Bubbling on PCB Board after SMT soldering
After SMT rflow oven soldering, the size of the nails appeared. The main reason is that the PCB substrate is filled with water vapor, especially the processing of multi-layer plates. Because the multilayer board is pre molded by multilayer epoxy prepreg before hot pressing, if the epoxy resin prepreg is too short for storage period, and the resin content is not enough, after pre drying and removing moisture vapor is not clean, it is easy to entrain water vapor after hot pressing. It is also due to the lack of glue in the semi solid plate, and the lack of binding force between the layer and the layer to leave the bubble. In addition, after PCB purchase, the storage time is too long, the storage environment is humid, and the pre drying is not timely before the patch production. The PCB patch is also prone to blistering after wetting.
After PCB purchase, it should be accepted in the rear, and the PCB patch should be pre baked for 4 hours at the temperature of (120 + 5) C.
The IC pin is open or weld after welding
(1) the poor coplanar property, especially the FQFP device, leads to pin deformation due to improper storage. If the placement machine does not check the coplanar function, it will not be easy to detect.
(2)The pin solderability is not good, IC stored for a long time, the Yellow pin solderability is not good, is a major cause of weld.
(3)The solder paste is poor in quality, low in metal content and poor in weldability. It is usually used for solder paste welded by FQFP devices, and the metal content should not be less than 90%.
(4) high preheating temperature, easy to cause the IC pin oxidation, make the weldability worse.
The size of the printing template window is small, so that the solder paste is not enough.
(1)Take care of the devices. Do not take the components or open the packing.
(2) the weldability of the components should be checked in production, and special attention should be paid to the IC storage period should not be too long (within one year from the date of manufacture), and the storage should not be subjected to high temperature and high humidity in the storage.
(3) Carefully check the size of the template window, should not be too large and should not be too small, and pay attention to the size of the PCB welding plate matching.
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