JB/T 7786-1995 Sampling method for inspection of power semiconductor devices
Some standard content:
Mechanical Industry Standard of the People's Republic of China
Sampling Method for Inspection of Power Semiconductor Devices
1 Subject Content and Scope of Application
This standard specifies the primary sampling plan, additional sampling plan and sampling procedure of the counting type. JB/T7786-1995
This standard applies to the factory (or batch) inspection, type (or periodic) test and delivery inspection of power semiconductor devices (including modules, components and accessories).
Referenced Standards
GB2828
GB2829
Counting Sampling Procedure and Sampling Table for Batch Inspection Counting Sampling Procedure and Sampling Table for Periodic Inspection GB4589.1 General Specification for Semiconductor Devices Discrete Devices and Integrated Circuits 3 Terminology
3.1 Unit Product
The basic unit divided for the needs of implementing sampling inspection. For example: a device, a component, a group of products, etc. 3.2 Inspection lot (abbreviation: lot)
Products collected for sampling inspection. 3.3 Batch (N)
Number of unit products contained in the batch.
3.4 Sample unit
Unit products extracted from the batch for inspection.
3.5 Sample
All sample units.
3.6 Sample size; sample quantity (n)
Number of sample units contained in the sample.
3.7 Nonconforming
The quality characteristics of the unit product do not meet the requirements. 3.8 Nonconforming product
One or more nonconforming unit products. 3.9 Number of nonconforming products per 100 units of product; batch quality (p) The total number of nonconforming products in the batch D divided by the batch N, and then multiplied by 100, that is: Number of nonconforming products per 100 units of product = Total number of nonconforming products in the batch (D) × 100 Batch (N)
3.10 Process average (p)
The average value of the batch quality of a series of first-submitted inspection batches. Note: The first-submitted inspection batch does not include the batch that was judged as nonconforming in the first inspection and was re-submitted for inspection after rework. Approved by the Ministry of Machinery Industry on October 9, 1995
Implementation on January 1, 1996
3.11 Acceptable quality level (AQL)
JB/T7786-1995
In sampling inspection, the process average upper limit of the continuous inspection batches that are considered acceptable. '3.12 Inspection; testing
The process of comparing unit products with technical requirements by measurement, test or other methods. 3.13 Counting inspection
The inspection to determine whether a unit product is qualified or unqualified according to a set or one technical requirement specified in the product technical standard. 3.14 Batch inspection
To determine whether the quality of each batch submitted for inspection meets the specified requirements, 100% inspection of the unit products in each batch or sampling from the batch is carried out.
3.15 Periodic inspection
In order to determine whether the stability of the production process meets the specified requirements within a specified period (specified by time or by the number of units of products manufactured), samples are taken from a batch or several batches that have passed the batch inspection. 3.16 Production finalization inspection
Periodic and batch inspection to determine whether a production line can batch produce products that meet the specified quality requirements. 3.17 Batch production inspection
Periodic and batch inspection to determine whether a production line can continue to batch produce products that meet the specified quality requirements after passing the production finalization inspection.
3. 18. Acceptable judgment number (Ac, c)
The maximum number of defective products allowed in the sample for making a batch acceptance judgment. 3.19. Unqualified judgment number (Re, r)
The minimum number of defective products not allowed in the sample for making a batch unqualified judgment. 3.20 Decision array
The qualified judgment number and the unqualified judgment number or the qualified judgment number series and the unqualified judgment number series are combined. 3.21 Sampling plan
The sample size or the sample size series and the decision array are combined. 3.22 Sampling procedure
The process of using the sampling plan to judge whether the batch is qualified or not. 3.23 Single sampling plan ||t t||A sampling plan composed of the sample size n and the judgment array [Ac, Re] or [c, r]. Note: A sampling plan is divided into three types according to the degree of strictness of the inspection: normal inspection, strict inspection and relaxed inspection. 3.24 Inspection level (IL)
The hierarchical correspondence between the batch size and the sample size of the batch submitted for inspection. 3.25 Sample size code
The letter code for the sample size determined according to the batch size and inspection level of the batch submitted for inspection. 3.26 Batch qualification probability (Pa)
For a batch with known quality, the probability of judging the batch as qualified according to a given sampling plan. 3.27 Random inspection characteristic curve ( OC curve)
The relationship curve between the probability of batch qualification and batch quality determined by a given sampling plan. 4 Procedure and implementation of sampling inspection
4.1 Procedure of sampling inspection
a) Clarify or formulate the criteria for the qualified product of the assessment unit: b) Form and propose inspection batches;
JB/T7786—1995
Specify the qualified quality level (AQL) and inspection level (IL); d) Determine the sample size code;
Search the sampling plan (n, Ac);
Draw sample n and inspect the sample;
g) Determine whether the inspection batch is qualified or unqualified. 4.2 Implementation of sampling inspection
4.2.1 The criteria for the qualified performance of the assessment unit's products are given in the product standards or order contracts and implemented through tests or experiments. 4.2.2 Composition of inspection lot
Inspection lot usually consists of unit products of the same design, type (basic model, size, host, etc.), production conditions and basically the same production time.
