Development of an integrated reflow soldering control system using incremental hybrid process knowledge

In this paper, we present an industrial application of intelligent knowledge-based reflow soldering control system to economically determine process parameters and assess the outputs for surface mount assembly. The system performance of surface mounting is significantly affected by three major interconnected process segments (including solder paste application, component placement, and solder reflow) and in combination. Many surface mount manufacturers have suffered both quality and productivity losses due to the lacks of effective line setup procedures, rapid process troubleshooting, and appropriate corrective action. This proposed system develops an integrated process control scheme, the framework of hybrid process knowledge extraction through neuro-fuzzy data training, and a knowledge-based system with a GUI man–machine interface for predicting and controlling the given system performance. The efficiency and effectiveness of the proposed system are illustrated using DPMO measurement and productivity analysis.     

Quality-oriented optimization of wave soldering process by using self-organizing maps

In this paper, the optimal process parameters of a wave soldering process were defined. The optimization was performed in respect to soldering quality by minimizing a cost function describing the total repairing cost of a wave-soldered printed circuit board (PCB). The data analysis stages were as follows. First, the process data were coded into inputs for a self-organizing map (SOM). Next, a function for the repairing cost was constructed and used to find the optimal map neurons. At the last phase, the optimal parameters were approximated on the basis of the reference vectors of the optimal neurons. The results showed clearly potential in the optimization of the wave soldering process, especially in the visualization of the optimal process conditions. Therefore, it would be useful to exploit the method more widely in the electronics industry.     

装配可靠性的模糊广义随机Petri网建模与分析

针对一般广义随机Petri网模型精度低的问题,将模糊数引入到广义随机Petri网,提出模糊广义随机Petri网的概念.结合模糊数包含信息多的优点,利用模糊广义随机Petri网对装配过程进行建模,通过同构的Markov链对模型进行定量分析.用模糊广义随机Petri网模型计算得到的装配可靠度与一般广义随机Petri网模型的装配可靠度进行分析比较,结果表明了模糊广义随机Petri网模型的精度更高.以数控磨床砂轮架为例,证明了上述方法的有效性.     

GO-FLOW法在产品装配过程可靠性分析中的应用*

借鉴可靠性工程理论,运用GO-FLOW法分析产品装配过程的可靠性。通过分析装配过程各工步之间的关系,建立起产品装配过程可靠性控制的一般框架模型。以齿轮油泵装配过程为例,建立起齿轮油泵装配过程的GO-FLOW图,并分析其信号流、操作符和运算规则;通过GO-FLOW运算,求出各信号流的故障率和可靠度,找到影响产品装配过程可靠性的关键环节。结果表明,GO-FLOW法在产品装配过程可靠性分析中的应用是方便有效的。     

A framework for an automotive body assembly process design system

This paper describes a framework for an automotive body assembly process design system. It is a computer-aided intelligent system that can automatically generate the optimal joint types and assembly sequences for the best dimensional quality. The backbone of this system is the Case-Based Reasoning (CBR) methodology, which works by searching through a case library created from previous designs whose identifying features resemble the current case. Algorithms for initial solution generation, dimension chain generation, joint design selections, assembly sequence generation, and tolerance analysis and optimization are developed. Based on the framework, a software tool called Body Build Advisor, or BBA, is developed. The software allows process designers to analyze candidate assembly schemes and achieve the best assembly process design prior to having detailed knowledge of geometry of the parts, and thus is ideal for architectural process design. In addition, the system has the advantage of an open structure that can be easily modified and adapted to accommodate existing assemblies and to suggest areas for improvement.     

