Pick and Place Process in Surface Mount Technology (SMT) : Core Principles, Technical Challenges and the Future

The Pick and Place (Surface Mount Technology) process is the core link of surface mount Technology (SMT), which precisely mounts microelectronic components to the designated positions on the printed circuit board (PCB) through high-precision automated equipment. This process directly determines the reliability, production efficiency and integration degree of electronic products. With the development of 5G communication, the Internet of Things and automotive electronics, Pick and Place technology has continuously broken through the limits of accuracy and speed, becoming the cornerstone of modern electronics manufacturing. This article will comprehensively analyze the operation mechanism and development direction of this process from aspects such as equipment structure, working principle, key technical challenges and future trends.

The Pick and Place device (surface mount machine) works collaboratively by multiple precision modules, and its core structure includes:

The feeding system conveys the components in the tape, tube or tray to the picking position through the Feeder. The tape feeder uses gears to drive the material tape to ensure the continuous supply of components. The vibrating bulk feeder adjusts the feeding rhythm by the vibration frequency (200-400Hz).

The surface mount technology (SMT) placement machine is equipped with high-resolution cameras and image processing algorithms. By identifying Mark points and component features on the PCB (such as pin spacing and polarity markings), it achieves sub-micron positioning accuracy (below ±15μm). For example, the flight vision alignment technology can complete component identification during the movement of the robotic arm, and the mounting speed can reach up to 150,48 points per hour.

The placement head adopts a parallel design of multiple suction nozzles (commonly 2 to 24 suction nozzles), and adsorbs the components through vacuum negative pressure (-70 kpa to -90 kpa). Components of different sizes need to be matched with dedicated suction nozzles: 0402 components use suction nozzles with a 0.3mm aperture, while larger components such as QFP require larger suction nozzles to increase the adsorption force by 79.

The X-Y-Z three-axis servo drive system, in combination with the linear slide rail, achieves high-speed (≥30,000CPH) precise movement. For example, in the area of large-sized components, the moving speed is reduced to minimize the influence of inertia, while in the area of micro-components, a high-speed path optimization algorithm is adopted to enhance efficiency 910.

The Pick and Place process needs to be closely coordinated with the front-end and back-end processes. The key steps include:

The solder paste is printed onto the PCB pads through the laser steel mesh (with an opening error of ≤5%). The squeegee pressure (3-5kg/cm²) and the printing speed (20-50mm/s) directly affect the thickness of the solder paste (with an error of ±15%). After printing, the volume and shape are ensured to meet the 410 standard through 3D solder paste inspection (SPI).

After the placement head takes materials from the Feida, the visual system corrects the angular offset of the components (θ axis rotation compensation), and the placement pressure (0.3-0.5N) needs to be precisely controlled to avoid solder paste collapse. For example, the BGA chip requires an additional exhaust hole design to optimize the soldering effect 410.

The reflow soldering furnace is divided into four stages: preheating, immersion, reflow and cooling. The peak temperature (235-245℃ for lead-free process) needs to be precisely maintained for 40-90 seconds. The cooling rate (4-6℃/s) is used to prevent the solder joint from embrittlement. The hot air motor speed (1500-2500rpm) ensures temperature uniformity (±5℃) 410.

Automatic optical Inspection (AOI) identifies defects such as offset and false soldering through multi-angle light sources, with a misjudgment rate of less than 1%. X-ray inspection (AXI) is used for the internal defect analysis of hidden solder joints such as BGA. The repair process uses hot air guns and constant-temperature soldering irons. After the repair, a secondary furnace verification is required.

Despite the maturity of technology, Pick and Place still faces the following core challenges:

Component 01005 (0.4mm*0.2mm) requires a mounting accuracy of ±25μm. Nano-scale steel mesh (thickness ≤50μm) and adaptive vacuum suction nozzle technology should be adopted to prevent material flying or deviation 410.

For QFN packaging, the steel mesh should be thinened to 0.1mm and exhaust holes should be added. 3D stacked packaging (such as SiP) requires the surface mount machine to support multi-layer alignment, and the laser drilling accuracy needs to be less than 0.1mm 410.

The reflux time of components such as leds needs to be shortened by 20% to prevent the yellowing of the lenses. Nitrogen protection (oxygen content ≤1000ppm) in hot air welding can reduce false welding caused by oxidation 47.

Artificial intelligence will be deeply integrated into the AOI system, and defect patterns will be identified through machine learning, reducing the misjudgment rate to less than 0.5%. Predictive maintenance systems can issue early warnings of equipment failures, reducing downtime by 30%410.

The modular surface mount technology (SMT) machine supports rapid switching of production tasks and, in combination with the MES system, enables multi-variety and small-batch production. AGV and intelligent warehousing systems can reduce material preparation time by 50%.

The popularization of lead-free solder (Sn-Ag-Cu alloy) and low-temperature welding processes has reduced energy consumption by 20%. Water-based cleaning agents replace organic solvents, reducing VOCs emissions by 90%310.

The 3D-IC technology for 5G and AI chips drives the development of surface mount technology (SMT) machines towards ultra-thin substrates (≤0.2mm) and high-precision stacking (±5μm), and laser-assisted placement technology will be the key.

The Pick and Place process continuously promotes the advancement of electronic manufacturing towards high density and high reliability through the collaborative innovation of precision machinery, intelligent algorithms and materials science. From nanoscale suction nozzles to AI-driven detection systems, the technological evolution has not only enhanced production efficiency but also provided core support for emerging fields such as smartphones, autonomous driving, and wearable devices. In the future, with the deepening of intelligent and green manufacturing, this process will play a more crucial role in the innovation of the electronics industry.