Rework Operations Research Articles

Energy-efficient scheduling for a flexible job shop problem considering rework processes and new job arrival

Sustainable production is not limited to environmental concerns only; It also provides economic benefits for businesses. Businesses that adopt sustainability principles can gain advantages in matters such as cost savings, competitive advantage, risk management, legal compliance and corporate reputation. Therefore, sustainability is no longer an option but a strategic imperative for businesses. For this reason, studies on energy-sensitive scheduling have started to increase recently. Another important factor in sustainable manufacturing is the reduction of scrap. Rework operations are required to reduce scrap. In this study, the multi-objective flexible job shop scheduling problem (MO-FJSP) that considers energy efficiency is discussed. The created model aims to minimize the energy consumption, total machine workload and makespan. In this study, new job arrivals are considered as dynamic events. Another dynamic event added to the model is the addition of rework processes between operations to reduce the scrap rate when a scrap decision is made during the production stages. The enhanced NSGA II algorithm was applied to solve this problem. The enhanced NSGA II algorithm was applied to test instances and its performance was compared using some of the multi-objective performance indicators. These experimental results prove the effectiveness of the proposed solution method.

An economic manufacturing quantity model with rework process for deteriorating products under maintenance-quality policy

ABSTRACT This paper presents an integrated model of three interrelated topics including the statistical process monitoring, maintenance scheduling, and production cycle length for imperfect manufacturing systems. The novelty of this paper is to take five features into consideration, including: (1) The produced items deteriorate over time, hence, the inventory is depleted in two ways i.e. responding to demand and gradually deteriorating products; (2) The non-conforming products can be reworked to increase the cost-saving by eliminating the waste items; (3) A non-uniform sampling scheme is employed such that the hazard rate does not exceed its threshold value; (4) The economic-statistical design of a control chart is used to accelerate the detection of process faults as well as reduce the risk of false alarms; and (5) The time value of money is taken into account to obtain more precise financial flow estimations. Finally, four comparative studies along with a sensitivity analysis on the most important parameters are conducted. The results confirm that considering the product deterioration and time value of money improves the model adaptability in real-world applications. Besides, employing the variable sampling scheme and the rework operations reduces the production rate of non-conforming items. The results also show that the total cost in economic-statistical model is slightly higher than that of the economic one. However, the economic-statistical model performs severely better than the economic one in terms of both in-control and out-of-control average run length metrics.

Applying data of historical defects to increase efficiency of rework in assembly

Due to the global trend towards individualized products, manufacturing processes have become more complex, especially in assembly systems of production companies. One major challenge is how to react quickly and correctly to randomly occurring errors caused by assembly staff. Operators reworking these defects face a high complexity when trying to fix previously caused errors. To support this task, historical data of rework operations can provide useful information on how to handle defects. For this, all data must be filtered in such a way that the most frequent, up-to-date and suitable rework solutions are identified for each error. Afterwards the relevant information for a rework jobs can be provided by assistance systems for reworking staff. Hereby the efficiency of reworking processes in assemblies can be increased.

Analytical Approach for the Examination of the Feasibility of Rework in Flow Assembly Lines

Since the beginning of the 20th century flow assembly lines are a global standard for manufacturing companies to produce serial products. The standardization and the allocation of assembly jobs in certain cycle times along the assembly line ensure productivity. All work operations in each cycle are allocated ideally in such a way that every operator uses the complete cycle time for the assembly jobs.One disadvantage of these flow assembly lines is the lack of time for possible rework operations. If a human error occurs, there is hardly any time for its correction. The alternative is to stop the line until the rework is done. These situations cause an interruption of work for the whole line, which is unproductive. Consequently most errors become evident at the end of the line and cause rework, which diminishes productivity as well.This paper helps to examine the feasibility of rework in flow assembly lines with regard to technical and organizational restrictions.

