The SMT process flow includes material preparation and loading, solder paste printing, solder paste inspection, component placement, reflow soldering, detection and repair.
1. Explanation of SMT basic terms
SMT: (Surface Mounted Technology) is the most popular technology and process in the electronic assembly industry at present.
AOI: (Automatic Optical Inspection) Automatic optical inspection is an equipment based on optical principle to detect common defects encountered in welding production. The machine automatically scans the PCB through the camera, collects images, compares the test limit solder joint with the qualified parameters in the database, checks the defects on the PCB through image processing, and displays/represents the defects through the display or automatic signs for repair by the maintenance personnel.
SPI: (Solder Paste Inspection) Solder paste detection machine, through laser 3D scanning, tests the height, area, volume, offset, tip, tin content difference, foreign matter, etc. of printed solder paste.
2. Basic knowledge of SMT operation
The temperature of SMT workshop is generally 18~26 ℃; The humidity is 30%~70%;
ESD wrist strap and ESD gloves/finger covers shall be worn before operating/handling PCBA;
The purpose of PCB vacuum packaging is to prevent dust and moisture;
After the IC is unpacked, if the humidity on the humidity display card is more than 30%, it indicates that the IC is damp and hygroscopic;
When baking IC, it is necessary to see the IC grade and the temperature resistance value of the tray;
PCB warpage specification shall not exceed 0.7% of its diagonal;
All materials, equipment, fixtures and instruments shall have clear and clear status identification and distinction, and shall be placed by category;
In the process of production and inspection, if any product falls to the ground, the product shall be returned to the first inspection station for inspection and all PCBA tests shall be conducted again.
