SMT production effICiency and processing considerations
Efficiency SMT patch handling has many aspects For example, if the total output is unchanged, the SMT patch production line is large and the production speed can be improved However, operating costs are also increasing Nowadays, the fierce competition in the electronic industry is unimaginable In the case of existing production lines, it is crucial to improve the placement rate and win customer satisfaction The factors influencing the placement rate of SMT and improvement measures are briefly introduced as follows:
SMT production line is mainly composed of screen printing machine, high-speed mounting machine, multi-functional mounting machine, reflow welder and AOI automatic detector. If two placement machines complete one placement process and the time (hereinafter referred to as placement time) is not equal, the placement rate will be affected. Specific methods:

1. Balance load distribution. Reasonably allocate the number of two placement elements to achieve load balanced distribution, so that the placement time of two placement machines is the same;
2. The mounter itself We all know that SMT placement machine itself has the maximum placement speed value, but it is usually not easy to realize this value This is related to the structure of SMT mounter. For example, X/Y structure mounter takes measures to make the mounter pick up as many components as possible at the same time On the other hand, when arranging the placement plan, the components of the same type are arranged together to reduce the number of nozzle changes when the placement head picks up PCB components, Save installation time
The SMT production line consists of many equipment. If any device is processing, if the speed is slow, the placement time will be delayed and the entire processing process will be affected. How to improve requires not only theoretical guidance, but also rich experience of field operators.
Process requirements and precautions for SMT chip processing
1. Solder paste printing: according to the appearance, the Flexible circuit board is placed on a special tray for printing. Generally, SMAll sEMI-automatic printing machine is used for printing, and manual printing can also be used, but the quality of manual printing is inferior to semi-automatic printing.
2. Placement during SMT processing: Generally, manual placement can be used, or a manual placement machine can be used to place a single component with high location accuracy.
3. PCB welding: reflow welding process is generally adopted, and spot welding can also be adopted under special circumstances.
High precision placement in SMT processing
Features: The FPC must have the positioning MARK of the base plate, and the FPC itself must be flat. In large-scale production, it is difficult to fix FPCs and ensure consistency, which requires high equipment. In addition, it is difficult to control the printing paste and placement process.
Key processes: 1. FPC fixation: fixed on the tray from printing patch to reflow soldering. The pallet used requires a smaller coefficient of thermal expansion. There are two fixing methods, and the placement accuracy is QFP lead spacing 0. Use this method when 65MM or larger
A. When the placement accuracy is QFP guide spacing 0. 65MM or less
B Method A: Set the pallet on the positioning template. FPC is fixed on the tray with a thin high temperature resistant adhesive tape, and then the tray is separated from the positioning template for printing. The viscosity of high temperature resistant tape shall be moderate, easy to peel after reflow welding, and there shall be no adhesive residue on FPC.
Solder paste printing: since the tray is equipped with a flexible circuit board, there is a high temperature resistant adhesive tape on the flexible circuit board for positioning, and the height is not consistent with the tray plane, so an elastic scraper must be used for printing. The composition of solder paste has a great impact on the printing effect, so it is necessary to select the appropriate solder paste. In addition, method B needs to be used for special treatment of printing templates.
Installation equipment: First, solder paste printing machine, the printing machine should be equipped with optical positioning system, otherwise the welding quality will be greatly affected Secondly, the FPC is fixed on the tray, but there is always some small gap between the FPC and the tray, which is SIMilar to the PCB substrate Therefore, the setting of equipment parameters has a great impact on printing effect, placement accuracy and welding effect Therefore, FPC placement requires strict process control