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How To Do Through Hole Soldering well ?

This article is aimed at exposing you to the essentials of through hole soldering. This is also called plated through hole soldering (PTH). We will examine in-depth the methods that are used for through hole soldering. We will mention all the tools that are used in through hole soldering and explain the purpose of the tool and how it can be used.

We will also expose you to tested guidelines that ensure proper through hole soldering and the entire through hole technology itself. This article will also differentiate the types of through hole components and what makes them different.

If you are new to through hole soldering, you are in the right place. This article is not for only amateurs, even experts will learn a thing or two.

Kinds of Through Hole Components

SMT Through Hole Soldering

Through-hole components may be categorized by the lead wire connection.The types are axial lead components and radial lead components. The lead wire of an axial through hole component passes in a parallel line and extends from the component on both ends. In the case of radial lead components, the lead wire extends from the same side of the through hole component. Both types of through hole components are useful in THT soldering.

Axial Lead Components

Axial leads are built to have lead wires that extend from both ends of a cylinder-shaped or log-like component.This type of component has a similar shape to wire jumpers and you can use it to cover small spaces on a printed circuit board (PCB).

Axial components are not perpendicularly placed on a PCB, which allows them to have a flat outline after they are soldered to the PCB. As a result of this, axial lead components offer designers the possibility of creating equipment that can easily slot into thin spaces.

Examples of axial lead components include; diodes, resistors, axial-leaded capacitors, rectifier diodes, and inductors.

Radial Lead Components

This through hole component type is designed with both ends of the lead wire protruding from the same end of the component vessel as opposed to their axial lead counterpart. Radial lead components are perpendicular to the board on which they are assembled and soldered to.

This makes them occupy less horizontal space on a board as opposed to the flat-lying axial lead components. This makes them suitable for high-density devices. Also, radial components are mobile and flexible on a PCB as a result of how both ends of the lead are affixed to one mounting surface.

Examples of radial lead components include; transistors, connectors, capacitors, resettable fuses, amplifiers, relays, ceramic capacitors, level shifters, potentiometers, voltage converters, electrolytic capacitors, coaxial connectors, integrated circuits (ICs), semiconductors, translators, RGBs, VDRs (voltage-dependent resistors), MOSFETs, LDRs, switches, photoresistors, voltage regulators, photodiodes, and buttons.


Anyone interested in electrical appliances or electronics coupled with through hole soldering must have a solid understanding of soldering.Soldering and electronic configuration are like peas in a pod. Soldering increases your options when it comes to electronic assembly. Even though you can now assemble components without soldering, it remains a skill that everyone should be conversant with.

Fixing and altering electrical devices should not be limited to electrical engineers and tech enthusiasts. Even product consumers can also learn a thing or two about the technology they use and how to repair, build or alter them. Soldering and particularly, through hole soldering makes you able to perform these functions.

What does solder mean?

Solder as an English term can be defined as a noun or as a verb. In the nominal form, solder is any sort of alloy that is usually of lead and tin that is used to join pieces of metal together. As a verb, solder means to join pieces of metal together.

Solder alloy was originally made up of lead, tin, and little amounts of some other inconsequential metals. This type of solder was called leaded solder. Scientists later found out that exposure to lead in huge quantities is poisonous to humans. The lead however offers us many benefits during through hole soldering due to its immense solderability and it melts at a lower temperature when compared to its alternatives.

After discovering the inherent danger in the continual use of lead in through hole soldering and general soldering, it was decided by some major players in the international community that lead should no longer be used in soldering. This led to the adoption of a directive by the European Union (EU) known as the Restriction of Hazardous Substances Directive (RoHS) 2006. This directive gave a restriction on using leaded solder in electrical equipment production.

The difference between lead-free solder and the leaded one is the absence of lead in the former.It consists majorly of tin and some other materials like copper and silver in little quantities. The RoHS emblem is engraved on the lead-free solder to confirm the standard of the solder to the purchasers.

Which Type of Solder is More Appropriate for THT Soldering?

In terms of safety, lead-free solder is the safer type of solder. However, lead solder is not disadvantageous. It remains a superb joining agent especially in through hole soldering. This makes it a preferred choice for many people. Ultimately, the solder choice is up to you as there is no perfect and fully beneficial choice.

The primary metal in a lead-free solder is tin. The melting point of tin is a lot higher than that of lead thus a stronger amount of heat is needed to melt tin and achieve liquidity. A lot of lead-free solder types contain a flux core. A flux is added to a lead-free solder to help it flow. These added effects make lead solder more cost-effective than lead-free one.

There are other choices of solder composition asides from lead and tin. You can do more research in that aspect. Also, bear in mind that solder wire is the appropriate form of solder for through hole soldering. Solder paste and other forms are not suitable. Solder paste is used in surface mount soldering. This will not be further discussed as this article is focused mainly on through hole soldering.

