Rework Cell Research Articles

Systematic mechanical design approach for a flexible printed circuit board assemblies (PCBA) rework cell: part II – conceptual design of soldering and desoldering system

PurposeThe purpose of this paper is to apply the developed systematic mechanical design methodologies, that are obtained in part I, to investigate their success in designing mechanics of a flexible printed circuit board assembly (PCBA) rework cell.Design/methodology/approachThe decision of soldering and desoldering tool, which is the most critical function of a PCBA rework or remanufacturing cell, significantly influences overall design concept. Therefore, the paper starts by applying the design methodology to the soldering and desoldering function. The same study is repeated for the rest of the sub‐functions but only the results are provided.FindingsAn application of rework machine design methodology for the design of a PCBA rework cell has been made available. In addition to this, the embedded knowledge, such as the requirements list, the function structure, the function/means tree, the weighted objective tree and evaluation chart for the soldering and desoldering function are provided.Practical implicationsThe paper is the first work providing both embedded knowledge and the application of the systematic design methodology for the design of a fully automated flexible PCBA rework cell. The methodology leads rework machine designers in a well‐controlled and structured design environment.Originality/valueThe design methodology can be applied to all functions or targeted on key weighted areas to ensure that the designed rework machine meets the key areas of concerns. Furthermore, the methodology is generic and may be used to develop other complex manufacturing sytems.

Systematic mechanical design approach for a flexible printed circuit board assemblies (PCBA) rework cell: part I – generic mechanical design procedure

PurposeThe generic design environment for a flexible printed‐circuit board assemblies (PCBA) remanufacturing cell contains four interrelated complex design domains. Mechanical design domains are really complex and the use of well‐proven mechanical product design methodologies does not help the designer. Hence, this paper aims to develop a generic systematic design methodology for a flexible PCBA remanufacturing cell.Design/methodology/approachThe study investigates the use of conventional mechanical product design techniques for the design of a flexible PCBA rework (remanufacturing) cell. It indicates problems and the weaknesses when conventional product design techniques are used for the development of flexible manufacturing systems (FMS). It then provides a new systematic mechanical design methodology for designing a flexible PCBA rework (remanufacturing) cell. The design methodology is intended to be generic in order to apply successfully to any FMS design.FindingsConventional product design methodology cannot be used directly for the design of a flexible PCBA remanufacturing cell. Hence, two design methodologies were developed: the generic FMS mechanical design methodology and a specific FMS design methodology for a PCBA rework cell. The first one was developed based on the tasks of the conventional product design process integrated with new design tools. The generic design methodology was then extended to obtain the second methodology for a PCBA rework cell design. Both of the methodologies were applied to a flexible PCBA rework cell design problem. Both design methodologies eliminated unusable design solutions at the early design stages of the conceptual design process and made the design process easier.Practical implicationsThe generic and specific design methodologies provide a better design environment, even for less specialized FMS designers.Originality/valueThe design methodologies may help for the commercialization of a flexible PCBA remanufacturing cell that may be used for SM rework and assembly.

Situation dependent decision selector for production control in testing and rework cell

This paper presents a production control approach for the testing and rework cell in a dynamic and stochastic computer integrated manufacturing (CIM) system. The proposed situation dependent decision selector (SDDS) observes the status of the system and jobs at every decision point, and makes its three different decisions on dispatching, pre-emption, and dispatching within pre-emption in real time. This paper also develops a new feature selection algorithm for the SDDS. Experimental results show that the SDDS is better than other static control rules and another dynamic control approach with respect to the number of tardy jobs.

Dynamic production control with dispatching within pre-emption

This paper deals with a production control problem for the testing and rework cell in a dynamic and stochastic computer integrated manufacturing (CIM) system. This research first defines dispatching within pre-emption for an extended form of pre-emption. A dynamic controller called competitive decision selector (CDS) is then modified and extended as CDSplus to handle three different production control decisions; dispatching, pre-emption, and dispatching within pre-emption. It observes the status of the system and jobs at every decision point, and makes its three different decisions in real time. The CDSplus dynamic control shows better performance than static control rules with respect to the number of tardy jobs.

Architecture of a dynamic production controller in CIM enterprise environments

This paper deals with a production control problem for the testing and rework cell in a dynamic and stochastic computer integrated manufacturing (CIM) system. A dynamic controller is designed to handle three different production control decisions; dispatching, pre-emption, and dispatching within pre-emption. The model of this system also helps users deal with a large number of input features in real situations. This paper describes a technical architecture of dynamic production control and design issues of a dynamic production controller. It explains the overall development processes of the system and functional diagrams in order to give readers a design guideline for the dynamic production controller.

