Causes and preventive measures of false welding of DIP plug-in and SMT patch welding
Analysis of Causes of Welding of DIP Plug-in and SMT Patch
1. The pad design is defective. There should be no through holes on the pads. The through holes will cause solder loss and insufficient solder; the pad spacing and area also need to be matched with standards, otherwise the design should be corrected as soon as possible.
2. The PCB board is oxidized, that is, the pad is black and does not shine. If there is oxidation, an eraser can be used to remove the oxide layer to reproduce the bright light. If the PCB board is damp, it can be dried in a drying box if suspected. The PCB board is polluted by oil stains, sweat stains, etc. At this time, it should be cleaned with absolute ethanol.
3. For PCBs that have been printed with solder paste, the solder paste is scratched and rubbed, which reduces the amount of solder paste on the relevant pads, resulting in insufficient solder. It should be made up in time. The method of making up can be made up with a dispenser or pick a little with bamboo sticks.
4. SMD (Surface Mounted Components) is of poor quality, expired, oxidized, and deformed, resulting in virtual soldering. This is the most common reason.
(1) The oxidized component is dark and not shiny. The melting point of the oxide increases. At this time, it can be soldered with more than 300 degrees of electric ferrochrome and rosin-type flux, but with more than 200 degrees of SMT reflow soldering and the use of less corrosive no-clean Solder paste is difficult to melt. Therefore, the oxidized SMD is not suitable for welding with reflow soldering furnace. When buying components, you must see if there is oxidation, and use them in time after you buy them. In the same way, oxidized solder paste cannot be used.
(2) Surface mount components with multiple legs have small legs and are easily deformed under the action of external force. Once deformed, the phenomenon of missing or missing welding will definitely occur. Therefore, it is necessary to carefully check and repair in time before welding.
(3) For PCBs printed with solder paste, the solder paste is scratched and rubbed, so that the amount of solder paste on the relevant pads is reduced, and the solder is insufficient, which should be filled in time.
Preventive measures for false welding and false welding of DIP plug-in and SMT patch:
(1) Strictly manage suppliers to ensure stable material quality;
(2) Components, PCBs, etc. are used first-come, first-served, and strictly moisture-proof, to ensure that they are used within the validity period;
(3) If the PCB is contaminated or expired and oxidized, it needs to be cleaned before it can be used;
(4) Clean the oxides at the tin furnace, runners and nozzles to ensure that the flowing solder is clean;
(5) The three-layer terminal structure electrode is used to ensure that it can withstand the temperature shock of more than two 260°C wave soldering;
(6) For components and PCB pads with larger heat capacity, the preheating method should be improved and a certain degree of thermal compensation should be carried out;
(7) Choose a flux with strong activity, and ensure that the flux is stored and used in accordance with the operating regulations;
(8) Set a proper preheating temperature to prevent the flux from premature aging.
