Greetings and welcome to today’s lecture. It is going to be a very interesting and interactive class about introduction to Through Hole Technology (THT) and Surface Mount Technology (SMT) that are applied in the process of designing the printed circuit boards.  A PCB board is made up of properly designed circuits that are composed of connecting wires/paths and various electrical components. The electrical components are mounted on the board. In fact, they are fixed to the board. If the components are not fixed, then there will be no durability and this might lead to various losses that can be avoided. In the process of mounting these components, here is where the through-hole technology and the surface mount technology come in.  They are very important processes in the design of printed circuit boards.

Overview.

This is one of the methods used in the attachment of components to PCB during the manufacturing process.

• THT is the oldest among these PCB attachment methods.
• For so long time it was the standard method that was used in the PCB assembly process.
• In the 1980s, when the surface mount technology process was introduced in the field of the PCB assembly, so many people thought that the THT method will become extinct but that is not the case.
• THT is used in all kinds of PCB designs i.e. Single Layer PCB, Multilayer PCB, Flexible PCB etc.

Through-Hole Technology (THT) is the method used in the attachment of the PCB electrical components and elements in the PCB whereby the components being placed have long leads that are soldered into the board through the holes drilled.

Process

• Dill holes on the PCB following the clients’ design.
• Select your components. They must have long leads. Also, remember components are on the design you have been given by the client.
• Place the components on the board and ensure that their leads are on the holes as defined in the design.
• Check that the components are in the positions described in the design to ensure that there will be no errors at the end of the process.
• Solder the terminals on the board accordingly. Ensure that the solder is on one side of the leads.
• Fill the other unsoldered side with flax.

Initially, this process was done manually hence it took a lot of time before coming up with a single complete board. Today, due to the changes in technology, it has become so easy to carry out the through-hole technology process. There are several automatic systems that aid out in the process and make it easy for the manufacturers, for example, the introduction of the automated insertion machines which actually helps in inserting the electrical elements into the drilled holes in the PCB before the soldering process starts.

Classifications of Through Hole Components.

We have talked about the electrical components being placed on the PCB boards through the through-hole. These components can be classified into two that is the radial leads components and the axial lead components.

The radial leads components.

From the image displayed, there is already something that is building up in your mind. Observe it well. Look at the leads. Can you see something common with the device leads? Yes of course. You are right! Both the two leads originate from the common side of the components. That is what we call a radial lead component. This method finds its application commonly in the packaging of the capacitors.

The components can be mounted either vertically or horizontally.

Let us have a look at that from the images below.

The vertical mounting of the Radial THT components.

on this method, the component is always place perpendicular to the board while the base is placed parallel to the board. complete joint. Soldering is done on one side of the terminal and the other side is filled with flax.

The horizontal mounting of the Radial THT components.

the contact body is fixed on the horizontal as you can see from the images. The leads exhibit a very nice bend and also spacing. This allows the proper filling of the solder on the component hence forming the strongest

The Axial leads Components.

• These are the most commonly used elements of the THT PCB methods components assembly.
• Here the leads of the components appear from opposite sides to each other. See what is in the attached image on the left.

Also, it can be classified as horizontal mounting and vertical mounting.

horizontal axial mounting method

Vertical axial mounting method.

Applications of the THT

• High voltage areas eg in the medical equipment.
• High mechanical stress devices eg military equipment.
• High power areas eg in the steam boilers.
• High temperatures operating devices eg in the nuclear plants.
• Prototyping and testing of components.

Advantages of using the THT method of PCB components Mounting.

1. The use of the THT method will ensure that you have a very strong mechanical bond compared to the SMTs components.
2. THT bound components have high resistance to wear and tear and this is made possible by the use of the large soldering deposits at the terminals.
3. The THT components are very easy to swap and repair the components hence they are the best for prototyping works.
4. It is best suited for places where strong mechanical applications are needed such as aerospace and military equipment.

Disadvantages of the THT method of PCB components Mounting.

1. Due to the drilling of the required holes, the production cost goes higher compared to the other method.
2. Also, drilling of the holes requires some additional time, hence the THT method takes a longer time compared to other methods.
3. This method limits the available routing paths for the multilayer PCBs because the drilled holes have to go through the given layers.
4. The technology being used in the industrial mass production of the THT types of the PCB is less reliable compared to the other methods used.

The Difference Between THT and The SMT in PCB.