8.3.2 Component Removal, Surface Mount J Lead Components, Hot Gas Method
Outline
This procedure covers one commonly used method for removing surface mount J lead 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.
Oven
General purpose oven for drying, baking and curing epoxies.
Soldering Iron
Properly maintained soldering iron and properly sized soldering iron tips.
Wipes
Nonabrasive, low-linting wipes for cleanup.
Heat Shield
During component rework, protection of nearby components is often mandatory to avoid collateral heat damage or inadvertent reflow. Collateral heat damage or unintended reflow of adjacent component solder connections can result in component damage, oxidation, de-wetting, pad damage, wicking, starved joints, and scorching. The rework technician must constantly be aware of the effect of heat on the target device or circuit, plus how it affects components near the target device on both sides of the assembly.
235-4010 Heat Shield Blanket
These are 5" x 7" sheets of fiberglass fabric, aluminum foil laminate with a pressure-sensitive adhesive backing. Heat Shield Blanket is designed to reflect 90% of the radiant heat energy. It will withstand continuous heat in the leaded and lead-free solder melt temperature range and short-term exposure at temperatures up to 1000°F/538°C. Heat Shield Blankets can be used in conjunction with Heat Shield Plates to create a more robust thermal shield with a more rigid structure.
235-4060 Heat Shield Plates
These are light gauge 5" x 7" aluminum sheets used primarily when simple heat deflection is required. Heat Shield Plates are easy to size, cut, form, and bond or tape into place using the high-temperature mask or high-temperature tape supplied in the kit. When using Heat Shield Plate material to deflect heat, leave a small space between the Heat Shield Plate and the protected component or area to avoid direct contact transfer of heat.
115-9010 Mask, High Temperature
This product is a high-temperature, quick cure, synthetic latex, peel-able solder mask supplied in syringes with dispensing needles. This mask can create free-form heat shielding or seal the edges of the Heat Shield Blanket or Heat Shield Plates. This mask cures at room temperature in 5 minutes. Once dried, it can be peeled off after use.
Images and Figures
Surface Mount J Lead 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.
Figure 3: A - Dot indicates pin 1;B - Indicates pin 5;C - Indicates direction of pin count.
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 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 air flow. 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 know precisely 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.
