CN101937212A - Process detection method and device - Google Patents

Abstract

The invention provides process detection method and device. The method comprises the steps of: obtaining the quality characteristic values of a product; computing the average value and standard deviation of the quality characteristic values of the product; setting an offset coefficient, wherein if the computed average value of the quality characteristic values of the product is less than a specification target value, the offset coefficient is associated with a specification lower limit, or else, the offset coefficient is associated with a specification upper limit; computing a process capability index which is associated with the specification upper limit, the specification lower limit, the offset coefficient and the standard deviation of the quality characteristic values of the product; and analyzing the technical capability of the process according to the process capability index. The process detection method and device can correctly analyze the state of the process and correct the difference or abnormal phenomenon in the process by adopting corresponding measures, so as to make the work procedure in a control (stable) state.

Description

Process detection method and device

Technical field

The present invention relates to field of quality control, particularly a kind of process detection method and device.

Background technology

Quality management mainly is by collecting data, disposal data, find out the rule of fluctuation, normal fluctuation is controlled at bottom line, eliminating the unusual fluctuations that systemic reason causes.Actual mass property that records and relevant criterion are compared, and take corresponding measure to correct to the difference or the abnormal occurrence that occur, thereby make operation be in state of a control, this process just is called quality control.Here the operation of indication is meant the process of five gross combined factors effects such as operator, machine, starting material, process and production environment, just the production run of product quality.Product quality is exactly the general performance of each qualitative factor role in the operation.

Process capability and process capability index are the important parameters in the Quality Control Technology, have reflected the production run state of product objectively.

Process capability also claims process capability, is meant that the crudy of process satisfies the ability of technical standard, and process capability is that expression production run outwardness a parameter of disperseing.For any production run, the quality of product always exists dispersedly, if process capability is high more, then the dispersion of the quality characteristic value of product will be more little; If process capability is low more, then the dispersion of the quality characteristic value of product will be big more.When process is in when stablizing, the quality characteristic value of product has 99.7% to drop in the scope of μ ± 3 σ, and wherein μ is the mean value of quality characteristic value, and σ is the standard deviation of quality characteristic value, so represent process capability with 6 times standard deviation (6 σ) usually.

The process capability index also claims process capability index, is meant operation in certain hour, is in the actual working ability under the state of a control (steady state (SS)).It is the intrinsic ability of operation, and it is the ability that operation is ensured the quality of products in other words.Process capability index reflection process capability satisfies the degree of the technical standard (specification of product) of product quality.At statistical Process Control (SPC) reference manual (second edition (Chinese), publish in July, 2005, DaimlerChrysler Corp, Ford Motor Company and General Motor corporation (GM) all) can find the introduction of relevant process capability and process capability index in chapter 1 and the chapter 4.

When the mean value (distribution center) of the quality characteristic value of product is identical with the specification desired value of product, the process capability index is represented with Cp, process capability index Cp common-used formula (1) expression:

$\mathrm{Cp}=\frac{\mathrm{USL}-\mathrm{LSL}}{6\mathrm{\σ}}---\left(1\right)$

Wherein, USL is upper specification limit value (upper specification limit), and LSL is specification lower limit (lowerspecification limit), and σ is the standard deviation of the quality characteristic value of product, (USL-LSL) is the deviation range that specification allows.σ is more little, and process capability index Cp value is big more, and then the technical capability of process is good more.

Specification desired value when mean value (distribution center) the skew product of the quality characteristic value of product, the process capability index is represented with Cpk, process capability index Cpk common-used formula (2) or (3) expression, following explanation for convenience, the process capability index Cpk in the formula (2) ₁Expression, the process capability index Cpk in the formula (3) ₂Expression:

Cpk ₁＝Cp(1-k ₁)

$k_1=\frac{|T-\mathrm{\μ}|}{(\mathrm{USL}-\mathrm{LSL})/2}---\left(2\right)$

Wherein, USL is the upper specification limit value, and LSL is the specification lower limit, and σ is the standard deviation of the quality characteristic value of product, k ₁Be deviation ratio, T is the specification desired value, and μ is the mean value of the quality characteristic value of product.

