In a sense, SMT technology has become the pillar and an important symbol of in-depth development of SMT. SMT mounting machines are the core and key equipment in the SMT product assembly production line. The advanced level of SMT processing mounting machines fundamentally determines the two requirements of the mounting process: mounting accuracy and mounting rate.

Firstly, the function of the PCB transmission device is to deliver the PCB that needs to be mounted to the predetermined position, and after the placement is completed, it is then sent to the next process. The transmission device is an ultra-thin belt line transmission system placed on the track. The belt line is usually divided into three sections: A, B, and C, and there is a PCB clamping device in the transmission section of section B, and infrared sensors in sections A and C. More advanced machines also come with barcode recognition equipment, which can set the input and output of PCBs and record the number of PCBs.

During the installation process, the circuit board must be fixed. This clamp prevents the circuit board from moving without hindering the available mounting area. On some devices, the clamp can automatically feed a new circuit board into the machine and send the circuit board filled with components to the next process. The transmission device can be divided into two types based on the type of SMT machine: integral guide rail and movable guide rail.

(1) Integral guide rail.

In this type of placement machine, the entry, placement, and delivery of the PCB are always on the guide rail. When the PCB is sent to the guide rail and advances to section B, there is a backward motion on the PCB board and it encounters the rear limit block, so the PCB stops running. At the same time, the top block with positioning pins below the PCB goes up, pushing the pins into the process holes of the PCB, and the clamping device on section B clamps the PCB.

Below the PCB, there is a support plate with array shaped circular holes. When the PCB enters the B section, an appropriate number of support rods can be installed on the plate according to the PCB structure. As the tabletop moves up, the support rod supports the PCB in a horizontal position, so that when the mounting head is working, it will not press down on the PCB and affect the mounting accuracy.

If the PCB does not have reserved process holes in advance, an optical identification system can be used to confirm the position of the PCB. At this time, the positioning pins on the positioning block can be removed. When the PCB is in place, the front and rear limit positioning blocks of the PCB and the clamping device jointly complete the positioning of the PCB. Usually, the accuracy of optical positioning is higher than that of mechanical positioning, but the positioning time is slightly longer.

(2) Movable guide rail

In another type of high-speed SMT machine, the B-section guide rail is fixed relative to the A and C sections, while the A and C sections guide rail can be lifted and lowered. When the PCB is sent from the printing machine to the A-section guide rail, the A-section guide rail is in high position and connected to the printing machine guide rail: When the PCB runs to the B-section, the A-section guide rail sinks to the same level as the B-section guide rail. The PCB is moved from section A to section B and clamped and positioned by section B. After the completion of PCB placement, it is sent to the C-section guide rail. The C-section guide rail moves up from the low position (at the same level as the B-section) to the same level as the equipment guide rail in the next process, and the PCB is sent from the C-section to the next process. The guide rails of different models have different structures, and the method mainly depends on the overall structure of the placement machine.