SPC基本认识(1)

7_Jun1StatisticProcessControl&IndexofProcessCapabilityJocelynChenRA/QRAQRATrainingCourse---7_Jun2WSESCSMPT1T2…………………TnMPProcessPerformanceProcessCapabilityTotalDimensionMeasurementCriticalDimensionPpkvalue“*”“p”NewProductQualificationFlowProcessDimensionCpkvalue“p”SPC7_Jun3Ppk與Cpk之差異PpkThe6rangeofaprocess’stotalvariation,whereisusuallyestimatedbythesamplestandarddeviation--Thisisthevariationduetobothcommonandspecialcause.CpkThe6rangeofaprocess’sinherentvariation,forstatisticallystableprocessesonly,whereisusuallyestimatedby--Thatportionofprocessvariationduetocommoncausesonly.2dR1)(12nxxnii2dR1)(12nxxnii7_Jun4Accuracy&Precision7_Jun5ProcessCapabilityIndexesCapabilityofAccuracy%100,minˆLSLmmUSLmCaXmUSLLSLˆ7_Jun6•評估產品製程平均與規格中心之偏移量•製程偏移越大,Ca值越大•Ca值0時,代表製程平均偏上限=0時,代表製程平均與規格中心一致0時,代表製程平均偏下限•改善方向(1)調整模具,製程參數,材料等以達到規格中心值(2)與客戶討論變更規格中心值,但需考慮組裝性問題(3)與客戶討論變更規格公差,但需考慮組裝性問題-允差設計,決定最適之規格公差||5.05.0||25.025.0||125.0125.0||CaCaCaCaCa意義說明AgradeBgradeCgradeDgrade7_Jun7ProcessCapabilityIndexesCapabilityofPrecisionXmUSLLSLˆˆ6LSLUSLCp67_Jun833.168ˆ6LSLUSLCp0.166ˆ6LSLUSLCp67.064ˆ6LSLUSLCp7_Jun9Cp意義說明•評估產品製程變異量(製程穩定狀況)•製程變異越大,Cp值越小•Cp值均為一正值•改善方向(1)調整模具,製程參數,材料等以降低製程變異(2)與客戶討論變更規格公差,但需考慮組裝性問題AgradeBgradeCgradeDgrade00.133.100.167.133.167.1CpCpCpCp7_Jun10ProcessCapabilityIndexespapkCCC1One-sidedspecificationtolerancesTwo-sidedsymmetricalspecificationtolerancesˆ3ˆUSLCpuˆ3ˆLSLCpl),min(plpupkCCCplpuppkCCCCorTwo-sidedspecificationtolerances(includedsymmetricalandunsymmetrical)7_Jun11Cpk意義說明•評估產品製程精準度的綜合指標•Cpk值0代表製程平均已偏移超出規格上限或規格下限1.0代表製程以達到3的水準1.33代表製程以達到4的水準•改善方向(1)調整模具,製程參數,材料等以降低製程變異(2)分別觀察Ca值與Cp值,就不足的部份改善.通常先求穩定製程(提高Cp值),再求減少偏移量(降低Ca值)7_Jun12CpkSigmaExpectedProbabilityofnonconforming2.0062ppb1.6650.57ppm1.33463ppm1.0032700ppm0.67245500ppm0.331317311ppmWhereppm=partspermillionandppb=partsperbillion.ProcessCapability