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32 PCB007 MAGAZINE I MARCH 2020 etch chemistry prepares the target pad with an ideal copper topography as the base for cop- per via fill plating. This promotes the well-de- fined grain growth of the electrolytic copper on the target pad. With normal thermo-mechani- cal cycling, the recrystallization of the copper grain orientation further promotes the desir- able continuous metallurgical structure. Studies with FIB using lamella cuts show the interface line to be uniform in grain size and structure (Figure 5). After thermal shock or cycling, the line between the target pad and electrolytic copper can be difficult to find. Na- no-voiding is not present, except for instances where it would be due to factors like oxidiza- tion or contamination. Figure 4: The microetch module has proven to be key to the increase in microvia reliability in direct metallization processes. Figure 5: FIB imaging of the interface between the electrolytic copper plating and the target pad. Leading-edge direct metallization technology allows for strong copper-to-copper bonding that performs excellently under thermal stressors. Blackhole Advanced Direct Metallization Line Configuration