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Quality Failures July 19, 2011

Posted by Tim Rodgers in Process engineering, Quality.
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Several months ago I had an interesting series of conversations with one of my customers while I was working at a leading electronic manufacturing services (EMS) company. It started one evening when he called to report an unexpectedly high rate of field returns for a product that had been manufactured and shipped from our factory for almost six months. His conclusion was that the factory quality system had failed, allowing these defective units to escape. He was referring to the collection of inspection and test processes that had been implemented in the factory during successive prototype builds, and run routinely during every day of production.

I agreed with his conclusion that there was a problem with the quality system. It was important for me to first understand if the processes had been implemented and executed correctly. Internal audits conducted during the prototype and production periods gave no indication of any problem, and there was no reason to believe that this product was treated any differently than the dozen other SKUs built and shipped over the same time with no unexpected field failures.

Significantly, the daily test and inspection results over the six months of production gave no indication of an emerging quality problem. These included measurements of critical parts at incoming inspection, control charts for process measures, cosmetic checks on the production line, end-of-line testing, out-of-box audits, and accelerated reliability testing. Production yields exceeded the contractual requirements, all critical parameters were within specification limits previously established by our customer, and nothing was trending in the wrong direction.

In spite of these findings, the system had clearly failed to provide an early indicator that could have alerted our factory or the customer. Unfortunately there was no evidence of a part or process change during production, and this suggested that the root causes of the poor quality had been present from the beginning, whether in the product design or the design of the manufacturing processes, and the EMS had only limited input to either. In addition, the EMS had limited experience building this product, with no engineering insight to possible field failures and their causes, and no access to the customer’s field failure reports.

In this specific case the circle came back around to a breakdown in properly qualifying the new product design for the necessary field performance and reliability. The factory quality system was implemented properly, but the system wasn’t designed to detect the causes of the field failures or provide an early warning of a process drifting out of control. It’s become a cliche, but it bears repeating: you can’t “test in” quality. In fact, the wrong testing executed perfectly can actually mask a quality problem, which is what happened in this example. Quality comes from an understanding of the relationship between design and customer expectations for the finished product, and the factory quality processes can only ensure that the design is being built correctly.

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