Lean Manufacturing with Six Sigma Implementation

Estimated reading time: 9 minutes

To remain competitive in the electronics manufacturing arena, it is essential to implement a lean manufacturing mindset - reacting and conducting business from the top down.

By Li Guo Chun

The electronics manufacturing community, especially in North America, must look for ways to reduce waste and cost from the moment materials are procured to the time products are shipped. This article introduces six sigma methods, discussing how they can be applied within an organization to achieve a lean production goal.

SMT manufacturers find it increasingly challenging to maintain their competitiveness and profitability. Reasons for this include increasing complexity of SMT processes, higher customer demands on quality and shorter lead times matched by cost reduction. This pushes companies to seek solutions to counter them. There are many solutions to face this challenge, however. One of the effective, proven strategies is the implementation of a six sigma initiative.

Overview of Six Sigma

Six sigma is a management philosophy targeting the creation of world-class quality standards and quality culture. It relies on the understanding of the processes of the supplier-manufacturer-customer value chain to derive a systematic methodology that optimizes the processes by using powerful problem-solving tools.

Six Sigma Philosophy

The six sigma management philosophy can be summarized as:

• Measurement - Specify quality and value in the eyes of customers, and measure customer requirement and process performance;
• Transparency - Management decision is based on data and fact, as well as understanding the gap through benchmarking;
• Optimization - Adopting a proactive approach to optimizing processes;
• Systemizing - An inherent focus to eliminate waste and variation throughout the entire value chain, and then standardizing the process;
• Consistency - Involve and empower all employees to cooperate without boundaries, and the existence of a mechanism to ensure the implementation and operation of optimized processes;
• Quality Culture - Continuous improvement in pursuit of perfection.

Six Sigma Methodology

Six sigma involves a cycle of progressive-project activity integrated with daily operation, during which the Define - Measure - Analyze - Improve - Control (DMAIC) methodology is applied. The DMAIC methodology allows the ability to have both a “macro” and “micro” perspective. It allows users to adopt a bird’s eye view of the entire system, as well as an in-depth view toward understanding the process (Figure 1). DMAIC helps project teams and employees take systematic steps to achieve tangible results.

Figure 1. DMAIC methodology.

First, at the Define Phase, adopt a bird’s eye view of the organization and customers’ critical issues. Based on this evaluation, prioritize them and finalize the high-potential improvement opportunities. Second, at the Measure Phase, enter the identified field or system to measure current performance by using suitable metrics to discover the focused problems. Third, at the Analyze Phase, the focused problem will be analyzed in-depth to identify the root cause. Fourth, at the Improve Phase, based on these new insights, brainstorm and evaluate creative solutions to make processes more productive and efficient. Finally, at the Control Phase, institutionalize the new process and implement a control system to keep it consistent.

Implementing Six Sigma: Two-fold Approach with Three Phases

The implementation of six sigma focuses on quality culture building, methodology, tools training and key project application. Six sigma is implemented through a two-fold approach. The first approach is fostering an excellent quality culture in the entire value chain, from supplier operation to customer service, to improve fundamental levels by using “common language and behavior” for standardization. The second approach is using nurturing experts on six sigma implementation to provide leadership for executing key business projects with breakthrough improvements. The implementation process is divided into three phases:

Phase One: Communication/Planning

• Communicate six sigma initiative as a common language;
• Plan goal targets and setup a measurement system to evaluate the performance;
• Create training and project plans.

Phase Two: Action and Monitor

• Track the progress of the training course and trained people;
• Track the progress of the project number and status.

Phase Three: Review and Recognition

• Review performance with matrix and document lessons learned;
• Recognize successful teams.

Successful Factors for Implementation

The six sigma initiative involves all employees within the organization, from top-level executives and shop-floor-level operators, as it covers both top-down and bottom-up activities (Figure 2). It will not be successful without commitment from the entire team. The critical factors for successful six sigma include commitment from all levels of employees; alignment of six sigma infrastructure and projects with organization goals; and training all levels of people through appropriate course designs and case-study sharing. Successful projects also should be recognized and transmitted as knowledge sharing.

Figure 2. Support structure for implementation.

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Six Sigma Methodology/Tools: Applications in SMT

To understand the application of six sigma methodology/tools in the SMT line, several examples using the DMAIC methodology are used. In one case study, the manufacturer was encountering a high SMT defect rate, resulting in unnecessary rework after the reflow process. A certain percentage of the defects escaped into the assembly line, and were distributed to field customers. This affected the company’s reputation and deteriorated customer satisfaction. Realizing the seriousness of the problem, the organization adopted the six sigma methodology.

Define Phase

To identify the main issues, a production total-defects-breakdown diagram was derived for analysis. By using the diagram, the team realized that the major issues affecting process quality were component soldering and placement quality. Therefore, a project team was developed.

Measure Phase

A stratified Pareto chart categorized by different production lines (or components) was created to identify the defects (Figure 3). Soldering and placement defects remain the top concerns for all lines, affirming the accuracy of the identified problems. Proceeding, Line A was studied as a model line to retrieve a more detailed analysis.

Figure 3. SMT defect breakdown by line.

