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Pin Grid Array and Variations (PGA / SPGA / CPGA / PPGA)
Pin Grid Array or PGA packaging is the standard used for most second through fifth generation processors, starting with the Intel 80286 over a decade ago. PGA packages are square or rectangular and have two or more rows of pins going around their perimeter. They are inserted into a special socket on the motherboard or daughtercard. PGA packaging was invented because newer processors with wider data and address buses required a large number of interface pins to the motherboard, and DIP packaging just was not up to the task.
PGA comes in two different main material types. The standard PGA used on most processors until recently is made from a ceramic material, and is also called CPGA for that reason. Some newer processors use a plastic package, called PPGA. The plastic package is both less expensive and thermally superior to the CPGA. It has a raised metal square area on its surface for heat transfer to the heat sink that works better than the CPGA does.
Eventually, as the number of connections for Pentium and later processors exceeded 200 and approached 300, Intel needed to be able to pack even more pins into the same amount of space. To do this, Intel staggered the pin layout so that they could be compressed more tightly. (The idea is similar to how a wine rack stacks bottles.) This is sometimes called SPGA. Pentium and later chips are made with this design.
Finally, the Pentium Pro processor uses a special form of PGA called a "dual pattern PGA". This is of course because the Pentium Pro has a dual-chip package containing both the chip itself and its miniaturized, integrated secondary cache.