SMT technology in SMT production usually refers to a certain way to accurately paste the chip components to the specified position of the PCB, the process is called "Pick and Place" in English, obviously it refers to the two actions of absorbing/picking and placing. In the early days of SMT, due to the relatively large size of chip components, people can achieve the above actions with simple tools such as tweezers, and there are still a few factories that still use or partially use manual placement of components. However, in order to meet the needs of large-scale production, especially with the refinement of SMC/SMD, people are paying more and more attention to the use of automated machines - SMT machines to achieve high-speed and high-precision placement components.
In the past 30 years, the SMT machine has developed from the early low speed (1-1.5 seconds/piece) and low accuracy (mechanical alignment) to high speed (0.08 seconds/piece) and high precision (optical alignment, patch accuracy +-60um/4δ). The high precision automatic placement machine is a mechatronics high-tech equipment composed of computer, optics, precision machinery, ball screw, linear guide rail, linear motor, harmonic driver, vacuum system and various sensors. In a sense, the SMT machine technology has become the pillar of SMT and an important symbol of in-depth development, the SMT machine is the most critical and complex equipment in the entire SMT production, and it is also the most difficult equipment to choose when people first establish the SMT production line.
This chapter will focus on the main structure, working principle, the main characteristics of various types of SMT mounters and IPC's latest acceptance standards for the purchase and organization of acceptance of SMT mounters.
9.1 Structure and characteristics of the mounting machine
At present, there are dozens of manufacturers producing SMT machines in the world, and there are hundreds of varieties of SMT machines, but whether it is a fully automatic SMT machine or a manual SMT machine, whether it is a high-speed SMT machine or a medium-low speed SMT machine, its overall structure has similarities.
The structure of the SMT machine can be divided into: frame, PCB transfer mechanism and support platform X, Y and Z/θ servo, positioning system, optical identification system, sticker head, feeder, sensor and computer operating software. The characteristics and principles of the above structures are summarized.
9.1.1 Rack
The frame is the basis of the machine, all the transmission, positioning, and transmission mechanisms are firmly fixed on it, and most models of the placement machine and its various feeders are also placed on it, so the frame should have sufficient mechanical strength and rigidity. At present, there are various forms of mounting machines, which can be roughly divided into two categories.
1. Integral casting type
The whole cast frame is characterized by strong integrity and good rigidity. The whole frame is aged after casting. The deformation of the frame is small and the work is stable. High-grade machines mostly use such structures.
2. Steel plate welding type
This kind of frame is made of various specifications of steel plates, etc., and then aged treatment to reduce stress deformation. Its integrity is a little lower than the whole casting, but it has the characteristics of simple processing and low cost. The weld is visible in appearance (removing the machine casing).
The type of frame the machine uses depends on the overall design and load bearing of the machine. Generally, the machine should be smooth, easy, and vibration free during operation (there will be no tipping over with metal coins on the machine), in a sense, the frame plays a key role.
9.1.2 Transmission mechanism and support platform
The role of the transfer mechanism is to send the PCB that needs to be attached to a predetermined location, and then send the SMA to the next process after the placement is completed.
The conveyor is an ultra-thin belt conveyor system placed on the track. Usually the belt is placed on the edge of the track, the belt is divided into A, B, C three segments, and the PCB clamping mechanism is provided in the transmission part of the B zone, and the infrared sensor is equipped in the A and C zone, the more advanced machine also has a barcode reader, which can identify the entry and send out of the PCB, and record the number of PCB.
The transfer mechanism is divided into two types according to the type of the mounter.
