Through-hole technology (THT) is significant in the history of printed circuit boards (PCBs). It was once the primary method of PCB production, with a design process similar to today’s surface mount technology (SMT). THT involved schematics and layout software, focusing on the larger through-hole components.
Drilling the holes into the board, where each component lead would pass through, required precision and patience, making it one of the most time-consuming steps in the process. Additional copper plating added to the through-holes ensured conductivity between the PCB’s layers, and a laborer often applied a solder mask to protect the copper traces and prevent solder bridges between components during soldering.
During the early stages of through-hole technology, workers manually placed the components onto the board, inserted their leads through the pre-drilled holes, and soldered them into place. This process was time-consuming and labor-intensive. However, with the advent of wave soldering machines, the automation of through-hole components began.
Once assembled, the boards were inspected–initially by humans and later with automated optical inspection (AOI) systems, and electrically tested to ensure functionality.
While some companies still utilize through-hole technology for components that require the robustness of through-hole mounting, it’s important to note that surface mount technology has revolutionized the design and manufacturing of printed circuit boards. Its introduction has significantly streamlined the process and enhanced the functionality of PCBs.
What is Surface Mount Technology?
Surface-mount technology (SMT) creates electronic circuits by mounting the components directly onto the circuit board’s surface. Unlike through-hole technology, where components with wire leads fit into holes on the circuit board, SMT components have either small leads or no leads. This technique has largely replaced the traditional through-hole manufacturing process, allowing more components on both sides of the PCB.
What are the Benefits of SMT?
Here are some critical points to consider about SMT:
- Reduced Size and Weight: SMT components are smaller than their through-hole counterparts, resulting in lighter and more compact designs, a crucial factor in modern electronic assembly and manufacturing.
- Enhanced Manufacturing Efficiency: SMT can be automated, allowing for faster and more efficient mass production of electronic assemblies.
- Lower Cost in Mass Production: Increased efficiency and reduced material costs mean lower overall costs for large manufacturing runs.
- Higher Circuit Densities: SMT enables mounting more components on both sides of the PCB, resulting in higher circuit densities and improved performance at high frequencies.
- Better Performance: SMT components’ smaller and shorter leads mean improved high-frequency performance because of reduced parasitic capacitance and inductance.
Are There Potential Disadvantages Associated with SMT?
Surface Mount Technology presents several design, assembly, and repair challenges. Although SMT allows for higher component density and automated manufacturing, some potential issues require addressing:
- Accuracy: In Surface Mount Technology, precision is not just important; it’s the key. Placing tiny components demands the utmost precision in manufacturing equipment to ensure correct component placement.
- Thermal Stress: During soldering, SMT components could be subjected to thermal stress, which, if not managed correctly, might lead to failure or reduced reliability.
- Soldering Quality: Ensuring high-quality solder joints can be challenging with SMT, especially for “fine-pitch” components (extremely close together). Defects such as tombstoning (components lifting from the pad), solder bridging (caused by excessive solder), and cold solder joints (insufficiently heated solder wire) can affect solder quality.
- Component Size: As component size decreases, handling and placement challenges increase exponentially, making manual repairs and rework an actual test of skill and patience.
- Inspection and Testing: Due to the smaller connections, traditional inspection methods might not be sufficient. Advanced techniques like automated optical inspection (AOI) and x-ray inspection may work better.
- PCB Design: High-density SMT designs may require more complex PCB layout techniques, including microvias and careful consideration of trace routing to prevent signal integrity issues.
As you work through your project involving SMT, you may encounter some of these challenges. However, the benefits of SMT typically will outweigh any downsides.
Final Thoughts
While surface mount technology (SMT) and through-hole technology have their respective advantages and application areas, the evolving landscape of electronics manufacturing is leaning towards SMT for most new designs. This shift, primarily driven by SMT’s superior space efficiency, allows for more components per unit area, which follows today’s trend toward the miniaturization of electronic devices.
Additionally, SMT offers enhanced performance at higher frequencies, greater reliability with fewer drilling holes in the board that could lead to potential failure points, and a significant reduction in labor costs due to higher levels of automation.
Despite the growing popularity of SMT, through-hole technology still has its place in specific applications. It excels in scenarios that demand stronger physical connections between layers, such as high-reliability products exposed to extreme environments or mechanical stress. Therefore, the choice between SMT and through-hole technology depends on the specific requirements of the electronic product under development.
The electronics landscape is constantly changing, and advancements in SMT are paving the way for more compact, efficient, and powerful electronic devices. While through-hole technology still has its applications, the future of electronics manufacturing is undoubtedly leaning towards surface-mount technology. This shift comes from the industry’s pursuit of innovation and efficiency, which SMT is well-positioned to deliver.