1、 JEDEC STANDARD Assessment of Average Outgoing Quality Levels in Parts Per Million (PPM) JESD16A (Revision of JESD16, March 1988) APRIL 1995 (Reaffirmed: September 2008) JEDEC SOLID STATE TECHNOLOGY ASSOCIATION NOTICE JEDEC standards and publications contain material that has been prepared, reviewed
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10、 or call (703) 907-7559 JEDEC Standard No. 16A -i- ASSESSMENT OF AVERAGE OUTGOING QUALITY LEVELS IN PARTS PER MILLION (PPM) Contents Page Introduction ii 1 Scope 1 2 Application 1 3 Reference publications 1 4 Definitions 1 5 Symbols 3 6 Assumptions 3 7 Procedures 5 7.1 Data accumulation for a single
11、 inspection. 6 7.2 Computing AOQ and variance for a single inspection. 6 7.3 Combining inspections within a group. 6 7.4 Combining groups within a class. 7 7.5 Combining classes. 7 7.6 Data exclusion. 8 7.7 Minimum total sample size. 8 7.7.1 Minimum total sample size criterion (graphic method). 9 7.
12、7.2 Minimum total sample size criterion (numeric method). 9 8 Reporting 10 Annexes A Examples 12 B Derivation of the minimum sample size criterion 17 C Derivation of the standard deviation of AOQ 21 D References 31 JEDEC Standard No. 16A -ii- ASSESSMENT OF AVERAGE OUTGOING QUALITY LEVELS IN PARTS PE
13、R MILLION (PPM) Introduction Improvements in manufacturing technology and methodology have resulted in corresponding quality improvements for electronic components. As a result, the traditional measure for reporting average quality levels in percent nonconforming needs to be replaced with a quantity
14、 more in line with the quality levels of today. That measure is parts-per-million or ppm. It is simply clearer to report estimated average component quality as 10 ppm, rather than the more cumbersome 0.001%. The ppm terminology applies to estimating the average outgoing quality (AOQ) level of a comp
15、onent, from lot acceptance results. This standard was developed to provide a uniform method of measurement and calculation of average outgoing quality levels. Minimum sample sizes and a method for aggregating data are provided. JEDEC Standard No. 16A Page 1 ASSESSMENT OF AVERAGE OUTGOING QUALITY LEV
16、ELS IN PARTS PER MILLION (PPM) (From JEDEC Council Ballot JCB-94-25 formulated under the cognizance of JC-13 Committee on Government Liaison.) 1 Scope This standard is intended to provide a uniform method of determining fraction nonconforming in finished components and to provide a standardized defi
17、nition of the quality index referred to as Average Outgoing Quality (AOQ). The method used here is primarily directed at components whose production or procured volume is large enough, during some predefined sampling period, to give statistically meaningful information. 2 Application This standard i
18、s intended to provide a method for the derivation and reporting of fraction non-conforming. The AOQ philosophy applies to the estimation of the average quality level of a product, not to lot acceptance plans. Since it is necessary to focus on accumulated lots to generate sufficient data for componen
19、t quality characterization, the method in this standard should not be used to establish ppm levels for individual lots or to form the basis for determining acceptability of product on a lot-by-lot or batch-by-batch basis. 3 Reference publications Publications referenced by this document are listed i
20、n annex D. 4 Terms and definitions For the purpose of this standard the following terms and definitions shall be used: 4.1 acceptance inspection: A sampling inspection or series of sampling inspections used to determine the suitability of a lot of material for shipment. 4.2 accept number (c): The ma
21、ximum number of nonconforming components in the sample for which acceptance of the lot is allowed under the sampling plan. JEDEC Standard No. 16A Page 2 4 Terms and definitions (contd) 4.3 average outgoing quality (AOQ): The average lot fraction nonconforming, in parts per million, from a series of
22、lots. 4.4 class: A categorization of similar characteristics for the purpose of reporting ppm nonconforming. Examples of classes include electrical (ppm2), visual/mechanical (ppm3), hermetic (ppm4), functional (ppm1). 4.5 fraction nonconforming: The unknown proportion nonconforming of the total popu
