Introduction: How to Solder a Through-hole Component

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There are two main types of through-hole components that we will go over in this "How to Solder" guide, axial-leaded through-hole components and dual in-line packages (DIP’s). If you’ve done a little bit of breadboarding, you’re probably already familiar with axial-leaded resistors and DIP IC’s. This guide will be helpful in taking your project designs form the breadboard to the circuit board. As a general rule, axial-lead components are easier to solder but require more preparation of the board before you actually begin, while DIP’s require more skill but less setup.

Before we begin, here are all the materials you’ll need:

  • Soldering Iron with chisel tip
  • Wire Solder
  • Solder Flux
  • Isopropyl Alcohol and tissues for cleaning
  • Acid Brush
  • Pliers (for lead forming)
  • Solder Wick
  • Printed Circuit Board (PCB)

Through-hole components If you're looking for a solder training kit to help illustrate some of these points, try BEST Electronics learning how to solder training kit at

Whether you are soldering DIP or axial lead-ed components, the techniques used are the same, the main differences are that DIP's have a polarity and more leads.

Step 1: Soldering Axial Leaded Components

Before you begin the soldering process it is important to prepare the site. These tasks take only a few minutes but make it much easier to get a good solder connection.

Start by cleaning the component leads and PCB with isopropyl alcohol and wiping them dry with a non-particulate generating kimwipe to ensure that the PCB is free of dirt or dust. Clean the soldering iron tip by getting it to temperature and wiping it on a damp water-infused sponge.

Tin the soldering iron tip by melting a small amount of solder onto the tip and wiping it off onto the sponge. This will make it easier for you to drive heat to the solder joint.

Tin the pads by applying solder to the pads and using the solder wick to remove it. This will make it easier for solder to stick to the pads. Be careful not apply too much pressure when using the solder wick, as this could damage the pads.

Step 2: Bend the Leads

While holding one of the leads of the component with pliers or using a "Christmas tree" as shown, gently push the component body until the lead is bent at a 90 degree angle. Repeat this for the other lead. ( See related videos for these techniques at BEST Youtube Channel) .

Step 3: Place the Part and Cut the Leads

Place the component, making sure that the leads are centered inside of the plated through-holes. Once the part is in place, bend the component leads back to hold the component in place. Inspect to make sure that the component lies flat on the PCB.

Cut the leads, making sure to leave enough length such that the component is still held in place, but not so much that the leads might interfere with anything else on the board.

Step 4: Solder the Part

Apply flux to both sides of the PCB to help with heat conduction. Flux will help you keep the soldering area clean and make sure the wettability is sufficient, a key part of creating a good solder joint.

Now to start soldering. Make sure to only apply solder to the underside of the board. The rule for through-hole soldering is that you can put flux on both sides but solder only on one. While holding the PCB in place with a heat resistant pad, tack solder to one side of the lead and place the soldering iron tip where the pad meets the lead. Apply a small amount of solder at this point. Then, move the solder wire to the other side of the lead in order to make a solder bridge.

Repeat the same process for the other lead.

Step 5: Clean and Inspect

Clean and inspect the final product to make sure that you’re satisfied with the results. The solder joint should be shiny in color, with a concave filet and good wetting to the lead. If you used a lead-free solder, the joint may be more dull in color than if you used tin-lead solder wire.

Step 6: Soldering DIP's

As before, clean PCB with isopropyl alcohol and wipe it dry with a tissue.

Make a note of the notch or the pin 1 marking on the component. This notch or marking should like up with the notch or marking on the PCB . Make sure the alignment is correct before soldering. DIP’s have a polarity to them and failing to line them up properly can permanently damage the chip.

Step 7: Apply Flux and Solder

Once the part is in place, apply flux to diagonally opposite leads on the underside of the PCB.

Tack a bit of solder onto the leads to hold the part in place. Make sure the component body is flush with the board to ensure a good connection.

Solder connections to every other lead. Put the tip of your solder wire next to the lead, then apply a little heat to reflow the solder. Create a soldering bridge using the same process as when soldering axial leaded components. Once you’ve done one row of connections , loop back and fill in the leads in between. Make sure to solder the tacked leads last, since they hold the chip in place.

Step 8: Clean and Inspect

Again, clean off any residue using isopropyl alcohol and inspect the solder joint for a smooth, shiny surface with good wetting.

NOTE: For hands-on training see BEST for Solder Certification & IPC Training Courses.