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?

To avoid overheating the board Signup and view all the answers

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

Apply the soldering iron to melt the remaining solder Signup and view all the answers

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

Cut off the used portion and dispose of it Signup and view all the answers

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

Burn or melt wire insulation. Signup and view all the answers

What is the recommended wattage range for soldering small parts?

20-60 W Signup and view all the answers

What is the primary purpose of tinning the iron tip?

To conduct heat to the components. Signup and view all the answers

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

Screwdriver, chisel, and pyramid Signup and view all the answers

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

To prevent the joint from moving during the cooling period. Signup and view all the answers

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

The production rate of the task. Signup and view all the answers

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

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

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

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

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

Keep it in a holder Signup and view all the answers

Why is it important to avoid overheating the soldering iron?

All of the above Signup and view all the answers

What should you do after making a solder joint?

Hold the work firmly in place until the joint has set Signup and view all the answers

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

Wicking during solder application Signup and view all the answers

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

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

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

The solder joint surfaces are smooth, nonporous, and undisturbed Signup and view all the answers

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

To retain the part during soldering Signup and view all the answers

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

0.5-2.29 mm Signup and view all the answers

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

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

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

Satin to bright Signup and view all the answers

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

Mechanically and electrically stable Signup and view all the answers

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

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

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

Four to seven turns Signup and view all the answers

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

Improved vibration characteristics Signup and view all the answers

What is the requirement for a Class A wire wrap?

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

Why is Class B wire wrap prohibited in aircraft?

It is not suitable for airborne hardware applications 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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Description

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