PCB Assembly

The Difference Between SMT & PTH Assembly: Which is Right for You?

SMT Technology Assembly

PCB assembly is the spine of electronic components and gadgets. PCB designers have very well-known assembly techniques. so, designers are designing the PCB according to mounting methods. All finished assemblies are processed with two types of PCB assembly techniques:

  • SMT (Surface Mount Technology)
  • PTH (Plated Through Hole)

What is SMT?

SMT is surface mount technology. This process starts with solder stencil printing. SMD components having a small flat type leads to soldering on pads. It is used for small-sized surface mount components like 0402,0201, 0603, UDFN, BGA, etc. With the help of this technology, we can place the electronic components on the PCB surface. SMT technology is easy to mount and less costly to manufacture. Enhanced PCB reliability and accuracy can be achieved through the SMT assembly. Because SMT technology is Easy to handle with the help of SMT fixtures. SMTs are well-known as SMDs and SMCs. The surface mount method used a PNP (pick and place machine) to place all SMD components. In the SMT assembly, reflow soldering is preferred to heat the solder & placed components are correct.

SMT and PTH assembly

In SMT, there are three types of assembly:

  1. Only SMD components are placed on the PCB for both sides.
  2. Through hole and SMD assembly. It had both types of components used on PCBs.
  3. In this type, it’s removed and placed only in Failure parts. It’s like rework.

Advantages

  1. Weight-saving and cost reducing
  2. Efficient and dependable PCB
  3. Improved PCB enhanced performance
  4. Easy to automation
  5. Higher part accuracy

Disadvantages

  1. Expensive equipment
  2. Difficult to inspect in a compact design
  3. Higher Cost for Small volume
  4. Low capacity
  5. Every order needs solder stencil for each revision

What is PTH?

PTH is thru-hole mount technology. It inserts the parts using its tails into holes on the PCB. These leads are soldered onto lands on the solder side of the board. After that wave soldering is applied by hand. PTH is the oldest technique for attaching PCB components in PCB assembly. It’s used for axial lead parts like larger heatsinks, transformers, resistors, capacitors, etc. There are many components placed on the PCB using this technology like connectors, edge mount connectors, through-hole strips, etc. This technology is called hand mount technology because through-hole components are placed with hand placement.

PTH Assembly

There are two types of PTH components:

  • Radial leads: In these parts, all the leads originate from one side to the component end. These parts are placed vertically or horizontally.
  • Axial leads: In these parts, leads occur from the opposite side of the part. These are placed only in a horizontal direction.

Advantages

  1. Strong part connection
  2. Enhanced testing
  3. Easy for debugging
  4. Dependable on hot temperature
  5. Easy to get Prototype boards

Disadvantages

  1. PTH needs a hole to place all parts, so that’s why production costs are increased.
  2. PTH components need more time to place parts.
  3. PTH is less dependable.
  4. PTH is not available when routing around the PTH parts.
  5. It requires more spacing between components.

SMT & PTH Assembly Difference

In the previous paragraphs, we know that PCB assembly can be divided into SMT assembly and PTH assembly to some extent. We’ve carefully analyzed the cons and pros of SMT assembly and PTH assembly. In this part, we will focus on the SMT & PTH assembly difference based on components, cost, soldering, speed, drilling, etc.

PCB components

Components: First, as we see from the SMT part, it had small-sized leadless parts and PTH components having radial leads for connections.

Cost: In terms of cost, SMT assembly is much cheaper than PTH assembly. So, most customers prefer to use SMT assembly to reduce costs in PCB assembly.

Automation: SMT assembly processes are more advanced and design skills than PTH, because automatic machines have placement program data.

Soldering: In SMT assembly, components are placed on the PCB surface using solder paste and in PTH, leads are soldered with a soldering iron on the solder side.

Speed: In production, SMT has well-designed equipment for faster placement and provides PCB with components in a brief time, and PTH has an auto insert to place PTH components but it’s slower than SMT.

Drilling: PTH assembly needs a drilling process to place the components and SMT assembly needs solder stencils including solder pads on PCB.

Quality Control: For quality control, PTH technology gives better detection of assembly issues rather than SMT assembly. Because SMT has a larger rework issue when some PCBs are not cleaned properly in PCB assembly.

Mechanical Resistance: PTH technology has a strong resistance to mechanical stress compared to SMT. SMT assembly is very less accurate against mechanical resistance.

Pricing: SMT components are more expensive than through-hole parts, because they are small in size and complex in manufacturing.

Compatibility: SMT technique has poor compatibility for some unique requirements of components.

Devices: SMT components have ESD (electrostatic-sensitive device). It needs some handling methods in a production house.

Mass Production: SMT gives a preferred choice to a high volume of parts with the help of high automation to increase production efficiency. However, PTH gives low volume with lower equipment requirements.

Inspection: SMT has AOI (automated optical inspection), X-ray, flying probe test, SPI (solder paste inspection), and ICT (In-circuit testing) for quality checks. And PTH has only manual inspection for quality inspection of solder joints.

High-Power Parts: Some high-power parts needed exact connections are not placed by the SMT assembly process. So PTH is the best choice for such parts.

Component Density: The surface mount technique gives a high density of components as compared to through-hole technique.

Fine Pitch Requirements: SMT assembly can meet fine pitch requirements while PTH cannot meet fine pitch requirements. Because SMD components require less space and give better efficiency and PTH components require more space to place parts on boards.

What’s Best for You?

After reviewing all the facts and the configuration process, I concluded that SMT assembly processes are extremely faster and quicker than PTH assembly in PCB assembly. Because it gives a high volume of production and efficiency to higher density and performance. 90 ℅ assembly vendors prefer SMT technology to place components in PCB assembly. Because it gives a compact design with the easiest solution and allows high component accuracy.

PTH is a unique process but it’s available for PTH mountings for relevant solutions. Because PTH technology is used for mechanical and electrical implementation.  Some manufacturers are still using PTH technology for manual configuration due to mass component volume.

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