Part Average Analysis PAA Rev. 2.0 / Mathematics part B Calculation rules for fault risk assessment and cpk-monitoring P AA

Risk figure R k Calculate the risk figure Rk Significance of anomalies 1 = Relevance of observed parameters (type) (U, I, t,....), depends on the circuit design 9 = Clear indication of technical defect (Leacage current, Voltage Drop) 3 = High probability to indicate technical defect (default value) 2 = Low probability to indicate technical defect 1 = Less relevance The relevance should be selected by the development engineers

Risk figure R k R k calculation, select component if R K  9 Statistical Process Analysis (SPA) cpk – monitoring for systematic failure detection The focus of the PAA is the detection of stochastical failures in standard processes. Systematical failures in manufacturing processes can be observed by a wide range of parameter distribution (  ) or continuous parameter drifts which lead to a reduction of the process ability characteristics cp and cpk. (VDA 4) For instance, ceramic capacitors can break by mistakes in the SMD assembly or in thermal processes with which the signal / noise ratio decreases and thus the distribution of the characteristic voltage values shows burglary cp-and cpk values. In this case the decreased cpk value with <1.67 is an unequivocal indicator for a preinjured product. With local cpk values < 2 and a symmetrical parameter distribution the quality of abnormal parts detection by PAA will be reduced. Notice, it has turned out suitable to calculate the local cpk value in supplement to the PAA, and to submit to a monitoring as in the following is described. The following definitions are based on standard processes with N  400 and M lokal  20 for all measuring parameters

Risk figure R k Calculation of the local gliding cpk value cpk (local) = MIN(cpk, USL (local); cpk, LSL (local)) For cpk (local) < 1.67 index (red): Process ability is insufficient; corrective action items should be defined. The product must be seperated in a stock, and can be requalified as good part by screening methods or by risk evaluation of the quality engineers, when the real cause for the bad cpk value has been found out. For cpk (local)  2.0 index (green): Process ability is sufficient. For 1.67 < cpk (local) < 2 index (yellow): Process ability is poor; corrective action items should be defined. In case, that there is no valid reglementation it is allowed to ship the product to the customer. But it is neccessary to sign up the product for a good tracebility in prevention of possible later reclaims. When the quality is recorded please give a hint, that the PAA observation level was reduced.