2.3.4 Coating Removal, Thermal Method
|
This coating removal procedure uses a controlled, low temperature,
localized heating method for removing thick coatings by an overcuring
or softening means.
To determine the appropriate coating removal procedure the
coating must first be identified. Refer to procedure number
2.3.1.
Caution
Soldering irons should not be used for coating removal as
their high operating temperatures will cause the coatings to
char and possibly delaminate the printed board base material. |
|
Coating Removal Required
At Outlined Area |
The use of thinned down soldering iron tips or soldering
iron heated thin cutting blades are not recommended since they
do not provide controlled heating and may present dangerous
sharp edges to the workpiece surface.
Tools and Materials
Brushes
Heated Blade or Thermal Parting Tool
Hot Air Tool
Knife
Wood Sticks
Figure 1: Lightly apply thermal tip to coating to soften
or granulate the material.
|
|
Procedure
- Thermal Parting Method |
| |
|
| 1. |
Select an appropriate thermal parting tip to
suit the workpiece configuration. Set the nominal
tip temperature, using the manufacturer's recommended
procedure.
|
| |
| 2. |
Apply the thermal parting
tip to the coating, using a light pressure.
The coating material will either soften or granulate.
Polyurethanes will soften and epoxies will granulate.
The tip temperature should be regulated to a
point where it will effectively "break down"
the coating without scorching or charring. (See
Figure 1).
|
| |
| 3. |
Gradually reduce the coating
thickness around the component body without
contacting the board surface
Clip leads of component parts that are known
to be faulty, thus permitting removal of the
part body separately from leads and solder joints.
Low pressure air or a brush should be used to
remove the loosened coating.
|
| 4. |
Once sufficient coating
has been removed, leaving only a small bonded
joint between the part body and printed board,
heat the component body with the thermal parting
tool or hot air jet to weaken the bond beneath
the component.
|
| |
| 5. |
Lift the component body free of the printed board using small pliers. |
Note
Twist the component prior to removal
to shear any remaining epoxy bond to the printed
board surface.
|
| 6. |
Once the component body
has been removed from the board surface, the
remaining coating material can be removed by
additional thermal parting. The remaining leads
and solder joints are then removed by appropriate
solder extraction means.
|
| |
|
Figure 2: Apply hot air to the work
area and use a wood
stick to remove the overcured coating.
|
|
Procedure
- Hot Air Method |
| |
|
|
By control of the gas/air temperature,
flow rates and jet shape, the hot air method can
be applied to almost any workpiece configuration
on both the component and solder side of the printed
board without damage. Extremely delicate work can
be handled in this manner while permitting direct
observation of the heating action.
|
| |
| 1. |
Set up the hot air tool per the
manufacturer's instructions. Adjust flow rate and
temperature to suit specific coating removal application. |
Caution
Never set the gas/air temperature
at a level that will cause scorching or charring
of the coating material or reflow the solder connections.
|
|
| |
|
Figure 3: Removal complete.
|
| 2. |
Apply the heated air jet
to work area. Apply light pressure using a wood
stick or other non marring tool to remove the
softened or overcured coating. All coating around
individual leads, solder joints and component
bodies can be removed in this manner. (See Fig.
2).
|
| |
| 3. |
When the coating has been removed,
use appropriate solder extraction method to remove
components if needed |
| |
|
|
Evaluation |
| |
|
| 1. |
Visual examination or UV light
may be used to verify complete removal of
coating. |
| |
|
|
|
