|8.2.1 Component Removal, Surface Mount Chip Components, Forked Tip Method
This procedure covers one commonly used method for removing surface mount chip components.
The goal when removing any component is to remove the component as quickly as possible.
Caution - Glued Components
A small dot of epoxy is often used to hold chip components in position during wave soldering processing. Typically these components will be located on the bottom side of a circuit board that has through hole components located on the other side. Whenever you see a board like this, you can generally assume that the chip components will be glued onto the board. You'll need to leave the tip on the component for one or two additional seconds in order to transfer enough heat to over-cure or soften the adhesive. If required take a wooden stick or curved tweezers and push the component sideways until the glue joint finally gives way.
Minimum Skill Level - Intermediate
Recommended for technicians with skills in basic soldering and component rework, but may be inexperienced in general repair/rework procedures.
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.
||Surface Mount Assemblies
Images and Figures
|Tools and Materials|
General purpose cleaner for removing contamination.
It is a challenge to undertake precision repair without a good microscope.
||Soldering Iron, Solder and Flux
A well maintained soldering iron is a must at every tech bench.
Nonabrasive, low-linting wipes for cleanup.
|Surface Mount Chip Component|
|Figure 1: Forked tip shown with solder added to cavity to enhance removal operation.|
|Figure 2: Removing SMT chip component with forked tip. After solder has melted lift tip out and up|
|Chip Capacitors generally have solid color bodies.|
|A - Stripe;B - Beveled Surface;The striped or beveled end is the "positive" (+) or "anode end".|
Forked tips are designed to fit over the top of chip components, and to reflow both solder joints at once. The ends of the forked tip fit over the component with just a slight amount of extra space for solder. Measure the overall length and width of the component with a caliper to select the proper size tip. Check the tip for proper fit prior to processing the part.
The tip should not fit the component so tightly that it will get lodged in the tip, but the tip should not be so loose that it will not conduct heat to the leads simultaneously. The size and shape of the forked tip will have an effect on the rate of heat transfer. Larger tips with more surface area will transfer heat faster than smaller tips.
Forked tips can be used to remove a number of different styles of chip components but the component must fit properly in the tool cavity. Since forked tips have a cavity, they require special cleaning and tinning procedures.
- Remove any solder from inside the tip cavity with a fiber tool.
Do not use a wire brush for any tip cleaning procedure. A wire brush can severely scratch a metal tip. Scratches allow oxidation to form on the base metal of the tip and this will severely decrease the useful life.
- Remove any oxidized solder by shocking the tip on a wet sponge.
- Add solder to the properly prepared tip. Fill the cavity until there is a fillet on each side of the tip. (See Figure 1) Add enough solder to help transfer the heat quickly but not so much that it will fall out when the tip is turned upside down.
The solder provides surface tension to lift the component off the pads after reflow. Since the tip has more metal surface area than the pads on the circuit board, the solder will be drawn toward the metal tip and so will the component.
Determine the direction the part is to be swept off the circuit board surface. Densely packed circuit board assemblies often leave only one direction for the rework tool to follow when sweeping the part off the surface.
SOT Component Removal
- Apply a small amount of liquid flux to both ends of the component.
- Place the forked tip directly over the top of the component. The extra solder on the tip will melt both solder joints. When the solder has melted slide the component out and up. (See Figure 2)
Once the component is removed from the circuit board it can be removed from the tip by the shocking sponge or with a dull blunt instrument applying downward pressure on the component.
- Clean the area.
Procedure for reference only.
"We were certain the circuit board we sent to you were beyond repair, but we sent them anyway. They came back, we tested them, and they all functioned perfectly. Job well done!"
A.Z. Guadalupe, Mexico
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