Beginners Guide: Soldering
This is a beginner’s guide to soldering. It serves only to provide a general idea of the tools and methods required to complete simple soldering tasks.
Last updated
This is a beginner’s guide to soldering. It serves only to provide a general idea of the tools and methods required to complete simple soldering tasks.
Last updated
What is soldering?
Soldering is a process of joining two metal surfaces together using a filler metal called solder. There are many applications for soldering, including metalworking, plumbing, jewelry making, and other decorative items. The focus for this guide will be on the manufacture and repair of printed circuit boards (PCBs) and other electronic equipment.
A soldering iron is a hand tool that heats up to melt solder. The most common style resembles a pen (Recommended for beginners). It will range from 15W to 30W and can be purchased for a reasonable price (< $25).
An improved version of the soldering iron is a soldering station. The ability to change the temperature is one of the soldering station's main advantages. This gives a variety of projects more flexibility and control. Soldering stations can be purchased for a reasonable price (< $100), but more advanced projects will require a more expensive model.
(Note: A soldering station is typically referred to as a soldering iron. This is a general term that most people use to describe the majority of soldering equipment used for electronics.)
Most soldering irons have an interchangeable tip. Tips come in a wide range of sizes and shapes and have numerous variations. These tips have different purposes and offer different advantages. The two most common types are the conical tip and chisel tip.
Conical Tip: Used in precision electronic applications. It has a fine tip that delivers heat to a smaller area without affecting the surroundings.
Chisel Tip: A wide tip better suited to solder wires or large components together. It can spread the heat out to a wider area.
(Note: Size selection is based on the size of the surface that needs to be heated.)
Cleaning the soldering tips is good house keeping and will extend the life of a solder tip.
Sponge: Pros – Comes with cheaper soldering kits. It is an effective and fast way to clean the solder tip. Cons – Cools down the tip so it needs to heat up again. It can also thermally shock the tip, reducing its lifespan. (Note: Must wet the sponge before use)
Brass Cleaner: Pros – Fast and easy to use. Does not thermally shock the tip as it does not need to be wet. Cons – It is abrasive and can scratch the chrome finish of the tip. (Note: Use a jabbing motion with the brass cleaner. Wiping increases the likelihood of flinging molten solder.)
The soldering stand aids in avoiding accidental material and surface contact with the hot tip. This includes assisting in preventing unintentional harm to your body, most commonly to your hand.
Solder is a metal alloy that is melted to form the bond between the components. Lead-free rosin core solder is the most popular type of solder used in electronics. Typically, this is constructed of a copper/tin alloy. Solder comes in different core and material types depending on the application. Additionally, the melting temperatures of solder vary depending on the type of material. For the ideal temperature setting, make sure to review the manufacturer's specifications.
Leaded solder (tin/lead) is still somewhat common but has become less popular due to health risks (Lead is a highly toxic metal). It does still have its applications due to its material properties, but extra precautions should be taken if this solder is used, including:
Wear gloves (nitrile or similar). These are either on the electronics bench or in the "dirty cube" under the fume hood.
Avoid touching your mouth, eyes, or other orifices through which the lead could enter your body.
Brush up leftover pieces of solder and wipe down the benchtop surface with a wet paper towel or alcohol wipe.
Remove your gloves before touching anything else, including your phone, skin, or food.
Wash your hands thoroughly when complete.
Solder also comes in a variety of diameters. There are two standard sizes: 0.032" and 0.062". If the project requires small electronics a thinner solder is advised. A thicker solder will be required for larger applications, like wires.
(Note: Do not buy acid core solder as this will damage circuits and components. This type of solder is mainly used for plumbing and metal working.)
Flux is a prepping agent for the soldering process. Flux helps solder flow by removing any oxidation and slightly etches the surface. This helps to form a strong metallurgical bond that prevents the solder joint from being weak.
Most PCBs are pre-fluxed during production and most solders have flux built in. For a simple connection additional flux will not be necessary but more complex soldering techniques may require it.
There are many types of flux depending on the project requirements, but a good choice is “no clean flux”. The light residue can be left on the board or easily cleaned if aesthetics is an issue. Other fluxes must be cleaned because they may cause corrosion. For the most effective method of cleaning the flux, adhere to the manufacturer's instructions.
Jigs are helpful because managing the soldering iron, components, and work piece simultaneously can be challenging. Custom jigs might be required, but for the majority of projects, straightforward clamp jigs will be sufficient.
Electrical Tape: Used to insulate and protect bare electrical wires. Comes in many colors. Is wrapped around the wire.
Shrink Tubing: Used to insulate and protect bare electrical wires. Preferred method as it provides better protection and looks professional. Comes in many colors and can have additional internal coatings such as a water-resistant resin. Heat shrinks the tubing around the wire. Remember to place the shrink tubing onto one of the wires before the joint is soldered. It may not be possible to place it after.
(Note: Tape and Tubing can also be used to mark wires based on things such as function, phase, and voltage.)
Here are some common tools that will be helpful to have while soldering.
