The first illustration, Figure 1, show a cut-away view of a typical OMPAC; Figure 2 shows a PLCC. Like other chip components such as PLCCs or QFPs, it contains an integrated circuit (die) with connections to the exterior so that it can be soldered (physically and electrically connected) to a circuit assembly. Unlike other leaded components, however, its connections to the circuit board or assembly are contained entirely under the body of the chip and are made by a grid-like array of solder balls, hence the term Ball Grid Array or BGA, the proper term for this type of chip component.

Once installed, BGAs have no outwardly visible connections to the board, but surprisingly, they are relatively simple to remove and replace using the correct procedures with the appropriate equipment. In addition, the BGA chip itself has very little mass compared to other components of comparable lead connections, like large QFPs, so they must be heated and processed more gently and carefully than traditional large chip components.

OMPAC chips can be sensitive to moisture, and are therefore packaged, when new, in sealed containers. When in service or exposed to the environment for any length of time, the may absorb moisture, and if heated too rapidly, can "popcorn" and delaminate. For defective OMPACs about to be removed from a circuit board, this is not a concern; however, new OMPACs should not be removed from their containers until ready for installation. Table 1 shows the allowable time that different components with different moisture sensitivity levels can be exposed to air before baking is necessary prior to soldering.

Sometimes it is desirable to remove a "good" OMPAC chip from a "bad" board, or protect a "good" board and its other components—such as adjacent OMPACs—from "popcorning" if it has been in a high-humidity environment. In such cases, the circuit board should be pre-baked to drive out any moisture prior to rework. A special nozzle for this purpose has been designed for the Chipmaster, Motorola oven nozzle, part number 01-80303E15. Otherwise, a temperature-controlled oven designed for drying and baking circuitry will be adequate. The chart (Table 2) will show what baking times at 125° will yield process "windows" during which time the OMPAC chip should be reworked: The controlled, gentle heating ramp rate of the Chipmaster ensures that "popcorning" or other thermally induced adjacent component damage will not occur or be a concern.

Replacement OMPACs readily self-align on their pads due to the surface tension of the solder. As long as the OMPAC has been located with a fair amount of precision and care, it will self-align once the solder balls underneath become liquid, during heating. The circuit board itself has been marked with guide lines to facilitate correct alignment by the operator. Figure 3 shows the pattern of connection for an OMPAC BGA, including alignment guides as marked on the circuit board. The illustration shows how much misalignment is acceptable—much more than would be allowable with a typical QFP. In addition to the BGAs self-alignment qualities, the solder balls supplied with the BGA provide the correct amount of solder for a perfect solder joint, so no additional solder need be applied to the board prior to replacement.