Modern electronic products utilize a complex electronic circuitry, commonly known as a Printed Circuit Board. The application and importance of PCBs span diverse fields, from military and aerospace industries to consumer electronics. The significance of PCBs in electronics has led to increased demand, which PCB manufacturing and electronic PCB assembly cater to.

　　PCB production involves design, manufacturing, and electronic PCB assembly. All stages of production require a degree of skill, technology, and modern equipment in manufacturing and assembly. However, this article will focus on electronic PCB assembly, specifically the available methods and applicable technologies.

　　 The Emergence of Electronic PCB Assembly

　　All printed circuit boards require electronic components such as resistors, transistors, diodes, etc., to perform their respective tasks. The target application primarily dictates the type of components that make up the PCB assembly. The history of assembling components is synonymous with the invention of a circuit board and an electronic component (transistor).

　　The definition of electronic PCB assembly refers to the process of connecting electronic components or parts to conductive traces or lines within the PCB. The copper traces usually require etching conductive pathways on copper laminate, while the copper laminate sandwiches a non-conductive substrate.

　　The general assembly process of a printed circuit board involves a series of stages. It includes solder paste application, component pick and place, soldering, inspection, and testing. These process steps are crucial for ensuring high-quality PCBA products are assembled. Therefore, each process step needs close monitoring. However, note that the printed circuit board assembly process steps depend on the PCBA technology deployed.

　　Electronic PCB assembly is primarily of two types, depending on the technology used for assembly. It can either employ the surface mount technology method or the through-hole technology method. While the PCB assembly process steps demonstrated above highlight the surface mount technology for PCBs, the case is slightly different for through-hole technology. It is also important to note that some PCBA companies combine both technologies in their printed circuit board assembly methods.

　　 So, what are the differences between these two different PCB assembly methods? How do they differ?

　　Printed circuit assembly processes can take one of two forms: surface mount technology or through-hole technology methods. The two technology methods employed in printed circuit board assembly include surface mount technology and through-hole technology.

　　 Through-Hole Technology

　　This is a unique electronic PCB assembly method. THT, also known as through-hole, involves connecting leaded components to the PCB board through pre-drilled holes. After placing the components in position, they are soldered to secure them in place. The process is done manually (hand-soldering), sometimes through automated machines.

　　The quality of the solder joint is always crucial for many reasons. First, the solder joint or joints represent the actual connection between the electronic component and the board. Its quality corresponds to the quality of the connection.

　　 Characteristics

　　The through-hole assembly method always provides a more robust mechanical connection when mounting components than SMT. However, it has a higher production cost compared to the surface mount technology method.

　　THT also limits the routing area for signal traces, especially on layers located just below the top or uppermost layer (for multilayer boards). This is because the holes must penetrate the entire stack-up layer to reach the other end. Therefore, through-hole technology is mainly suitable for larger components such as electrolytic capacitors. Such components require extra mounting strength or support strength—in this case, components like plug connectors.

　　 Process

　　Before the leads are passed through or into the holes, the pads and holes need preparation. The leads require specific orientation to ensure the bends are above the solder joint, thus reducing solder requirement and heat.

　　The second step is to uniformly heat the pads or holes and the leads. The heating helps liquefy the solder, ensuring the solder adheres to both surfaces (holes).

　　The flow of molten solder forms solder joints at the top and bottom of the hole. Since the soldering is done on the top of the board, you need to inspect the bottom to ensure sufficient solder. Another aspect you need to check is the quality of the solder joints. However, some components may require solder application from both sides to guarantee quality. Remember, sufficient clearance between holes allows for seamless solder flow. Conversely, too little or small clearance may hinder solder flow, resulting in under-soldering at either end.

　 　Importance

　　Direct Prototyping: PTHT or THT allows for quick prototyping compared to SMT. You can solder the leaded THT components through wave soldering or hand soldering. Breadboarding of the PCB design is also possible before making the actual board.

　　High Power Tolerance: THT components easily meet high-power requirements. This is made possible because THT components tend to run flush with the board, enabling them to withstand high voltages as well as mechanical and environmental stresses.

　　Incredible Physical Connection: THT or PTH helps establish a strong mechanical connection between the board and the electronic components. Components may include capacitors, transformers, semiconductors, connectors, etc. Such electronic components must withstand high power, high voltage, and mechanical stress.

　　Component Durability. THT technology is well-suited for establishing a robust physical connection between the board and the components. Therefore, components are firmly secured in place by solder at both ends, thus enhancing their durability.

　　 Applications

　　Most designers prefer using the through-hole assembly method for prototyping. It is easy using breadboard-based sockets. But for high-frequency or high-speed designs, prototyping may require surface mount technology assembly. It minimizes stray inductance and capacitance in the leads (wires) that may impair the circuit’s functionality. Also, ultra-compact designs may also dictate SMT assembly, including its prototyping stage.