Hardware Reference
In-Depth Information
million transistors). As a result, the Nehalem Core i7 processors have a yield of 240 die
candidates per wafer, about half of the yield of the Northwood.
The industry began moving to the 90-nanometer (0.09-micron) process in 2004, the
65-nanometer in 2006, the 45-nanometer process in 2008, and the 32-nanometer process
in 2010.
Thesewillstillbemadeon300mmwafersbecausethenextwafertransitionisn'texpected
until 2014, when a transition to 450mm wafers is expected.
Table 3.8
shows the CPU manufacturing process and silicon wafer size transitions for the
first30yearsfromwhentheprocessordebuted(1971-2001).
Table3.9
showsthecontinu-
ing evolution of these transitions from 2002 through the present, and all the way to 2022,
including several planned future transitions.
Note that not all the chips on each wafer will be good, especially as a new production line
starts. As the manufacturing process for a given chip or production line is perfected, more
and more of the chips will be good. The ratio of good to bad chips on a wafer is called the
yield
. Yields well below 50% are common when a new chip starts production; however,
by the end of a given chip's life, the yields are normally in the 90% range. Most chip
manufacturers guard their yield figures and are secretive about them because knowledge
of yield problems can give their competitors an edge. A low yield causes problems both
in the cost per chip and in delivery delays to their customers. If a company has specific
knowledge of competitors' improving yields, it can set prices or schedule production to
get higher market share at a critical point.
After a wafer is complete, a special fixture tests each of the chips on the wafer and marks
the bad ones to be separated later. The chips are then cut from the wafer using either a
high-powered laser or a diamond saw.
After being cut from the wafers, the individual dies are retested, packaged, and retested
again. The packaging process is also referred to as
bonding
because the die is placed into
a chip housing in which a special machine bonds fine gold wires between the die and the
pins on the chip. The package is the container for the chip die, which essentially seals it
from the environment.
After the chips are bonded and packaged, final testing is done to determine both proper
function and rated speed. Different chips in the same batch often run at different speeds.
Specialtestfixturesruneachchipatdifferentpressures,temperatures,andspeeds,looking
forthepointatwhichthechipstopsworking.Atthispoint,themaximumsuccessfulspeed
is noted and the final chips are sorted into bins with those that tested at a similar speed.
One interesting thing about this is that as a manufacturer gains more experience and per-
fects a particular chip assembly line, the yield of the higher-speed versions goes way up.
