Surface Mount PCBs
Surface mounting is one of the two major mounting methods of components on a PCB. Such PCB requires soldering pads on the surface to mount components, but not necessary to have through holes. Surface mounting is also called SMT(surface mount technology), and the related devices or components package is called by SMD(surface mount device). The other main mounting method is through hole mounting(THM).
Nowadays it is a development trend to make the electronic products smaller and smaller, thinner and thinner, lighter and lighter. So it requires the components to have the same features of small, thin and light. The surface mount components are able to be made in small size, thin thickness and light weight. So the surface mounting method is more and more widely used in electronic products.
Even though THM components are secured stronger by leads/pins running through the board, which helps the board hold up in more stressful environments. Many of the SMT components are able to ignore the solder strength problem due to very small size and light weight.
Moreover the assembly process of SMT components are easier, efficient and economic. The higher cost of components itself is balanced with the lower cost of preparing and assembling the THM components. The THM board needs to have holes drilled, which can be an expensive process, as well as being time consuming.
Another benefit of SMT components is that they donot require through holes, and their size is smaller, which saves a lot space on PCB boards. On the other hand, THM boards requires through holes. Drilled holes must pass through all layers of the PCB. Therefore, routing on multilayer boards is more challenging for THM.
Manufacturing of SMT is an easier process. SMT soldering is able to use automatic equipment and 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.
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.
In summary, in most circumstances, SMT will provide a more cost effective and more reliable board, and be suitable for high production runs.