This article discuss how to apply solder paste on PCBs step by step. Read about it on the link below.
Solder paste placement is probably the most critical stage of the PCB assembly process, and most assembly problems can be traced back to poor paste placement. If you want to avoid time-consuming manual rework on your assembled boards, it’s essential that you have a clean, precisely positioned layer of solder paste. A few extra minutes ensuring that your paste layer is correct can easily save hours of rework with a hot air gun and a soldering iron later. Thankfully, there’s nothing magic about it.
Solder Paste placement – [Link]