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50 The PCB Magazine • October 2015 meet the customers' specific requirements. By using six sigma principles and lean techniques together, PCB manufacturers can reduce both process variation and cycle time together effectively. Getting Started The PCB manufacturing process is by na- ture a batch process, following a predeter- mined sequence that is developed to meet the products' specific design requirements. In PCB manufacturing not all products go through the exact same process, which complicates the task of cycle time reduction. As an example, a standard multilayer board will probably not be laser-drilled or plasma-etched unless it has some very unique characteristics. And HDI products may cycle through lamination, drill - ing, laser drilling, plating and etching two or more times before moving on to solder mask application. Cycle time reduction efforts for these two products will require individual evaluation. At first glance we might say that the overall manufacturing operation cannot be "leaned" because lean doesn't lend itself to batch pro- cessing or multiple process sequences, but this is not correct. Any process can be made leaner and a batch process can certainly be lean. Mul- tiple process sequences are routinely managed in a lean environment as long as each are evalu- ated separately and each piece of equipment, process step and work-hour can be accounted for. The key concept to lean is keeping the process flowing consistently, be it batch or in- dividual piece. To be truly lean a process must flow continuously, with a minimal amount of non-value added processes. The real hindrance to lean is not a result of batch processing but of waste—both time and resources—that can sometimes result. One last point on batch pro- cessing: Smaller is usually better. Reducing the batch size will most likely be a part of the final cycle time reduction solution. The next question is this: How do we im- prove flow and remove non-value added waste? First, we need to look at the overall production process. PCB manufacturing is for the most part a series of production lines. In a greenfield facil- ity we can expect that the layout has been op- timized to reduce steps and minimize waste. In facilities where new processes or capacity have been added after the initial layout was complet- ed the result may not be optimized and waste may be inherent in the system. Whenever pos- sible this waste needs to be removed. In a lean environment the product is pro- duced only when it is needed. Producing any more or less results in waste. Each PCB manu- facturer will need to determine both takt time and cycle time to determine the correct rate for production. Takt time is customer demand leveled against the actual time the factory has to produce the product. Cycle time is the working time it takes to complete the process. It's takt time that sets the rhythm for manu - facturing. Most factories will then use a pull system (Kanban) that minimizes the work in process to achieve continuous flow. To be suc- cessful in maintaining continuous flow once it has been established the processes must be capable and reliable, which is where six-sigma adds its value. Process Flow Diagrams Many companies have embarked on lean training and use lean principles to remove waste and lower manufacturing cost. We have all been involved in a 5S housecleaning or par- FeATure Figure 1: Key elements of lean. PRACTICAL APPLICATION OF LEAN SIx-SIGMA TO DRIvE CyCLE TIME REDUCTION, PART 1