8.4.2 Component Removal, Surface Mount Gull Wing Components, Hot Gas Method
Outline
This procedure covers the most commonly used methods for removing surface mount Gull Wing components.
Note: The goal when removing any component is to remove the component as quickly as possible.
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.
Cleaner
General purpose cleaner for removing contamination.
Microscope
Precision microscope with stand and lighting for work and inspection.
Soldering Iron
Properly maintained soldering iron and properly sized soldering iron tips.
Wipes
Nonabrasive, low-linting wipes for cleanup.
Images and Figures
Surface Mount Gull Wing Component
Figure 1: Nozzle at left heats the leads and pads. Nozzle at right heats component, leads and pads.
Figure 2: After solder has melted lift component straight up.
Preparation
This method uses hot air nozzles that do not touch the component. Gas or air is heated and forced through a specially designed nozzle and directed onto the component leads and surface pads.
Hot gas/air nozzles come in several sizes to accommodate many of the different styles and sizes of components. Measure the overall length and width of the component to select the proper size tip. Check the nozzle for proper fit prior to processing the part. Some hot gas/air nozzle designs will heat only the component leads and pad area. (See Figure 1, Left Side) Some hot air nozzle designs heat the entire component, the leads, and the pad area. (See Figure 1, Right Side)
Hot gas/air can be used to remove a number of different styles of SMT components, but the heated gas/air must be directed onto the leads and pads and away from the top of the component and circuit board surface.
Hot gas/air nozzles may or may not include vacuum assistance to lift the component off the circuit board surface.
Procedure
Place the pre-heated circuit board on the Positioning Table. A heated positioning table is available to pre-heat the circuit board or can be used to maintain the pre-heated temperature when many components need to be removed from one circuit board.
Apply a small amount of liquid flux to all leads of the component.
Place the nozzle directly over the top of the component and activate the airflow. When the solder has melted, actuate the vacuum assist or lift off the component with a vacuum pen. Lift the component straight up. (See Figure 2)
It's difficult to precisely know how long to dwell prior to safely removing the part. This is further complicated by the fact that when removing a bank of components, parts subsequent to the first come off much faster. Obviously, the smaller the part, the quicker it reflows. Small SMT components may reflow in a few seconds, and large SMT components may take more than a minute.
