The thickness of the mesh board determines the amount of welded paste printing on PCB. Too many welded paste will cause the bridge to connect when the return welding. Therefore, it is recommended that the QFN package of 0.5mm spacing uses a net board with a thickness of 0.12mm thickness and a 0.65mm spacing QFN packaging with a net board with a thickness of 0.15mm. It is recommended that the mesh opening size can be appropriately smaller than the pad to reduce the occurrence of the welded bridge connection. As shown in Figure 5. (2) Netboard design of heat dissipation pads

　　When welding the exposed pads at the bottom of the chip and the hot pads on the PCB, the gas in the pores and the gas in large -sized pads will overflow due to the heat pores and large -sized pads. All kinds of defects (such as sputtering, welding balls, etc.), but it is almost impossible to eliminate these pores, only reduce the pores to the lowest amount. Therefore, in the design of the mesh area of the hot pad pad, it is necessary to carefully consider it. It is recommended to open multiple small openings in the area instead of a large opening. The typical value of 50%to 80% 5 shown. Practice has proved that the thickness of the welded joints of 50 μm is very helpful for improving the reliability of the board level. In order to achieve this thickness, it is recommended that the thickness of the hot -hole design of the hot -hole design should be at least 50%. For the through -hole, the coverage rate should be at least at least More than 75%.