The Topic of Cost of PCBA Starts from SMT Process
Application scenarios of SMT
PCB, also known as printed circuit board, is an important electronic device, which is also the support of electronic components, and the carrier of electronic connection of electronic components. Because it is made by electronic printing, it is called a "printed" circuit board.
PCBA=PCB+Assembly is the PCB with a patch
SMD refers to the abbreviation of a series of process processes that are processed on the basis of PCB. SMT is currently the most popular technology and process in the electronic assembly industry.
Definition of SMT and THT
SMT is one of the most popular production processes in the electronics assembly industry. It meets the requirements of mobile phones and computers for lightness and mass production. The PCBA assembled by SMT has high assembly density and light weight, and realizes automated mass production. The characteristic is that the solder joints and the components are on the same plane as the upper board, and the soldering process is reflow soldering.
The use of THT in the automotive electronics industry still cannot be replaced in a short period of time, but it has been gradually replaced in the consumer electronics industry. The PCBA made by the THT process has a long distance between electronic components and a larger board area. The characteristic is that the components and solder joints are located on both sides of the board.
Advantages of SMT over THT
1. High assembly density, small size and light weight of electronic products.
2. High reliability, strong earthquake resistance, and low solder joint defect rate.
3. Good high frequency characteristics, reduce electric frequency and radio frequency interference.
4. It is easy to realize automation and improve production efficiency.
5. Save materials, energy, equipment, manpower, time, etc.
SMT basic process
Upper board → solder paste printing → solder paste inspection → patch → reflow soldering → AOI optical inspection → visual inspection/repair → lower board
Core process: solder paste printing, patch, reflow soldering
SMT packaging type
Tape packaging, the most common packaging form for small components, is distinguished by wideband, hole spacing and wideband diameter.
Common bandwidth: 8, 12, 16, 24, 32, 44, 56mm
Common tape diameters: 7, 12, 15 inches.
Pay attention to the position of the component in the tape.
SMT hybrid installation
For some requirements that require both SMT and THT, the mixed use of reflow soldering and wave soldering is inevitable. It should be noted that wave soldering must be after reflow soldering. First, because the reflow soldering machine is full of hot air, first After wave soldering and then entering the reflow soldering machine, the solder paste may be melted again. Second, because most of the electronic components assembled in the THT process have pins, and the reflow conveyor belt will cause uneven placement.
Discussion problem record
1. Will SMT completely replace the THT process?
Answer: It is related to industry requirements and development trends. Under the influence of mobile phone industry design trends, PCBA requires miniaturization and planarization, so the THT process in the consumer electronics industry has been gradually eliminated. However, in the automotive and industrial control electronics industries, there are not so clear requirements for space, and components or modules with excessive current are still limited by space, and the use of THT technology is still relatively frequent.
2. Under what circumstances are THT's automation and manual switching?
1. The components are larger.
2. Components with specially designed pins.
3. The quantity is small, and the labor cost is higher.
3. Automobiles and SMD have higher requirements than industrial grades, why?
1. There are different requirements for the deviation value caused by the patch.
2. The components in automotive electronics are expensive, and if the patch causes scrapping, the loss will be huge.
3. The automotive industry has stricter requirements for temperature, vibration, and waterproofing.