Inspection lot can be production lot, sales lot or transportation lot, or different from them. Inspection lot can be a production lot or several production lots.
4.2.3 Provision of acceptable quality level
Acceptable quality level (AQL) specifies different values according to the importance of product performance parameters or non-conformity (defect). The principles for determining the AQL value are:
a) The AQL value of basic performance parameters related to safety and reliability or fatal defects should be lower than the AQL value of general important performance parameters or serious defects;
b) The AQL value of important performance parameters or serious defects should be lower than the AQL value of general performance parameters or minor defects; the AQL value of devices, components or modules should not be greater than the AQL value of the whole machine; c)
d) The AQL value of discrete devices should not be greater than the AQL value of components or modules; the AQL value of parts and accessories constituting devices should not be greater than the AQL value of devices. e)
4.2.4 Provisions on inspection levels
The inspection level (IL) is divided into three levels: general inspection level 1, I, I and four levels: special inspection level S-1, S-2, S-3, S4. Unless otherwise specified, the general inspection level 1 should usually be adopted. In the implementation of sampling inspection, if the level of inspection level is not indicated or explained, it should be considered as general inspection level 1. Special inspection levels are used when the batch size is small or a small sample is required. When the batch size N and the qualified quality level AQL are constant, the sample size n and the discrimination power vary with the inspection level. The sample size and discrimination power gradually increase or increase from left to right with the following inspection levels: S-1, S-2, S-3, S-4, I, I, I
In addition to being related to the batch size and sample size, the inspection level should also be specified separately according to the importance of product performance parameters or defects in principle. In addition, when using special inspection levels, attention should be paid to coordinating with the qualified quality level to prevent the contradiction that the minimum sample at a smaller AQL is larger than the maximum sample obtained by the inspection level (such as S-1 or S-2). 4.2.5 Retrieval of sampling plan
a) Unless otherwise specified, the normal inspection sampling plan should be used at the beginning of the inspection; the sample size code is obtained by looking up Table 1 based on the batch size N of the inspection batch and the specified inspection level IL; b)
The corresponding sample size n is found in Table 2 based on the obtained sample size code; d) The judgment array [Ac, Re] is found in Table 2 based on the sample size n and the specified qualified quality level AQL. Thus, the specific sampling plan (n, Ac, Re) is obtained.
If the intersection of the row where n is located and the column where AQL is located in Table 2 is an arrow, the first judgment array pointed by the arrow and the sample size of the row where this judgment array is located should be used. When the sample size n corresponding to the first judgment array pointed by the arrow is equal to or greater than the batch size N, then N is the sample, that is, all unit products in the batch are inspected. 4.2.6 Sampling and inspection
Samples should be randomly selected from the inspection batch. The sampling method should be representative of the batch quality. When the inspection batch consists of several layers, samples should be drawn in layers according to the proportion of the layer size to the batch. The batch samples are composed of samples from each layer of the batch. According to the 21
JB/T7786—1995
inspection items, inspection methods and qualified criteria for unit products specified in the product standard or order contract, all unit products in the sample are inspected one by one, and the total number of unqualified products (d) is accumulated. 4.2.7 Rules for judging the qualification of the batch
After the sample is inspected, if the number of unqualified products in the sample is less than or equal to the qualified judgment number (dAc replaces d≥Re to judge the batch as a non-conforming batch, and the two are completely equivalent.
4.2.8 Strict inspection and relaxed inspection
When the batch is first submitted for inspection using the normal inspection one-time sampling plan, if it is unqualified after full inspection screening or repair, when it is submitted for inspection again, if the strict inspection is used, the strict inspection one-time sampling plan specified in Table 4 of GB2828 or the sampling plan that is one level stricter than the AQL of the normal inspection shall be used.
The conditions from normal inspection to relaxed inspection and from relaxed inspection to normal inspection shall comply with 4.6.3 (transfer rules) of GB2828. The relaxed inspection one-time sampling plan shall be implemented in accordance with Table 5 of GB2828. 5.1 Overview
The batch allowable non-conforming rate (LTPD) sampling plan is mainly used for periodic inspection of power semiconductor devices. Table 3 gives the LTPD sampling plan (single sampling) for large batches (N>10n) with a confidence level of 90%; Table 4 gives the LTPD sampling plan for batches less than or equal to 200. Table 5 is compiled by selecting the LTPD value from Table 3, according to the qualified judgment number c=2 and the inspection level I of the sample size close to the AQL sampling plan. This table gives two sampling plans corresponding to the AQL value and the LTPD value. This table is limited to sampling plans with a qualified judgment number not greater than 4 and a batch size not greater than 150,000.
