Page 354 - A Practical Guide from Design Planning to Manufacturing

324 Chapter Ten

large die, silicon cost is reduced. A single defect can cause the loss of a
die, but if a processor is composed of multiple separate die, the impact
of each defect is less. Whether overall costs are reduced depends upon
the defect density, total die area required, and the relative costs of single
die and MCM packages. Figure 10-11 compares the cost of a two-die
MCM versus a single-die solution.
Splitting functionality into multiple die always reduces silicon costs,
but the impact is much greater if the total silicon area is large or the
defect density is high. Very large die are especially costly to produce
because they are more likely to have defects. Splitting a design into
multiple die prevents a single defect from causing the loss of all the sil-
icon area, and the total silicon cost grows much more slowly as the total
area needed increases.
The package and assembly costs are not impacted by the silicon area
but are much higher for an MCM compared to a single-die package.
Whether costs are reduced by using an MCM depends on whether the
increase in package cost is larger than the savings in silicon cost.
Because silicon costs are small for small die, below a certain total sili-
con area a single-die solution will be cheaper. However, if a single die
would be very large, dividing the design into multiple die and creating
an MCM product can ultimately be less expensive to manufacture.
The additional cost of an MCM package depends upon the type of
substrate used. MCMs do not use molded plastic substrates, making the

5
Total cost single die

4
Silicon cost
Single die Two die
cheaper cheaper single die
Relative die cost 2 Total cost
3

two die

Silicon cost two die
1

0
50 100 150 200 250 300 350
2
Total die area (mm )
Figure 10-11 Two-die MCM vs. single-die costs.