23、lation of components. Estimates of fraction nonconforming are derived from samples. 4.6 group: A subdivision of a class based on inspection conditions or criteria (e.g., device type, product family, test temperature, sample size). Lots that are members of the same group receive the same set of inspe
24、ctions in that group. 4.7 inspection: The assessment of a characteristic and its comparison to a standard. Examples of inspections include low temperature electrical test, room temperature test, visual inspection. 4.8 lot: An aggregate of components from which the sample is selected. 4.9 lot accepta
25、nce rate (LAR): An estimate of the probability of lot acceptance under the sampling plan, i.e., the probability that the sample contains no more than c nonconforming components. 4.10 nonconformance: A component characteristic that does not conform to an individual specified criterion. 4.11 nonconfor
26、mity: A single component that has one or more nonconformances. These nonconformities may be placed into classes for reporting purposes. 4.12 parts per million (ppm): The unit of measurement used to describe Average Outgoing Quality giving the number of nonconformities for each million units. 4.13 sa
27、mple period: The period of time selected by the manufacturer to accumulate data for the calculation and reporting of AOQ. JEDEC Standard No. 16A Page 3 5 Symbols The following symbols are used in this standard: Symbol Formula Definition AOQ True value of the average outgoing quality. AOQ Estimate of
28、 AOQ. c Sample plan acceptance number. L Total number of lots inspected. LR Total number of lots rejected. LAR 1(LR/L) Lot acceptance rate. m S/L Average sample size. N Total number of components in lots inspected. D Total number of nonconforming components found from all samples. S mxL Total number
29、 of components sampled. p D/S Fraction of nonconforming components found in all samples. UB1Upper bound of a one-sided confidence interval for AOQ. LB2Lower bound of a two-sided confidence interval for AOQ. UB2Upper bound of a two-sided confidence interval for AOQ. 2Variance of AOQ. 2Standard deviat
30、ion of AOQ. 6 Assumptions The following assumptions are used by this standard. Users should confirm that these assumptions are met for the component whose quality is to be reported. 6.1 Attribute sampling inspection is being conducted on components that have completed manufacturing processes affecti
31、ng the criteria being reported. 6.2 Equipment must be calibrated according to MIL-STD 45662, ANSI/ASQC Q9001/Q9002, or ANSI/ASQC-M1. Accuracy and precision must be in accordance with manufacturers internal documents or applicable procurement requirements. Statistical controls for the test process sh
32、all be in accordance with EIA 557. For the purpose of estimating AOQ, test equipment can be used interchangeably provided the requirements of this paragraph are satisfied. JEDEC Standard No. 16A Page 4 6 Assumptions (contd) 6.3 Lots of components that fail acceptance inspection are reprocessed 100%,
33、 and all nonconforming components are removed from the lot or the lot is removed from consideration for shipment and discarded. The nonconforming components that were removed may or may not be replaced by conforming components. In the case of c_0 sampling schemes, nonconforming components found in t
34、he sample of accepted lots are removed from the sample and may or may not be replaced by conforming components before the sample is returned to the lot for shipment. 6.4 All confirmed nonconforming components observed during the first submission to final acceptance inspection are included in the cal
35、culation of the total number of nonconforming components found in samples (D) unless excluded according to 7.6. Data from resubmitted lots are not used in the calculation of AOQ. 6.5 Single, multiple or skip lot sampling may be used if appropriate (e.g., multiple temperature or hermeticity inspectin
36、g). Double counting of nonconforming components is not allowed. 6.6 The total number of components sampled (S) shall include only components actually inspected. 6.7 AOQ values shall be reported for inspected characteristics only. Characteristics actually inspected and accompanying inspection results