Table 6 gives the LTPD sampling plan for four confidence levels. Sampling plans with a confidence level less than 90% are usually used for mechanical, climatic and environmental tests and durability tests.
5.2 Sample size n and search procedure for LTPD sampling plan For sampling with batches greater than 200, the sample size n can be found in Table 3 or Table 6 based on the specified LTPD value and the selected qualified judgment number c. For sampling of batches less than or equal to 200, in principle, the sample size n is determined by the batch N, the specified LTPD and the selected qualified judgment number c. The search procedure is: first, find the sub-table that needs to be further searched in Table 4; in this sub-table, find the batch column that is equal to or closest to the inspection batch batch N (if the actual batch is between the two columns, you can choose any one of the two columns); in the column where the batch column is located, find the LTPD value that is equal to or closest to the specified LTPD value, and the n corresponding to the left end of the row where this LTPD value is located is the required sample size. If there is no LTPD value in the batch column that is equal to or less than the specified LTPD value, 100% inspection should be used. The qualified judgment number of the LTPD sampling plan (once) is usually selected as 1, and the maximum does not exceed 4. 5.3 Additional sampling and batch qualified judgment rules
When sampling for the first time, after inspecting the sample, if the number of defective products d in the sample is less than or equal to the qualified judgment number c (dc, the batch is judged as unqualified. When d,>c appears after the first sampling of sample ni, an additional sampling plan can be adopted to select a new qualified judgment number cz greater than c: and the corresponding sample size n2 (total sample size), but it can only be added once. The additional samples must undergo all inspections of unqualified items.
The additional sampling plan only inspects the additional sample size △n (nz一n,), and the unqualified judgment number in △n is d2. If d,+d≤cz, the batch is judged as a qualified batch. If di+dz>c2, the batch is judged as an unqualified batch. When using the additional sampling plan, the same LTPD and confidence level (CL) as the first sampling plan must be maintained. The qualified judgment number c of the first sampling plan is usually selected as 1, and the qualified judgment number of the additional sampling plan is selected as 2 (see Table 7). 5.4 Strict inspection
The strict inspection is carried out one level stricter than the specified LTPD value in Table 3 or Table 4. 22
Batch range
91~150
151~280
281~500
501~1200
12013200
3201~10000
10001~35000
35001~150000
150001~500000Www.bzxZ.net
>500001
Note: Use the first
JB/T7786—1995
Table 1 Sample size code
Special inspection level
Table 2 Normal inspection single sampling plan
Ac ReAc Re
sampling plan,
if the sample size is equal to or greater than the batch
+=use the first sampling plan 22
General inspection level
AcReAcRe
then conduct 100% inspection.
Qualified
Constant (e)
(r=e+1)
JB/T7786-1995
Table 3 LTPD sampling plan for large batches
(confidence level 90%)
The sample size is determined based on the Poisson index
binomial limit.
The minimum quality level required for the acceptance of an average of 19/20 batches (approximately equal to (AQL)) is shown in brackets for reference only. Table 4
Hypergeometric sampling plan for small batches with batches less than or equal to 20040
JB/T7786—1995
Table 4 (complete)
①This table gives the LTPD values corresponding to a specific primary sampling plan (qualified judgment number, sample size and batch size). ②This table is calculated for batches less than or equal to 200 based on the hypergeometric distribution (exact theory). 150
③The LTPD of a sampling plan is defined as: the corresponding percentage defective rate when the probability of acceptance of the batch is 0.10 under the plan. The LTPD defined in this way is not necessarily the achievable batch defective rate involving the batch. 25
JB/T7786—1995
Table 5AQL sampling plan and LTPD sampling plan 0.15
Note: The sample size obtained by the sampling plan in this table is closest to the sample size given by the inspection level 1, 0.65
sample size code C to N (5~500). Table 6 LTPD sampling plan with different confidence levels
Confidence level
Sample size (n)
Sampling once (n)
Additional sampling (n,)
Additional number (n :-n)
Confidence level (CL)
Additional notes:
JB/T7786—1995
Table 7 Commonly used LTPD additional sampling plans
Sample size
This standard is proposed and managed by the Xi'an Power Electronics Technology Research Institute of the Ministry of Machinery Industry. This standard is drafted by the Xi'an Power Electronics Technology Research Institute. The main drafter of this standard. Qin Xianman
Qualified judgment number
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