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Analyze and Improve Phase

The focus is on the analysis of placing misalignment defects. In this example, the placement machine was configured with two revolver heads equipped with 12 nozzles, respectively. To analyze the root cause of part misalignment, a multiple-variation study was conducted to investigate head, nozzle and placement-angle variation. A multiple-variation chart and a main-effects-plot chart were used to show that the largest variations came from different head and nozzle variations: head-to-head placement varies about 30 µm average while nozzle 3, for example, varies about 20 µm. Upon further investigation, these root causes were identified and counter actions taken. These details were noted:

Nozzle design: Not suitable for component shape. The solution is to design a special nozzle for these types of components.

Nozzle vacuum: Nozzle is worn and dirty. The solution is to implement a new method to clean the nozzle and setup a schedule to check and change the nozzle regularly.

Feeder operation: Daily procedures executed on feeders are not suitable, trouble-shooting methods are not correct and maintenance quality is not controlled.

Solution: Standardize feeder-maintenance items, time interval, checklist and operation instructions to control feeder quality.

Head calibration: Head variation is not monitored during maintenance. The solution is to update the maintenance checklist and methods to control maintenance quality.

Based on these recommendations, action tasks were implemented and maintained in a Placement Process Control Plan for daily operation controls (Table 1).

Next, the printing process was analyzed to rectify solder bridges and open defects. Because solder volume is one of critical output for reflecting soldering defects, a design of experiment (DoE) was conducted to optimize the process settings and obtain the desired solder-volume specification. In this experiment, the outputs are printing-volume measurements, which reflect soldering quality, and component pull force measured after reflow process, which reflect process reliability. From this overlaid plot, the desired process window for input settings was obtained, which means setting printing speed at the 0.5 level and pressure at the 0 level, meeting both solder volume and pull-force specification requirements. A robust process-design window was achieved.

Control Phase

The Process Control Plan and parameters settings were finalized based on experiment results and analysis. The checklist was updated and the standardized process was implemented and monitored daily. After implementing the process for a month, the defects Pareto chart (Figure 4) was updated and reported to compare before-and-after results. Data show that soldering and placement defects were reduced significantly with the new processes.

Figure 4. SMT defects breakdown after project.

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Conclusion

The DMAIC methodology and related tool applications enabled project teams to adopt a step-by-step process to systematically understand process characterization. The DMAIC practice can help employees develop good problem-solving habits to discover the root cause of problems, avoiding guesswork that may be derived from subjective personal experience. This methodology also can serve as a guide for teams to achieve robust process performance. Six sigma fosters a solution-oriented culture that focuses on improving processes directed at eradicating current problems permanently, while streamlining them to achieve targets through DMAIC.

DMAIC methodology and tools help companies achieve quality improvements in their manufacturing processes. Through this continuous improvement, new processes make it easier for companies to achieve higher quality, shorter lead times and reduced costs in these challenging times.

For a complete list of figures, please contact the author.

For a lean manufacturing study from Libra Industries, view this article at www.smtmag.com.

Li Guo Chun, black belt program manager for quality project improvement, Siemens L&A EA Singapore, may be contacted at guochun.li@siemens.com.

Lean Manufacturing - The Human Element

During 2003 and 2004, one EMS provider* embarked on a lean manufacturing business structure. While not without challenge, the company experienced a high level of acceptance for the transition because they recognized and cultivated the personnel factor throughout the process. Once the decision to transition to lean manufacturing was made, the Operations Management team studied literature and attended training sessions. They also began benchmarking best practices in the industry with competitors and customers. Resistance to change and the lack of buy-in at the lower levels were observed in the failings of these initiatives. An effort to foster acceptance of lean manufacturing throughout the organization became a key factor in a successful conversion.

The management team reviewed execution strategies and determined that a concurrent demonstration and training program would be most effective. Between 2003 and 2004, the plant work floor was converted into cell-based processes, and the full implementation occurred.

The company used the services of a local community college’s business center** to develop a custom training program. With the help of job-training grants from the state of Ohio, the provider leveraged internal resources. The course was given to ten successive groups of associates attending a series of eight one-hour sessions. About 1,200 hours of training time was conducted prior to the full conversion to lean. The program consisted of theory, case studies and hands-on demonstrations, as well as on-the-job projects.

Participants for the first session were selected based on their history of team orientation. When the first team had completed half of their training, they were allowed to revise a cellbased workspace anchored by one of the company’s four automated circuit board assembly lines. The cell included all operations from start to finish. To establish a smooth workflow, the traditional approach of moving batches of partially complete product from one department to the next was eliminated.

Benefits of this were two-fold: Associates not selected for the demonstration team began requesting the schedule for their training sessions; and new processes were “piloted” in a controlled environment, allowing the company to develop a tested solution for the balance of their operations. Upon completion of the training, the demonstration cell had operated for five months, and all associates had been trained.

In January 2004, the entire company began operations in cell-based lean manufacturing techniques. To date, it has experienced increases in inventory turns (from four per year to over ten), in-process yields, reduced changeover time, reduced downtime, reductions in returned materials to less than 1% and lower associate turnover. The buy-in and enthusiasm of the associates has been a significant factor in that success.

* Libra Industries, Mentor, Ohio.** Lakeland Community College’s Center for Business and Industry, Mentor, Ohio.

Rod Howell, president, Libra Industries, may be contacted at (440) 974-7770; e-mail: sales@libraind.com.