If the components you are working with are small, a thin wire is more suitable for the through hole soldering. If the components are large, use a thicker wire for an easier through hole soldering process.

What is Through Hole Technology?


The origin of through hole technology (THT) can be traced to as far back as the 1950s. Through hole technology is a kind of electronic circuit construction that entails implanting leads of through hole components through holes bored into printed circuit boards (PCBs) then soldering the leads on the other side. This process is also called through hole assembly.

Point-to-point construction was the technology used in circuit construction before the arrival of through hole technology. Through hole technology was the method used to assemble components on a printed circuit board (PCB) until the emergence of surface mount technology during the late 1980s.

Benefits of Through HoleTechnology

Soldering through hole components is relatively old technology. However, it is still a useful method. Through holesoldering makes the bond between the printed circuit board and the through hole components very strong. Thus, through hole soldering is an appropriate method for electronic equipment that will be subjected to mechanical stress or excess heat. Transformers are an example of such equipment.

Also, it is easy to maneuver through hole PCBs. This makes them suitable for testing and manufacturingprototypes.In addition, the holes are well spaced which allows through hole soldering by hand.

THT soldering could be cost-effective. When working with through hole PCBs you do not have to generate a different solder template every time you alter the PCB.  This could help save a lot of money especially if the design undergoes a couple of spins or more before it is satisfactory. Also, tin-lead solder can be used during THT soldering. This solder is the cheapest exterior metallization.

The Soldering Iron

The soldering iron is the backbone of the soldering process. It is the number one tool needed for soldering. Asides from the through hole components and the printed circuit board, the non-negotiables that are necessary if you want to carry out through hole soldering are the soldering iron and some solder.

There are different types of soldering iron. There are simple ones and complex ones but they all virtually have the same mode of operation. Below is an insight into the parts of a soldering iron.

Anatomy of a Soldering Iron

The Tip

An iron is incomplete if it lacks an iron tip. The tip functions as the first part of the iron that absorbs heat and it gives way for the solder to circulate the components being fused. When applied, solder sticks to the iron tip, but it is commonly misunderstood that the tip spreads the solder.

What the tip does is that it transfers heat, this increases the temperature of all the various metal components to the extent that the solder begins to melt. You can change the tip of most irons, in the event that you need a new tip or you prefer a tip with a different design. Tips are available in various shapes and sizes to accommodate whichever component you choose to use.  

The wand

An iron tip is held by the wand. The wand is the only part the user handles. Usually, wands are made of various insulating materials (for example rubber) to disallow the heat coming from the tip to transfer to the outer part of the wand but inside the wand, you’ll find metal contacts and wires that enable the transference of heat to the tip from the outlet or base. This two-sided role of preventing burns and heating makes a great quality wand highly appreciated.

The base

At the base of any soldering iron is found a control box that allows temperatures to be adjusted. The wand is attached to the base because the electronics in the base provide heat for the wand. There are both digital and analog bases, digital bases have a button for setting the temperature and a display that shows current temperature levels while in analog bases temperature is controlled by a dial.

On some bases, you can find some extra features like heat profiles which enable you to urgently change the level of heat supplied at the tip to allow for the soldering of some components.

The soldering iron stand

This is also known as the cradle. This part of the soldering iron is responsible for holding the iron when it is out of use. An iron that is not in use could easily pose a danger. It could burn other tools on the work desk or even burn the work desk and result in a full-blown fire. It can even harm you. The hot soldering iron was not made for skin contact.

The stand helps to prevent all this from happening. The cradle can either be a simple metal stand or a more complex device that shuts off the soldering iron when it is placed on the stand. This type will make sure your tip will not have time-induced wear effects.

Other Soldering Tools

Brass sponge

Soldering tip rust is an inevitable effect of soldering. Your soldering iron tip will become darker and the solder will not stick on its surface anymore. Lead-free solder particularly causes corrosion because it contains impurities that affect the tip of your soldering iron over time.

The brass sponge is used to wipe off this black build-up from the soldering iron tip. The brass sponge is the most suitable material for cleaning the tip. Brass sponges also help to peel off the residue solder on your tip even when in use. This would not affect the heat level of the iron.

In the past, wet sponges were used for this purpose. However, they pose a risk of spoiling the tip of the soldering iron. Do not use a wet sponge.    

Water Soluble Flux Pen

As we have discussed, flux is an organic agent added to a lead-free solder to help it flow. Flux pens are used to apply liquid flux on difficult components. This makes the solder join appear better. Do not leave unused water-soluble flux on the PCB. This can lead to oxidation of the board and the through hole components.

