While running the metalizing plant, if we take a
few seemingly small precautions, they can go a long way in ensuring optimum
usage of energy, expensive materials and thereby money. And as we know, money
saved is money earned.
fig.1: Evaporation Boat
Figure 1 shows the Evaporation Boat. Aluminum
wire is fed into the cavity of the hot Evaporation Boat (heated
up to 1500⁰C) where -
1.
It melts
2.
Forms a small pool to
fill the cavity
3.
Evaporates to form
vapor
4.
Vapors stick to the
substrate to make a thin coating
Ideally the aluminum wire should touch the
Evaporation Boat between the 1/3 part and the 1/2 part from the wire feed end;
never before or after this. The following photos demonstrate the right as well
as the wrong position of the feed wire.
Positioning the aluminum wire too close to the
edge of the Boat will not make the cavity fill up uniformly with the molten
metal. This leads to –
Ø Non-uniform coating of the aluminum on the substrate.
Ø Wastage of the Al wire since this will cause excess molten metal to
fall off the boat from one end.
Ø Wastage of electricity.
Ø Shorter life span of the Evaporation Boat since improper feeding of
the wire will cause variation of temperature across the Boat.
Ø Faulty metalizing: When a molten pool of the metal forms in one part
of the Boat’s cavity while the other part remains relatively cold, SPITTING
phenomenon takes place. In SPITTING, the liquid metal overheats and bursts
forth or ‘jumps’ out of the cavity in small quantities and either sticks to the
vacuum chamber walls or on to the substrate.
Written by: Anshuman Punj.
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Written by: Anshuman Punj.
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