${\mathrm{Cpk}}_2=\min (\mathrm{CpU},\mathrm{CpL})$

$=\min (\frac{\mathrm{USL}-\mathrm{\μ}}{3\mathrm{\σ}},\frac{\mathrm{\μ}-\mathrm{LSL}}{3\mathrm{\σ}})---\left(3\right)$

Wherein, USL is the upper specification limit value, and LSL is the specification lower limit, and σ is the standard deviation of the quality characteristic value of product, and μ is the mean value of the quality characteristic value of product.

In general, process capability index Cpk value is big more, and then the technical capability of process is good more.Table 1 has provided at LSL=0, USL=6, and T=3, σ=0.5, under the situation of Cp=2, computation process Capability index Cpk ₁And Cpk ₂Value:

Table 1

	LSL						T						USL
														μ	0	0.5	1	1.5	2	2.5	3	3.5	4	4.5	5	5.5	6
Cpk 1	0	0.33	0.67	1	1.33	1.67	2	1.67	1.33	1	0.67	0.33	0
														Cpk 2	0	0.33	0.67	1	1.33	1.67	2	1.67	1.33	1	0.67	0.33	0

As can be seen from Table 1, when specification desired value T is the central value of specification lower limit LSL and upper specification limit value USL, calculation process Capability index Cpk ₁And Cpk ₂Be identical, can be according to process capability index Cpk ₁Or Cpk ₂Come the state (technical capability of process in other words) of analytic process.

Yet, when specification desired value T is not the central value of specification lower limit LSL and upper specification limit value USL, that is to say that specification desired value T departs from the center of specification lower limit LSL and upper specification limit value USL, according to process capability index Cpk ₁Or Cpk ₂Come the state of analytic process to go wrong.Table 2 has provided at LSL=0, USL=6, and T=2, σ=0.5, under the situation of Cp=2, computation process Capability index Cpk ₁And Cpk ₂Value:

Table 2

	LSL				T								USL
														μ	0	0.5	1	1.5	2	2.5	3	3.5	4	4.5	5	5.5	6
Cpk 1	0.67	1	1.33	1.67	2	1.67	1.33	1	0.67	0.33	0	0	0
														Cpk 2	0	0.33	0.67	1	1.33	1.67	2	1.67	1.33	1	0.67	0.33	0

As can be seen from Table 2, process capability index Cpk ₁Or Cpk ₂The fine or not degree that can not reflect the technical capability of process objectively, for instance, in average value mu=0 when (LSL is identical with the specification lower limit), the process capability index should minimum (be 0, the technical capability of process be the poorest), and process capability index Cpk ₁In average value mu=0 o'clock is not minimum.In average value mu=2 when (T is identical with the specification desired value), the process capability index should maximum (be Cp, the technical capability of process be best), and process capability index Cpk ₂In average value mu=3 o'clock maximum.

Therefore, when specification desired value T departs from the center of specification lower limit LSL and upper specification limit value USL, application process Capability index Cpk ₁Or Cpk ₂The state of analytic process can be inaccurate.

Summary of the invention

What the present invention solved is when the specification desired value departs from the center of specification lower limit and upper specification limit value, and the state of using existing process Capability index analytic process can inaccurate problem.

For addressing the above problem, embodiment of the present invention provides a kind of process detection method, comprising:

Obtain the quality characteristic value of product;

Calculate the mean value and the standard deviation of the quality characteristic value of described product;

Deviation ratio is set, wherein, if the mean value of the quality characteristic value of the product of calculating gained is less than the specification desired value, then described deviation ratio is related with the specification lower limit, if the mean value of the quality characteristic value of the product of calculating gained is greater than the specification desired value, then described deviation ratio is related with the upper specification limit value;

The computation process Capability index, the deviation ratio of described process capability index and upper specification limit value, specification lower limit and described setting and to calculate the standard deviation of quality characteristic value of product of gained related;

Technical capability according to the process capability index analysis process of calculating gained.

For addressing the above problem, embodiment of the present invention also provides a kind of process pick-up unit, comprising:

Acquiring unit obtains the quality characteristic value of product;

First computing unit calculates the mean value and the standard deviation of the quality characteristic value of described product;

The unit is set, deviation ratio is set, wherein, if the mean value of the quality characteristic value of the product of calculating gained is less than the specification desired value, then described deviation ratio is related with the specification lower limit, if the mean value of the quality characteristic value of the product of calculating gained is greater than the specification desired value, then described deviation ratio is related with the upper specification limit value;

Second computing unit, computation process Capability index, the deviation ratio of described process capability index and upper specification limit value, specification lower limit and described setting and to calculate the standard deviation of quality characteristic value of product of gained related;

Analytic unit is according to the technical capability of the process capability index analysis process of calculating gained.

