sequence is first determined. The component-loading order is then established. In addition, other current approaches are used to solve the problem based on the upper bound on component changeovers between two jobs. However, consideration of current magazine status could be a source for total set-up time reduction. In this paper, a new approach is developed to establish board sequence and component-loading order simultaneously. Each board sequence position and component-loading order are obtained together from the process of current set-up determination. The obtained solution is then improved further by the combination of bias and random search processes. Some experiments are tested to confirm theoretical judgement.     

AUTOMATED PROCESS PLANNING FOR PRINTED CIRCUIT CARD ASSEMBLY

Printed circuit card assemblies form the core of a vast array of contemporary manufactured products. The technologies for assembling printed circuit cards require a hierarchy of complex decisions for grouping card types and processes, staging components at assembly machines, arranging feeders, and sequencing placement operations. This paper is motivated by the largely unmet needs of industrial process planners for computer aids. Our objective is to develop a framework for the printed circuit card assembly process planning problem and to assess the current state of the research on appropriate models and solution methods. We first provide an overview of the essential elements of printed circuit card terminology, assembly technologies, and assembly system operations. Then we propose a decision hierarchy, survey the published literature, and identify needs for future research.     

Detection of capacitor electrolyte residues with FTIR in failure analysis

Detecting leakage from liquid aluminum electrolytic capacitors is not easy. Typically there is very little evidence of leakage because the electrolyte is volatile and leaves behind only trace residues. Liquid aluminum electrolytic capacitors are known to cause catastrophic failures where there is complete loss of functionality due to a short or open circuit. In the study presented in this paper, printed circuit board assemblies from a test and measurement system used in a clean room environment failed. Two units failed, causing burning in a particular area on the printed circuit board assembly. The failure area included several surface mount liquid aluminum electrolytic capacitors, and several others were mounted very close to the burnt region. A study was initiated to evaluate the cause of failure. Careful optical inspection revealed some residues on the outer side of the rubber seals of two of the electrolytic capacitors. Through using Fourier transform infrared analysis and a process of experimentation and analysis, it was determined that the residues were produced by liquid electrolyte that leaked out of the capacitor at some point in the field. The leaked electrolyte that came out of the capacitor was believed to be the cause of failure that led to the burning of the printed circuit board assembly.     

Position Measurement in Industrial Drives by Means of Low-Cost Resolver-to-Digital Converter

A fully integrated board for resolver-to-digital conversion is proposed in this paper. It is based on a combined analog/digital circuit, which allows one to track the shaft angle of a standard resolver in a digital form. Furthermore, the board also provides the feeding signal for the resolver-rotor circuit. All the tuning and configuration settings, which allow one to adapt different kind of resolvers to the proposed system, can be easily implemented directly on the board. The final assembly is a compact low-cost resolver-to-digital converter. The entire board design and implementation are described in this paper. In addition, several tests at different resolver speeds have been performed for validation.     

A note on ‘balancing printed circuit board assembly line systems’

In a recent paper of (Lapierre, S.D., Debargis, L. and Soumis, F., Balancing printed circuit board assembly line systems. Int. J. Prod. Res., 2000, 38, 3899–3911.), the authors considered the balancing of a PCB assembly line consisting of several pick-and-place machines. The authors claimed that, for the particular machine type they considered, the component placement time is independent of the placement sequence of the components and then concentrated on allocating component types to machines and configuring the feeders on each machine to balance the line. We show that, the placement time is actually dependent on the placement sequence and thus, it needs to be accounted for if a more accurate line balance is looked for.     

PCB assembly scheduling for collect-and-place machines using genetic algorithms

In printed circuit board (PCB) assembly, collect-and-place machines, which use a revolver-type placement head to mount electronic components onto the board, represent one of the most popular types of assembly machinery. The assignment of feeders to slots in the component magazine and the sequencing of the placement operations are the main optimisation problems for scheduling the operations of an automated placement machine. In this paper, we present different genetic algorithms (GAs) for simultaneously solving these highly interrelated problems for collect-and-place machines in PCB assembly. First we consider single-gantry machines as the basic type of machinery. In the conventional GA approach all placement operations and the feeder-slot assignment are represented by a single chromosome. In order to increase the efficiency of the genetic operators, we present a novel GA approach, which integrates a clustering algorithm for generating sub-sections of the PCB and grouping the corresponding placement operations. It is shown that the proposed GAs can be extended to schedule dual-gantry placement machines, which are equipped with two independent placement heads and two dedicated component magazines. Hence, component feeders have to be allocated between the two magazines. To solve this allocation problem, two different heuristic strategies are proposed. Finally, detailed numerical experiments are carried out to evaluate the performances of the proposed GAs.     

线路板印刷用Cu纳米粒子的研究进展

综述了电路印刷油墨用Cu纳米粒子在合成表征及应用方面的研究现状和发展趋势,并从工艺角度对其工业化生产做出了简要分析;归纳了电路板印刷油墨用Cu纳米粒子抗氧化技术进展;展望了今后印刷电子电路中Cu纳米导电材料的研究方向。