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PGA Chip Packaging

PGA packaging has been the most common chip package used until recently. It was used starting with the 286 processor in the 1980s and is still used today for Pentium and Pentium Pro processors. PGA takes its name from the fact that the chip has a grid-like array of pins on the bottom of the package. PGA chips are inserted into sockets, which are often of a ZIF (Zero Insertion Force) design. A ZIF socket has a lever to allow for easy installation and removal of the chip.

Most Pentium processors use a variation on the regular PGA called SPGA (Staggered Pin Grid Array), where the pins are staggered on the underside of the chip rather than in standard rows and columns. This was done to move the pins closer together and decrease the overall size of the chip when a large number of pins is required. Figure 3.5 shows a Pentium Pro that uses the dual-pattern SPGA (on the right) next to an older Pentium 66 that uses the regular PGA. Note that the right half of the Pentium Pro shown here has additional pins staggered among the other rows and columns.

Figure 3.5 PGA on Pentium 66 (left) and dual-pattern SPGA on Pentium Pro (right).

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