Compared with prior art, said process detection method and device are according to the mean value of the quality characteristic value of product and the relation of specification desired value, the deviation ratio of difference setting up procedure Capability index, therefore, do not need to consider whether the specification desired value of product departs from the center of upper specification limit value and specification lower limit, just can obtain accurately to reflect the process capability index of status of processes according to the deviation ratio of described setting, and then the technical capability of analytic process exactly.

Description of drawings

Fig. 1 is the process flow diagram of the process detection method of embodiment of the present invention;

Fig. 2 is the structural representation of the process pick-up unit of embodiment of the present invention.

Embodiment

Embodiment of the present invention is according to the mean value of the quality characteristic value of product and the relation of specification desired value, and the deviation ratio of difference setting up procedure Capability index is to obtain accurately to reflect the process capability index of status of processes.

Fig. 1 is the process flow diagram of the process detection method of embodiment of the present invention, comprises the steps:

Step S11 obtains the quality characteristic value of product.

Step S12 calculates the mean value and the standard deviation of the quality characteristic value of described product.

Step S13, deviation ratio is set, wherein, if the mean value of the quality characteristic value of the product of calculating gained is less than the specification desired value, then described deviation ratio is related with the specification lower limit, if the mean value of the quality characteristic value of the product of calculating gained is greater than the specification desired value, then described deviation ratio is related with the upper specification limit value.

Step S14, computation process Capability index, the deviation ratio of described process capability index and upper specification limit value, specification lower limit and described setting and to calculate the standard deviation of quality characteristic value of product of gained related.

Step S15 is according to the technical capability of the process capability index analysis process of calculating gained.

Each step to the process detection method of embodiment of the present invention is elaborated below.

Step S11 obtains the quality characteristic value of product.Described product can be the making result of a certain step in the production run, also can be the net result that obtains after finishing in steps.The quality characteristic value of described product is a detected value of all products being tested (for example reliability testing) or sample testing acquisition, has reflected the mass property of the product that production run obtains objectively.The quality characteristic value of product can be the data value of Normal Distribution such as length, weight, time, intensity for example, also can be the data value of obeying binomial distribution such as unacceptable product number, percent defective, number of defects for example.With the semiconductor fabrication process is example, and the quality characteristic value of product can be serviceable life, inefficacy product ratio of precision, the chip of the degree of depth, the photoetching alignment of growth for Thin Film thickness, etching or the like.

Step S12 calculates the mean value and the standard deviation of the quality characteristic value of described product.The average value mu of the quality characteristic value of product and standard deviation sigma are calculated according to formula (4):

$\mathrm{\μ}=\frac{1}{n}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{X}_i$

$\mathrm{\σ}=\sqrt{\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\frac{{(X_i-\mathrm{\μ})}^2}{n-1}}---\left(4\right)$

Wherein, X _iBe the quality characteristic value of product, n is the product sum.

Step S13, deviation ratio is set, wherein, if the mean value of the quality characteristic value of the product of calculating gained is less than the specification desired value, then described deviation ratio is related with the specification lower limit, if the mean value of the quality characteristic value of the product of calculating gained is greater than the specification desired value, then described deviation ratio is related with the upper specification limit value.

According to the average value mu of the quality characteristic value of product and the relation of specification desired value T, deviation ratio is set respectively, deviation ratio k is provided with according to formula (5):

$k=\left\{\begin{array}{cc}\frac{T-\mathrm{\&mu;}}{T-\mathrm{LSL}}& \mathrm{\&mu;}\&le;T\\ \frac{\mathrm{\&mu;}-T}{\mathrm{USL}-T}& \mathrm{\&mu;}>T\end{array}\right.$ Or $k=\left\{\begin{array}{cc}\frac{T-\mathrm{\&mu;}}{T-\mathrm{LSL}}& \mathrm{\&mu;}<T\\ \frac{\mathrm{\&mu;}-T}{\mathrm{USL}-T}& \mathrm{\&mu;}\&GreaterEqual;T\end{array}\right.---\left(5\right)$

Wherein, USL is the upper specification limit value, and LSI is the specification lower limit, and T is the specification desired value.When the average value mu of the quality characteristic value of product equates with specification desired value T, deviation ratio k=0.

