Component placement is a very important aspect of PCB assembly. There are different ways of mounting components on a circuit board. Each of these approaches has its benefits and disadvantages. The type of mounting technology used in a circuit board determines its functionality.
Sometimes, the application requirements determine the type of mounting technology to use. It is important to know how these technologies work. Therefore, this article will shed more light on the difference between SMT, THT, and SMD.
THT VS SMT
THT and SMT are the two major types of mounting technology for PCB. These technologies are used in mounting electronic components on circuit boards. However, there are differences between these two technologies. To have a better understanding, it is important we shed more light on THT vs SMT
What is THT?
THT stands for through hole technology. It is a method of mounting electronic components on circuit boards. THT involves drilling holes through the PCB and inserting the leads via those holes. THT plays a crucial role in PCB fabrication.
This technology involves the placement of component leads into drilled holes on a bare board. Manufacturers solder these leads onto pads on the other side of the board. The manufacturer does this using reflow soldering or wave soldering equipment. THT was a common approach for mounting components until the advent of SMT. Despite the popularity of SMT, THT has proved resilient as it offers several benefits.
THT replaced electronics assembly techniques like point-to-point construction. This technology has been used since the 1950s. The through hole technology is ideal for creating interconnections between layers on boards.
What is SMT?
SMT means surface mount technology. This technology is the more recent method of mounting components on circuit boards. It replaced the through hole technology due to certain benefits it offers. SMT involves mounting electronic components on the surface of the PCB directly.
This technology uses automation. SMT makes use of pick and place machines to place electronic components on boards. This technology is considered the second revolution of electronic assembly. SMT uses both wave soldering and reflow soldering to solder components.
The advent of SMT has helped to reduce the cost of manufacturing while maximizing PCB space. SMT was developed in the 1960s and became popular in the 1980s. This technology is ideal for high-end PCBs. The use of SMT has resulted in smaller components. Also, it has enabled the placement of components on the two sides of the board.
In surface mount technology, manufacturers mount electrical components without drilling. These components feature no leads or smaller leads. Here, there is a specific amount of solder paste the manufacturer applies to the board. Since there are not many drilled holes on SMT boards; they are more compact for better routing.
Comparing THT vs SMT
THT and SMT are two reliable mounting technologies in PCB assembly. However, SMT is more reliable and more common. There are differences between these two technologies. While SMT replaces THT, THT is still being used in PCB assembly.
THT inserts electronic component leads into drilled holes on a circuit board. Most times, manufacturers carry out this technique manually. SMT technology doesn’t require as many drilled holes as THT does. The use of pick and place machines in SMT makes the technique much easier for manufacturers.
SMT doesn’t require leads and can be directly mounted on the circuit board. Whereas, THT requires lead wires that manufacturers place in drilled holes. SMT requires advanced production and design skills compared to THT.
THT vs SMT In terms of manufacturing costs, THT involves a higher cost of manufacturing than SMT. However; capital investment for automated equipment is higher than that of THT. THT is ideal for certain applications. Through hole boards are ideal at the prototype stages of a project. For a through hole board, manufacturers don’t need to produce a new solder stencil anytime the circuit board goes through a revision change.
THT vs SMT via through hole technology. This technology is ideal for the manufacturing of bulky components. SMT is ideal for higher circuit speeds since it features fewer holes. Unlike THT, SMT allows assembly automation which is ideal for the production of higher volumes at reduced costs.
SMT provides more board space during assembly, unlike THT which uses up the board space. THT helps manufacturers to check mechanical problems during validation. The manufacturer can fix this problem during redesign without any assembly difficulties. However, in SMT, this is difficult to fix. This is because warp and twist is easier to fix on a manually-assembled PCB.
SMD vs THT
What is SMD?
Surface mount device (SMD) is an electronic component placed on a circuit board. PCB manufacturers can place SMD on circuit boards through SMT. There are various types of SMD components. All SMD components work together to enable the functioning of a circuit board. Examples of SMD components include chip resistors, capacitors, and diodes among others.
Let us discuss a few below;
A capacitor is a type of SMD component. This component features a rectangular block of dielectric. The dielectric contains several interleaved metal electrodes. A transistor is another SMD component available on a circuit board. The resistance of this component is built in the ammeter and the base.
SMD resistors are another type of SMD component. There are chip and network resistors. The three digits on the chip resistor are the resistance value. The significant digits are the first and second digits. The network resistor comprises many resistors with similar parameters. This resistor uses the same resistance identification method as the chip resistor.
SMD vs THT – What is the difference?
It is important to know the difference between SMD and THT. A lot of times, most people confuse these two terminologies. Through hole technology involves the soldering of through-hole components on a circuit board. Manufacturers use hand soldering or wave soldering to complete this process. In THT, the component leads pass through the drilled holes on the boards.
SMDs are components manufacturers place on circuit boards through SMT. Manufacturers use solder paste to place SMDs on the bare board. Surface mount devices feature shorter leads that enable a greater electrical connection. THT involves soldering through hole components onto a circuit board by wave soldering. The component leads go through the drilled holes of the boards.
