cause：

7.1 Poor coplanarity, especially FQFP devices, lead to deformation due to improper storage, if the placement machine does not have the function of checking coplanarity, it is sometimes difficult to find.

7.2 Poor solderability of pins, long IC storage time, yellowing of pins, and poor solderability are the main reasons for virtual soldering.

7.3 The solder paste has poor quality, low metal content and poor solderability. The solder paste usually used for FQFP device soldering should have a metal content of not less than 90%.

7.4 If the preheating temperature is too high, it is easy to cause oxidation of the IC pins, which makes the solderability worse.

7.5 The stencil window size is so small that the amount of solder paste is insufficient.

Solution:

7.6 Pay attention to the storage of the device, do not take the component or open the package casually.

7.7 The solderability of components should be checked during 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 should not be subject to high temperature and high humidity during storage. ]

7.8 Double check the stencil window size, it should not be too large or too small, and pay attention to match the size of the PCB pads. (Source: Munich Shanghai Electronic Production Equipment Exhibition)