CASA Part 66: De-Soldering Tools and Practices

De-Soldering Tools

• De-soldering is the removal of solder and components from a circuit for troubleshooting, repair, and salvaging components.
• There are two ways to remove solder: with solder wick (also known as de-soldering wick or copper braid) and with a de-soldering pump (solder sucker).
• De-soldering wick is the most common method and should be attempted first unless you have significant prior skill using a de-soldering pump.

Solder Wick

• Solder wick is a cheap and effective way to de-solder a joint.
• Select a suitable width of braid and press it down onto the cold joint using the hot tip of the iron.
• Molten solder is drawn up by capillary action into the braid.
• Once everything has melted, the wick is lifted along with the solder and then cut off and disposed of.

Soldering Iron

• Soldering irons are available in ranges from 20 to 500 W.
• Irons with ratings of 60, 100, and 200 W are recommended for general use in aircraft electrical wiring.
• Pencil irons with a rating of 20-60 W are recommended for soldering small parts.
• A lightweight 55-W iron with a 315°C Curies point tip control is recommended for printed circuit soldering.

Selection of Soldering Tip

• The tip transfers heat from the element into the work, and for maximum efficiency, the tip face must suit the joint to be soldered.
• The shape of the tip face should provide the best fit into the joint and consequently the best heat flow.
• The optimum tip face should be between two-thirds and three-quarters of the joint diameter.
• Screwdriver, chisel, and pyramid shapes are recommended.

Application of Heat and Solder

• Apply flux-core solder at the exact point between the metal and the soldering iron.
• Hold the iron directly against the assembly.
• Melt the solder on the joint, not the iron.
• Place the soldering iron firmly against the junction.

Securing the Joint

• Whenever possible, make sure the joint is mechanically secure before soldering.
• When this is not possible, make sure it is held rigid during the cooling period.

Protection Against Overheating

• Do not allow the iron to overheat.
• Disconnect the iron when it is not in use (between operations), or use a heat-dissipating stand.

Cooling the Solder Joint

• When the solder joint has been made, hold the work firmly in place until the joint has set.
• Allow solder joints to cool naturally.
• Do not use liquids or air blasts.

Solder Technique PCB

• When the solder joint is made, a brown waxy substance (flux residue) is left on the joint.
• Flux residue is slightly corrosive and must be removed from the joint before soldering can be considered complete.
• If the flux residue is not removed, it will gradually destroy the component leads or circuit board tracking material.

Inspecting a PCB Solder

• In a quality solder connection on a PCB, the solder joint surfaces are smooth, non-porous, and undisturbed, with a finish varying from satin to bright.
• The fillet completely wets all elements of the connection and is concave in shape, feathering out smoothly to the edge of the pad.
• Leads terminated straight through the PCB must extend 0.5-2.29 mm beyond the pad surface.

Solderless Wire-Wrapping

• Solderless wire-wrapping is done by helically wrapping a solid uninsulated wire around a specially designed termination post to produce a mechanically and electrically stable connection.
• Three major components are used during the solderless wire-wrapping process: wrapping wire, wire-wrap post, and wire-wrap tool.

Number of Turns in a Wire Wrap

• The countable turns are those turns of bare wire in intimate contact with the corners of the terminals.
• Wrapped terminations usually have four to seven turns of bare wire wrapped around the terminal post.
• The exact number of turns varies depending on the wire gauge used and the terminal size.
• There are two types of wire-wrap classifications: Class A (Modified Connections) and Class B (Conventional Connections, prohibited in aircraft).