Through-hole PCB assembly is a method used in electronics manufacturing where components with leads (wires or metal legs) are inserted into pre-drilled holes on a printed circuit board (PCB) and soldered to pads on the opposite side. This technique is one of the oldest methods of PCB assembly and continues to be used for its reliability and strength in creating durable connections.
Through-Hole Assembly Processes
Step by step processes of Through-Hole Assembly.
Components Sorting
Sorting enough components and PCBs, plus spare parts, to cover potential defects, rejected parts, or issues may occur in production and ensures consistent quality and smooth, uninterrupted production, maintaining efficiency in the assembly process.
Component Placement
Components are placed manually by operators or with the assistance of automated machines that place the leads of the components into the holes on the PCB.
Soldering
After placement, the components are soldered to secure them to the board. There are several soldering techniques used: Wave Soldering: The most common method for mass production, where the assembled PCB is passed over a wave of molten solder that sticks to the exposed metallic areas of the board (including the leads of the through-hole components). Manual Soldering: Used for prototypes or small batch sizes, where each joint is soldered individually using a soldering iron. Selective Soldering: A machine-driven process that selectively solders parts of the PCB without exposing the entire board to molten solder, useful for boards with both through-hole and surface-mount components.
Inspection and Testing
After soldering, boards are often inspected manually under a microscope, by automated optical inspection (AOI), or through other testing methods like in-circuit testing (ICT) to ensure that there are no soldering faults and that components are properly connected.
PCBA Cleaning
Flux residues are cleaned from the board after soldering.
THT Advantages & Disdvantages
Strong Mechanical Bonds
The leads passing through the board make the components less likely to detach, which is particularly valuable for applications subject to mechanical stress or extreme environmental conditions.
Ease of Soldering
Through-hole soldering techniques are well-established, making them easier to inspect and repair because the solder joints are generally accessible.
Power Handling
Through-hole components typically have higher power ratings than their surface-mount counterparts, making them ideal for high-power applications.
Higher Cost
The drilling and manual processing involved can make through-hole assembly more expensive compared to surface-mount technology (SMT). And if manual soldering + wave soldering, there will be need fixture(s), it's not cheap.
Slower Production
Through holes components need handing soldering or insertion and wave soldering, it's much slower compared to surface-mount technology (SMT). Another the labor cost is not cheap nowdays.
Limited Routing Space
The holes in the PCB can limit the available space for routing traces on multilayer boards, potentially complicating PCB design.
Applications
Through-hole technology is often chosen for devices requiring high reliability and robust components, such as in military and aerospace electronics, industrial machinery, and consumer electronics where durability and long service life are crucial. Despite the rising prevalence of surface-mount technology for its miniaturization benefits, through-hole assembly remains relevant for specific applications where reliability and strength are paramount.