BENEFITS OF TRANSMISSION LINE METAL-INSULATOR-METAL CAPACITORS IN MASS PRODUCTION OF RF CIRCUITS

Coupling capacitors or DC blocks are essential tuning elements in RF/microwave applications. Their role becomes imperative in cascade amplifiers to isolate drain voltages of preceding MMIC from the gate voltage of the following chip where both RF and DC signals are carried through the same line. The purpose of this study is to explain the benefits of a newly designed thin film coupling capacitor called as transmission line metal-insulator-metal capacitor (TL MIM Cap), which serves as a DC block capacitor in microwave circuits. This novel structure provides a unique solution, which cannot be achieved with traditional single layer ceramic capacitor (SLC) structure. It combines two discrete circuit elements into one: “Microstrip transmission line of required length and width” with a “serially attached coupling capacitor”. Thin film capacitive layers ranged from 0.5pF to 50pF, which are typically needed for microwave frequencies within 1–40 GHz, constructed and embedded into 50 Ohm impedance transmission lines in series. Substrates like quartz, glass, or alumina can be used to minimize losses and to achieve higher RF/microwave performance. We used copper traces as conductive layers for optimal conductivity. After manufacturing TL MIM Caps, we tested several capacitance values for 1pF, 5pF, 15pF and 30pF corresponding to a wide frequency range. The RF tests we performed showed that TL MIM Caps exhibited a minimum of 20dB return loss and a maximum of 0.3 dB insertion loss at 1–40GHz range. We also found our technique comes with some workmanship advantages in high frequency circuit assembly as follows: Traditional coupling capacitor attachment with silver epoxy on top of a microstrip transmission line is a manual operation, which requires well trained and experienced technicians. In contrast, using the TL MIM Caps in our high frequency hybrid modules, we found that the process caused errors were eliminated such as the micro short circuit effect caused by conductive epoxy. Therefore we improved yield in assembly stage of the circuits. In addition, improvements are observed in production processes such as less consumption of adhesives (epoxy), no technician failure caused wastes, elimination of extra curing process to attach capacitors, no short circuit inspection, rework, or re-cure operations to fix assembly errors. Last but not least, blocking capacitors are embedded into the microstrip transmission lines in TL MIM Caps. This ensures that having the lowest possible impedance since very short wire bond exists from the bond pad of the TL MIM Cap to the adjacent circuit element.

Clustering Return Items in a Multi-Layer Multi-Product Reverse Supply Chain Using Data Mining

In the reverse supply chain the basic concern is to categorize the returned materials in the usable or non-usable ones for performing the required operations to resend them in the supply chain. Companies can obtain more confidence from their consumers to carry out continuous revers logistics removing the defective products. To begin the reverse multi-layer multi-product supply chain and after collecting the returning commodities, we cluster them via k-mean algorithm in Matlab software environment. The results are used to perform a sampling process to deliver the commodities to the related layer for rework and repair operations. The computations show an extensive reduction in the human resource costs for separation of the returning items and increasing the efficiency.

Effects of multiple BGA rework on strength of solder joints

PurposeThe purpose of this paper is to investigate effects of the multiple rework of ball grid array (BGA) components on mechanical strength of BGA balls, as well as any possible intermetallic (IMC) embrittlement, and obtain data correlated with possible estimation on the maximum permitted limits of BGA rework.Design/methodology/approachIn this paper, mechanical strength of BGA components assemblies with multiple numbers of rework operations was evaluated. Mechanical evaluation was conducted using BGA ball shear tests and four‐point bending tests of BGA assemblies. Test samples were prepared under the following conditions: virgin, one, two, three and five BGA reworks. Failure mechanism was evaluated using cross‐section and SEM analysis.FindingsThe results show that both ball shearing tests and four‐point bending tests indicates that strength of BGA solder ball itself was not reduced significantly after repair/rework operation from one to five cycles. The IMC structure layer after rework is a mixture of IMC, Sn‐rich and Pb‐rich phases. This mixture layers with thickness even more than 10 μm in thickness does not show reduction of strength of BGA solder balls and do not cause premature embrittlement. However, the bonding strength of the copper pads to the laminates is reduced with rework/repair operation, with the great reduction coming from the first and second rework operation.Practical implicationsIn general, the industry recommends two rework cycles for BGA components on the same spot. This study indicates that further rework (up to five) causes little degradation, therefore there is room to increase the total rework cycle limit beyond recommended two for plastic BGA components.Originality/valuePresented test results shows that in most cases industry overestimates risks associated with increased embritlement of the BGA solder joints due to the intermetallics growth after multiple BGA rework operations. Strength reduction of BGA assemblies is mostly associated with reduction of bonding strength of the copper pads to the laminates is reduced with rework/repair operation and number of reworks could be increased in most cases.

