BLACK PAD DEFECT: INFLUENCE OF GEOMETRY AND OTHER FACTORS

摘要

Black pad is a defect associated with electroless nickelrnimmersion gold (ENIG) plating. The immersion goldrnplating process is possible through galvanic attack to thernnickel plating. Black pad defect occurs when, through thisrnprocess, excess nickel is removed, resulting in arnphosphorus-rich layer at the nickel interface. In its mostrnsevere occurrences, black pad can cause dewetting or nonwettingrnof the solder resulting in poor solder joint reliability.rnLatent failures may occur as a result of this defect. Blackrnpad can only be detected by destructive analysis. As featurernsizes decrease, ENIG is becoming more prevalent in thernindustry. Due to the end use of such products, such failuresrncould be quite costly.rnRecent studies of PWB’s and BGA components with thernENIG plating, indicate geometry as well as other factorsrninfluence the occurrence of black pad defect. The issues tornbe discussed include pad geometry, copper surfacernroughness, the influence of solder mask, phosphorusrncontent, stress, nickel grain structure and gold thickness.