An algorithm for the automatic generation of an assembly process for modular fixture parts

In metal mold production systems, rapid, high-quality, and low-cost production technologies are needed. In these systems, assembly tasks to make fixtures to immobilize the mold are required. The mold must be firmly fixed in order to resist the force generated by NC machine tools. In this article, we discuss the automatic generation of an assembly process for modular fixture parts in the systems. The assembly drawing of the parts can be obtained from STEP/AP203, which is a text file of CAD/CAF data. In these data, the shape and configuration of all assembled fixtures are included. The shape of each fixture is constructed with planar, cylindrical, and conical surfaces. From the data, the number of surfaces in contact with other surfaces is derived for each part, and valid contacts are judged for their degree of importance. A tree of contacts among all fixtures is derived. In the numerical examples, the assembly process is automatically generated by our proposed method. It is shown that a suitable assembly process is obtained.     

Use of the dirichlet process for reliability analysis

Recently, many researchers apply the non-parametric Bayesian approach to predict the reliability of highly complex electronic systems. The Dirichlet process is the most common model for the non-parametric Bayesian analysis. The Kuo's simulation procedure [6] for Dirichlet process under a variance reduction techniques introduced in Chien and Kuo (1994) [2] is applied for a Weibull-distributed system. Optimal burn-in time is determined given the cost parameters. A model, the percentage of good items in a lot, is used to explain when the Dirichlet process is not a proper choice.     

Parametric study of flip-chip packaging for an MEMS device with diaphragm

A backside-etched silicon chip with a polysilicon diaphragm flip-chip attached on a printed wiring board and globally bumped on a FR4 printed circuit board was investigated through a finite element analysis for determining three key parameters of flip-chip chip size packaging, namely, the size of solder bump, and the thickness of the printed wiring board with/without U8437-3 underfill. Four kinds of thermal-induced stresses and deformations in the diaphragm, solder bump, and printed wiring board were evaluated for the parametric study. As the simulation results show, the thermal-induced stresses in the diaphragm and solder bump can be reduced effectively if the printed wiring board is thinner. However, the printed wiring board is still required to be sufficiently thick to prevent warping. In addition, the underfill material also can reduce the induced stress occurring at the interface between the solder joint and the chip and improve reliability. In general, the parametric study can provide a basis for the flip chip package of a MEMS device with a diaphragm, such as a MEMS microphone, MEMS pressure sensor, etc.     

Measuring and evaluating maintenance process using reliability,risk, and test metrics

In analyzing the stability of a software maintenance process, it is important that it is not treated in isolation from the reliability and risk of deploying the software that result from applying the process. Furthermore, we need to consider the efficiency of the test effort that is a part of the process and a determinate of reliability and risk of deployment. The relationship between product quality and process capability and maturity has been recognized as a major issue in software engineering based on the premise that improvements in the process will lead to higher-quality products. To this end, we have been investigating an important facet of process capability-stability-as defined and evaluated by trend, change and shape metrics, across releases and within a release. Our integration of product and process measurement serves the dual purpose of using metrics to assess and predict reliability and risk and to evaluate process stability. We use the NASA Space Shuttle flight software to illustrate our approach     

Development of an end-point detector for parylene deposition process

Parylene is an emerging material for MEMS. It is an organic material that is grown by using the chemical vapor deposition method at room temperature. The deposition thickness is commonly controlled by the amount of solid-phase dimer loaded in a sublimation chamber. In a conventional deposition machine, the end point of the process is designated by the moment the dimer is exhausted. However, this end-of-process criterion does not offer precise, repeatable control of film thickness. We present the results of the development of an in situ end-point detector for a Parylene chemical vapor deposition process. The detector is based on the thermal transfer principle and can be implemented on commercial parylene deposition systems with minimal system modification. Such a sensor enables a user to stop the deposition when a targeted thickness is reached. The end point detector is very simple to implement on existing parylene deposition systems. A series of such sensors with different target deposition thickness would allow extraction of the actual deposition rate within a deposition run.     

