PCB surface mount welding 5 major reasons and solutions, poor wet wet wet reflections reflect the solder and substrate welding in the welding process, do not generate a repercussions between metals after moisturizing, but form a leakage or less welding . It is caused by most of the outer surface of the weld area, or the solder resist, or the outer table of the silver is formed, such as the outer surface of the silver, the outer surface of the tin, etc., the outer surface of the tin, etc. bad. Others, the residual aluminum, zinc, cadmium, etc. in the weld, is more than 0.005%, and the moisture absorption effect of the flux decreases, and it can also be wetted. In wave welding, if the gas is present in the surface of the substrate, it is also easy to attack this. Therefore, in addition to performing suitable welding workers, the outer table of the substrate should be prevented, and the suitable solder is selected, and the reasonable welding temperature and time are set. PCB surface mount welding two, the seizures of the bridge joint bridge, mostly the severity of the solder excess or solder printing, or the substrate welding area is extraordinary, SMD mounting offset, etc., in SOP, QFP circuit During the tend to be fine, the bridge will form an electrical short circuit and affect the use of goods. As a correction method: 1, to avoid the skinning of the solder paste. 2, the scale setting of the substrate welding is to fit the design needs. 3, SMD's mounting orientation is within the range of rules. 4, the substrate wiring gap, the coating accuracy of the solder resist, is necessary to fit the rules. 5. Develop appropriate welding technical parameters to avoid mechanical oscillations of the weld machine conveyor belt. Third, the seizures of solder ball solder balls are multi-seizures to heat the heating during the welding process, which causes the solder scavenging, other and solder printing dislocation, collapse. Pollution, etc. also contacts. Avoiding the countermeasures: 2. Perform a corresponding preheating technique in accordance with the type of welding. 3. If the printing of the solder is collapsed, the misplaced product is deleted. 4. The use of solder paste should be fitted with demand, no moisture absorption. Fourth, the crack welding PCB is just off the welding area, because the thermal expansion of the solder and the joint is in the emergency or hot effect, the SMD will simultaneously attack, welded PCB, during diet, during transport, it is also necessary to cut the impact stress to SMD. Bending stress. The outer surface mounting item is designed, and the distance to reduce the heat expansion should be considered to accurately set the conditions and cooling conditions such as heating. Select extensive outstanding solder. 5. Poor suspension bridges is that one end of the finger element is separated from the welding area and is obliquely or erect. The reason for the episode is too fast, the heating direction is not too balanced, the choice of solder paste, preheating before welding, and welding Area, SMD self-shaped, wettability. Avoiding strategies: 1. SMD's storage should fit the demand. 2, the printing thickness scale of the solder is accurate. 3. Adopt reasonable preheating methods to achieve uniform heating during welding. 4, the scale of the substrate welding area should be appropriately formulated. 5. Cut the outer surface tension of the SMD end at the time of molten the solder.