BGA package, that is ball grid array package, is a surface mount device that uses solder balls arranged in an array as pins. There are four basic types of BGA: PBGA, CBGA, CCGA and TBGA. Generally, it is the bottom of the package that is connected to a solder ball array as a lead-out terminal.
The optical alignment adopts prism imaging through the optical module while the non-optical alignment is achieved by aligning the automatic BGA rework station according to the screen printing lines and points of the PCB board. For some larger BGA devices, non-optical alignment has no problem. After all, due to the surface tension of the solder, in theory, even if the placement offset reaches 50%, during reflow soldering, the BGA device will also be welded in place due to surface tension. But for fine and small BGA devices, it is not easy to rely on eyes alone. So a typical optical alignment principle is introduced here.
Note that the red and blue in the optical alignment schematic are the two imaging paths. Among them, the red solid line and dotted line represent the solder ball imaging path of the BGA chip to be soldered, while the blue solid line and dotted line represent the pad imaging path of the PCB to be soldered. Both images will be reflected into the CCD camera by the prism mirror and then appear on the surface to help the operator to achieve the optical alignment operation.
To ensure soldering and that there will be no damage to the device due to uneven heat or influence on the peripherally soldered devices, this operation requires a PCB preheating device at the bottom as well as the use of a specially designed heating hood on the upper part. Even if this is the case, guys, it is necessary to protect the peripheral devices to prevent re-melting during the reheating process and thus affect the welding quality.
The hot air hood is designed to ensure a good and quick completion of the removal and soldering operations of the BGA rework station components. It is divided into inner and outer layers, and the outer layer is a good shield so that the hot air in the work will not be affected by the external temperature, therefore, the temperature control is stable. The inner layer of hot air flows out through the gaps and exhaust holes between the inner and outer layers, so that the working hot air flow is relatively stable, and it is not easy to cause mechanical effects on the device.
For different BGA devices, there are different thermal properties due to the difference in the number of pins and the device substrate, so the rework parameters are also different. Therefore, it is recommended that you should strengthen the collection and sorting of welding parameters of automatic BGA rework stations in daily welding to form a valuable database.