This coating removal procedure uses a controlled, low temperature, localized heating method for removing thick coatings by an overcuring or softening means.
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.
The use of thinned down soldering iron tips or soldering iron heated thin cutting blades is not recommended since they do not provide controlled heating and may present dangerous sharp edges to the workpiece surface.
To determine the appropriate coating removal procedure, the coating must first be identified. Refer to procedure number 2.3.1.
Minimum Skill Level - Advanced
Recommended for technicians with soldering and component rework skills and exposure to most repair/rework procedures, but lacking extensive experience.
Conformance Level - High
This procedure most closely duplicates the physical characteristics of the original, and most probably complies with all the functional, environmental and serviceability factors.
Hot Air Tool
Tool and nozzles to deliver precise flow of hot air.
Thermal Parting Tool
Thermal removal tool using controlled heat through specially shaped tips.
Images and Figures
Coating Removal Required At Outlined Area
Figure 1: Lightly apply thermal tip to coating to soften or granulate the material.
Figure 2: Apply hot air to the work area and use a wood stick to remove the overcured coating.
Figure 3: Removal complete.
Procedure - Thermal Parting Method
Select an appropriate thermal parting tip to suit the workpiece configuration. Set the nominal tip temperature using the manufacturer's recommended procedure.
Apply the thermal parting tip to the coating using 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)
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.
Once the 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.
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.
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.
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.
Set up the hot air tool per the manufacturer's instructions. Adjust flow rate and temperature to suit specific coating removal applications.
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.
Apply the heated air jet to the 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 Figure 2)
When the coating has been removed, use the appropriate solder extraction method to remove components if needed.
Visual examination or UV light may be used to verify the complete removal of the coating.