10ml formic acid, 15ml water, solution neutralised to pH7 then elemental iodine added until solution turns dark brown
dipping the CPU for 1-2 minutes with agitation from time to time is enough to dissolve the gold plating
no addition treatment of the CPUs
even the heat paste was on
transistor with thick gold plating
etching rate at room temperature 0.5-1um/min
gold precipitation using ascorbic acid powder
small additions with stirring until the solution changes colour
solution becomes cloudy
even the gold letters have been dissolved
after a couple of minutes there is visible gold sediment at the bottom of the beaker