Recently, SMT steel mesh has been used. The problem is that the residual solder paste on the laser steel mesh after use is difficult to clean. Especially on the TQFP. At first, it was blown with a hot air gun. These solder pastes became tin beads, and they scraped down. However, if you do this, you will worry that the SMT steel mesh will be scrapped several times. The influence of the printing process on the welding effect of the patch, the place that needs attention, can also be regarded as the details.

1. Scraper pressure, blade speed, and demolding speed The single process parameters have a great influence on the quality of solder paste printing. The solder paste printing quality on different types of pads has the same reaction to the change of process parameters. The print quality of small-sized pads is more likely to fail to meet acceptance criteria in this case.

2. The blade pressure has no obvious influence on the solder paste printing quality under the premise of ensuring the internal pressure of the solder paste, but the excessive pressure will affect the patch steel mesh, PCB alignment accuracy, and accelerate the laser steel mesh and scraper wear. The printed solder paste first increases and then decreases as the blade pressure increases, and the solder paste height decreases as the blade pressure increases.

3. The speed of the scraper has a great influence on the printing quality. The printing quality is reduced with the increase of the speed. The main watch is missing, stained and so on. At the same time, the volume of solder paste printed decreases first and then increases with the increase of the speed of the blade, and the height of the solder paste has no obvious relationship with the speed of the blade.

4. The printing quality decreases with the increase of the demolding speed, which is mainly caused by pulling the tip on the elongated pad of QFP, blocking the opening of the SMT stencil and causing the lack of printing. At the same time, the volume of the printed solder paste is off. The mold speed increases first and then decreases, and the height of the solder paste first increases and then decreases as the demolding speed increases.

5. Combining the solder paste printing process and the clay characteristics of the solder paste, it is determined through analysis that the above-mentioned effects of each process parameter on the printing quality are caused by the integration of the solder paste edge performance and the solder paste content pressure.

6. The process window of solder paste printing was determined through experiments. The previous surface mount test verified the previous research on the influence of process parameters on solder paste printing performance, and verified the accuracy of the process window. The process window can be actual production. for reference.