Soldering Through-Hole and Surface Mount (SMT) Components to a PCB

2021-04-16 | By Will Siffer

License: Attribution Non-commercial Solder

Solderless breadboards are great for prototyping, but for a permanent design, it is usually necessary to solder components to a circuit board.

Although this can seem like a daunting task for the first time, it can be easy and rewarding as long as you work to stay safe and precise.

Follow this guide for some tips and tricks on being successful for your first time soldering!

Like all projects, safety is always the first priority. With soldering there are a couple of hazards that we need to avoid:

• Burns from touching the hot element of the soldering iron
• Possible lead poisoning from the solder material
• Flying debris from the circuit board

By wearing safety glasses and long sleeves, we can prevent our eyes and arms from being hit by the leads trimmed off of the circuit board as well as protect our arms from touching anything that gets accidentally heated during the soldering process. To avoid lead poisoning, we need to make sure to use Lead-free solder whenever possible and to wash our hands frequently during the project.

 In the following project we will use these tools and materials:

• Soldering iron
• Desoldering Pump
• Solder wick
• Solder
• Heat Gun
• Assorted PCBs and components to practice with

Solder comes in many forms but usually can fall into the categories of rosin core or solid core. Rosin core solder is nice since the rosin in the strand will act as a flux to guide the molten solder onto the component and board. Solid core solder can be more expensive, and will usually require some sort of flux to guide the solder in a similar way. Flux is important to soldering since it helps keep solder from bridging gaps and allows it to flow more easily.

Once you have gathered all of your materials, it's time to make your first connection! First, we are using a through-hole example.

• Place the component on the board, use a piece of tape to secure it in place.
• Clean the iron with a sponge or iron cleaner and apply some solder to the tip of the iron. This is called “tinning the tip”.
• Bring the tip of the iron to the board and touch the end to both the metal pad and the resistor leg to preheat the connection area.
• After about a second or two bring the solder strand in and touch it to the opposite side of where the iron is. The solder should melt and fill the area.
• Once it has filled the connection area, you can pull the strand and iron away from the connection area and repeat with the other side of the component.

From there you can repeat these steps with the rest of the through-hole components!

Once you have made all your connections, inspect the board for any bridges or short circuits that could have happened during the soldering process. If you find that you’ve made a mistake, use the soldering iron to heat the affected area, and either a desoldering pump or solder wick to remove excess solder.

After your board is fully assembled, the excess wire and connections can be trimmed using a set of flush wire cutters to further prevent accidental connections. And that’s it! Now it's time to test your board!

But what if your design has surface-mount components? The process is similar, and can be even done in the same way as before with a soldering iron!

• Place the component on the board and then use the soldering iron to place a small amount of solder on one of its pins to hold it in place.

• While being careful not to apply too much heat you can solder the rest of the connections, cleaning the first connection up at the end if you need to.

Another way you can solder with surface mount components is to use solder paste and a heat gun. Solder paste is a paste full of tiny balls of solder suspended in a flux solution. Using it can allow you to place solder everywhere you need, place the components, and then apply heat with a heat gun to set the connections!

Just like before, if you make a mistake that’s okay, just remove the part and use some solder wick to clean up the connection pad.

Once all the connections are made, you can apply power and test your board to check if any connections need to be repaired!

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