37、 comprising the data for AOQ calculations shall be included in the manufacturing internal documentation and shall be available for review. 6.8 Nonconformities that are not component-related shall not be included in the calculation of AOQ. 6.9 A single component with nonconformities in more than one
38、class should be included only in the class that would have the most severe impact. 6.10 The estimator of AOQ given in equation (1) of 7.2 is appropriate if, for each lot, the sample size for the lot does not exceed 10% of the lot size. 6.11 The estimates of p and LAR shall be determined using the sa
39、me samples. JEDEC Standard No. 16A Page 5 7 Procedures Figure 1 Procedure Flow Chart JEDEC Standard No. 16A Page 6 7 Procedures (contd) 7.1 Data accumulation for a single inspection Using the results from the first submission into final acceptance inspection, sum the number of observed nonconforming
40、 components (D), sum the number of sampled components (S), sum the number of components in lots inspected (N), sum the number of lots rejected (LR), and sum the number of lots inspected (L). The sample period shall not exceed one year. 7.2 Computing AOQ and variance for a single inspection 7.2.1 Usi
41、ng the data totals from 7.1, the single inspection AOQ (AOQinspection) given by Schilling (1982) is: 6inspection10LARpAOQ = (1) 7.2.2 When c = 0, an approximation of the variance 2for AOQ, as defined in equation (1) is given in Annex C as: 2L)2mp(31LmL1)p(L32+ (2) If this approximation yields a nega
42、tive result, then use the exact formula in Annex C. 7.2.3 If the sample size for any lot exceeds 10% of the lot size, then AOQ defined in equation (1) should be multiplied by NS1 . Equation (1) then becomes: 6inspection10NS1LARpAOQ = (1) Similarly, equation (2) becomes: 123210NS12L)2mp(31LmL1)p(L +
43、(2) 7.3 Combining inspections within a group For groups with more than one inspection, compute AOQ for each inspection within a group. Next compute the overall group AOQ by summing the AOQs for each inspection. It is important that lots within a group receive the same set of inspections. This means
44、that a lot can belong to only one group within a class. JEDEC Standard No. 16A Page 7 7 Procedures (contd) 7.3.1 Example One group of components is tested at three temperatures (low, room, and high). Let the AOQ for each test be denoted as follows: AOQinspection1= AOQ for low temperature test, AOQin
45、spection2= AOQ for room temperature test, AOQinspection3= AOQ for high temperature test. The overall group AOQ is calculated as follows: AOQgroup= AOQinspection1+ AOQinspection2AOQinspection3(3) 7.4 Combining groups within a class To combine groups within a class such as electrical, mechanical, or h
46、ermetic, construct a weighted average according to the following guidelines. 7.4.1 For each group compute AOQgroup7.4.2 Let AOQgroup ibe the AOQ for group i and Ngroup ibe the total number of components in lots for group i. Also let there be k groups (e.g., i = 1 to k). Combine group AOQs within a c
47、lass using weighted averages according to the following algorithm: groupkgroup2group1groupkgroupkgroup2group2group1group1classN . N N)N x (AOQ )N x (AOQ )N x (AOQAOQ+= (4) 7.4.3 Let i2be the variance of the AOQ estimate for group i. The variance of AOQclassis then found from equation (4) to be: 2gro
48、upkgroup2group1groupk2groupk2group22group22group12group122wt)N . N (N)N x ( )N x ( )N x (+= (5) Note that this is not a weighted average of 2groupvalues. 7.5 Combining classes Classes such as electrical, mechanical, or other classes may be combined into a total AOQ by adding the class AOQs. Caution
49、should be used when combining classes. The result is a worst case estimate of AOQ and can be erroneously inflated if the volume of product in each class is significantly different. JEDEC Standard No. 16A Page 8 7.5 Combining classes (contd) EXAMPLE Let AOQelectrical= AOQ for the electrical class, AOQmechanical= AOQ for the mechanical class, AOQother= AOQ for some other class. Compute the total AOQ (AOQtotal) for all classes by AOQtotal= AOQelectrical+ AOQmechanical+ AOQother(6) 7.6 Data exclusion
