Part Average Analysis PAA Rev. 2.0 / 2005

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Part Average AnalysisPAA Rev. 2.0 / 2005
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• 2. Mathematics part BCalculation rules for
  fault risk assessment and cpk-monitoring

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Risk figure Rk

• Calculate the risk figure Rk
• Significance of anomalies
• 1 6 lt ki lt 103 10 lt ki 1009
  ki gt 100
• 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

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Risk figure Rk

• Rk calculation, select component if RK ?
  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 lt1.67 is an unequivocal indicator for
  a preinjured product.
• With local cpk values lt 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 Mlokal ? 20 for all
  measuring parameters

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Risk figure Rk

• Calculation of the local gliding cpk value
• cpk (local) MIN(cpk, USL (local) cpk, LSL
  (local))
• For cpk (local) lt 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 lt cpk (local) lt 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.