Complexity in rework cells: theory, analysis and comparison

Although the word complexity is often used by engineers who are trying to re-design or re-organize a system, a formal definition of the term is often lacking. This paper introduces and extends the application of the concept of entropy to the quantitative analysis of complexity in the design and study of manufacturing systems. Sequence disorder complexity and routing complexity are defined in the context of manufacturing systems specifically including rework cells. Different kinds of rework cells are defined and their parameters presented. The difference between input and output sequences is studied with respect to rework cell system parameters and we introduce a quantitative complexity metric to measure the difference between alternative rework cells. The emphasis of this paper is on providing a comprehensive comparison on system performance of several structures of rework cells in terms of complexity, cost and quality. The paper concludes that both the choice of rework cells structure and system parameter selection are important to the design of rework cells.

Design of a flexible assembly and remanufacturing cell for advanced SM components: selection of cell design concept based on reflow tools

PurposeTo design a flexible integrated robotic assembly and rework (remanufacturing) cell for assembly, selective assembly and rework of advanced surface mount components (SMCs) using the generic methodology developed in this paper.Design/methodology/approachManual rework procedures are investigated for all advanced SMCs. General and specific component‐related rework considerations are obtained and necessary tooling candidates for automation are determined. This is followed by determination of the specific automated rework procedure and selection of suitable tooling for automated robotic rework and generation and evaluation of design concepts.FindingsThe developed methodology, which considers the reflow tool at the centre of the development process, has worked well in designing a flexible integrated robotic assembly and rework cell.Practical implicationsThis study identified the rework requirements for advanced SMCs, the essential features for rework reflow tools, criteria for comparing reflow tools, and a generic procedure for design and concept selection.Originality/valueIt provides valuable knowledge for designers of flexible integrated robotic assembly and rework cells for assembly, selective assembly and rework of advanced SMCs.

Data-Mining Approach to Production Control in the Computer-Integrated Testing Cell

This paper presents a data-mining-based production control approach for the testing and rework cell in a dynamic computer-integrated manufacturing system. The proposed competitive decision selector (CDS) observes the status of the system and jobs at every decision point, and makes its decision on job preemption and dispatching rules in real time. The CDS equipped with two algorithms combines two different knowledge sources, the long-run performance and the short-term performance of each rule on the various status of the system. The short-term performance information is mined by a data-mining approach from large-scale training data generated by simulation with data partition. A decision tree-based module generates classification rules on each partitioned data that are suitable for interpretation and verification by users and stores the rules in the CDS knowledge bases. Experimental results show that the CDS dynamic control is better than other common control rules with respect to the number of tardy jobs.

Determination and comparison of surface mount component rework cycle times of manual and fully automated robotic rework stations for rework technology selection

The aim of this paper is to provide a complete decision framework to find out when it is appropriate to use an automated robotic rework station for surface mount (SM) component rework. For this purpose, the results of the performance tests on the cell and manual rework cycle times (RCTs) have been determined using experimental studies. These are followed by the comparison of the experimental results, rework effectiveness, parametric rework cycle determination and overall rework cost studies. As a conclusion, a framework has been suggested by comparing automated versus manual rework stations to find out when it is appropriate to use an automated robotic rework cell. Furthermore, it provides manual and automated RCTs for SM components.

Cost and performance analysis of a robotic rework cell

Printed circuit board assembly (PCBA) rework is an acceptable process step in PCBA manufacturing and widely performed using manual and semi-automated tools. Until recently, there has been a lack of international effort for the development of a fully automated rework system mostly due to the predicted high capital cost of such system. Since robots are used in PCBA manufacturing, PCBA robots are equipped and have been developed with multi-functional capabilities to assemble and inspect PCBAs. If the same equipment is used for rework, the high cost of the robot, on account of vision and other sensory needs can be eliminated and this can justify the investment. A robot-based rework system thus becomes an alternative technology to manual or semi-automated rework. Because there is no information on which technology is most appropriate, a model has been developed to predict the cost of reworking PCBAs using semi-automated and automated-robotic rework technologies. These two alternative rework technologies are analysed and compared to give an indication of how appropriate is a robotic rework cell.

