Title: 3.3 Through-Hole Soldering: Detailed Instructions - Read This
Course: Electronics Assembly & Soldering (Sandbox) > Section: Module 3: Through-Hole Solder and Desolder Instructions

How to Solder: Detailed Instructions

1) Turn on the Soldering Iron

It won't take long to heat to 650 degrees F.

2) Component Placement

Bend the leads as necessary and insert the component through the proper holes on the board. To hold the part in place while you are soldering, you may want to bend the leads on the bottom of the board at a 45-degree angle. Bending the leads in this manner is called clinching them. This works well for parts with long leads, such as resistors. Components with short leads such as IC sockets can be held in place with a little masking tape, or you can bend the leads down to clamp onto the PC board pads.

In the image below, a resistor is ready to solder and is held in place by slightly bent leads.

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Place Component

In general, it is best to start with the smallest and flattest components (resistors, diodes, etc.) and then work up to the larger components (capacitors, transformers) after the small parts are done. This keeps the board relatively flat, making it more stable during soldering. It is also best to save sensitive components (transistors, IC chips) until the end to lessen the chance of damaging them during assembly of the rest of the circuit.

3) Apply Heat

Apply a very small amount of solder to the tip of the iron. This is called tinning the tip. This helps conduct the heat to the component and board, but it is not the solder that will make up the joint.

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Apply heat to the joint.

To heat the joint, you will lay the tip of the iron so that it rests against both the component lead and the board. It is critical that you heat the lead and the board; otherwise, the solder will simply pool and will not stick to the unheated item. The small amount of solder you applied to the tip before heating the joint will help make contact between the board and the lead. It normally takes a second or two to get the joint hot enough to solder, but larger components and thicker pads/traces will absorb more heat and can increase this time.

If you see the area under the pad starting to bubble, stop heating and remove the soldering iron, because you are overheating the pad and it is in danger of lifting. Let it cool, then carefully heat it again for much less time.

4) Apply Solder

Once the component lead and solder pad have heated up (after about 1 second), you are ready to apply solder. Touch the tip of the strand of solder to the component lead and solder pad, but do not touch the tip of the iron. If everything is hot enough, the solder should flow freely around the lead and pad.

You will also see the flux melt or liquefy, bubble around the joint (this is part of its cleaning action), flow out, and release smoke. Continue to add solder to the joint until the pad is completely coated and the solder forms a small mound with slightly concave sides. This will not take much time. If it starts to ball up, you have used too much solder or the pad on the board is not hot enough. Once the surface of the pad is completely coated, you can stop adding solder and remove the soldering iron (in that order). Don't move the joint for a few seconds as the solder needs time to cool and solidify.

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Apply solder to the joint.

5) Inspect Joint and Clean Up

Once the joint is made, you should inspect it. Check for bad joints or solder bridges. If the joint checks out, move on to the next.

To trim the lead, use cutters to cut at the top of the solder joint.

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6) Maintain a Clean Work Space

When soldering, maintaining a clean work space is very important to avoid harming you, someone else, and/or the equipment.

Keep clipped leads in a pile and discard when you are finished soldering.

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