Surface Mount Technology (SMT) is one of the core technologies in the field of electronic manufacturing. By directly mounting microelectronic components on the surface of printed circuit boards (PCBS), it has replaced the traditional through-hole mounting technology and has become a key driver for the miniaturization and high performance of modern electronic products. From smartphones to aerospace equipment, SMT is everywhere and can be called the "invisible engineer" of the electronics industry.
SMT originated in the 1960s and was first developed by IBM of the United States. It was initially used in small computers and aerospace equipment (such as the navigation computer of the Saturn launch vehicle).
The core of SMT lies in "mounting" and "soldering". Its process is highly automated and mainly consists of the following steps:
Using a stainless steel template cut by laser (with a thickness of 0.1-0.15mm), solder paste is precisely printed onto the PCB pads through a scraper. Solder paste is made by mixing solder powder and flux. The printing thickness needs to be controlled (usually 0.3-0.6mm) 69.
Key equipment: Fully automatic solder paste printer, in conjunction with SPI (solder paste detector) for 3D scanning to ensure print quality 69.
The surface mount machine grabs components (such as resistors, capacitors, and chips) through vacuum nozzles and achieves an accuracy of ±0.025mm with a visual positioning system. It can mount over 200,000 points per hour.
Difficulties: Special nozzles are required for irregular-shaped components (such as flexible connectors), and BGA packaging relies on X-ray detection to check the integrity of the solder balls.
By precisely controlling the temperature curve (preheating, soaking, reflow, cooling), the solder paste is melted and reliable solder joints are formed. The peak temperature of lead-free processes is usually 235-245℃, and the high-temperature zone lasts for 40-60 seconds.
Risk control: The cooling rate should be ≤4℃/s to avoid lattice defects at the solder joints.
Compared with traditional through-hole technology, SMT has achieved breakthroughs in multiple dimensions:
Surface mount technology is not only the technical cornerstone of electronic manufacturing, but also an invisible force driving humanity towards the intelligent era. From "mounting" to "soldering", from micrometers to nanometers, every advancement of SMT is reshaping the boundaries of electronic products. In the future, with the integration of new materials and intelligent technologies, SMT will continue to write a technological legend of being "small but powerful".