Designed experiments to investigate the solder joint quality output of a prototype automated surface mount replacement system

A robotic remanufacturing system at Rensselaer has been developed to replace fine pitch surface mounted components on a populated printed circuit board (PCB). The performance goal is to maximize the quality of the solder joint output to optimize the system's throughput. The purpose of this paper is to present the process parameters determined for obtaining a good solder joint with the rework cell. Developed here and to show an analysis of the solder joint quality obtained from the developed system. Maximizing the rate of correctly reworked components by the system is not chosen as a goal for measuring the system's performance. This is because rework is a low volume process and the cell being used, is an experimental prototype system.

Equipment selection, integration and interfacing of a robotic PCBA component rework cell

Defects are still common in printed circuit board assembly (PCBA) technology despite all the improvements made, and rework of PCBA is inevitable and performed manually in PCBA manufacturing floors since the cost of each component and the PCB itself may be hundreds of pounds. On the contrary, a lack of international effort for the early development of fully automated rework equipment has been hindered due to high cost predictions and complex process requirements. Therefore, there is a growing need for automated rework. Since the requirement is to automate manual rework using an industrial robot, choosing appropriate hardware and suitable methods is very important to meet the economic and ultimate rework requirements. Hence, a robotic rework cell has been developed as part of a robotic assembly cell where much of the required equipment is already present to meet the economic concerns. This paper illustrates the importance of rework tool selection for a successful development. It therefore presents the required techniques and the chosen tooling. After the introduction of the tooling, integration of tools and interfacing of control equipment are presented. Finally it describes the layout of the cell and concludes with recommendations and future studies with regard to chosen tooling and automation requirements.

Software architecture of a printed circuit board assembly (PCBA) robotic rework cell

Defective printed circuit board assembly (PCBA) is inevitable despite the improved statistical process control methods in PCB manufacturing. Currently, manual rework equipment is normally used to correct the defects. Whilst PCBA manufacturing is highly automated, rework has not yet been successfully fully automated and it is still very much operator dependent despite the high cost of this. It is generally recognised that the lack of international effort to develop a fully automated rework cell is mostly because of the anticipated cost of a such a system. A fully automated robotic rework cell has been developed, implemented and manufactured at the University of Salford, UK. This cell was designed to be an integrated part of a PCBA cell and to perform assembly, rework and in-process inspection so that the system with shared resources can be economically justified. This paper summarises the hardware and, in particular, describes the architecture of the software of the automated rework cell which is capable of removing and replacing both surface mount (SM) and through-hole (TH) components of single-sided defective PCBAs.

THE LIMITS OF AUTOMATING ELECTRONIC COMPONENT REWORK

The increased complexity, cost and lead count of surface mount (SM) components, coupled with the increased density of circuit assemblies, have demanded more accurate and sophisticated rework equipment. Hence, semi automated rework equipment capable of reworking key components has experienced continuous growth in the market. Since then, a considerable amount of investment has been made on the semi-automated component rework equipment. However, now it has become important to consider a fully automated rework because the skill required to rework defective components has increased to an extent where manual replacement and solder dispensing are essentially impossible steps of rework, and because there is a demand for consistent, reliable and high quality repairs and health hazards associated with the use of chemicals. In this field, three different research groups have so far attempted to develop the automated rework cell. All three groups have published materials mainly concentrated on how to reduce operator involvement; improve rework system integration; and reduce damage to printed circuit board assemblies (PCBAs) and adjacent components. However, the limits of automating electronic component rework and main rework concerns related to the automation have not been reported yet. Therefore, this paper discusses the difficulties and restrictions in automating electronic component rework both for through-hole (TH) and SM components including standard, fine and ultra-fine pitch SM components.

Plastic Ball Grid Array Attachment: Assembly and Reliability Performance

As plastic ball grid array (PBGA) components proliferate, card assembly questions arise about the robustness of the module to card attachment process. A designed experiment was performed to measure the sensitivity of card assembly yields to normal assembly process variation. Experimental variables include card thickness, ball pad size on the card ball grid array (BGA) site, module moisture exposure and ball planarity of a 225 I/O PBGA. Another set of PBGA test cards, assembled under optimum process conditions, was subjected to accelerated thermal cycle (ATO) testing. ATC testing also included a rework cell. Overall, the PBGA module attachment process demonstrated robustness. The initial attach and reworked modules proved to be reliable. This paper focuses on the details of the test conditions and the results.

