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90 The PCB Magazine • May 2017 6. Voids Description: An area, most commonly on res- in, where there is a gap in the plated copper in the holes. Characteristics: Voids can cause opens. Possible Causes: a) Incomplete neutralization of the permanganate. b) Improper shadow or other metallization processing. c) Under-cured resin. The lessons learned are many: • Optimize drilling including monitoring of chip loads and drill bit quality • Ensure proper cure of the resin during lamination • Desmear may require additional help from plasma as the higher performance resin materials are more resistant to attack from alkaline permanganate • Do not expect the electrolytic copper plating process to make-up for poor hole-wall quality and the existence of wedge voids PCB Michael Carano is VP of technology and business develop- ment for RBP Chemical Technology. To reach Carano, or read past columns, click here. Figure 7: Note fine-line interconnect defect caused by drill smear that was not removed from interconnect. Figure 8: Voids in plated through-hole. (Source: RBP Chemical Technology) THE DESMEAR DEFECT GUIDE

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