PCBA Tech - What are the methods of PCBA double-sided reflow soldering?

The method of double-sided reflow soldering of PCBA in SMT technology workshop adopts red glue process on one side and solder paste process of SMT technology equipment on the other side. This method is applicable to PCB circuit boards with dense electronic components and different heights and sizes of components on one side. In particular, the gravity of large electronic components is large, and then it will fall off after reflow welding in the SMT technology production workshop. At this time, the red glue will be more firm in case of heat.

The process flow of red glue is as follows: 1. Incoming inspection 2. Screen printing solder paste on side a of PCB 3. Patch 4. AOI or QC inspection 5. Reflow welding on side a 6. Turnover 7. Screen printing red glue or red glue on side B of PCB (note that whether red glue or red glue is used to apply red glue to the middle part of the component, and the red glue must not pollute the pad so that the component foot cannot solder) > patch > drying > cleaning > detection > repair.

Here, it is also necessary to pay attention to the PCBA welding on the solder paste surface before drying the red glue surface. Because the drying temperature of red glue is relatively low, it can be cured at about 180 degrees. If the red glue surface is dried first and then the solder paste surface is operated, it is easy to cause the parts of electronic components on PCBA to fall off. After all, the adhesion of red glue is not as good as tin, and the temperature should be as high as more than 200 degrees when passing through the solder paste board, which is easy to make the cured red glue become brittle and cause a large number of components to fall off.

Both sides of PCBA adopt solder paste process. This method is applicable to many components on both sides, and both sides of PCBA board have large dense pin IC or BGA PCB board. Because if you point red glue, it is easy to make the IC pin and pad out of alignment.

The solder paste process flow is as follows: first incoming material inspection by the patch processing plant > screen printing solder paste on side a of PCB > patch > QC or AOI inspection > reflow soldering on side a > turnover > screen printing solder paste on side B of PCB > patch > QC or AOI inspection > reflow soldering > cleaning > inspection > repair. It should also be noted here that in order to avoid the falling off of large components when passing through the B surface of PCB circuit board, SMT technical operators should set the temperature of the melt welding area in the lower temperature zone of reflow soldering slightly lower than that in the upper temperature zone of reflow soldering when setting the reflow soldering temperature. In this way, the tin below will not melt again, causing the falling off of components.