The hot air temperature setting is too high, so that the BGA corners are bent downward and the solder joints are crimped. This phenomenon is called "hot ear phenomenon". If the heart bridges, it is generally too fast to cool down during repairs. Note: Hot air rework is a one-way, uneven heating process.
When a smt product is repaired, the solder joints at the corners appear.
The chip is a CSP package with a pitch of 0.5 mm and a solder ball diameter of 0.3 mm.
Rework the workstation using the Conceptronic 2000.
Reworked 20 pieces and only repaired 3 pieces, mainly BGA core solder ball bridge. At first, it was suspected that it was BGA, but there was no obvious change after the treatment, and then the cooling air problem was solved.
The BGA slice of this case is shown in Figure 1.
It is found that the CSP package has an intermediate bulging phenomenon (non-popping phenomenon. There is no delamination in the middle of CSP). The height of the solder joint at the center of the CSP is 183um, and the height at the corner is 158um.
The above are the technical problems that customers will have when performing BGA rework. The countermeasures given by our company are:
In the PCB factory, the core of the BGA rework is the temperature difference between the upper and lower sides of the BGA on the control circuit board, which generally cannot exceed 10C.
If the four corners are connected, the preheating time and temperature should be extended, the wind speed should be reduced, and the inner and outer solder joints of the BGA should be melted at the same time to avoid the fact that the solder balls of the BGA are not completely melted. melt.
If the heart is bridged, turn on the bottom preheater to cool in the warm air to avoid the first solidification of the solder ball at the corners.
The above is the sharing of the pcb factory, I hope to help you!