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PCB007-Nov2021

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78 PCB007 MAGAZINE I NOVEMBER 2021 The Plating Forum by George Milad, UYEMURA e ENIG Specification 4552 was issued in 2002. Since then, it has undergone a series of amendments and revisions to meet ever- changing industry requirements. Although it started as a thickness specification that did not reference lead-free soldering or nickel corro- sion, its latest iteration, 4552B, addresses all aspects of nickel corrosion. e IPC Specification 4552B was issued in April 2021 as a performance specification. It is already having a profound effect on how the industry (suppliers, manufacturers, and end users) views the ENIG surface finish. e doc- ument is a revision of its predecessor, 4552A, issued in 2017. Revision 4552A addressed nickel corrosion for the first time. It described the corrosion defects as viewed in a cross-sec- tion at 1000X magnification by coining the terms "spike," "spreader spike," and "black band." It also addressed the level of corrosion and defined three levels. e levels were based on depth of defect and frequency of occurrence in the field of view at 1000X magnification. ENIG Specification 4552A went a long way in defining the defect and its evaluation. e way the specification read was that if a single Level 3 defect was encountered, the product was The Significance of IPC ENIG Specification 4552 Revision B deemed "rejectable." Rejecting a production lot due to a single occurrence of a Level 3 defect in the 1000X field of view did not make any sense. ere had to be a method to determine the fre- quency of occurrence or prevalence of corro- sion in the board. is was addressed in the revised ENIG specification 4552B. In revision 4552B, the term "product rat- ing" was introduced. Product rating is a way to assess the frequency of occurrence or prev- alence of the corrosion defect. Product rating is determined by assessing the defect levels of multiple cross-section locations (seven for a through-hole and five for a single pad). To arrive at a product rating, a cross-sec- tion of the board is examined at lower mag- nification (200X) where multiple holes are within the field of view. e specification then states that holes or pads with the most preva- lent defects are to be evaluated at 1000X (Table 2). e results are tabulated, and a product rat- ing value is extrapolated depending on the fre- quency of each of the levels. is is a significant development in corro- sion evaluation. Now there is a standardized method for corrosion evaluation that produces a product rating number. Specification 4552B Table 1: Revision 4552A addresses corrosion effects.

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