Automated CO2 Composite Spray Cleaning System for HDD Rework Parts

Many advanced assemblies require high-volume and cost-effective selective cleaning during various stages of assembly or rework operations. Due to component compatibility problems and drying challenges, partially assembled devices cannot be immersed in or sprayed with aqueous cleaners or solvents. Newer dry cleaning techniques such as carbon dioxide (CO2) aerosol spray cleaning processes (snow cleaning) have proven to be challenging to implement in automated high-volume manufacturing operations. Issues associated with conventional snow cleaning include high costs of operation, lack of process consistency, ineffective controls, and the requirements for a supply of high-purity liquid CO2. Advanced CO2 composite spray [CO2(solid)-compressed dry air (CDA)(gas)] cleaning is an effective alternative to traditional spray and immersion cleaning processes and to conventional snow cleaning for selectively removing contaminants and films from partially assembled hard disk drive (HDD) components during the remanufacturing or rework process. CO2 consumption is reduced using a composite spray, while spray cleaning control and performance is improved. CO2 composite spray cleaning performance is dependent on the position, speed, and motions of the spray applicator, which are matched to comply with HDD factory output. Stored spray cleaning programs deliver precise cleaning seven days a week, 24 hours per day, with uptimes exceeding 99.9% over a 6-month period. Monitoring and controlling composite spray cleaning process parameters including spray pressure and composition, scanning speed, and pallet/part identification are done automatically. Operator interaction is limited to loading and unloading pallets for continuous system operation.

Effects of thermal history on the intermetallic growth and mechanical strength of Pb‐free and Sn‐Pb BGA solder balls

PurposeTo investigate effects of the thermal history on intermetallic thickness and morphology and on the resulting shear strength of the ball attachment for a variety of BGA components.Design/methodology/approachIn this study, a variety of BGA components with balls made of Pb‐free Sn‐Ag‐Cu (SAC) 305, Sn‐Pb eutectic and high‐temperature 90Pb‐10Sn alloys, were subjected to different thermal histories, including up to ten reflow cycles, and aged at 125°C from 24 to 336 h. The intermetallic thickness and morphology after these thermal events were then examined under optical and scanning electronic microscopes. Ball shearing tests were conducted to investigate effects of the thermal history and intermetallic thickness and morphology on shearing strength of these solder balls.FindingsThe results show that effects directly from intermetallic layers may or may not be detectable; and the shear strength of solder balls is largely dependent on the solder alloy and its microstructure. Shear strength increases are observed after multiple reflow cycles and ageing at elevated temperature for the two Pb‐bearing alloys, while the SAC305 lead‐free alloy shows slight reductions in both strength and ductility after thermal exposure.Practical implicationsPresented results can be used for estimation of reliability for electronic assemblies subjected to multiple rework and repair operations, which expose sensitive components, such as BGAs, to elevated temperatures.Originality/valueIt is believed that a sound understanding of the effects of intermetallic morphology and thickness on reliability of BGA solder balls can lead to more intelligent choice of soldering processes, as well as to rework/repair process optimisation and to establishing their operational limits.

