575:
of the process window are ±99%. A PWI greater than or equal to 100% indicates that the profile does not process the product within specification. A PWI of 99% indicates that the profile runs at the edge of the process window. For example, if the process mean is set at 200 °C, with the process window calibrated at 180 °C and 220 °C respectively; then a measured value of 188 °C translates to a process window index of −60%. A lower PWI value indicates a more robust profile. For maximum efficiency, separate PWI values are computed for peak, slope, reflow, and soak processes of a thermal profile.
556:
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51:
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affecting production, the steepest slope in the thermal profile is determined and leveled. Manufacturers use custom-built software to accurately determine and decrease the steepness of the slope. In addition, the software also automatically recalibrates the PWI values for the peak, slope, reflow, and
574:
Each thermal profile is ranked on how it fits in a process window (the specification or tolerance limit). Raw temperature values are normalized in terms of a percentage relative to both the process mean and the window limits. The center of the process window is defined as zero, and the extreme edges
495:
of the plotted sample statistic. Control limits describe what a process is capable of producing (sometimes referred to as the "voice of the process"), while tolerances and specifications describe how the product should perform to meet the customer's expectations (referred to as the "voice of the
251:
that quantifies the robustness of a manufacturing process, e.g. one which involves heating and cooling, known as a thermal process. In manufacturing industry, PWI values are used to calibrate the heating and cooling of soldering jobs (known as a thermal profile) while baked in a
259:
PWI measures how well a process fits into a user-defined process limit known as the specification limit. The specification limit is the tolerance allowed for the process and may be statistically determined. Industrially, these specification limits are known as the
518:). One specification outlines that a signal is defined as any single point outside of the control limits. A process is also considered out of control if there are seven consecutive points, still inside the control limits but on one single side of the mean.
619:
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statistics, the area bracketed by the control limits will on average contain 99.73% of all the plot points on the chart, as long as the process is and remains in statistical control. A false-detection rate of at least 0.27% is therefore expected.
510:
Control limits are used to detect signals in process data that indicate that a process is not in control and, therefore, not operating predictably. A value in excess of the control limit indicates a special cause is affecting the process.
610:, with four profile statistics logged for each thermocouple, would have a set of twelve statistics for that thermal profile. In this case, the PWI would be the highest value among the twelve percentages of the respective process windows.
1060:
603:(i.e. highest number) in the set of thermal profile data. For each profile statistic the percentage used of the respective process window is calculated, and the worst case (i.e. highest percentage) is the PWI.
790:{\displaystyle {\text{PWI}}=100\times \max _{i=1\dots N \atop j=1\dots M}\left\{\left|{\frac {{\text{measured value}}_{}-{\text{average limits}}_{}}{{\text{range}}_{}/2}}\right|\right\}}
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The tolerance values specified by the end-user are known as specification limits – the upper specification limit (USL) and lower specification limit (LSL). If the process
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34:
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on either side of the process mean, and are known as the upper control limit (UCL) and lower control limit (LCL) respectively. If the process
420:
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Process Window Index for a thermal process. Green blurbs denote that the PWIs are within specification, red depicts out of specification.
1116:
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To help determine the capability of a process, statistically determined upper and lower limits are drawn on either side of a process
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soak processes. By setting PWI values, engineers can ensure that the reflow soldering work does not overheat or cool too quickly.
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106:
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290:. To help determine whether a manufacturing or business process is in a state of statistical control, process engineers use
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on a control chart remains within these specification limits, then the process is considered a capable process, denoted by
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377:. Within this process window, values are plotted. The values relative to the process mean of the window are known as the
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on the control chart remains within the control limits over an extended period, then the process is said to be stable.
463:
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It is often not known whether a particular process generates data that conform to particular distributions, but the
196:
413:
381:. By using PWI values, processes can be accurately measured, analyzed, compared, and tracked at the same level of
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Using PWI values, processes can be accurately measured, analyzed, compared, and tracked at the same level of
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264:, and values that a plotted inside or outside this window are known as the process window index.
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distribution at least 95% of the data will be encapsulated by limits placed at 3 sigma.
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average limits = the average of the high and low (specified) limits of the statistic
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An example of a process to which the PWI concept may be applied is soldering. In
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The manufacturing industry has developed customized specification limits known as
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Statistical measure that quantifies the robustness of a manufacturing process
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1028:
Houston, Paul N; Brian J. Louis; Daniel F. Baldwin; Philip
Kazmierowicz.