Step S14, computation process Capability index, the deviation ratio of described process capability index and upper specification limit value, specification lower limit and described setting and to calculate the standard deviation of quality characteristic value of product of gained related.

Process capability index Cp, Cpk ₄(for the ease of following comparison, process capability index Cpk in the present embodiment ₄, to be different from process capability index Cpk ₁, Cpk ₂) calculate according to formula (6):

$\mathrm{Cp}=\frac{\mathrm{USL}-\mathrm{LSL}}{6\mathrm{\&sigma;}}---\left(6\right)$

Cpk ₄＝Cp(1-k)

Wherein coefficient of deviation k calculates gained for step S13.When the average value mu of the quality characteristic value of product equates with specification desired value T, deviation ratio k=0, process capability index Cpk ₄=Cp.

Table 3 has provided at LSL=0, USL=6, and T=3, σ=0.5, under the situation of Cp=2, computation process Capability index Cpk ₁, Cpk ₂And Cpk ₄Value:

Table 3

	LSL						T						USL
														μ	0	0.5	1	1.5	2	2.5	3	3.5	4	4.5	5	5.5	6
Cpk 1	0	0.33	0.67	1	1.33	1.67	2	1.67	1.33	1	0.67	0.33	0
														Cpk 2	0	0.33	0.67	1	1.33	1.67	2	1.67	1.33	1	0.67	0.33	0
Cpk 4	0	0.33	0.67	1	1.33	1.67	2	1.67	1.33	1	0.67	0.33	0

As can be seen from Table 3, when specification desired value T is the central value of specification lower limit LSL and upper specification limit value USL, calculation process Capability index Cpk ₁, Cpk ₂And Cpk ₄Be identical.

Table 4 has provided at LSL=0, USL=6, and T=2, σ=0.5, under the situation of Cp=2, computation process Capability index Cpk ₁, Cpk ₂And Cpk ₄Value:

Table 4

	LSL				T								USL
														μ	0	0.5	1	1.5	2	2.5	3	3.5	4	4.5	5	5.5	6

Cpk 1	0.67	1	1.33	1.67	2	1.67	1.33	1	0.67	0.33	0	0	0
														Cpk 2	0	0.33	0.67	1	1.33	1.67	2	1.67	1.33	1	0.67	0.33	0
Cpk 4	0	0.5	1	1.5	2	1.75	1.5	1.25	1	0.75	0.5	0.25	0

As can be seen from Table 4, when specification desired value T departs from the center of specification lower limit LSL and upper specification limit value USL, calculation process Capability index Cpk ₁, Cpk ₂And Cpk ₄Be differentiated.

Consolidated statement 3 and 4, table 5 have provided process capability index Cpk ₁, Cpk ₂And Cpk ₄Characteristics relatively:

Table 5

	Cpk 1	Cpk 2	Cpk 4
				Is Cp independent of T (Cp and T are irrelevant)?	Be	Be	Be
When μ=T, the Cpk maximum (=Cp)?	Be	Not	Be
				When μ=LSL or μ=USL, Cpk=0?	Not	Be	Be
When μ-LSL=3 σ or USL-μ=3 σ, Cpk=1?	Not	Be	Not
				Is with T center symmetry or proportional symmetry?	Be	Not	Be
Cpk is with | T-μ | increase and linearity reduces?	Be	Not	Be
				Is suitable T the central value of USL and LSL and the center that T departs from USL and LSL?	Not	Not	Be

Consolidated statement 4 and 5 can be seen, when specification desired value T departs from the center of specification lower limit LSL and upper specification limit value USL, compared to process capability index Cpk ₁And Cpk ₂, process capability index Cpk ₄The technical capability that more can reflect process objectively.Process capability index Cpk ₄Both be applicable to that specification desired value T departed from the situation at the center of specification lower limit LSL and upper specification limit value USL, be applicable to also that specification desired value T was the situation of the central value of specification lower limit LSL and upper specification limit value USL.