Solder wick

This can be referred to as the eraser while the soldering tip is the pencil. Solder wick is very useful if you want to remove parts (desoldering). Solder wick is also called a desoldering braid. Solder wick is made by braiding thin-sized copper wire together. The copper soaks up the solder and this acts as a form of ‘erasing’ excess solder.

Solder Vacuum

Solder vacuum is a very useful tool in through hole soldering. You can use it to suck out left-over solder in holes on the PCB.The solder usually gets into the hole if you desolder a component.

Tip Tinner

This is an organic mixture that is used for cleaning the soldering iron tip. It also helps to avoid rust. It is mildly acidic.

Procedure for Soldering Through Hole Components

This procedural guideline will cover the earlier mentioned categories of through hole components.They include axial lead through hole components and radial lead through hole components. In the process of soldering through hole components, you will discover that radial lead components are more difficult to solder in comparison to their axial lead counterparts.

However, axial lead requires more setup for the through hole soldering process. Some materials are necessary for soldering through hole components. They include; solder flux, pliers, wire solder, a chisel tip soldering Iron, a printed circuit board (PCB), acid brush, solder wick, cleaning agent, and tissues.

The techniques for THT soldering are similar for both component types. What differentiates them is that radial lead components are divergent because both ends of the lead wire are on the same side.

Axial Lead Component Through Hole Soldering

Through hole soldering begins from the preparation stage. You should make the site ready for soldering. This does not take too long and it makes the whole through holesoldering process smoother.  

The first step is to use isopropyl alcohol to clean the boards and the component leads and wipe them dry. The wiping should be done with a Kim wipe that does not generate particles. This helps to rid the PCB of dust or dirt. Get the soldering iron heated and clean the tip with a damp sponge.

Melt a little quantity of solder on the soldering iron tip. The purpose of this is to tin the iron. Use the sponge to wipe off the small quantity of solder on the tip. This procedure makes the tip transfer more heat while soldering through hole components.  

You should also apply solder to the pads to tin them. You can remove the solder with a solder wick. This step makes the solder and the pads glue easily. Be gentle when applying the solder wicks lest you impair the pads in the process of cleaning them.

Curve the end of the leads

Use a plier to hold an end of the component leads and softly apply pressure on the body of the component the lead is perpendicular to the body of the component. Duplicate this procedure on the other end of the lead.

Insert the components and shorten the leads

Insert the leads inside the plated through-holes. After insertion, gently press the component towards the board to make them stay firm on the board. Ensure that the component is flatly positioned on the printed circuit board.

Shorten the length of the leads to fit the board appropriately. An overstretched lead will affect the placement of other components on the PCB. Also, the through hole soldering process will not appear neat and well done.

Solder the component to the board

Flux should be applied on the sides of the printed circuit board to ensure heat is conducted. Flux serves a wetting and cleaning function for the part being soldered. This is a very important part of achieving standard through hole soldering.

This is when the through hole soldering starts. Solder is applied to the underside of the PCB only. A rule applies to through hole soldering as regards flux. Flux may be administered to both sides however, only one side should be soldered.

While the board is properly held by a heat-resistant pad, clasp solder to an end of the lead and apply the tip of the iron to the place where the lead and the pad meet. Put a little quantity of solder at this juncture. Then create a solder bridge by transferring the solder wire to the other end of the lead.

Carry out this process again for the unsoldered lead.

Scrutinize and clean

Scrutinize the end product to know if it meets your standard. Once you are done with the through hole soldering, the solder point should have a shiny outlook and a hollow filet. If the solder you used is lead-free, then the solder point may appear dull in comparison to that of a tin-lead solder composition.

Radial Lead Component Through Hole Soldering

As earlier discussed, use isopropyl alcohol to clean the printed circuit board before you start through hole soldering. Get a tissue to gently wipe it.

Rubflux on the PCB and solder

Once you have rightly placed the components on the board, rub flux on opposite leads that have been inserted on the PCB’s underside.

Fasten a small amount of solder against the leads. This helps to firmly hold the component during through hole soldering. Ensure that the body of the component lies flat on the PCB to confirm a firm connection to the board.

Solder every point of connection with the leads. Place your solder wire beside the lead then use the soldering iron to melt the solder. Repeat the process you used in creating the soldering bridge when you soldered the axial lead components.  

Scrutinize and clean

Just as we discussed for the axial lead components, check the solder joint if it is up to standard. It should have a shiny and smooth outlook. Clean the board and wipe off any isopropyl alcohol residue.

Remember flux is used to enhance the flow of lead-free solder. If you use lead-free solder for your through hole soldering, you must properly clean residue flux off the board. If left unattended, it can oxidize the board and the through hole components.

Small brushes are effective for cleaning PCBs. Use them with isopropyl alcohol for great results.


Through hole soldering process is a very easy and straightforward one. We are sure that you understand the whole process after going through this article. Just take time to understand the article and follow the steps.




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