Boost PC performance: How more available memory can improve productivity
Ashrae 18.6
1. 1995 2000 2005 2010 2015 2020
Primary
Process Areas
ISO Class 3 ISO Class 5 ISO Class 5 ISO Class 6 ISO Class 6 ISO Class 6
Wafer Level
Environment
N/A ISO Class 3 ISO Class 1 ISO Class 1 ISO Class 1 ISO Class 1
Typical Filter
Coverage
(% of Ceiling)
100%
80% to
100%
60% to
100%
50% to
80%
40% to
75%
40% to
75%
Nominal
Average Room
Air Velocity,
fpm (m/s)
90 (0.45) 70 (0.35) 60 (0.3) 60 (0.3) 50 (0.25) 50 (0.25)
Typical ACH,
10 ft (3 m)
Ceiling Height
540 420 360 360 300 300
Typical ACH,
12 ft (3.7 m)
Ceiling Height
450 350 300 300 250 250
Typical ACH,
16 ft (5 m)
Ceiling Height
338 263 225 225 188 188
18 · Cleanrooms in Semiconductor and Electronics Facilities 349
ACH, the decreases in ACH for fabs is being driven by comprehensive review of contam-
ination risk versus cost reduction. Reducing room filter coverage and average room veloc-
ity impacts cleanroom construction costs and operating costs. Operating cost savings can
be 10–20 W/ft2
(100–200 W/m2
) (range based on 1.3–2.0 in. w.c. [325–500 Pa] total
pressure). There are limits to decreases in ACH, filter coverage, and average room veloc-
ity based on risk evaluation to exposed wafers, recovery time, and ability to maintain tem-
perature control. With high internal heat loads from the process equipment, the equipment
must be cooled with sufficient cleanroom ACH or by other sources, such as water-cooled
process equipment.
18.18.1 CLEANROOM FAN SELECTION
The selection of process area cleanroom fans is contingent upon the process area lay-
out and its relationship to the overall building configuration. Many fab cleanrooms were
built using a large cleanroom recirculation air handler (RAH) located adjacent to the
cleanroom space. This design approach tended to result in longer cleanroom recirculation
air paths. The proliferation of small, compact FFUs that contain a fan and appropriate
cleanroom filters has become ubiquitous for wafer fab cleanrooms. Fab operators desire
high reliability, low first costs, negative pressure plenums, and low operating costs. FFU
technology has developed to provide all three. With networked FFUs, cleanroom operators
can monitor the performance of each FFU and remotely control them if they desire. While
central station fans may have lower cost per unit of capacity, when one adds in the installa-
tion and ductwork costs, the cost advantage is minimized. Having thousands or tens of
thousands of FFUs in a fab provides thousands of failure points. However, when one unit
fails, only a small portion of the overall air volume is lost, and with remote monitoring the
failing units can be identified and replaced. New electronically commutated (EC) motors
4. Some fab ceilings may be as high as 24 ft (7.3 m) when overhead cranes or transport systems are
within the cleanroom.
Table 18.6
Cleanliness
Class (ISO
2015) Filter
Coverage and
ACH Evolution
![1995 2000 2005 2010 2015 2020
Primary
Process Areas
ISO Class 3 ISO Class 5 ISO Class 5 ISO Class 6 ISO Class 6 ISO Class 6
Wafer Level
Environment
N/A ISO Class 3 ISO Class 1 ISO Class 1 ISO Class 1 ISO Class 1
Typical Filter
Coverage
(% of Ceiling)
100%
80% to
100%
60% to
100%
50% to
80%
40% to
75%
40% to
75%
Nominal
Average Room
Air Velocity,
fpm (m/s)
90 (0.45) 70 (0.35) 60 (0.3) 60 (0.3) 50 (0.25) 50 (0.25)
Typical ACH,
10 ft (3 m)
Ceiling Height
540 420 360 360 300 300
Typical ACH,
12 ft (3.7 m)
Ceiling Height
450 350 300 300 250 250
Typical ACH,
16 ft (5 m)
Ceiling Height
338 263 225 225 188 188
18 · Cleanrooms in Semiconductor and Electronics Facilities 349
ACH, the decreases in ACH for fabs is being driven by comprehensive review of contam-
ination risk versus cost reduction. Reducing room filter coverage and average room veloc-
ity impacts cleanroom construction costs and operating costs. Operating cost savings can
be 10–20 W/ft2
(100–200 W/m2
) (range based on 1.3–2.0 in. w.c. [325–500 Pa] total
pressure). There are limits to decreases in ACH, filter coverage, and average room veloc-
ity based on risk evaluation to exposed wafers, recovery time, and ability to maintain tem-
perature control. With high internal heat loads from the process equipment, the equipment
must be cooled with sufficient cleanroom ACH or by other sources, such as water-cooled
process equipment.
18.18.1 CLEANROOM FAN SELECTION
The selection of process area cleanroom fans is contingent upon the process area lay-
out and its relationship to the overall building configuration. Many fab cleanrooms were
built using a large cleanroom recirculation air handler (RAH) located adjacent to the
cleanroom space. This design approach tended to result in longer cleanroom recirculation
air paths. The proliferation of small, compact FFUs that contain a fan and appropriate
cleanroom filters has become ubiquitous for wafer fab cleanrooms. Fab operators desire
high reliability, low first costs, negative pressure plenums, and low operating costs. FFU
technology has developed to provide all three. With networked FFUs, cleanroom operators
can monitor the performance of each FFU and remotely control them if they desire. While
central station fans may have lower cost per unit of capacity, when one adds in the installa-
tion and ductwork costs, the cost advantage is minimized. Having thousands or tens of
thousands of FFUs in a fab provides thousands of failure points. However, when one unit
fails, only a small portion of the overall air volume is lost, and with remote monitoring the
failing units can be identified and replaced. New electronically commutated (EC) motors
4. Some fab ceilings may be as high as 24 ft (7.3 m) when overhead cranes or transport systems are
within the cleanroom.
Table 18.6
Cleanliness
Class (ISO
2015) Filter
Coverage and
ACH Evolution](https://image.slidesharecdn.com/ashrae18-191214052349/85/Ashrae-18-6-1-320.jpg)
