For the repairs of QFN, because the welding point is completely at the bottom of the component packaging, any defects such as bridges, roads, and tin balls need to be moved away, so it is somewhat similar to the repairs of BGA. QFN is small in size, light weight, and they are used on high -density assembly boards, making it more difficult to repairs than BGA. At present, QFN repairs are still a part of the urgent development and improvement of the entire surface installation process. In particular, it is necessary to use welded paste

　　A reliable electrical and mechanical connection between QFN and the printed board is indeed difficult. At present, there are three kinds of feasible coating ointments: one is to use the traditional use of the small silk net printing solder balla Print the welding balm directly on the pad of the component. The above methods need to be very skilled to repair the workers to complete this task. The choice of repairs equipment is also very important. It must have a very good welding effect for QFN, but also to prevent the general components from blowing off due to the hot air volume.

　　QFN's PCB pad design should follow the general principles of IPC. The design of thermal pads is the key. It plays a role in thermal conduction. Do not cover it with a welded layer, but the excessive hole design is best to block the welding. When designing the mesh board of the hot pad, the release of the welding paste must be considered at 50%to 80

　　Within %, how much it is appropriate, related to the welding layer of perforated, the pores during welding are inevitable. Adjust the temperature curve to minimize the pores. QFN packaging is a new type of packaging. Whether it is PCB design, technology, or detection and repairs, we need to do deeper research.