Step S15 is according to the technical capability of the process capability index analysis process of calculating gained.The grade that can in advance the process capability index be divided into the technical capability intensity of some expression processes, the corresponding process capability index range of each grade; Then according to the process capability index range at the process capability index place of calculating gained, the technical capability intensity of decision process; According to the technical capability intensity of judging, take corresponding measure so that process is in state of a control.Table 6 has provided the grade of process capability index, the technical capability intensity of correspondence and an example of the corresponding measure that can take:

Table 6

Correspondingly, embodiment of the present invention also provides a kind of process pick-up unit, as shown in Figure 2, comprising: acquiring unit 21, first computing unit 22, unit 23, second computing unit 24 and analytic unit 25 are set.

Acquiring unit 21 obtains the quality characteristic value of product.With the semiconductor fabrication process is example, and the quality characteristic value of product can be serviceable life, inefficacy product ratio of precision, the chip of the degree of depth, the photoetching alignment of growth for Thin Film thickness, etching or the like.

First computing unit 22, the quality characteristic value of the product that obtains according to described acquiring unit 21 calculates the mean value and the standard deviation of the quality characteristic value of described product.Wherein, the mean value of the quality characteristic value of product and standard deviation are calculated according to formula (4).

Unit 23 is set, the mean value of the quality characteristic value of the product that calculates according to described first computing unit 22 and the relation of specification desired value, deviation ratio is set, wherein, if the mean value of the quality characteristic value of the product of calculating gained is less than the specification desired value, then described deviation ratio is related with the specification lower limit, if the mean value of quality characteristic value of product that calculates gained is greater than the specification desired value, then described deviation ratio is related with the upper specification limit value.Deviation ratio is provided with according to formula (5).

Second computing unit 24, the computation process Capability index, the standard deviation of described process capability index and upper specification limit value, specification lower limit and the described quality characteristic value that deviation ratio that unit 23 is provided with, product that described first computing unit 22 calculates be set is related.The process capability index calculates according to formula (6).

Analytic unit 25 calculates the technical capability of the process capability index analysis process of gained according to described second computing unit 24.Analytic unit 25 can be divided into the process capability index grade of the technical capability intensity of some expression processes in advance, the corresponding process capability index range of each grade; Then according to the process capability index range at the process capability index place of calculating gained, the technical capability intensity of decision process; And, take corresponding measure so that process is in state of a control according to the technical capability intensity of judging.

In sum, said process detection method and device are according to the mean value of the quality characteristic value of product and the relation of specification desired value, the deviation ratio of difference setting up procedure Capability index, therefore, do not need to consider whether the specification desired value of product departs from the center of upper specification limit value and specification lower limit, just can obtain accurately to reflect the process capability index of status of processes according to the deviation ratio of described setting.

In process of production, use said process detection method and device, the state of analytic process takes corresponding measure to correct at difference that occurs in the process or abnormal occurrence exactly, thereby makes operation be in control (stablizing) state.

Though the present invention discloses as above with preferred embodiment, the present invention is defined in this.Any those skilled in the art without departing from the spirit and scope of the present invention, all can do various changes and modification, so protection scope of the present invention should be as the criterion with claim institute restricted portion.

Claims (10)

1. a process detection method is characterized in that, comprising:

Obtain the quality characteristic value of product;

Calculate the mean value and the standard deviation of the quality characteristic value of described product;

Deviation ratio is set, wherein, if the mean value of the quality characteristic value of the product of calculating gained is less than the specification desired value, then described deviation ratio is related with the specification lower limit, if the mean value of the quality characteristic value of the product of calculating gained is greater than the specification desired value, then described deviation ratio is related with the upper specification limit value;

The computation process Capability index, the deviation ratio of described process capability index and upper specification limit value, specification lower limit and described setting and to calculate the standard deviation of quality characteristic value of product of gained related;

Technical capability according to the process capability index analysis process of calculating gained.

