【正文】 Course Contents 1. Introduction 2. Data types and basic definitions 3. Distributions summary statistics 4. Sampling Single Variable Analysis 5. Control chart 6. Process capability study 1 What is a Control Chart? ? A trend chart with control limits ? Graphical representation of process performance, where data is collected at regular time sequence of production ? Valuable tool for differentiating between a mon cause a special cause ? Evaluating whether a process is or is not in a state of statistical control ? It lets the data ‘talk’ by itself basis for datadriven decisions 2 Control Limits A typical control chart consists of three lines : Upper Control Limit (UCL) Center Line (CL) Lower Control Limit (LCL) CL: The average (measure of location) process performance when the process is incontrol UCL LCL: The range of ‘usual’ process performance when the process is stable. Lines drawn 3 standard deviations (3 sigma) on each side of the center line. 3 How to Setup a Control Chart? ? Select an area which allows for fruitful application ? Identify critical parameters to be monitored based on the feedback from customers, level of quality reliability, process performance, etc. as reflected in the FMEA of the specific operations – Inherently unstable parameters or high excursions – Low process capability – Critical process inputs – Customers required parameters ? Select measurement tools. Verify the measuring equipment is accurate, stable capable by performing Measurement Capability Analysis (MCA). 4 ? Select appropriate type of control chart to be used ? Decide sampling plan (based on variance ponent analysis from PDC) – How samples are to be taken – Subgroup sample size (n) – Frequency of data collection ? Gather data to establish the control chart. A minimum of 30 subgroups is required over a time frame as determined by the sampling plan. ? Plot the data in time order on a Trend Chart How to Setup a Control Chart? 5 ? Check the control chart assumptions see your site statistician for advice if these assumptions are not met. ? Compute the control limits plot them on the trend chart ? Outliers identification exclusion – Exclude the Outof Control (OOC) points or outliers for which there are verified/confirmed special causes from the chart – Repute the control limits, excluding the OOC points – If there are fewer than 30 points remaining at any time, collect more data. It’s very important that the control limits are calculated using at least 30 subgroups. How to Setup a Control Chart? 6 ? Validate the puted control limits against data collected by replotting the control chart with data new control limits – Do the limits detect known problems? – Are the limits too sensitive? Would they flag problems you do not know how to react to? ? Use the control limits established to monitor the critical parameter identified ? For each every identified critical parameters, every machine should have a separate control chart with separately puted control limits How to Setup a Control Chart? 7 Control Chart Classifications Classifications of control charts are depending on the type of data ? Variables data – A characteristic measured on a continuous scale resulting in a numerical value – . Kerf Width, BLT, Void Size, Bond Pull Strength, Coplanarity, Ball Height, etc. ? Attributes data – A characteristic measured by of conforming nonconforming to a specification. Output is classified as pass/fail or accept/reject. – . Broken Wire, Lifted Bond, FM, Chipping, Bent Lead, etc. – Can be expressed in terms of fraction, percentage, count or DPM 8 Control Charts For Variables Control Chart Symbol Description Sample Size X R X Mean of Sample Must Be Equal (MeanRange) Chart R Range of Sample Must Be Equal X MR (Individual X Individual Measurement One Moving Range) Chart MR Range Between Individual Measurement Two X S (MeanStandard X Mean of Sample Must Be Equal Deviation) Chart S Standard Deviation of Sample Must Be Equal Note: For X MR Chart, MR Chart is optional. 9 Cont r ol Char t W hen to Us e? X R w hen s ub grou pin g o f s amples or (Me an Range) Char t me as ure ment s is a pp lic able n 1 0 X MR w hen s ub grou pin g is no t a pp lic able (In dividu al Movi ng du e t o sing le un it re ading may take Ra ng e) Char t a lon g t ime, un it re ading is e xr eme ly e xpensi ve , e t c. w hen it39。 s m on to hav e si ng le me as ure ment s pace d t ime apar t X S w hen s ub grou pin g o f s amples or (Me an S t and ar d me as ure ment s is a pp lic able De vi atio n) Char t n 1 0Control Charts For Variables Note: S Chart can also be used for any subgroup sample size (