Extended liaison as an interface between product and process model in assembly

This paper describes the use of liaison to better integrate product model and assembly process model so as to enable sharing of design and assembly process information in a common integrated form and reason about them. Liaison can be viewed as a set, usually a pair, of features in proximity with which process information can be associated. A liaison is defined as a set of geometric entities on the parts being assembled and relations between these geometric entities. Liaisons have been defined for riveting, welding, bolt fastening, screw fastening, adhesive bonding (gluing) and blind fastening processes. The liaison captures process specific information through attributes associated with it. The attributes are associated with process details at varying levels of abstraction. A data structure for liaison has been developed to cluster the attributes of the liaison based on the level of abstraction. As information about the liaisons is not explicitly available in either the part model or the assembly model, algorithms have been developed for extracting liaisons from the assembly model. The use of liaison is proposed to enable both the construction of process model as the product model is fleshed out, as well as maintaining integrity of both product and process models as the inevitable changes happen to both design and the manufacturing environment during the product lifecycle. Results from aerospace and automotive domains have been provided to illustrate and validate the use of liaisons.     

A repository for design, process planning and assembly

This paper provides an introduction to the Design, Planning and Assembly Repository available through the National Institute of Standards and Technology (NIST). The goal of the Repository is to provide a publically accessible collection of 2D and 3D CAD and solid models from industry problems. In this way, research and development efforts can obtain and share examples, focus on benchmarks, and identify areas of research need. The Repository is available through the World Wide Web at URL http://www.parts.nist.gov/parts.     

A quasi-renewal process for software reliability and testing costs

This paper models software reliability and testing costs using a new tool: a quasi-renewal process. It is assumed that the cost of fixing a fault during software testing phase, consists of both deterministic and incremental random parts, increases as the number of faults removed increases. Several software reliability and cost models by means of quasi-renewal processes are derived in which successive error-free times are independent and increasing by a fraction. The maximum likelihood estimates of parameters associated with these models are provided. Based on the valuable properties of quasi-renewal processes, the expected software testing and debugging cost, number of remaining faults in the software, and mean error-free time after testing are obtained. A class of related optimization problem is then contemplated and optimum testing policies incorporating both reliability and cost measures are investigated. Finally, numerical examples are presented through a set of real testing data to illustrate the models results     

Wavesolder assistant: An expert system to aid troubleshooting of the wave soldering process

This paper discusses WAVESOLDER ASSISTANT — a computer-based expert system whose goal is to provide interactive advice about the cause and possible resolution of problems encountered in wave soldering electronic circuit boards. The system contains knowledge that has largely been derived from manufacturing personnel directly involved with the wave soldering process. The system queries the user for information relevant to the problem selected, and applies its information to determine causes of the problem. On request, it explains how the query is related to the goal.     

Estimation of all-terminal network reliability using an artificial neural network

The exact calculation of all-terminal network reliability is an NP-hard problem, with computational effort growing exponentially with the number of nodes and links in the network. During optimal network design, a huge number of candidate topologies are typically examined with each requiring a network reliability calculation. Because of the impracticality of calculating all-terminal network reliability for networks of moderate to large size, Monte Carlo simulation methods to estimate network reliability and upper and lower bounds to bound reliability have been used as alternatives. This paper puts forth another alternative to the estimation of all-terminal network reliability — that of artificial neural network (ANN) predictive models. Neural networks are constructed, trained and validated using the network topologies, the link reliabilities, and a network reliability upperbound as inputs and the exact network reliability as the target. A hierarchical approach is used: a general neural network screens all network topologies for reliability followed by a specialized neural network for highly reliable network designs. Both networks with identical link reliability and networks with varying link reliability are studied. Results, using a grouped cross-validation approach, show that the ANN approach yields more precise estimates than the upperbound, especially in the worst cases. Using the reliability estimation methods of the ANN, the upperbound and backtracking, optimal network design by simulated annealing is considered. Results show that the ANN regularly produces superior network designs at a reasonable computational cost.Scope and purposeAn important application area of operations research is the design of structures, products or systems where both technical and business aspects must be considered. One expanding design domain is the design of computer or communications networks. While cost is a prime consideration, reliability is equally important. A common reliability measure is all-terminal reliability, the probability that all nodes (computers or terminals) on the network can communicate with all others. Exact calculation of all-terminal reliability is an NP-hard problem, precluding its use during optimal network topology design, where this calculation must be made thousands or millions of times. This paper presents a novel computationally practical method for estimating all-terminal network reliability. Is shown how a neural network can be used to estimate all-terminal network reliability by using the network topology, the link reliabilities and an upperbound on all-terminal network reliability as inputs. The neural network is trained and validated on a very minute fraction of possible network topologies, and once trained, it can be used without restriction during network design for a topology of a fixed number of nodes. The trained neural network is extremely fast computationally and can accommodate a variety of network design problems. The neural network approach, an upper bound approach and an exact backtracking calculation are compared for network design using simulated annealing for optimization and show that the neural network approach yields superior designs at manageable computational cost.     

