Book Excerpt: The Electronics Industry’s Guide to… The Evolving PCB NPI Process, Chapter 1

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Chapter 1
How the NPI Process Has Changed and Where We're Going

When forging into unknown territory or exploring new ground, it can help to look at where we’ve been so we can orient ourselves.

Just a few decades ago, electronics manufacturing companies were producing high volumes of few products. The efficiency of electronics manufacturing lines is measured by overall equipment effectiveness (OEE) and total effective equipment performance (TEEP). Back then, this meant optimizing the time it took to build a single board. If the time it took to build one board could be reduced by a few seconds, the savings would be multiplied by the number of boards being built. This could be in the hundreds of thousands or millions of boards, with no changes in the line configuration. If it took a day to change over from one product to another, it didn’t matter because the TEEP/OEE was driven by the time it took to build a board.

For example, consider that it takes 35 seconds to place components on a single board, and I need to make 250 boards. My handling time (the time it takes to load a board into the machine and get it out after) is 10 seconds, then the total time to build the 250 boards will be (35 + 10) • 250 = 11,250 seconds. This equates to about 188 minutes, or approximately three hours. If it takes four hours to changeover—namely reconfigure the line before starting a different PCB—to a new product, my OEE will be less than 50%, considering no other external factors. As the batch size goes down, the changeover time dominates the OEE figure.

In today’s high-mix, low-volume production environments, performance is further enhanced with line efficiency. Line efficiency is the ratio of the number of hours during which a high-volume, pick-and-place machine places parts on the PCB, divided by the number of hours during which the SMT assembly lines are staffed (placement time/staffed time x 100). It is a solid number, simple to obtain, and has great value as a key performance indicator.

With higher product mixes, the number of NPIs being processed increases. Changeovers on the shop-floor line can happen daily or many times a day. This also means the time it takes to process the source design data has increased. This data-processing time is becoming a more important consideration compared to when NPI processing was not a daily task in the lower mix environment. As product mix has gone up, there has been a move from mixed vendor lines focused on ultimate through-put to single vendor lines focused on flexibility and shorter changeovers. There may be more than one pick-and-place vendor brand in the factory, but each line commonly has only one brand now.

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