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22 PCB007 MAGAZINE I NOVEMBER 2024 An internal Motorola study found that units reworked in production oen encountered problems during early customer use, even though the defects identified were corrected during production. Rework can frequently stress a unit non-standardly and predispose a product to early failure 4 . Denson found a sim- ilar occurrence in semiconductor manufactur- ing, where the reliability of computer chips was statistically correlated with the die yield 5 . ese studies suggest that circumstances in detecting and reworking defects in some units may produce undetected damage on other units. When delivered to customers, these weaknesses oen contribute to early failures. Defects are any items that exhibit a depar- ture from specifications. A defect does not nec- essarily mean that the product cannot be used; it only indicates that the product result is not as intended. In essence, defects refer to quality characteristics. Generally, the count of defects is assumed to follow a Poisson distribution. Process Yield Statistics and Distributions Feature Article by Dr. Pat Valentine UYEMURA e costs of poor quality include all expenses incurred by not making or providing a perfect product the first time, including scrap, rework, re-purchasing raw materials, labor, and inven- tory 1 . Companies operating at a three-sigma quality level can spend about 25% of their annual sales remediating poor quality costs 2 . Other esti- mates put the costs of poor quality in the range of 25–40% 3 . Poor quality can destroy a company. Unexpected product failures significantly increase sales, general, and administrative (SG&A) costs and lead to increases in invento- ries and fixed assets required to support oper- ations. ese indirect costs erode profitability more than those directly attributable to war- ranty claims processes. Product recalls nega- tively impact businesses financially and result in adverse publicity. Customers expect printed circuit boards to meet their specifications.