Optimization of Test/Diagnosis/Rework Location(s) and Characteristics in Electronic System Assembly

In this paper, an optimization methodology is used to select the locations and characteristics of test, diagnosis and rework operations in electronic systems assembly processes. Real-coded genetic algorithms are used to perform a multi-variable optimization that minimizes the yielded cost of products resulting from an assembly process that includes test/diagnosis/rework operations characterized by costs, yields fault coverage, and rework attempts. A general complex process flow is analyzed using the algorithms proposed in this paper, and a multichip module assembly process flow is used to demonstrate that the methodology can identify optimum test and rework solutions that result in a reduction in yielded cost.

Internet-based electronics manufacturing troubleshooting tool for surface mount PCB assembly

Increasing product complexity, decreasing component size, and using double-sided boards have made surface mount technology (SMT) based electronics manufacturing (EM) components more difficult to assemble. This has resulted in the economic troubleshooting of EM defects being one of the main problems facing all manufacturers. Although the authors have made significant improvements in the EM process, it has been shown that the implemented changes in the automated lines have not yet produced a high enough percentage of reliable finished products. The objective of this current development is to make a contribution towards these EM processes by creating an Internet-based intelligent system of circuit board defect detection so that EM process flaws that necessitate rework operations can be identified prior to manufacturing runs. With the development of this system, the need to rework the defective components will be minimized for any assembly line and assembly line process parameters, which cause some reliability problems (such as solder balls, insufficient solder at joints, burnt joint connections, bridged leads, voids, skewed leads, and unformed joints) will be troubleshot directly, and the rework will be greatly reduced from the EM assembly line. This paper reports the current development and its structure.

Overlapping Decomposition: A System-Theoretic Method for Modeling and Analysis of Complex Manufacturing Systems

A system-theoretic method, referred to as overlapping decomposition, is presented to evaluate the performance of a complex manufacturing system with assembly, parallel, rework, feedforward, and scrap operations. The idea of the method is to decompose the complex system into a set of serial production lines, with the first or last machines of each serial line overlapped with another line, and to modify the parameters of overlapping machines to accommodate the effects of machines and buffers in other lines. Iterative procedures are introduced to estimate the system production rate. The convergence of the procedures and the uniqueness of the solutions are proved analytically and the accuracy of the estimates is evaluated numerically. Note to practitioners - Many large volume manufacturing systems consist of complex operations, for instance, assembly, disassembly, rework loop, parallel lines, feedforward lines, scrap, etc. Development of a performance evaluation method to provide fast and accurate analysis of system throughput is important for design and continuous improvements. This paper introduces a system-theoretic method, referred to as, overlapping decomposition, to analyze the performance of such complex manufacturing systems. The complex system is decomposed into overlapped serial production lines and modifications are introduced to accommodate the coupling effects among all these lines. From the theoretical point of view, this paper presents the proofs of the convergence of recursive procedures and the uniqueness of solution. From the application point of view, the method has obtained good results in solving practical problems on the factory floor.

The effects of rework on the shopfloor control in wafer fabrication

The purpose of this paper is to study the effect of rework operations on the shopfloor control’s strategies, including order release and dispatching. An attempt is made to determine the performance of various production control strategies on the system performance indicators under different levels of rework rate. Also the interaction of order release and dispatching strategies under different rework operations is investigated. Some representative shopfloor control (SFC) strategies are considered in our simulation model. It was found that the effect of rework operation on the system performance is significant. The order release and dispatching strategies’ performance is affected by the rework operation. The performance is improved dramatically if a suitable combination of order release and dispatching strategies is adopted. Under different rework rates and performance indicators a suitable combination of SFC strategies is suggested in this paper.

