Processor Types and Specifications - Upgrading and Repairing PCs - page 85

Early PGA variations mounted the processor die in a cavity under the substrate, whereas
so-called“FlipChip”versionsmounttheprocessordieupsidedownsothatlessexpensive
solder bonding rather than expensive wire bonding can be used to connect the processor
die to the chip package.
Unfortunately, there were some problems with attaching the heatsink to an FC-PGA chip.
The heatsink sat on the top of the die, which acted as a pedestal. If you pressed down
on one side of the heatsink excessively during the installation process (such as when you
were attaching the clip), you risked cracking the silicon die and destroying the chip. This
was especially a problem as heatsinks became larger and heavier and the force applied
by the clip became greater. Intel and AMD now use a metal cap called a heat spreader
over the top of the CPU to prevent damage when the heatsink is installed. This type of
packaging is known as FC-PGA2 and was used by Intel for all Pentium 4 and subsequent
chips. AMD began to use it with its Athlon 64 processors and subsequent chips.
Future packaging directions may include what is called bumpless build-up layer (BBUL)
packaging. This embeds the die completely in the package; in fact, the package layers
are built up around and on top of the die, fully encapsulating it within the package. This
embeds the chip die and allows for a full flat surface for attaching the heatsink, as well
as shorter internal interconnections within the package. BBUL is designed to handle ex-
tremely high clock speeds of 20GHz or faster, but is not yet necessary.
Single Edge Contact and Single Edge Processor Packaging
Intel and AMD used cartridge- or board-based packaging for some of their processors
from1997through2000.Thispackagingwascalled single edge contact cartridge (SECC)
or single edge processor package (SEPP) and consisted of the CPU and optional separate
L2 cache chips mounted on a circuit board that looked similar to an oversized memory