3-4
The coating material can best be identified through proper documentation; for example, technical
manuals and engineering drawings. If this information is not available, the experienced technician can
usually determine the type of material by testing the, hardness, transparency, thickness, and solvent
solubility of the coating. The thermal (heat) properties may also be tested to determine the ease of
removal of the coating by heat. The methods of removal discussed here describe the basic concept, but
not the step-by-step "how to" procedures.
THERMAL REMOVAL.—Thermal removal consists of using controlled heat through specially
shaped tips attached to a handpiece. Soldering irons should never be used for coating removal because the
high temperatures will cause the coatings to char, possibly damaging the board materials. Modified tips or
cutting blades heated by soldering irons also are not used; they may not have proper heat capacity or
allow the hand control necessary for effective removal. Also, the thin plating of the circuit may be
damaged by scraping.
The thermal parting tool, used with the variable power supply, has interchangeable tips, as shown in
figure 3-1, that allow for efficient coating removal. These thin, blade-like instruments act as heat
generators and will maintain the heat levels necessary to accomplish the work. Tips can be changed easily
to suit the configuration of the workpiece. These tips cool quickly after removal of power because their
small thermal mass and special alloy material easily give up residual heat.
Figure 3-1.—Thermal parting tips.
The softening or breakdown point of different coatings vary, which is a concern when you are using
this method. Ideally, the softening, point is below the solder melting temperature. However, when the
softening point is equal to or above the solder melting point, you must take care in applying heat at the
solder joint or in component areas. The work must be performed rapidly to limit the heating of the area
involved and to prevent damage to the board and other components.
HOT-AIR JET REMOVAL.—In principle, the hot-air jet method of coating removal uses
controlled, temperature-regulated air to soften or break down the coating, as shown in figure 3-2. By
controlling the temperature, flow rate, and shape of the jet, you may remove coatings from almost any
workpiece configuration without causing any damage. When you use the hot-air jet, you do not allow it to
