In recent years, with the large number of electronic products to small, light, high density development, especially the use of handheld equipment, components in materials technology are the original SMT technology presents a great challenge, so that the rapid development of SMT. Semiconductor packaging is constantly evolving. There are increased demands for increased functionality, added utility, and smaller sizes. Surface Mounting (SMT) is a very important technology when mounting components on a PCB.
With the reliability of SMT, SMT components are secured to the board by solder. THM components are secured by leads running through the board. The result is that the THM boards can hold up in more stressful environments. As a result, boards used in military or aerospace situations often specify THM boards, as the conditions they are used in may include very high or very low temperatures, or rapid acceleration.
Manufacturing of THM is a more complex process. SMT soldering is completed using reflow ovens, while THM requires hand-soldering, and needs soldering on both sides of the board. SMT rarely requires soldering on both sides of the board. As a result, components can only be placed at the rate of hundreds per hour, so manufacture is relatively slow compared to SMT boards.
In contrast, SMT has components mounted directly onto the surface of the PCB. Virtually all components are now manufactured using SMT. The process is considerably more cost effective for most requirements. The component leads in THM are replaced by vias, which are small components designed to allow a conductive connection between layers. SMT allows used of components such as BGAs that allow for shorter leads and more interconnection pins. They can deliver higher speed processing.
SMT PCBs are generally smaller and have a higher component density. They have more ‘real estate’ to work with. Components can be installed very quickly, at rates of thousands of placements per hour. The solder joints are more reliable; and through programming with appropriate quality controls, can be completed quickly and efficiently.
In summary, SMT will usually provide a more cost effective and more reliable board, and be suitable for high production runs. In contrast, THM boards have become a specialist product, providing a valuable tool in specific situations such as high temperatures, or situations that may involve mechanical stress.