The process of manual decapsulation usually starts with milling a hole in the package so that
the acid will affect only the desired area above the chip die (Figure 50). The tools necessary for
this operation are available from any DIY shop for less than £10.
The commonly used etching agent for plastic packages is fuming nitric acid (>95 %), which is a
solution of nitrogen dioxide NO2 in concentrated nitric acid HNO3. It is very strong nitrifying
and oxidizing agent; it causes plastic to carbonise, and it also affects copper and silver in the
chip carrier island and pins. Sometime a mixture of fuming nitric acid and concentrated
sulphuric acid H2SO4 is used. This speeds up the reaction with some types of packages and also
prevents the silver used in bonding pads and chip carrier from reacting.