Automated removal and replacement of surface mounted devices in electronic assembly

A unique robotic assembly, in-process inspection and rework cell has been developed as an extension of an assembly cell to deal with single sided printed circuit board assemblies (PCBAs) since rework of surface mount (SM) PCBAs are essential. The cell is capable of formulating and planning the rework based on the automatic test equipment (ATE) and CAD/CAM data and is able to remove and replace the standard SM and through-hole (TH) components automatically without an operator involvement. This paper specifically discusses the quality of SM rework for each rework step. It starts with the summary of surface mount rework technology and the development of the automated cell including the tools for automated SM rework and an overall system structure. It is followed by the evaluation of SM component rework. In this part, the results of automated removal and replacement of SM components are presented and evaluated including the rework steps of fluxing, component removal, pad cleaning, solder dispensing, component placement and reflow. It finally concludes with the economic justification of the developed unique rework cell and findings of SM rework evaluation.

Automated removal and replacement of through-hole components in robotic rework

The need for computer controlled, fully automated rework stations has increased recently due to potential difficulties involved in manual rework of printed circuit board assemblies (PCBAs). An autonomous fully-automated robotic rework cell has been developed for the rework of TH and SM components. This paper concentrates on TH component removal and replacement issues. After a brief introduction to TH rework technology and overall cell structure, it draws attention to the main issues of component removal with regard to gripping and heating. Two multifunctional grippers that are unique in their design are presented as a solution for clinched TH component removals. Since heat is the major issue in the process, dwell times for component removal and replacement are given based on a full scale experimental study. Results of automated TH rework evaluations include the success of leg cutting, spray fluxing, removal and replacement of components.

NON-CONTACT TEMPERATURE MEASUREMENT IN SM COMPONENT REWORK

Although surface mount assembly equipment has been rapidly developed during the last decade, surface mount device rework equipment is still largely basic and its development has not kept pace. The rework process is still viewed as a side issue, even when manufacturers consider the quality of the reworked board to be as good as the original board. An important consideration in rework is the control of the heating of the surface mount (SM) component, and although various attempts have been made to automate the heating process, the rework heating process is unfortunately still not as good and uniform as those for conventional SM reflow. Primarily, the techniques used for rework are manually assisted, and usually rely on the rework operator's judgement in the observation and control of the rework process. A real-time closed-loop controlled rework-reflow system, capable of reflowing all SM components regardless of their heat capacity, type of Printed Circuit Board Assembly (PCBA) and the position of components on PCBA, has been developed as part of a fully automated robotic rework cell. The reworkreflow system is a separate unit, which can be easily adapted for use in any manual rework system. An important part of the system is a non-contact sensor, for real-time measurement of the reflow temperature and its feedback to the device controller unit. The paper describes the closed-loop controlled reflow system employed in the automated robotic rework cell, highlights the problems associated with its use, and then summarizes the requirements for non-contact temperature measurement in reworking SM components. The principles of non-contact measurement and the importance of emissivity for temperature measurement are also highlighted, and the experimental results of the true emissivity of the SM components are presented.

Cell Controller Software Modelling for PCBA Rework Cell

Rework is an integral part of printed circuit board assembly (PCBA) manufacturing. However, the state‐of‐the‐art for PCBA rework still relies on operator activity and is therefore semi‐automatic. As a result, the quality of rework depends very much on the skill of the operator. When developing an automatic PCBA rework cell, the cell controller is an essential part which organises and controls the overall rework operation. This paper describes the software modelling of the cell controller for the PCBA rework cell which has been implemented for reworking through‐hole and surface mounted components. The software model is based on hybrid representations and rule‐based control.

The significance of desoldering and resoldering methods in robotic automated rework

The rework of printed circuit board assembly (PCBA) has been tacitly accepted as necessary since PCBA manufacturing began. Manual rework is unreliable, time-consuming and expensive, and there is a growing need for automated rework. Further, as future assembly methods such as tape automated bonding and chip on board come into use, the ability of humans to perform the rework function at all is in doubt! Currently, with the increasing use of fine-pitch devices, the need for computer-controlled mechanical rework stations has become more important. While PCBA has, in the main, been successfully automated, the same developments have not been evident in component rework. In this paper, commercial reflow techniques for both through-hole (TH) and surface-mount (SM) component rework are discussed and analysed, with the intention of determining the most appropriate to an experimental robotic assembly cell extended to perform single-sided rework based on a batch size of one. The paper shows the importance of the desoldering and resoldering techniques for a fully automated robotic rework cell, examines various possibilities for developing the cell based on different reflow techniques and proposes the most suitable one. It then describes the configuration of reflow equipment in the cell, and concludes with quality and cost data for the cell based on the chosen reflow techniques.