Through hole components have been around for a long time – those little bug looking parts on circuit boards with leads coming off and going through the board. Though hole (TH) components have one or more conductive leads, or pins, and those are perfectly matched to holes in a protoboard or printed circuit board (PCB). The component is inserted into this copper hole pattern, called the footprint, and is then soldered into place. Although in the 90’s and after we have seen a massive shift to surface mount components for their smaller size and ease of manufacturability, through hole devices are long from extinct and still find plenty of application in modern electronics. As a beginner through hole soldering is a good place to start learning.

PCB Soldering Styles

This guide will aim to introduce, and familiarize you with the process of soldering through hole components to any circuit board. With a little practice, you’ll be soldering up circuits with confidence and ease!

Through Hole Soldering Guide

Mount The Component – Insert the component into the desired footprint, or location if working with a proto board. Pull the leads down tight until the component is sitting flush on the board. Bend the two leads slightly away from one another to hold the part down tight.

THD Insert
THD Leads Bent
THD Heating Lead

Apply Heat – Once placed correctly, place the tip of the soldering iron onto the connection such that it contacts both the lead of the component and the pad of the circuit board. Hold this position for a few seconds to allow the pad and lead to heat up. Too long and the pad be become delaminated from the circuit board. (We’ve all done it!)

Note: It can be beneficial to apply a small amount of solder to the tip of the iron before beginning this step to help get a good thermal connection.

Apply Solder – After a few seconds of heat, push the solder wire into the opposite end of where you have placed the iron on the joint. The goal is to not melt any solder on the iron itself, but rather get the pad and lead hot enough to melt the solder. If the pad and lead are not hot enough the solder will not properly bind to them, forming a bad connection. A fume extractor can be handy if you’re doing a lot of soldering as the fumes can be annoying. Don’t blow on the solder joint to cool it! The solder needs to cool naturally to form the correct metallurgical structure and blowing on it can result in a weak “cold joint” that will fail. Cold joints have a dull grainy texture while good joints have a shiny smooth finish. Lead free solders don’t produce as shiny of a solder joint, so don’t be fooled.

THD Solder Contact
THD Joint Made

Snip the Leads! –  If your joint was soldered properly, take your handy flush cutters and snip the excess lead just above the top of the cone that should have formed. That’s all there is to it! Play around with the temperatures, angles, solder feed rates and quantities to perfect your technique.

Solder joint graphic

Need something to practice on? Chekout out kits and tools in the store to build something cool today!

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