Plastic BGA

Hello: 1. Yes, it is necessary to reball a PBGA after removal from the board. Once the part has been removed, the quantity of solder on the balls is out of control. This condition will not only result in an unacceptable variation in solder quantity per joint, but it will also cause a non-planarity between the package and PWB during re-placement which can increase the liklihood of defects upon reflow. The two more popular methods to reball is the use of a stencil and solder paste or the direct application of solder spheres; there is rework equipment on the market to do both procedures. I am not aware of any "overwhelming" reasons to use one or the other; it depends alot on the size of the BGA, the throughput in the rework station, etc. However, an important point to recognize the number of reflow cycles to which the plastic package will be subjected: (1) initial reflow; (2) removal; (3) reballing; and (4) re-installation onto the PWB. One needs to verify that the survivability of the package has not been exceeded and/or that the appropriate pre-baking procedures are being followed prior to EACH reflow step.

2.Re-installation of the package should always follow as closely as possible to the initial soldering process. Therefore, the PWB must also be prepared by removal of excess solder in order to re-establish the necessary planarity for the PBGA upon placement. If paste was used in the first process, it should be used again since the same ball size represents that same quantity of solder being brought to the pad by the package. The same deposit thickness/quantity should be required.

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