Many SMT factories often encounter some poor quality during production. As a member of SMT processing factories, based on experience, I have summarized a few packages and problems that are most prone to problems (according to the difficulty):

(1) QFN: The most common undesirable phenomenon is bridging and false welding (open welding).

(2) Dense foot components: such as SOP QFP below 0.65mm, the most prone to undesirable phenomena are bridging and virtual soldering (open soldering).

(3) Large-pitch, large-size BGA: The most common undesirable phenomenon is solder joint stress fracture.

(4) Small-pitch BGA: The most common undesirable phenomenon is bridging and virtual soldering (open soldering).

(5) Long fine pitch surface mount connector: The most prone to undesirable phenomena are bridging and virtual soldering (open soldering).

(6) Micro switches and sockets: The most common undesirable phenomenon is the ingress of rosin inside.

The main reasons for common problems are:

(1) The bridging of fine pitch components is mainly caused by poor solder paste printing.

(2) The solder joint cracking of large-size BGA is mainly caused by moisture.

(3) The bridging and virtual soldering of small-pitch BGA are mainly caused by poor solder paste printing.

(4) The unsoldering of transformers and other components is mainly caused by the poor coplanarity of the component pins.

(5) The bridging and unsoldering of the long fine pitch surface mount connector is largely due to the inconsistent PCB soldering deformation and the socket layout direction.

(6) The rosin in the micro switches and sockets is mainly caused by the capillary action formed by the structural design of these components.