SBS - The Best Value in QMS software

Implementation of 8 or 9 Points Above/Below Centerline question

Q

q1spa

#1
I have question on proper implementation of "8 pts above/below centerline" rules.

Our spc charts (semiconductors) consist each "point" being a summary statistic of individual points measured on a wafer. Each wafer is a point on the chart. There are typically anywhere from 1 to 5 wafers from each lot (typical lot size is 25 wafers).

I'm not sure it is proper to mix both wafer to wafer and lot to lot variation on the same chart - but that is probably a different topic.

For the "8 above/below" rule, is the intent to be 8 lots (rather than 8 individual wafers)? Since we now within-lot variation (wafer-to-wafer) is typically much tighter than lot to lot -- it seems you will trigger a trend rule much earlier than makes sense (ex: measure 3 wafers per lot - all slightly above the mean - you wil trigger violation halfway thru the 3rd lot) - but no real special cause of variation to fix. It seems lot-based would make more sense.

Any input or past experience would be helpful.
Thank you
 
Elsmar Forum Sponsor
T

t.PoN

#2
Since we now within-lot variation (wafer-to-wafer) is typically much tighter than lot to lot
How do you evaluate the "within lot variation"?

let me get this straight:
You have a lot size of 25 waffer
you have unequal sample size (some times, 3 and others are 5)
You don't take the average of the sample or the range.
You plot each sample 3 or 5 times based on the sample size?

I just want to know how did you calculate your limits?

Y don't you use a simple X' and R chart?
 
Last edited by a moderator:

Steve Prevette

Deming Disciple
Staff member
Super Moderator
#3
Whether it is lots or individual units, there are "rules" for declaration on a series of results in a row the same side of the centerline. I use 7 (based upon Acheson Duncan), but Wheeler uses 8 and Minitab uses 9.

If you are going to use lots, you need the lot size to be consistent for "traditional" xbar - R. Since you lot size is varying, it may make more sense to plot individual wafers. There are ways to construct avg - sigma charts with varying lot sizes, but the control limits (standard deviaion) calculations can get difficult.
 
Q

q1spa

#5
Sorry for confusion. Thanks for the replies
We do plot the mean and sigma for each wafer (as well as individual raw data for each wafer vs spec) - 3 charts. The mean and sigma chart is summary from raw data pts of each wafer. There is no "lot-level" calculation or summary on the chart. CLs are calculated based on the points on the chart (wafers). Most of the lots will have 3 wafers sampled.

To make it a more straightforward question - assume every lot has 3 wafers, would it make more sense to adjust the data used for the 8 (or 7 or 9) above/below calculation to use 24 points? (3 wafers per lot * 8 lots, for example) since lot to lot variation is much larger than wafer to wafer.

Thanks
 
T

t.PoN

#6
You either plot it as a lot or as individual.

Go back to the construction of the chart when you first calculated the limits. What variation did you use? the lot to lot or the wafer to wafer?
If you used wafer to wafer variation, then that's the variation to evaluate against.

You can't build your chart based on individual variation and evaluate based on lot variation, can you?

Note: I still suggest a p chart or X'chart, I'm not convinced on how you treat your data? is it normally distributed?
 
Last edited by a moderator:
Q

q1spa

#7
Thanks for the suggestion. Yes, it is normally distributed. I recently joined and not convinced this method is sound (each wafer is a point on chart, but lot-to-lot variation is known to be larger component of variation in this industry) I wanted to get other thoughts from SPC experts.
 

Steve Prevette

Deming Disciple
Staff member
Super Moderator
#8
To make it a more straightforward question - assume every lot has 3 wafers, would it make more sense to adjust the data used for the 8 (or 7 or 9) above/below calculation to use 24 points? (3 wafers per lot * 8 lots, for example) since lot to lot variation is much larger than wafer to wafer.

Thanks
Straightforward answer - No.

Whatever you are plotting, stick to whatever rule you settle on (7, 8, or 9). Do not try to multiply by lot size.

Now - if there are dependencies between wafers, such as say three in a row would have the same value, guaranteed, then you need to relook at the use of SPC as an underlying assumption in SPC is you are plotting sequential, independent results. It may be worth having a "first item in lot" SPC chart to see if such dependencies exist.
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#9
You either plot it as a lot or as individual.

Go back to the construction of the chart when you first calculated the limits. What variation did you use? the lot to lot or the wafer to wafer?
If you used wafer to wafer variation, then that's the variation to evaluate against.

You can't build your chart based on individual variation and evaluate based on lot variation, can you?

Note: I still suggest a p chart or X'chart, I'm not convinced on how you treat your data? is it normally distributed?
your part of the way there, the OP needs to treat each component of variation separately. however, the data do NOT have to be Normally distributed.
by the way, you can have variable limits for continuous data if you have a variable sample size.

the issue here is the choice of subgrouping and control chart type. The OP is charting more than 2 components of variation and eh doesn't have a homogenous process (the factors that affect within wafer variation are not the factors that affect wafer to wafer variation nor are the factors that affect wafer to wafer variation the same as the factors that affect lot to lot variation. a standard X bar R chart will not work.

If the OP can post an example of their data we can give more precise help.
 
