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24 SMT007 MAGAZINE I JULY 2021 Feature Article by Bob Neves MICROTEK CHINA New products, new designs, but still the age- old question persists, "How long will it live and what will its quality of life be?" Assembled printed circuit boards (PCBAs) are a complex system of materials, components, and inter- connections that all need to work as intended for the product to reliably operate during its expected life. All it takes is one piece of that complex system to fail and the product's life span will disappoint. To manage this disappointment in life—in this case reliability failure—the first step is to categorize the influence that each piece of this complex PCBA system has on the life of the product. In addition, as the PCBA is subjected to very high temperatures during component attachment, the influence that each piece has on life may change before and aer the attach- ment process, so simulation of this attachment process prior to any life prediction testing is vital to understanding the true life expectancy of a PCBA. Evaluating all the parts and systems in a PCBA system is an overwhelming task to say the least, so I tend to follow the Pareto princi- ple when looking to pare down the list to some- thing more manageable. e Pareto principle roughly states that 80% of consequences come from 20% of the causes. is nugget of wisdom came from Joseph M. Juran who studied the work of Vilfredo Pareto and ultimately pub- lished his Quality Control Handbook in 1951, which is still used today as a basis for manage- ment of quality and quality control. e next step in the process is identifying the 20% that will cause most of a product's life problems and subsequently focusing efforts on reducing the disappointment in life from these items. Active and passive components, PCBs, subsystems, connectors, wiring harnesses— the list goes on. Once you have identified a set of likely offenders, you will need to decide how to evaluate them for their effect on premature life failure. Terms like "infant mortality," "fatal anom- aly," "long-term reliability," "Weibull analysis," and "latent defects" are thrown around when The Meaning of (PCB) Life

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