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The main factors that prevent the components from standing up are as follows:
1. Select a strong solder, the solder printing accuracy and component placement accuracy also need to improve.
2. The external electrodes of the device need to have good wettability and wet stability. Recommended: The temperature below 400C, the humidity below 70%RH, the use of the components into the use of the period can not exceed 6 months.
3. Use a small land width dimension to reduce the surface tension on the end of the element when the solder melts. In addition, the printed thickness of the solder can be appropriately reduced, for example 100um.
4. The welding temperature management conditions setting is also a factor for the alignment of components. The general goal is that the heating should be uniform, especially before the weld fillets at the connecting ends of the components are formed, and there is no fluctuation in equalized heating.
Poor wetting means soldering of the solder and the circuit substrate (copper foil) during the soldering process, or the external electrodes of the SMD. After being wetted, no mutual reaction layer is generated, resulting in missing or poor soldering failure. The reason for this is that the surface of the soldering zone is mostly contaminated or stained with a solder resist or caused by the formation of a metal compound layer on the surface of the joint. For example, silver has sulfides on the surface, and oxides on the surface of tin can cause poor wetting. In addition, when aluminum, zinc, cadmium, or the like remaining in the solder exceeds 0.005% or more, activation may be reduced due to moisture absorption of the flux, and wetting defects may also occur. Therefore, anti-fouling measures should be taken on the surface of the soldered substrate and the surface of the component. Choose the right solder and set a reasonable solder temperature profile.
Reflow soldering is a complex and critical process in the SMT process. It involves automation, materials, fluid mechanics, metallurgy, and other sciences. In order to obtain excellent soldering quality, all aspects of the soldering process must be thoroughly studied.