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ASIC costing.

The cost of a chip divides into two parts: non-recurring engineering (NRE) and per-device cost.
Item Cost (KUSD) Total (KUSD)
NRE: 6 months : 10 H/W Engineers 250 pa 1250
NRE: 12 months : 20 S/W Engineers 200 pa 4000
NRE: 1 Mask set (45nm) 3000 3000
RE:An 8 inch wafer 5 5n
TOTAL 5 8125 + 5n

For small quantities: share cost of masks with other designs e.g. MOSIS offers multiproject wafer (MPW).

Chip cost versus area

The per-device cost is influenced by the yield --- the fraction of working dice.

The fraction of wafers where at least some of the die work is the `wafer yield'. Historically yields have been low, but was typically close to 100 percent for mature 90 nm fabrication processes, but has again be a problem with smaller geometries in recent years. The fraction of die which work on a wafer (often simply the `yield') depends on wafer impurity density and die size. Die yield goes down with chip area.

The fraction of devices which pass wafer probe (i.e.~before the wafer is diced) and fail post packaging tests is very low. However, full testing of analog sections or other lengthy operations are typically skipped at the wafer probe stage. Assume processed wafer sale price might be 5000 dollars:

Assume 99.5 percent of square millimetres are defect free.
Area Wafer dies Working dies Cost per working die
2 9000 8910 0.56
3 6000 5910 0.85
4 4500 4411 1.13
6 3000 2911 1.72
9 2000 1912 2.62
13 1385 1297 3.85
19 947 861 5.81
28 643 559 8.95
42 429 347 14.40
63 286 208 24.00
94 191 120 41.83
141 128 63 79.41
211 85 30 168.78
316 57 12 427.85
474 38 4 1416.89

For a chip with regular structure, such as a memory or an FPGA, additional hidden capacity can be deployed by burning fusible straps (aka links) during wafer probe test. This increases yield despite the larger area shipped in defect-free dies. AMD marketed a range of 3-core CPUs where the 4th, present on the die, had been strapped off.


23: (C) 2008-17, DJ Greaves, University of Cambridge, Computer Laboratory.