Thread starter Similar threads Forum Replies Date
P APQP Implementation Pain Points APQP and PPAP 1
S Implementation of QMS ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 1
T SOC2 preparation and trainings for implementation team Other ISO and International Standards and European Regulations 1
SABRINA DJILALI SAIAH Implementation of the ISAS-MEDIA 9001 standard in a TV channel ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 7
S Sequence of ISO 9001:2015 Implementation Steps ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 6
S ISO9001:2015 Implementation / update plan template ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 2
M ISO14971:2019 - Verification of implementation and effectiveness of risk control ISO 14971 - Medical Device Risk Management 3
S ISO 9001 implementation in a Gold exporting business ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 3
K Implementation 2013/59/Euratom CE Marking (Conformité Européene) / CB Scheme 4
C Implementation ISO 9001: 2015 ? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 3
S Practical Implementation of ISO 14971 ISO 14971 - Medical Device Risk Management 6
G Issues/Roadblocks with APQP implementation APQP and PPAP 7
Dean Bell Implementation of Controls as per SOA for Stage 2 Audit IEC 27001 - Information Security Management Systems (ISMS) 0
O ISO13485 implementation - Are internal audits expected before stage 1 audit? Design and Development of Products and Processes 3
N ERP Software Implementation Manufacturing and Related Processes 3
C New to Site - Request Help with API Q2 Implementation Oil and Gas Industry Standards and Regulations 9
F Will the EU postpone 2017/745 MDR Implementation - COVID-19 Impact Medical Device and FDA Regulations and Standards News 11
J MDD to MDR transition - Time required for the implementation of the MDR EU Medical Device Regulations 7
L AS9146 Implementation and Compliance AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 5
J Looking for a template SOP for UDI implementation for EU Medical Devices EU Medical Device Regulations 1
G Defining performance metrics for DFMA implementation Design and Development of Products and Processes 2
C Design and implementation of process audits as defined within IATF 16949 IATF 16949 - Automotive Quality Systems Standard 2
B ISO 9001 Implementation Time Frame ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 19
M UDI transition period and implementation EU Medical Device Regulations 6
G Strategy for IEC62304 implementation half way into the software development process IEC 62304 - Medical Device Software Life Cycle Processes 9
M Informational EU – EMA revised guidance – Questions & Answers on Implementation of the Medical Devices and In Vitro Diagnostic Medical Devices Regulations ((EU) 201 Medical Device and FDA Regulations and Standards News 2
R ISO 13485 QMS Implementation Training ISO 13485:2016 - Medical Device Quality Management Systems 7
D Preventive Maintenance Implementation 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 5
Emran.mi Measurement system analysis - Can you help me about implementation MSA for CMM device Manufacturing and Related Processes 2
K China UDI Implementation for October 1st 2019 China Medical Device Regulations 4
R ISO 13485 QMS sequence of implementation ISO 13485:2016 - Medical Device Quality Management Systems 4
M Informational From RAPS – EU MDR/IVDR: US Raises ‘Serious Concerns,’ Urges 3-Year Implementation Delay Medical Device and FDA Regulations and Standards News 3
M Informational TGA – European implementation of Medical Device and IVD Regulations – Implications for Australia Medical Device and FDA Regulations and Standards News 0
M Informational Medtech Europe presentation – – Industry Perspective on the Implementation Status of the MDR/IVDR Medical Device and FDA Regulations and Standards News 0
M Informational EU – Employment, Social Policy, Health and Consumer Affairs Council Public session (Health) – AOB – medical devices Implementation of the regulation o Medical Device and FDA Regulations and Standards News 0
M Informational EU – Medical devices: Implementation of Regulation (EU) 2017/745 on medical devices (MDR) – Information from the Irish and German delegations Medical Device and FDA Regulations and Standards News 0
M Informational Medtech Europe – Open letter to the European Commission on the implementation and readiness status of the new Medical Device Regulation (MDR) Medical Device and FDA Regulations and Standards News 0
M Informational Publication of Draft Health Canada Implementation Guidance for the International Medical Device Regulators Forum Table of Contents Format Medical Device and FDA Regulations and Standards News 0
A New Supplier implementation - PPAP vs APQP APQP and PPAP 9
M Startup Company - Implementation of ISO 13485 ISO 13485:2016 - Medical Device Quality Management Systems 19
D AS9100D implementation question AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 9
L Implementation of ISO 27001 as part of the GDPR compliance journey Other Medical Device Related Standards 2
J Implementation of Total Quality Management/Starting a Quality Department Reliability Analysis - Predictions, Testing and Standards 9
P IATF 16949 implementation needs and requirements IATF 16949 - Automotive Quality Systems Standard 3
A Policies Mandatory or essential for ISO 27001 implementation IEC 27001 - Information Security Management Systems (ISMS) 6
A ISO/IEC 27001 - Issue during implementation of system IEC 27001 - Information Security Management Systems (ISMS) 3
A ISMS implementation - ISO 27001: 2013 Company Objectives IEC 27001 - Information Security Management Systems (ISMS) 1
V ISO 9001:2015 Implementation Packages ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 28
G IEC 61010 - Single Fault Condition - Protective Impedance Implementation IEC 60601 - Medical Electrical Equipment Safety Standards Series 1
A EMS - ISO 14001:2015 Implementation ISO 14001:2015 Specific Discussions 4

Similar threads

Top Bottom