CASA Part 66: De-Soldering Tools and Practices
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Questions and Answers

What is the primary purpose of de-soldering in electronics?

  • To increase the circuit's power output
  • To enhance the circuit's aesthetics
  • To attach a new component to the circuit
  • To troubleshoot and repair the circuit (correct)
  • Which tool is recommended for beginners to remove solder from a joint?

  • Solder wick (correct)
  • De-soldering pump
  • Soldering iron
  • Tweezers
  • What happens when a solder wick is pressed onto a cold joint?

  • The solder is pushed away from the joint
  • The solder is melted and solidified immediately
  • The solder wick is damaged
  • The solder is drawn up by capillary action into the braid (correct)
  • Why is it essential to take care when using a solder wick?

    <p>To avoid overheating the board</p> Signup and view all the answers

    What should you do if the joint will not come apart easily?

    <p>Apply the soldering iron to melt the remaining solder</p> Signup and view all the answers

    What should you do with the solder wick after de-soldering?

    <p>Cut off the used portion and dispose of it</p> Signup and view all the answers

    What is the primary consequence of using an iron with excessive heat capacity?

    <p>Burn or melt wire insulation.</p> Signup and view all the answers

    What is the recommended wattage range for soldering small parts?

    <p>20-60 W</p> Signup and view all the answers

    What is the primary purpose of tinning the iron tip?

    <p>To conduct heat to the components.</p> Signup and view all the answers

    What is the recommended soldering iron tip shape for maximum efficiency?

    <p>Screwdriver, chisel, and pyramid</p> Signup and view all the answers

    Why is it important to ensure the joint is mechanically secure before soldering?

    <p>To prevent the joint from moving during the cooling period.</p> Signup and view all the answers

    What is the primary consideration when selecting a soldering iron for a specific task?

    <p>The production rate of the task.</p> Signup and view all the answers

    What is the recommended way to apply flux-core solder?

    <p>Apply the flux-core solder to the exact point between the metal and the soldering iron</p> Signup and view all the answers

    Why is it necessary to avoid heavy 'rocking' pressure when soldering?

    <p>The iron does not have sufficient heat capacity for the job or has not been properly prepared</p> Signup and view all the answers

    What is the recommended way to handle the soldering iron when not in use?

    <p>Keep it in a holder</p> Signup and view all the answers

    Why is it important to avoid overheating the soldering iron?

    <p>All of the above</p> Signup and view all the answers

    What should you do after making a solder joint?

    <p>Hold the work firmly in place until the joint has set</p> Signup and view all the answers

    What should you avoid when handling silver-coated wire during solder application?

    <p>Wicking during solder application</p> Signup and view all the answers

    What is the primary reason for removing flux residue from a solder joint?

    <p>To prevent the corrosive nature of the flux residue from damaging the component leads or circuit board</p> Signup and view all the answers

    What is the characteristic of a good solder connection on a PCB?

    <p>The solder joint surfaces are smooth, nonporous, and undisturbed</p> Signup and view all the answers

    What is the purpose of bending leads up to 30° from the vertical plane?

    <p>To retain the part during soldering</p> Signup and view all the answers

    What is the acceptable extension of leads beyond the pad surface in a PCB?

    <p>0.5-2.29 mm</p> Signup and view all the answers

    What happens if flux residue is not removed from a solder joint?

    <p>The corrosive nature of the flux residue gradually destroys the component leads or circuit board</p> Signup and view all the answers

    What is the characteristic of the finish of a good solder connection on a PCB?

    <p>Satin to bright</p> Signup and view all the answers

    What is the primary characteristic of a solderless wire-wrapping connection?

    <p>Mechanically and electrically stable</p> Signup and view all the answers

    What is the purpose of counting the turns in a wire wrap?

    <p>To ensure the required number of turns for a stable connection</p> Signup and view all the answers

    What is the typical range of turns in a wire wrap?

    <p>Four to seven turns</p> Signup and view all the answers

    What is the primary advantage of a Class A wire wrap?

    <p>Improved vibration characteristics</p> Signup and view all the answers

    What is the requirement for a Class A wire wrap?

    <p>One half to two turns of insulated wire in contact with three corners</p> Signup and view all the answers

    Why is Class B wire wrap prohibited in aircraft?

    <p>It is not suitable for airborne hardware applications</p> Signup and view all the answers

    Study Notes

    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).

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    Learn about de-soldering tools and techniques used in electronics for troubleshooting and repair. Understand the importance of removing components from a circuit board.

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