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427: in this section. Unsourced material may be challenged and removed.
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567:, a thermal profile is the set of time-temperature values for a
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range = the high limit minus the low limit of the statistic
1012:(2 ed.). Automotive Industry Action Group (AIAG). 2005.
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A graphical representation of the PWI for a thermal profile
316:
on the control chart. The control limits are set at three
514:
To detect signals one of several rule sets may be used (
1061:"A Method for Quantifying Thermal Profile Performance"
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is the ability of a process to produce output within
1009:Statistical Process Control (SPC) Reference Manual
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362:
824:measured value = the statistic's measured value
595:Example of a PWI for peak, soak, and slope values
638:
571:such as slope, thermal soak, reflow, and peak.
516:Control chart § Rules for detecting signals
886:National Institute of Standards and Technology
881:NIST/Sematech Engineering Statistics Handbook
221:
8:
982:. Circuits Assembly Magazine. Archived from
480:, used to judge the stability of a process.
389:available to other manufacturing processes.
275:available to other manufacturing processes.
483:Control limits should not be confused with
606:For example, a thermal profile with three
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973:Hall, Jim; Zarrow, Phil (February 2002).
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443:Learn how and when to remove this message
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491:which are completely independent of the
1030:"Taking the Pain Out of Pb-free Reflow"
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821:(number of statistics per thermocouple)
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976:PWI: Process Optimization Made Simple
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7:
425:adding citations to reliable sources
939:Godfrey, A. B (September 1, 2000).
846:Control chart § Chart details
642:
462:, are horizontal lines drawn on a
25:
613:The formula to calculate PWI is:
537:allow the inference that for any
545:PWI in electronics manufacturing
401:
297:
49:
1132:Statistical charts and diagrams
1035:. Lead-Free Magazine. p. 3
535:Vysochanskij–Petunin inequality
412:needs additional citations for
363:{\displaystyle {\hat {C}}_{pk}}
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469:, usually at a distance of ±3
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1:
1063:. KIC Thermal. Archived from
876:"What is Process Capability?"
599:The PWI is calculated as the
150:Information and communication
1137:Statistical process control
1088:Kazmierowicz, Phil (2003).
383:statistical process control
279:Statistical process control
269:statistical process control
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1117:Electronics manufacturing
811:(number of thermocouples)
941:Juran's Quality Handbook
841:Acceptable quality limit
94:Industrial technologies
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531:Chebyshev's inequality
460:natural process limits
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1127:Brazing and soldering
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58:Manufacturing methods
1142:Statistical distance
1122:Industrial processes
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569:variety of processes
523:normally distributed
421:improve this article
379:process window index
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241:Process window index
18:Process Window Index
471:standard deviations
464:statistical process
318:standard deviations
249:statistical measure
86:Agile manufacturing
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284:Process capability
81:Lean manufacturing
1090:"Process Control"
907:External link in
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16:(Redirected from
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485:tolerance limits
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375:process windows
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184:Process control
76:Flow production
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549:Main article:
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456:Control limits
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433:September 2022
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71:Job production
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1067:on 2011-07-13
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989:on 2011-07-13
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580:thermal shock
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506:Control chart
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1094:. Retrieved
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496:customer").
493:distribution
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419:Please help
414:verification
411:
378:
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329:data plotted
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322:data plotted
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945:McGraw-Hill
910:|work=
578:To avoid
475:statistic's
254:reflow oven
1111:Categories
1096:2008-12-10
1071:2010-09-30
1039:2008-12-10
993:2008-12-10
891:2008-06-22
862:References
601:worst case
504:See also:
716:−
671:…
654:…
635:×
565:soldering
346:^
173:IEC 62264
132:Six Sigma
900:cite web
835:See also
539:unimodal
533:and the
35:a series
33:Part of
817:= 1 to
807:= 1 to
800:where:
587:Formula
247:) is a
951:
163:ISA-95
158:ISA-88
1033:(PDF)
987:(PDF)
980:(PDF)
747:range
202:SCADA
177:B2MML
949:ISBN
915:help
521:For
478:mean
385:and
314:mean
271:and
639:max
632:100
625:PWI
500:Use
487:or
423:by
245:PWI
197:DCS
192:PLC
168:ERP
137:TQM
127:TOC
122:QRM
117:VDM
112:TPM
107:RCM
102:PLM
1113::
1080:^
1048:^
1018:^
963:^
947:.
923:^
904::
902:}}
898:{{
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