SPC

outcome when no proper chart stratification is applied to control charts

unable to monitor individual tool performance; control limits aren't sensitive to detect real issues

Z-Score Chart (normalized chart)

w/normalized data instead of original data; allows monitoring of different processes w/a single chart.

good SPC control strategy should have

well defined process/product characteristic to be controlled; sampling plan; control chart set up properly; detailed reaction mechanism

proper ooc commenting allows others to understand

what investigation has been carried out; what has been done to affected process / equipment product; what escalation response is required?

Cpk is a process capability index that takes into account

where the process is running relative to its target

Cpk compares the __ and __ of the car compared to the parking spot

width / location

Cp compares the

width of the car to the width of the parking spot

p-chart

proportion of defective items when sample size changes

5 number summary breaks data into

quartiles: min, 25th%, 50th% [median], 75th%, max

measures of variation

range, standard deviation, inter-quartile range, and box plot summary

after process improvement, process owner should

re-calculate control limit based on data after the improvement

process improvement

reduce common cause from system

sampling plan includes

sampling frequency; sub-level sampling plan; sampling method at every level (e.g., random or fixed)

4 elements of good SPC control strategy

sampling plan, control charts, OOC, reaction mechanism

product disposition includes

scrap, downgrade, rework, or rewrite CQDR

median is better measure of central tendency for __ data

skewed

nonrandom variation caused by

special cause: unexpected event, shock to process

control chart plots process data over time to monitor

stability of process

individual chart versus moving range chart

static versus dynamic, re time

stratification

technique to split data into subgroups to determine if any contain special cause variation

Cp >= 1

textbook def of "capable process"

OOC rules detect patterns

that would be unlikely to occur if there is no process change

UWMA (UnWeighted Moving Average) chart [rolling T chart]

tighter control limits; detect process change w/slow trending or small size of shift.

over-adjustment comes from

treating each deviation from target as if it were the result of a special cause; manual adjustments can become an additional source of variation.

typical process changes we want to detect in a control chart

trend, shift, outliers, cyclical

charts classifications

trend; control

when detecting both big and small shifts using SPC charts, you're required to

turn on 2 or more OOC rules; set up both individuals chart and EWMA/UWMA together

process change investigation looks at

type of change that occurred; when change began; material affected by change; magnitude of change;

np chart

# of defective parts when sample size is constant

c-chart

# of defects on a part

process stability = % OOC =

# of samples w/ OOC rules violations / total samples

3 sigma rule of normal distribution

68% of data within +/- 1 sd; 95% within +/- 2 sds; 99.7% within +/- 3 sds

xbar chart

A plot of sample means over time used to assess whether a process is in control.

S Chart

Control chart that tracks sample standard deviations

Taguchi Loss Function

Cost of quality ("risk") increases as a quadratic function as conformance values move away from the target.

Cpk

Cp, but takes centering into account

reaction mechanism

Out-of-Control Action Plan (OCAP): explains how to react

SPC is part of

PCS - process control systems

Cp (capability index) =

Upper spec limit - lower spec limit / (6*sigma[variation=1/2sd])

what type of control chart used when there are known systematic source of variation present in the process

Xbar-R chart?

R-chart

a control chart that tracks the "range" within a sample; it indicates that a gain or loss in uniformity has occurred in dispersion of a production process

Levey-Jennings chart

a graph used to plot and visualize the results of control samples over time; form of individuals chart and a special case of the common Shewhart X-bar chart

most common OOC rule

any single data point falls outside 3sigma limit from centerline

run-to-run

automatically adjust process recipes to compensate for known disturbances and allow process to run on target

u-chart

average # of defects per unit

purpose of SPC charts

detect changes to a process as they occur rather than detecting them at final product testing, OR, worse, at the customer

EWMA (exponentially weighted moving average) chart

better small trend detection of capability

normal chart to detect

big drift

product vs process control

product measured by spec limits; process measured by control limits.

Cp < 1

cannot fit

important to measure __ and __ together

central tendency / variation

random variation caused by

common cause: inherent to process; expected

CWDR

continue-on quality deviation report

key elements of control chart

control limits [based on statistical distribution of the data]; center line indicating process current running mean; out of control (OOC) rules

M****n chart categories

critical(customer special), area, engineering

trend up or down rule used if

data is independent

shift high or low rule used if

data is independent and median is used as center line

spec limits and control limits are

derived independently

Reaction Mechanisms typically include

description of alarm that failed; primary contact; process change investigation; investigation of root cause; troubleshooting guide; instructions on product disposition; does tool/chamber need to be brought down; documentation

well defined process/product characteristic determined by

design rule; engineering knowledge; customer request

good spc control strategy should have

detailed reaction mechanism for OOC signals; properly set up control chart; sampling plan of collecting data on characteristic for SPC; well-defined process/product character to be controlled

Fault detection

detect abnormal equipment operation through monitoring of tool trace data

problem solving

detect and remove special cause from system

PML

product monitoring list

process considered stable over time when

distribution is consistent and we have an understanding of expected data value

Cp = 1

exactly fits

OOC [control]

for process disposition

OOS [spec]

for product disposition

p[proportion]-chart

fraction non-conforming; monitor changes in avg. quality level; identify control points that call for corrective action

process capability

how well does my process compare against customer's specifications

manually adjusting every run to compensate for last deviation from target; adjusting runs that deviate more than 1S from target

leads to over-adjustment

common sources of variation in a process

lot-to-lot; within-lot; site-to-site; within-unit; unit-to-unit within batch; batch-to-batch; tool to tool

process disposition includes

maintenance, parameter tuning

6 sources of variation [6 m's]

man; machine; method; material; mother nature; measurement system

"central tendency" measure

mean, median, mode

3 parts of SPC

measurement system, detection mechanism, reaction mechanism

type of control charts

measures of central tendency; measures of variation;

IQR is the __ of the data

middle 50%

spc charts help

monitor stability of process or equipment over time; trigger OOC rules; follow reaction mechanism or Out-of Control Action Plan

point out of control limit

most common ooc rule

Attribute Charts

p-chart, np chart, c-chart, u-chart

mode is the __ value of the distribution

peak

Cp > 1

plenty of space

process control is

proactive

control limits are used for

process disposition

spec / alarm limits are used for

product disposition