Foaming on PCB substrate after SMA soldering
The main reason for the appearance of nail size blisters after SMA welding is also the moisture entrained in the PCB substrate, especially in the processing of multilayer boards. Because the multilayer board is made of multi-layer epoxy resin prepreg and then hot pressed, if the storage period of epoxy resin semi curing piece is too short, the resin content is not enough, and the moisture removal by pre drying is not clean, it is easy to carry water vapor after hot pressing. Also due to the semi-solid itself glue content is not enough, the adhesion between layers is not enough and leave bubbles. In addition, after the PCB is purchased, due to the long storage period and humid storage environment, the chip is not pre baked in time before production, and the moistened PCB is also prone to blister.
Solution: PCB can be put into storage after acceptance; PCB should be pre baked at (120 ± 5) ℃ for 4 hours before placement.
Open circuit or false soldering of IC pin after soldering
Causes:
1) Poor coplanarity, especially for fqfp devices, leads to pin deformation due to improper storage. If the mounter does not have the function of checking coplanarity, it is not easy to find out.
2) Poor solderability of pins, long storage time of IC, yellowing of pins and poor solderability are the main causes of false soldering.
3) Solder paste has poor quality, low metal content and poor solderability. The solder paste usually used for welding fqfp devices should have a metal content of no less than 90%.
4) If the preheating temperature is too high, it is easy to cause the oxidation of IC pins and make the solderability worse.
5) The size of printing template window is small, so that the amount of solder paste is not enough.
terms of settlement:
6) Pay attention to the storage of the device, do not take the component or open the package.
7) During production, the solderability of components should be checked, especially the IC storage period should not be too long (within one year from the date of manufacture), and the IC should not be exposed to high temperature and humidity during storage.
8) Carefully check the size of the template window, which should not be too large or too small, and pay attention to match the PCB pad size.
Post time: Sep-11-2020