Survey of rework practices in the UK electronics assembly industry

A survey of rework practices of the UK electronics assembly industry has been undertaken. Rework of electronics components in the UK was found to be dominated by the use of soldering irons. Many companies did not control tip temperatures, rework times, background heating or the number of rework operations which could be undertaken on any one component. Few companies followed the recommendations of the component manufacturers aimed at preventing damage to thermally sensitive components. It was found that those companies which did control rework temperatures, did reduce rework temperatures for surface mount components. In general, rework temperatures were much higher than those recommended by the component manufacturers. A great deal of cleaning was undertaken after rework, with most companies doing some form of local cleaning. Most companies reused components even if only on an occasional basis.

FCOB reliability evaluation simulating multiple rework/reflow processes

Flip-chip assembly [direct chip attach (DCA) or flip-chip on board (FCOB)] on printed wiring boards (PWBs), in conjunction with conventional leaded device surface mount technology, is beginning to proliferate in compact and portable systems. DCA with conventional controlled collapse chip connection (C4) bumps requires solder coated bond pads to allow joining in typical surface mount technology (SMT) reflow cycles. A flip-chip device on a typical FCOB/SMT board will usually experience no high temperature excursions after the die joining and underfill encapsulant cure unless the board undergoes a rework cycle. FCOB single chip packages and multichip modules are now in development with standard C4 bumps, and a new Motorola E-3 bump which requires no solder on bond pads. These solder interconnects must be stable through multiple heat treatments expected in subsequent system level assembly and repair operations. Flip-chip plastic ball grid arrays (FC-PBGAs) will typically undergo three solder reflow, or reheat, cycles to /spl sim/220/spl deg/C subsequent to initial flip-chip reflow assembly. The multiple reheats are for BGA ball attach, board level BGA SMT assembly, second side BGA SMT assembly, and possible rework operations. In this paper, the effect of multiple reheats on the solder connection microstructure and strength (before, and after, underfill encapsulation), and the integrity of the underfill encapsulant adhesive and cohesive strength is reported, using both FCOB single chip packages and multiple chip modules. The effect of multiple reheats on electrical resistance of daisy chain nets, and die stress (radius of curvature), is also reported. Hot air gun rework (before underfill) is simulated and standard belt furnace reflows are utilized. Cross sections of bump connections and underfill interfaces were studied to assess changes induced by the temperature exposures. The reliability of the FCOB assemblies was assessed via temperature cycle, thermal shock, and autoclave tests.

The effects of text and rework operations on the flow of materials in circuit card assembly

The effects of text and rework operations on the flow of materials in circuit card assembly

The effects of test and rework operations on the flow of materials in circuit card assembly

Abstract This paper presents a structured approached for analyzing the effects of test and rework operations on material flow in systems that assemble circuit cards. Stages that effect quality (e.g., vendor preparation of components, pooling, assembly processes, and test and rework) are identified and representative models of each are presented. Each product is treated as a composite of multiple components, each of which is vulnerable to a variety of defects. Test is treated as fallible and rework as imperfect. Several procedures that accomplish rework are considered. Examples demonstrate some fundamental effects of test and rework operations on material flow. Management implications for improving material flow are discussed.

Optimal Lot Sizing, Process Quality Improvement and Setup Cost Reduction

This paper seeks to demonstrate that lower setup costs can benefit production systems by improving quality control. It does so by introducing a simple model that captures a significant relationship between quality and lot size: while producing a lot, the process can go "out of control" with a given probability each time it produces another item. Once out of control, the process produces defective units throughout its production of the current lot. The system incurs an extra cost for rework and related operations for each defective piece that it produces. Thus, there is an incentive to produce smaller lots, and have a smaller fraction of defective units. The paper also introduces three options for investing in quality improvements: (i) reducing the probability that the process moves out of control (which yields fewer defects, larger lot sizes, fewer setups, and larger holding costs); (ii) reducing setup costs (which yields smaller lot sizes, lower holding costs, and fewer defects); and (iii) simultaneously using the two previous options. By assuming a specific form of the investment cost function for each option, we explicitly obtain the optimal investment strategy. We also briefly discuss the sensitivity of these solutions to changes in underlying parameter values. A numerical example illustrates the results.