In SMT reflow (surface mount technology) welding process, virtual welding is a common and serious concern. In order to avoid the occurrence of virtual welding, prevention and control can be carried out from the following 6 aspects:
First, the selection of high-quality materials and components
Electronic components and PCB board: Select high-quality electronic components and PCB board quality to ensure good solderability and weldability and reduce virtual welding caused by material problems.
Solder materials: Select qualified solder materials to ensure the purity and quality of solder, and avoid using solder materials containing impurities or impurities.
Second, optimize the welding process
Control welding temperature and time:
Reasonably set the preheating temperature, heating temperature and time of reflow welding to ensure that the solder can be fully melted and form a good connection with the pad and component pins.
Avoid welding temperature is too high or time is too long to cause the solder joint to melt or form bubbles, but also to prevent the temperature is too low to cause the solder is not completely melted.
Optimize PCB board design:
Reasonably design the pad spacing and area of the PCB board to ensure that the solder can fully cover the pad and form a good connection with the component pins.
Reduce the number of welding points and reduce the possibility of virtual welding.
Third, strict quality control
Check electronic components and PCB boards:
Strict inspection of electronic components and PCB board before welding to ensure that there is no oxidation, contamination, deformation and other problems.
Timely replacement or treatment of faulty electronic components and PCB boards.
Monitor the welding process:
1, SPI Solder Paste detection: Before welding, use SPI (Solder Paste Inspection) technology to check the solder paste printing quality to ensure the uniformity and consistency of the solder paste, so as to prevent the occurrence of virtual welding.
2, AOI Inspection: After the welding is completed, AOI (Automated Optical Inspection) technology is used for automatic optical inspection, which can find the poor welding products in time and deal with them.
3, X-ray detection: for BGA and other package types of components, because the solder joint is hidden under the component, it can not be found directly through visual inspection. At this time, X-ray detection technology can be used to see through the internal structure of the component and find possible virtual solder joints.
Regular maintenance and inspection of welding equipment and processes to ensure that the equipment is in good condition.
Fourth, improve the working environment
Moisture-proof treatment:
Strict moisture-proof treatment of electronic components and PCB boards to ensure that they are used within the validity period.
The storage environment should be kept dry and clean to avoid moisture or contamination of components and PCB boards.
Cleaning work:
Regularly clean welding equipment and working environment to reduce the accumulation of impurities and pollutants.
V. Setting and optimization of reflow welding process parameters
1. Solder paste selection: the quality of solder paste directly affects the welding quality of SMT patch processing. Therefore, well-known brands of solder paste should be selected to improve the quality of welding.
2, printing parameters adjustment: according to the specific situation of different PCBA processing, the solder paste printing parameters need to be adjusted. These parameters include scraper type, scraper pressure, scraper Angle, printing speed, and steel mesh process. Proper process parameter setting is a necessary condition for SMT chip processing quality.
3, reflow temperature curve setting: reflow is the main welding method for SMT patch processing, and the setting of its temperature curve is very critical. Too long or too short time in the welding zone may lead to false welding, false welding and other bad welding phenomena. Therefore, the temperature curve of reflow welding should be set reasonably according to the specific welding material and component characteristics.
6. Operator training and skill upgrading
1. Regular training: Regular training for operators to improve their skill level and quality awareness. Ensure that they are familiar with the welding process and equipment operation, and can accurately identify and deal with problems during the welding process.
2, standardized operation: Develop standardized operating processes and specifications to ensure that each operator can operate in accordance with a unified standard. This helps reduce welding quality problems caused by human factors.