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the pros and cons of pcb surface finishes continues the most used finish in the PCB industry due the growth and implementation of the RoHs regulation. Advantages: • Flat surface • No Pb • Good for PTH • Long shelf life Disadvantages: • Expensive • Not re-workable • Black pad/black nickel • Damage from ET • Signal loss (RF) • Complicated process Figure 4: PCB with ENIG surface finish. 34 The PCB Magazine • January 2014 Gold/Hard Gold Hard electrolytic gold consists of a layer of gold plated over a barrier coat of nickel. Hard gold is extremely durable, and is most commonly applied to high-wear areas such as edge connector fingers and keypads. Unlike ENIG, gold's thickness can vary by controlling the duration of the plating cycle, although the typical minimum values for fingers are 30 μin gold over 100 μin nickel for Class 1 and Class 2, and 50 μin gold over 100 μin nickel for Class 3. Hard gold is not generally applied to solderable areas, because of its high cost and its relatively poor solderability. The maximum thickness that IPC considers to be solderable is 17.8 μin, so if this type of gold must be used on sur-