The Ongoing Challenge - Tutorial
The Illusion Of Capacity
Incorporating the Complexity Of FAB Capacity (tool deployment & operating curve)
into Central Planning for Demand-Supply Networks for the production of
semiconductor based packaged goods with substantial non-FAB complexity
Cycle Time Tax and the Operating Curve
in steady-state start patterns
part 2 of 4
Ken Fordyce & John Fournier, IBM
Prof. John Milne, Clarkson University
Dr. Harpal Singh, CEO Arkieva
Fordyce, Fournier, Milne, Singh
Illusion of FAB Capacity in Central Planning – hunt for CAPAVAIL
1
Hunt for CAPAVAIL
and
the Operating Curve
Fordyce, Fournier, Milne, Singh
Illusion of FAB Capacity in Central Planning – hunt for CAPAVAIL
2
Outline
•
Overview of the Demand Supply Network for the production of semiconductor based package
goods
–
•
Decision Tiers
–
–
•
Planned lack of tool uniformity
Inherent variability
Basics of Aggregate Factory Planning
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–
–
•
Aggregate FAB Planning
Central Planning
Two major challenges
–
–
•
Warring factions
Can this wafer start profile be supported
Near Term Deployment
WIP Projection
Basics of Central Planning
–
–
Basic Functions
Historical emphasis on non-FAB complexity
•
–
Handle FAB Capacity with limits stated as wafer starts
•
–
Alternate BOM for example
Wafer start equivalents evolved to nested wafer starts
Second look at capacity (CAPREQ and CAPAVAIL)
•
•
Linear methods in central planning engines
FAB complexity creates miss match
• Operating Curve and Cycle time Tax
Fordyce, Fournier, Milne, Singh
Illusion of FAB Capacity in Central Planning – hunt for CAPAVAIL
3
definitions
• CAPREQ - establishing a consumption rate for each unit
of production by that manufacturing activity for the
selected resource
• CAPAVAIL - providing the total available capacity for the
resource. connecting manufacturing releases (starts) to
resource consumption with a linear relationship
Fordyce, Fournier, Milne, Singh
Illusion of FAB Capacity in Central Planning – hunt for CAPAVAIL
4
CAPAVAIL, Cycle Time, & a Taxes
• Central & FAB Planning make two demand supply network decisions
– quantity of wafer starts (explicit decision made by CPE)
– committed cycle time (input to CPE)
• Typically cycle time is “fixed” and not linked to starts decision
• In fact committed cycle time influences capacity available
– Longer cycle times, more effective capacity available
– Shorter cycle times, less effective capacity available
• since capacity available influences starts, the two decisions (starts
and cycle time are not independent
– Shorter cycle time, less starts
– Longer cycle time more starts
• use operating curve to link cycle time and effective capacity
available via a cycle time tax
Fordyce, Fournier, Milne, Singh
Illusion of FAB Capacity in Central Planning – hunt for CAPAVAIL
6
Trade-off between effective capacity available and cycle time
MM1 comparison full MM1 and Squeezed
Xfactor calculated for traditional MM1
xfactor from Sullivan - Fordyce 10% Sqeezed
xfactor from Sullivan-Fordyce 20% Squeezed
24.00
22.00
For Blue Operating Curve
to achieve a CTM of 5.00
Requires accepting
Tool utilization of 80%
20.00
18.00
16.00
xfactor
14.00
IDLE
IS
TAXto accept
If you are willing
Which Means
20% of your capacity
has to SIT IDLE
12.00
10.00
CTM of 6.0, then only 17% of your
capacity has to sit idle
08.00
Effective CAPAVAIL is
80% of “Raw” CAPAVAIL
06.00
04.00
02.00
00.00
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
Effective CAPAVAIL is
0.5583%
0.60 0.65
0.70 0.75 CAPAVAIL
0.80 0.85 0.90
of “Raw”
0.95
1.00
machine utilization
Fordyce, Fournier, Milne, Singh
Illusion of FAB Capacity in Central Planning – hunt for CAPAVAIL
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Martin-Morrison Operating Curve – some basics
Cycle Time Estimate Based on Utilization
 util M
CTM  1  offset   
1  util M








CTM is the cycle time multiplier of raw process time (RPT) – measure of cycle time
util is tool utilization of the entity (expressed as a percentage) – facility, tool set,
checkout clerks, etc.
offset represents several of aspects of the process that generate wait time that
cannot be eliminated.
M is the number of identical parallel machines or servers. Typically this value ranges
from 1 to 4
α represents the amount of variation in the system (arrival times, service times
(including machine outage, raw process time (RPT), and operator availability)) and
controls how long the curve stays flat. The lower the value of α the less variation
and the longer the curve stays flat.
Fordyce, Fournier, Milne, Singh
Illusion of FAB Capacity in Central Planning – hunt for CAPAVAIL
9
Martin-Morrison Operating Curve – some basics
Utilization Required based on Cycle Time Decision
1
M
 CTM  (offset  1)

util  
 CTM  (offset  1)   
Solve Previous Equation for Util
Given a CTM target, calculate tool utilization required
 Utilization fraction of tool set required to meet cycle time commit
This drives idle without WIP
10
Fordyce, Fournier, Milne, Singh
Illusion of FAB Capacity in Central Planning – hunt for CAPAVAIL
Capacity Available Tax Rate to meet cycle time commit
Capacity Available Tax Rate 1  util
where util is a function
of the cycle time commit and the operating curve for tool set




CAPAVAIL tax rate is required idle without WIP to meet cycle time target
If the cycle time target requires a 80% utilization, then the “tax” is 20%
If the raw CAPAVAIL is 100 units, then 20 units must be “set aside” to meet the
cycle time commit
20% of the time the tool set should be ready to go, but idle no WIP
11
Fordyce, Fournier, Milne, Singh
Illusion of FAB Capacity in Central Planning – hunt for CAPAVAIL
Martin-Morrison Operating Curve – some basics
Capacity Required Uplift Factor (ULF)
to meet cycle time commit
1
CAPREQ Uplift Factor (ULF) 
util




Alternative is to place “tax” on capacity required (CAPREQ)
This is done with uplift factor
If util is 0.80, then the uplift factor is 1.25 (=1/0.8)
If core CAPREQ is 10, CAPREQ to account for required idle
capacity is 12.5 = (10 x 1.25)
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Fordyce, Fournier, Milne, Singh
Illusion of FAB Capacity in Central Planning – hunt for CAPAVAIL
Therefore effective Capacity Available
depends on the cycle time commit
• relationship normally not a component of CPE formulations
• cycle time “decisions” are made prior to creation of the central
plan in “off line” analysis and seen as an “estimate” of
capability as much as a decision
• in aggregate FAB planning using algebraic methods
incorporating cycle time tax is straightforward, but
cumbersome
• Challenge is to incorporate this into the day to day
central planning process where complications
abound
– example ramp up or ramp down of cycle time
14
Fordyce, Fournier, Milne, Singh
Illusion of FAB Capacity in Central Planning – hunt for CAPAVAIL