What is Through-Hole Technology (THT) in PCB

When it comes to electronic assembly, SMT and SMD are often the focal points of discussion, overshadowing the power of Through-Hole Technology. While the trend towards miniaturization is evident, with SMT technology clearly superior to THT technology in this regard, it’s undeniable that THT has made significant contributions to reliability and ease of rework. In this article, TechSparks will delve into this overlooked technology, understanding its technical features and applications.

What is Through-Hole Technology

We know that the circuit board that exists in electronics is called a PCBA board, and consists of two parts: the PCB and components. Initially separate, they become an integrated whole through assembly and soldering. Through-Hole Technology is one means of achieving this process. A closer look at the PCBA board reveals two types of component structures: surface-mounted and inserted.

Through hole components and surface mount components

The purpose of THT technology is to serve inserted components. It involves drilling holes in the PCB during the manufacturing process, creating through-holes, and then inserting and soldering the components to form the PCBA board. In the early stages of PCB development, assembly heavily relied on the ancient THT technology. However, with the advent of surface mount technology, THT’s share in PCBA has gradually diminished. THT technology possesses the following key characteristics:

  • Reliability: Through-hole components have longer pins designed to penetrate the entire thickness of the PCB, ensuring a more robust connection after soldering. This feature is advantageous, especially in high-vibration applications.
  • Heat Dissipation: Due to different connection methods, through-hole technology allows the PCB to have a larger connection area, optimizing the circuit’s heat dissipation path for better thermal performance. Heat generated by high-power components can efficiently transfer along the pins to the external environment.
  • Replacement: Sometimes, the need arises to replace components. SMT assembly poses challenges as components are placed on top of PCB pads, making replacement difficult. In contrast, THT assembly involves directly inserting components, facilitating desoldering and replacement.
  • Size: THT technology is associated with through-hole components, and the pins of these components need to pass through the PCB via holes, resulting in larger component spacing and wasted space. This is often not suitable for compact and high-density designs.
  • Cost: While automated through-hole assembly is achievable today, compatibility issues may arise with some oversized components, necessitating manual assembly, thereby increasing PCBA manufacturing costs.

Some components suitable for through-hole technology include Radial Leaded Components, Axial Leaded Components, DIP Components, Headers and Connectors, and Thru-Hole Resistors and Capacitors.

Through-Hole PCB

The electrical connection between the PCB and components relies on the combination of through-holes and pins. Here, we provide a brief introduction to some common holes to enhance understanding of Through-Hole PCB:

Through-Hole: Holes that traverse the entire PCB, including both PTH and NPTH, with through-hole technology used for PTH.

pth and npth comparison chart

Blind Via: Similar to through-holes but only partially penetrates the thickness of the PCB.

Blind Via visual

Buried Via: Hidden within the internal layers of the PCB and not visible externally.

Buried via visual diagram

Via-in-Pad: Uses back drilling to remove excess signal reflections between the component pad and the through-hole.

Via-in-pad visual image

Different holes are marked in the design phase, indicating the hole’s location and its connection with components. In the manufacturing phase, the designed pattern is printed on copper layers, and the various PCB layers are pressed together to form a unified whole. Then, the drilling process creates through-holes, and the walls of the holes are coated with a layer of conductive copper through chemical deposition or electroplating, completing the Through-Hole PCB manufacturing.

Through-Hole Assembly

Complete Through-Hole technology not only includes the manufacture of Through-Hole PCB but also involves the assembly process of installing Through-Hole components into PTH holes and soldering them. This process can be achieved using automation or manual methods.

Automation:

  1. Import assembly-related files into the equipment to guide the assembly process.
  2. Based on file instructions, grasp the required components and insert them into the specified holes.
  3. Establish connections between the component pins and through-holes using wave soldering.

Manual:

  1. Apply appropriate soldering flux to the component pins.
  2. Heat the soldering iron for 1-2 minutes to ensure the solder melts immediately.
  3. Apply solder to the soldering point while simultaneously bringing the soldering iron close to complete the soldering.
  4. Finally, remove excess pin parts.

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