Soldering is an ancient art, dating back to at least ancient Egypt, where soldering was used in creating jewelery. For Electronics , the process is specifically used to create joints that that allow for conductivity of electricity and to protect against water movement through a joint .
- It is done by applying a melted layer of filler material (solder) to bridge the joint.
Unlike welding, which melts the basic metals to combine the two components being joined, soldering melts only the solder that forms the joint between components.
Solder is a soft metal compound that is melted to join components within a circuit. Do not use plumber’s solder; look for solder with a rosin core 60/40 type (a mixture of 60 percent tin and 40 percent lead) which has a melting range of 183 degree to 190 degree celcius or one of the lead free solder that are designed for electronics soldering. It is wire-shaped alloy sold coiled in spool.
An alloy is a combination of two metals.
Liquid flux is a chemical agent used to prepare your board for soldering. A flux bottle has a needle that allows for precise application of the flux. In soldering, flux is a compound that prepares a surface base metal so that it can be joined efficiently with solder.
- It reduces oxides to prevent oxidation during the soldering process.
- Flux also assists in wetting which is the process of reducing the surface tension of the base metal so that the liquid solder can make better contact with it.
To get a better sense of wetting think of a bead of water on a newly waxed car. The water forms a bead because of the greater surface tension of the waxed surface. In other words, the water does not make good contact with the surface.
- The flux prevents beading
of solder, enabling the solder to adhere as a flat droplet instead of an angled bead.
Solder is of often sold already combined with flux, in the form of rosin-coredor flux- cored solder. This is often all the flux you need in a basic printed circuit board (PCB) solder. If you are working with surface-mount soldering, you may also want to prepare the surface of the PCB and the component itself with additional liquid flux.
Rosin is a pine tree that has been used as a flux for many hundreds of years for its ability to reduce friction.
Soldering Iron and Tips
A soldering iron is the tool used to melt solder to form joints. It has a plastic handle and a metal tip that heats up. The type of soldering iron we recommend has variable power but no temperature control. Generally, if you are just starting out in electronics, you should look for a relatively low power unit (25-50 W) that can accept a variety of tips and comes equipped with a stand and an on/off indicator light. Our iron has a place for sponge for wiping off any solder residue after each use. If yours doesn’t come with sponge, you will need to buy one and keep it on hand when soldering.
You will also want at least two different types of tips: one with a flat head much like a screwdriver (this is one that will come with your iron) and one with a fine point. Tips are usually made of a copper core because of copper’s conductivity. The tips are then covered with iron, chrome and nickel to provide hardness and better high temperature performance.
For the projects in this site, we use a Weller WLC 100. This is a good starter iron but it does have some drawbacks, the iron itself is not grounded and you can control only the power and not the temperature and for most uses it is more than up to this task.
Solder sucker and solder wick is used to suck up excess solder from your projects. A solder wick does the same sort of things but is more precise. You typically use the sucker first to get the bulk of excess solder off and then use the wick to remove what’s left.
Prepping for Soldering
Before beginning a soldering project, you must first prepare your workspace and materials. Make sure you have adequate ventilation so the irritants in the flux and solder are diluted by fresh air. You should have adequate room to work and to organize your equipment and components. Make sure components and the board you are using are clean. Use a brass Sponge (with no soap) to remove any waxy or oily substance.
Prepare Your Soldering Iron
Prep your Soldering Iron by following these steps:
- Make sure your iron’s tip is clean and shiny. Know which part of the tip is the proper work area.
- Prepare your sponge by dampening it (not soaking it wet until it is dripping wet).
- Turn your iron on. Follow your manufacturer’s instructions for the proper settings for the solder you are using.
- Wipe the iron’s tip on the damp sponge and apply a bit of solder to the tip to tin it. Tinning helps in the even heat transfer from your iron to the solder, so even your tip is pre-tinned, it’s a good idea to re-tin every time you wipe the tip with the sponge. You can also buy the tinner, which is a dip-in product that cleans and tins tips.
Irons are hot! Follow these safety tips when soldering:
- Don’t touch a hot iron’s tip.
- Don’t leave a hot iron unattended.
- Don’t set a hot iron on anything but its stand.
- Wait until the iron has cooled completely before storing it.
- Know where your fire extinguisher is. Be sure it is rated for electrical fires (Class C) and is up to date.
- Keep the iron’s power cord out of the way so you don’t risk tripping over it.
A Steady hand is always your best tool. Hold your iron like a pen, with a comfortable relaxed grip. Then follow these steps:
- If you are soldering a particularly heat-sensitive component (such as transistor), attach a heat sink to the lead.
- Heat the connection you want to make, not the solder. Hold the connection with the tip for a few seconds.
- Apply a little solder and let it flow into a small volcano shape over the connection.
- Remove the solder, then slowly remove the iron, all while maintaining a steady hand so as not to disrupt the joint.
- Keep everything still as you inspect the joint. It looks like it needs more solder, repeat steps 2 through 5.
Don’t worry if you make a mistake. You can always remove the solder and reapply it.
If any solder joints are cracked, incompletely connected, or overlap onto other components or traces, it’s best to start over, remove the solder (a process called de-soldering) and then try again.
Keep in mind that melted solder can cause severe burns. Always wear protective eyewear, avoid loose clothing and use caution when soldering. Follow these steps for de-soldering:
- Clean the area around the solder joint. Again, steel wool should do the job nicely.
- Gather your tools: soldering iron, solder sucker and soldering wick.
- Heat the joint to melt the solder.
- Depress the plunger on the solder sucker: when the solder melts, use the solder sucker to take up the solder. This may be the only step you need to take to remove all the solder.
- If there are bits of solder left, heat a portion of solder wick (enough to hold the remaining solder) and place it on the remaining solder. It should suck up the remaining solder.
- Clean the area with steel wool to remove any remaining rosin or solder bits.
By Kiran Bhatt