Wire strippers/cutter
Pliers
Tweezers
Solder Sucker
Desolder Braid (Wick)
The most fundamental consideration for any project is safety. There are a few things to keep in mind when soldering.
Always be aware of where the soldering iron is. High temperatures can be reached by soldering irons. The temperatures range from 600 to 650 °F on average, and depending on the application, some are even higher. When not in use, put the soldering iron back on the stand. (Note: Soldering is still regarded as hot work even when there isn't an open flame present. Avoid using near combustibles.)
Solder in a well-ventilated area. Fumes from soldering are damaging to your eyes and lungs. Some solder even contains lead which is highly poisonous.
Wear safety glasses/goggles. This will protect against accidental splashes of hot solder.
Wash your hands. Any task would benefit from this practice, but especially after soldering. Hand washing lowers the possibility of contamination and potential material ingestion from the soldering process. Remember that some solder contains lead.
(Note: Lead solder while being phased out is still common to find. Make sure to double check the solder you are using.)
Tinning the tip will help heat transfer and protect the tip. All tips eventually wear out, but it will extend the life of the tip. Each job should begin with this.
Step 1: Let the soldering iron heat up.
Step 2: Clean the soldering iron tip.
Step 3: Touch the solder to the tip and allow it to flow around. (Note: You will not need much solder; do not use excessive amounts.)
Step 4: The solder iron is ready for use.
Most PCBs are pre-fluxed during production and most solders have some flux built in. For a simple connection additional flux will not be necessary but more complex soldering techniques may require it. Add flux only when necessary.
Have all your tools ready to go. It can be inconvenient to repeatedly stand up to get a tool. It also increases the possibility of knocking the soldering iron over (dangerous) and losing small parts (personal experience).
Step 1: Mount the component. Place the component on its surfaced mount pads or insert it into the component holes.
Step 2: Heat the solder joint. Make sure the soldering iron is fully heated and touch the tip of the iron (at about a 45-degree angle) to the copper pad and component lead(wire). Keep it in place for about 3-4 seconds.
Step 3: Apply the solder to the joint. Continue holding the soldering iron to the pad. Try not to let the solder touch the soldering iron directly. You want the joint to be hot enough to melt the solder when it is touched to the pad itself. If the joint is too cold, it will form a bad connection.
Step 4: Finish the solder joint. Once the joint has received enough solder, remove the iron and allow it to cool naturally. (Note: DO NOT BLOW ON IT, this can cause a bad joint). A proper joint is smooth and shiny. It should look like a volcano or cone. If there is too much solder, it will look like a ball and possibly leak onto nearby components or solder joints. If you heat the solder too much it will be a dull color. Once the joint is complete snip the excess leads (wire) if applicable.
(Note: Reading this guide is a good start but the next best step is to watch a soldering tutorial. Here is one https://www.youtube.com/watch?v=6rmErwU5E-k . There are several videos available on this subject. Practice is all that is left at that point.)
Step 1: Tin the wires. Heat the ends of the wires and apply some solder till fully coated.
Step 2: Connect the wire together. For simple applications this could just be touching them together (although mechanically weak still a good electrical connection). For more mission critical applications various techniques are used to create a stronger solder joint.
(Note: Here is an example of a more advanced technique https://www.youtube.com/watch?v=O-ymw7d_nYo )
Step 3: Heat the solder joint on the wires with the iron. Let the solder melt and fuse the wires together. Apply additional solder if necessary.
Step 4: Finish the solder joint. Once the joint has received enough solder, remove the iron and allow it to cool naturally. (Note: DO NOT BLOW ON IT, this can cause a bad joint). The connection should have enough solder and still be shiny. A burnt solder joint will have a darker hue and create a weaker joint.
Step 5: Protect the solder joint. This will protect against a short or someone being shocked by the exposed wire. Additionally, this will lengthen the life of the joint and help prevent corrosion. Electrical tape or electrical shrink tubing can be used for this. Shrink tubing is the recommended approach as it better protects the joint and looks professional. (Note: Remember to place the shrink tubing onto one of the wires before the joint is soldered. It may not be possible to place it after.)
(Note: Reading this guide is a good start but the next best step is to watch a wire soldering tutorial. Here is one https://www.youtube.com/watch?v=uj_PbRBirkQ . There are several videos available on this subject. Practice is all that is left at that point.)
Solder has the added benefit of being removable. This comes in handy when replacing broken components or fixing mistakes in the soldering process.
Step 1: Place a piece of desoldering braid (wick) on the top of the solder joint.
Step 2: Heat the soldering braid with soldering iron and it will absorb the solder. This may require changing approach angles to remove all the solder.
Step 3: Remove the component. The component can now be replaced if necessary. Remember to re-flux the PCB board as it was removed in this process.
Optional: You might want to use a solder sucker first if there is a lot of solder to remove. It will get the bulk of the solder. The desolder braid can then be used to remove the remainder.
Soldering is a skill that takes practice. Sometimes mistakes happen, and a solder joint will need to be redone or a component will be broken. There are also many different soldering techniques depending on the application. This will require further research or even the involvement of someone with technical expertise. At the end of the day just take your time and learn the process step by step.