Through hole technology offers stronger mechanical bonding. This technology is ideal for electronic devices likely to suffer from mechanical stress. THT manufacturers use hand and soldering or wave soldering for the THT process.
SMDs are smaller than the components in THT. SMD components can be so small to be clearly seen by the naked eye. Due to the size of SMDs, they save more space on the bare circuit board. SMD components rely on solder balls to enable improved bonding capability.
THT provides more mechanical bonds than SMT. However, the extra drilling in THT makes it more expensive to create the circuit board. Therefore, THT is ideal for more bulky parts. For instance, electrolytic capacitors need extra mounting quality to withstand pressure.
What is the Difference Between SMD and SMT?
SMD refers to the electronic component manufacturers mount on a bare circuit board. SMT is a type of mounting technology PCB manufacturers use to mount SMDs on a PCB. SMT uses a pick and place machine to mount SMDs on circuit boards. This technology replaces the through hole technology.
The advent of SMT has enabled PCB manufacturers to easily mount SMDs on circuit boards. The process of SMT includes solder paste printing, component placement and reflow soldering. The placement of SMD is a very important stage in surface mount technology. SMD and SMT work hand in hand.
Advantages and Disadvantages of SMT
SMT has its advantages and disadvantages.
Advantages
- Smaller PCB design
SMT enables manufacturers to place more electronic components on the circuit board. This helps to achieve a more compact and lightweight design. Manufacturers prefer this technology due to this benefit. PCBs specifically designed with SMT also offer higher circuit speeds. Hence, these PCBs are ideal for high-frequency applications.
- Enhanced mechanical performance
SMT provides enhanced mechanical performance under vibration conditions. Therefore, SMT PCBs are ideal for use in applications extremely exposed to vibration. SMT comprises high-end components which enable multitasking.
- Higher densities
One of the greatest benefits of SMT is the ability to achieve higher levels of component density. The high densities are a result of the smaller size of electronic components. Also, the elimination of drilling mounting holes helps to achieve higher densities. SMT uses both sides of the circuit for mounting components.
- Quicker Assembly
SMT uses pick and place machines to place components on PCBs. This enables simpler and quicker PCB assembly. Some machines can place over 136,000 components every hour. SMT allows manufacturers to attach components through selective soldering. Manufacturers can also customize the selective solder process for each component.
- Low manufacturing costs
SMT reduces the costs of manufacturing printed circuit boards. SMT parts are cheaper that through-hole parts. This mounting technology is a budget-friendly option for PCB manufacturers.
Disadvantages
- Surface mount technology replaced THT due to the benefits it offers. However, this technology has its disadvantages too.
- Small lead can make it difficult to repair
- SMT isn’t ideal for components that produce much heat. This is because the solder will melt under high temperature
- The SMT process requires high-skilled or professional operators. Also, it requires expensive automated equipment.
- Less solder for solder joints might tamper with the reliability of the solder joints. This is a concern for PCB assemblers.
Advantages and Disadvantages of THT
Through hole technology existed before the advent of SMT. THT has proved to be very useful in some cases. However, it has got its own limitations. Below are some advantages and disadvantages of this technology.
Advantages
- Stronger mechanical bond
THT provides enhanced mechanical bonds. This makes THT assemblies suitable for high mechanical or electrical stress environments. Manufacturers prefer to use THT in applications often subjected to stress.
- Resistance to wear and tear
THT components can withstand wear and tear. This is because of the solder joints that extend over the board’s width.
- Ideal for fast prototyping
THT components are ideal for prototypes and testing. This is because these components are very easy to swap out. THT is suitable at the prototype stages of an application. The prototype layout can make use of THT components to enable quick assembly of the board.
Disadvantages
- THT requires the drilling of holes. This increases the cost of production. Also, it takes time to drill these holes, which increases production time.
- The drilled holes must go through every layer of the PCB. Hence, THT limits the available routing clearance on a multilayer circuit.
- The wave soldering process ensures the soldering of THT components. This process is not as reliable as the reflow soldering process.
Considerations for SMT Designs
The type of materials and surface finish manufacturers use play a crucial role in SMT boards. It is ideal to use more planar surface finish when using finer-pitch SMDs. Manufacturers should ensure they evaluate the base laminate. SMT PCBs need higher soldering temperatures than THT PCBs. This is as a result of the lead-free surface finishes frequently used.
Materials that meet certain standards will withstand high soldering temperatures. These materials also resist several thermal cycling shocks. These shocks may happen when two-sided SMT boards are being assembled. PCB assemblers can reduce the possibility for solder shorts by removing soldermask openings for vias.
With dimensional accuracy in mind, it is crucial to design-in flatness. To achieve this, balance copper coverage from layer to layer and fill large empty areas with copper.
Conclusion
While SMT has been the mainstay of the PCB industry, THT is still ideal for certain applications. THT vs SMT show that the two technologies have got their strengths and weaknesses. The huge difference between SMT and THT lies in their mounting techniques. SMT mounts SMDs on circuit boards without many drilled holes. THT requires component leads and many drilled holes. SMDs play a crucial role in surface mount technology. SMD components are carefully mounted on circuit boards by assemblers.
