Through-hole technology is the common method for mounting electronic components onto a printed circuit board. It replaced early assembly techniques like point-to-point technology, which was the popular method before 1950s. The through-hole method involves the insertion of leads through holes, soldering on the other side. The leads (capacitors, resistors and diodes) are bent into 90-degree angles in opposite directions for mechanical strength. These leads are fixed into place using a soldering rod. Soldering can be done manually or using a wave-soldering machine.
Advantages of using through-hole method:
1. It provides stronger and more reliable mechanical bonds. It is ideal for those components that need to withstand mechanical stress like transformers and connectors. It is also the best choice for prototyping or testing.
2. It is ideal for heavy or bulky components that need better mounting strength like semi-conductors and electrolytic capacitors.
3. It is also recommended for electromechanical relays and plug connectors which need strong support while on the printed circuit board.
4. It is a perfect tool for engineers who design prototypes using breadboard sockets.
Disadvantages of through-hole method:
1. It is relatively expensive because there is a need to drill multiple holes into the board.
2. It entails a lengthier production time.
3. It limits space because holes need to be drilled in different areas of the printed circuit board to secure components into place.
In the 1980s, surface-mount technology (SMT) became the newer method to assemble the components to the surface of printed circuit board. The vital component parts are placed directly on the board. It is not applicable for mounting big transformers and powerful semi-conductors which can affect the device with their high temperatures. It uses smaller leads or short pins in various forms. Its popularity boomed during the 1990s.
The method reduces the labor costs and increases the rate of production due to high-degree of automation. IBM used this pioneering method in its small-scale computer assembly, then applied it to more comprehensive projects such as the Launch Vehicle Digital Computer, which was used to guide vehicles. Surface-mount technology is mostly used today in both engineering and manufacturing sectors.
Advantages of using Surface-mount technology:
1. It allows for the creation of a smaller printed circuit board which is in demand for use in more compact and lightweight devices. It also solves the space problem in making small gadgets.
2. It is faster to carry out than through-hole because it merely requires a few holes, or no holes at all, depending on the design. Assembly of components can be done for mass production purposes.
3. It uses reflow ovens that guarantee soldering quality for joint formation.
4. It provides stability against vibration.
5. It uses leadless components which make the circuit neater and simpler.
6. It provides higher circuit speeds because of its more compact form. This high-performance level is one of the reasons why most manufacturers use this method.
7. It uses high-end components that allow for multitasking.
8. It can use both sides of the circuit board, providing higher density performance.
9. It assures low induction and resistance of connections, reducing the effects of RF signals.
10. It automatically corrects small errors on component placement because the molten solder pulls other components in perfect alignment with solder pads.
11. It uses top-quality SMT parts at lower cost compared to through-hole parts.
12. It emits low radiations due to its compact radiation loop area.
Disadvantages of SMT:
1. It makes repair more difficult due to the small lead spaces.
2. It is not applicable for prototyping which uses plug-in snap and play tool.
3. It does not guarantee the capacity of the solders’ connections to withstand the compounds used during potting application. It may or may not be damaged when going through this thermal process.
Given these numerous pros and cons, it’s important for those planning to choose between through-hole and SMT to think thoroughly before making a pick.