Precision PCB Fabrication, High Frequency PCB, High Speed PCB, Standard PCB, Multilayer PCB and PCB Assembly.
The most reliable PCB custom service factory.
PCBA Tech
The difference between SMT and through-hole technology
PCBA Tech
The difference between SMT and through-hole technology

The difference between SMT and through-hole technology

2021-11-06
View:39
Author:Downs

SMD, THD, THT, SMT, THM, SOIC, QFN, these electronic terms may bring unnecessary confusion to emerging electronics enthusiasts. But the terminology and technology are much simpler than they first seem. Next, SMT manufacturers will introduce when and why to use them.

SM stands for surface mounting and TH stands for through hole, which refers to two different methods of mounting components on a printed circuit board. T, D, M, C, or A following SM or TH represent technology, equipment, installation, components or components, respectively, and their use is often loose. For example, because SMD is made using SMT, because it uses SMC in the SMA process. Circuit boards that use SM and TH components at the same time are called hybrid devices.

Initially, all electronic components were installed through through holes. The through-hole component has metal leads, and these leads are fed through plated holes on the circuit board. Then solder the ends of the leads to the pads on the opposite or solder side. Drilling and the pads that make up the plated through holes will take up valuable space on the PCB surface, especially in multilayer boards, because the drilling will take up space on all layers.

More and more space constraints have given birth to surface mount technology, and with it comes a new era of more compact and portable electronic devices. Surface mount components may or may not have leads, but most importantly, they are designed to be soldered directly to the surface of the board on the same side as the component body. Therefore, both sides of the board can be easily used for installation, and electroplating drilling is not required.

pcb board

In order to connect traces in the circuit layer, vias can be used instead, which have the same structure as plated through holes, but much smaller. They can even be designed to connect only specific layers and take up specific space. Therefore, the absence of plated through holes can greatly save the space of SMD devices.

 In addition, the size and footprint of SM components can be minimized compared with TH components. The lead wire can be completely eliminated, which is beneficial to the contact terminal at the end of the assembly body.

 As a result, many components can now be found in SMD packages, such as resistors, capacitors, inductors, and even LEDs. The size of these components can be reduced to the size of a grain of sand (0201/0603 package). The structure is the same as plated through holes, but smaller. They can even be designed to connect only specific layers and take up specific space.

 Therefore, the absence of plated through holes can greatly save the space of SMD devices. In addition, the size and footprint of SM components can be minimized compared with TH components. The lead wire can be completely eliminated, which is beneficial to the contact terminal at the end of the assembly body. In SMD devices, the absence of plated through holes can save a lot of space by itself.

However, miniaturization will affect the reliability of SMD equipment. Due to the complexity of welding and the extra precision required to produce such boards, SMD assembly lines often have a large number of defects, and these defects may be difficult to repair. The final plank is also very delicate, and you must be very careful. On the other hand, circuit boards assembled with TH components are very strong due to large solder joints extending across the entire width of the circuit board. This attribute is desirable in military or industrial applications and may subject the device to strong shocks and vibrations.

 ost is another important consideration to keep in mind. SM components are generally cheaper than TH components, but the SMA process is much more expensive than THA. Surface mount assembly requires some large and highly advanced equipment and materials, such as pick and place machines, reflow ovens, and of course custom templates. The through-hole assembly requires some solder, a soldering iron, and a pair of sturdy hands. Although you can use some tools to manually solder several SM components, this can be an irritating process, especially when you are dealing with many components that are barely visible to the naked eye. Therefore, it makes sense to use SMT in mass production with a high degree of automation and speed and retain THT for small projects and prototypes that may require manual adjustments.

 From an amateur's point of view, when learning ropes, you can definitely start with through-hole components. Moving to SMT may seem daunting and may not even be necessary. The real advantage of SMT lies in making smaller, more compact equipment possible and making mass production almost completely automated. But for small-scale production and household projects, it may be difficult to realize the cost and speed advantages of SMT. Therefore, unless you really need it, it is best to stick to a through-hole plate.

The main advantage of SMT is that the use of SMT components can achieve huge component density and volume reduction. Efforts for smaller, more compact devices have pushed the dimensions of components to the limit, and in the modern age of electronics, THT has become "out of date". But despite early predictions about its demise, through-hole technology and components are still valuable, and in the long run, it seems to still exist. Through-hole PCB assembly and SMT assembly services are available at reasonable prices.