2. process detection method as claimed in claim 1, the deviation ratio of described process capability index and process capability index are:

$\mathrm{Cp}=\frac{\mathrm{USL}-\mathrm{LSL}}{6\mathrm{\&sigma;}}$

Cpk ₄＝Cp(1-k)

$k=\left\{\begin{array}{cc}\frac{T-\mathrm{\&mu;}}{T-\mathrm{LSL}}& \mathrm{\&mu;}\&le;T\\ \frac{\mathrm{\&mu;}-T}{\mathrm{USL}-T}& \mathrm{\&mu;}>T\end{array}\right.$ Or $k=\left\{\begin{array}{cc}\frac{T-\mathrm{\&mu;}}{T-\mathrm{LSL}}& \mathrm{\&mu;}<T\\ \frac{\mathrm{\&mu;}-T}{\mathrm{USL}-T}& \mathrm{\&mu;}\&GreaterEqual;T\end{array}\right.$

Wherein, Cp, Cpk ₄Be the process capability index, USL is the upper specification limit value, and LSL is the specification lower limit, and σ is the standard deviation of the quality characteristic value of described product, and k is a deviation ratio, and T is the specification desired value, and μ is the mean value of the quality characteristic value of described product.

3. process detection method as claimed in claim 1 is characterized in that described specification desired value departs from the center of upper specification limit value and specification lower limit.

4. process detection method as claimed in claim 1 is characterized in that, described specification desired value is the central value of upper specification limit value and specification lower limit.

5. process detection method as claimed in claim 1 is characterized in that, described technical capability according to the process capability index analysis process of calculating gained comprises:

The grade that in advance the process capability index is divided into the technical capability intensity of a plurality of expression processes, the corresponding process capability index range of each grade;

According to the process capability index range at the process capability index place of calculating gained, the technical capability intensity of decision process;

According to the technical capability intensity of described judgement, take corresponding measure so that process is in state of a control.

6. a process pick-up unit is characterized in that, comprising:

Acquiring unit obtains the quality characteristic value of product;

First computing unit calculates the mean value and the standard deviation of the quality characteristic value of described product;

The unit is set, deviation ratio is set, wherein, if the mean value of the quality characteristic value of the product of calculating gained is less than the specification desired value, then described deviation ratio is related with the specification lower limit, if the mean value of the quality characteristic value of the product of calculating gained is greater than the specification desired value, then described deviation ratio is related with the upper specification limit value;

Second computing unit, computation process Capability index, the deviation ratio of described process capability index and upper specification limit value, specification lower limit and described setting and to calculate the standard deviation of quality characteristic value of product of gained related;

Analytic unit is according to the technical capability of the process capability index analysis process of calculating gained.

7. process pick-up unit as claimed in claim 6 is characterized in that, the deviation ratio of described process capability index and process capability index are:

$\mathrm{Cp}=\frac{\mathrm{USL}-\mathrm{LSL}}{6\mathrm{\&sigma;}}$

Cpk ₄＝Cp(1-k)

$k=\left\{\begin{array}{cc}\frac{T-\mathrm{\&mu;}}{T-\mathrm{LSL}}& \mathrm{\&mu;}\&le;T\\ \frac{\mathrm{\&mu;}-T}{\mathrm{USL}-T}& \mathrm{\&mu;}>T\end{array}\right.$ Or $k=\left\{\begin{array}{cc}\frac{T-\mathrm{\&mu;}}{T-\mathrm{LSL}}& \mathrm{\&mu;}<T\\ \frac{\mathrm{\&mu;}-T}{\mathrm{USL}-T}& \mathrm{\&mu;}\&GreaterEqual;T\end{array}\right.$

Wherein, Cp, Cpk ₄Be the process capability index, USL is the upper specification limit value, and LSL is the specification lower limit, and σ is the standard deviation of the quality characteristic value of described product, and k is a deviation ratio, and T is the specification desired value, and μ is the mean value of the quality characteristic value of described product.

8. process pick-up unit as claimed in claim 6 is characterized in that described specification desired value departs from the center of upper specification limit value and specification lower limit.

9. process pick-up unit as claimed in claim 6 is characterized in that, described specification desired value is the central value of upper specification limit value and specification lower limit.

10. process pick-up unit as claimed in claim 6 is characterized in that, described analytic unit comprises according to the technical capability of the process capability index analysis process of calculating gained:

The grade that in advance the process capability index is divided into the technical capability intensity of a plurality of expression processes, the corresponding process capability index range of each grade;

According to the process capability index range at the process capability index place of calculating gained, the technical capability intensity of decision process;

According to the technical capability intensity of described judgement, take corresponding measure so that process is in state of a control.

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