Bi-criterion optimisation for configuring an assembly supply chain using Pareto ant colony meta-heuristic

An assembly supply chain (SC) is composed of stages that provide the components, assemble both sub-assemblies and final products, and deliver products to the customer. The activities carried out in each stage could be performed by one or more options, thus the decision-maker must select the set of options that minimises the cost of goods sold (CoGS) and the lead time (LT), simultaneously. In this paper, an ant colony-based algorithm is proposed to generate a set of SC configurations using the concept of Pareto optimality. The pheromones are updated using an equation that is a function of the CoGS and LT. The algorithm is tested using a notebook SC problem, widely used in literature. The results show that the ratio between the size of the Pareto Front computed by the proposed algorithm and the size of the one computed by exhaustive enumeration is 90%. Other metrics regarding error ratio and generational distance are provided as well as the CPU time to measure the performance of the proposed algorithm.     

数控机床功能部件可靠度建模与维护预警系统开发*

为了提高机床可靠性,深入分析了机床功能部件故障数据,研究了采用两重威布尔分段模型建立机床功能部件可靠度分布模型的方法与极大似然方法确定模型参数的过程。提出了基于可靠性分析的机床维护预警系统开发,阐述了预警系统原理设计过程与功能模块设计方法。系统的实例应用表明,该方法对机床预防维护非常合理有效。     

Numerical and experimental investigations of the formation process of ferrofluid droplets

This paper reports both experimental and numerical investigations of the formation process of ferrofluid droplets in a flow focusing configuration with and without an applied magnetic field. In the experiment, the homogenous magnetic field was generated using an electromagnet. The magnetic field in the flow direction affects the formation process and changes the size of the droplets. The change in the droplet size depends on the magnetic field strength and the flow rates. A numerical model was used to investigate the force balance during the droplet breakup process. A linearly magnetizable fluid was assumed. Particle level set method was employed to capture the interface movement between the continuous fluid and the dispersed fluid. Results of the droplet formation process and the flow field are discussed for both cases with and without the magnetic field. Finally, experimental and numerical results are compared.     

Optimization of pin through hole connector in thermal fluid–structure interaction analysis of wave soldering process using response surface methodology

This paper presents an optimization of pin through hole (PTH) connector in the wave soldering process; the optimization was performed by using response surface methodology. The geometrical and process parameters (i.e., offset position, pin diameter, offset angle, and solder temperature) were optimized by using response surface methodology via central composite design for the wave soldering process. Thermal fluid–structure interaction aspects were considered in the optimization. A mesh-based parallel code-coupling interface was employed to connect both fluid and structural solvers. The interactive relationship between independent variables (i.e., offset position, pin diameter, offset angle, and solder temperature) and the responses (i.e., filling time at 75% volume, von Mises stress, and maximum displacement) were investigated. The generated empirical models were examined and well substantiated by the simulation results. The optimum geometrical and process parameters of the wave soldering process for the PCB and PTH connector were as follows: 0.12 mm of PTH offset position, 0.17 mm of PTH diameter, 0° of offset angle, and 473 K of molten solder temperature.