How to Soldering or Desoldering Circuit Board

Soldering and desoldering are essential skills for anyone working with electronics, from hobbyists to professional technicians. These techniques allow you to create, modify, and repair electronic circuits by joining or removing components on a printed circuit board (PCB). In this comprehensive guide, we'll explore the art of soldering and desoldering, covering everything from basic techniques to advanced tips and safety precautions.

Introduction to Soldering and Desoldering

What is Soldering?

Soldering is the process of joining two or more metal items together using a molten filler metal called solder. In electronics, this technique is used to create electrical connections between components and the circuit board, ensuring a reliable and conductive bond.

What is Desoldering?

Desoldering is the reverse process of soldering, where you remove solder to separate components from a circuit board. This is useful for replacing faulty components, modifying circuits, or salvaging parts from old electronics.

Essential Tools and Materials

To get started with soldering and desoldering, you'll need the following tools and materials:

Soldering Techniques

Preparing for Soldering

1. Clean the workspace: Ensure your work area is clean and well-ventilated.
2. Gather materials: Collect all necessary tools and components.
3. Prepare the soldering iron: Turn on the soldering iron and allow it to heat up to the appropriate temperature (usually between 300°C to 380°C).
4. Clean the soldering tip: Use a damp sponge or brass wool to clean the tip of the soldering iron.

Basic Soldering Steps

1. Apply flux: If necessary, apply a small amount of flux to the area to be soldered.
2. Tin the tip: Melt a small amount of solder onto the tip of the iron to improve heat transfer.
3. Heat the joint: Place the soldering iron tip on the component lead and the PCB pad simultaneously.
4. Apply solder: Touch the solder to the heated joint, not the iron tip. Allow it to flow and form a small, conical shape.
5. Remove heat: Withdraw the soldering iron and allow the joint to cool naturally.
6. Inspect the joint: Check for a smooth, shiny finish and good connection.

Types of Solder Joints

Desoldering Techniques

Using a Desoldering Pump

1. Heat the solder joint with the soldering iron.
2. Place the tip of the desoldering pump close to the molten solder.
3. Quickly remove the soldering iron and activate the pump to suck up the molten solder.
4. Repeat if necessary to remove all solder.

Using Desoldering Wick

1. Place the desoldering wick on top of the solder joint.
2. Apply the heated soldering iron on top of the wick.
3. As the solder melts, it will be absorbed into the wick.
4. Remove the wick and iron simultaneously.
5. Cut off the used portion of the wick and dispose of it properly.

Hot Air Rework Station Method

For surface-mount components:

1. Apply flux to the component leads.
2. Use the hot air gun to heat the entire component evenly.
3. Once the solder melts, use tweezers to carefully remove the component.
4. Clean excess solder from the PCB pads using a desoldering pump or wick.

Safety Precautions

Soldering and desoldering involve high temperatures and potentially harmful materials. Follow these safety guidelines:

1. Wear safety glasses to protect your eyes from solder splatter.
2. Work in a well-ventilated area or use a fume extractor to avoid inhaling harmful fumes.
3. Never touch the heated parts of the soldering iron or freshly soldered joints.
4. Keep a clean, organized workspace to prevent accidents.
5. Wash your hands after handling solder and flux to avoid ingesting lead or other harmful substances.
6. Properly dispose of waste materials, including used solder and flux residues.

Troubleshooting Common Issues

Advanced Techniques

Working with Surface Mount Devices (SMDs)

1. Use solder paste: Apply a small amount of solder paste to the PCB pads.
2. Place the component: Carefully position the SMD on the pads.
3. Reflow the solder: Use a hot air station or reflow oven to melt the solder paste.
4. Inspect and touch up: Check for proper alignment and connections, touching up with a fine-tipped soldering iron if needed.

Drag Soldering

Drag soldering is an efficient technique for soldering multiple pins on ICs or other multi-pin components:

1. Apply flux to the pins and pads.
2. Tin the soldering iron tip with a small amount of solder.
3. Drag the tip across the pins at a 45-degree angle, allowing solder to flow onto each pin.
4. Use desoldering wick to remove any solder bridges between pins.

Reworking Ball Grid Array (BGA) Components

BGA rework requires specialized equipment and skills:

1. Preheat the PCB to reduce thermal stress.
2. Remove the old component using a hot air rework station.
3. Clean and prepare the pads on the PCB.
4. Apply flux and position the new BGA component.
5. Use a BGA rework station to accurately heat and reflow the solder balls.
6. Allow for slow cooling to prevent warping or other damage.

Maintenance and Care of Soldering Equipment

Proper maintenance of your soldering equipment ensures longevity and consistent performance:

Soldering Iron Care

1. Keep the tip clean: Regularly clean the tip with a damp sponge or brass wool.
2. Tin the tip: Always tin the tip before storage to prevent oxidation.
3. Replace tips: Change tips when they become pitted or unable to hold solder.
4. Check temperature: Periodically verify that the iron is maintaining the correct temperature.

Desoldering Pump Maintenance

1. Clean regularly: Disassemble and clean the pump to remove solder residue.
2. Replace nozzle: Change the nozzle if it becomes clogged or damaged.
3. Lubricate: Apply a small amount of lubricant to the plunger mechanism if it becomes stiff.

Workspace Maintenance

1. Clean work surface: Regularly clean your soldering mat or work surface to remove flux and solder residues.
2. Organize tools: Keep tools and materials organized and easily accessible.
3. Dispose of waste: Properly dispose of used solder, flux, and other materials.

Frequently Asked Questions

1. What temperature should I set my soldering iron to?

The ideal temperature depends on the type of solder and components you're working with. For most electronics work with lead-free solder, a temperature between 315°C to 370°C (600°F to 700°F) is suitable. For lead-based solder, you can use a slightly lower temperature, around 300°C to 330°C (570°F to 625°F).

2. How do I know if I've created a good solder joint?

A good solder joint should have a smooth, shiny, concave shape that resembles a small mountain or volcano. It should provide a solid mechanical and electrical connection between the component lead and the PCB pad. If the joint looks dull, grainy, or has an irregular shape, it may be a cold joint and should be redone.

3. Is it necessary to use flux when soldering?

While modern solders often contain flux, using additional flux can greatly improve the quality of your solder joints, especially when working with oxidized surfaces or when reworking existing joints. Flux helps to clean the surfaces and promotes better solder flow, resulting in stronger and more reliable connections.

4. How do I prevent damaging sensitive components while soldering?

To protect sensitive components:

1. Use a heat sink (like a small alligator clip) on component leads to absorb excess heat.
2. Minimize soldering time to reduce heat exposure.
3. Allow joints to cool naturally rather than blowing on them.
4. Use an anti-static wrist strap when handling static-sensitive components.
5. Consider using a temperature-controlled soldering iron with a lower temperature setting.

5. What's the difference between lead-based and lead-free solder?

Lead-based solder typically contains 60% tin and 40% lead, while lead-free solder is usually made of a mix of tin, copper, and silver. Here are the key differences:

Lead-free solder is now more commonly used due to environmental and health regulations, but lead-based solder is still preferred in some applications where reliability is critical.