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Defects

Introduction

"Zero Defects" is Step 7 of "Philip Crosby's 14 Step Quality Improvement Process" .A performance standard and methodology developed by Philip B. Crosby that states if people commit themselves to watching details and avoiding errors, they can move closer to the goal of zero.

DPU and DPMO

DPU

DPU or Defects Per Unit is the average number of defects observed when sampling a population.

DPU = Total Number of Defects / Total population

Consider 100 electronic assemblies going through a functional test. If 10 of these fail the first time around, we have a first pass yield of 90%. Let's say the 10 fails get reworked and re-tested and 5 pass the second time around; the 5 remaining fails pass on the third attempt. Feel free to work out how this would look as a rolling yield.

DPMO

Defects per million opportunities (DPMO) is the average number of defects per unit observed during an average production run divided by the number of opportunities to make a defect on the product under study during that run normalized to one million.Defects Per Million Opportunities. Synonymous with PPM.

To convert DPU to DPMO, the calculation step is actually DPU/(opportunities/unit) * 1,000,000.

Yield

Measurement of yield through the process identifies possible opportunities for improvement (OFI’s).

Brainstorm possible reasons why the yield changes through the process and over time

measure yield at every step in the process, not just at the end.

understand the inputs of the process, do not focus just on the outputs.

talk to mixed groups of people involved in the process.

Traditional Yield traditional yield of the process, inclusive of any rework ((Total out/Total In)*100)

First Time Yield yield exclusive of rework -gives 1st time yield of each process step

Rolled Throughput Yield yield of whole process, exclusive of rework -gives the cumulative 1st time yield at any step in a process.

Normalised Yield “average” yield of whole process sometimes used to calculate sigma metric