PCBs intended for extreme environments often have a conformal coating, which is applied by
dipping or spraying after the components have been soldered. The coat prevents corrosion and
leakage currents or shorting due to condensation.The earliest conformal coats were
wax;modern conformal coats are usually dips of dilute solutions of silicone
rubber,polyurethane,acrylic,or epoxy. Another technique for applying a conformal coating is
for plastic to be sputtered onto the PCB in a vacuum chamber. The chief disadvantage of
conformal coating is that servicing of the board is rendered extrmely difficult.
Many assembled PCBs are static sensitive,and therefore must be placed in antistatic bags
during transport.When handling these boards,the user must be grounded (earthed).Improper
handling techniques might transmit an accumlated static charge through the board ,damaging
or destroying components.Even bare boards are sometimes static sensitive.Traces have become
so fine that it's quite possible to blow an etch off the board(or change its
characteristics) with a static charge.This is especially true on non-traditional PCBs such
as MCMs and microwave
PCBs.
