For the incomplete solder joint in BGA repair, it means that the volume of the solder joint is insufficient, and the BGA solder joint with reliable connection cannot be formed in BGA welding. The characteristic of the incomplete solder joint is that the shape of the welding joint is significantly smaller than that of other solder joints when AXI inspection is conducted. For this BGA problem, the root cause is insufficient solder paste.
Another common cause of incomplete solder joints encountered in BGA repair is the core-suction phenomenon of the solder, and the BGA solder flows into the through hole due to the capillary effect to form information. Patch offset or solder print offset and BGA pad and defect through the hole without solder resistance film isolation may cause the core suction phenomenon, resulting in not full BGA solder joint. In particular, it should be noted that if the welding resistance film is damaged during the repair process of the BGA device, the core suction phenomenon will be aggravated, resulting in the formation of incomplete solder joints.
Incorrect design can also lead to the production of incomplete solder joints. If a hole is designed on the BGA pad, a large part of the solder will flow into the hole. At this time, if the amount of solder paste provided is insufficient, a low Standoff welding point will be formed. The way to make up for it is to increase the printing amount of solder paste, take into account the amount of solder paste absorbed by the hole in the plate when designing the steel mesh, and ensure the sufficient amount of solder paste by increasing the thickness of the steel mesh or increasing the opening size of the steel mesh; Another solution is to use microporous technology instead of the plate hole design, thus reducing the loss of solder.
Another factor that produces incomplete solder joints is the poor coplanarity of the device and the PCB. If the solder paste printing amount is sufficient. However, the gap between BGA and PCB is inconsistent, that is, poor coplanarity will also appear not full solder joints. This is especially true in CBGA.
Therefore, the main measures to solve the problem of incomplete solder joints in BGA welding are as follows:
1、 Print enough solder paste;
2、 Cover the hole with solder resistance to avoid solder loss;
3、BGA repair stage to avoid damage to the solder resistance layer;
4、Printing solder paste sound accurate alignment;
5、The accuracy of BGA patch;
6、Correct operation of BGA components in the repair stage;
7、To meet the coplanarity requirements of PCB and BGA, to avoid the occurrence of warping, for example, you can take appropriate preheating in the repair stage;
8、The use of microhole technology instead of plate hole design to reduce the loss of solder.