A PCBA circuit board product screening method based on reliability requirements

Abstract

This invention discloses a PCBA (Printed Circuit Board Assembly) product screening method based on reliability requirements, comprising: assessing the early failure rate of the PCBA product; generating a reliability target value for the product based on the early failure rate and preset conditions; establishing a functional relationship between the reliability target value and the early failure rate, the stress intensity used for screening, and the screening time; and determining the optimal screening stress intensity and screening time in conjunction with the preset conditions. This method helps PCBA manufacturers to accurately determine screening results and costs; ensures that PCBA products maintain a reliable level while controlling screening costs; and helps PCBA manufacturers accurately screen products with potential failures, thereby improving product reliability and optimizing production efficiency.

Description

Technical Field

[0001] This invention relates to the field of integrated circuit technology, and in particular to a method for screening PCBA circuit board products based on reliability requirements. Background Technology

[0002] During mass production of PCBA circuit boards, a high early failure rate can occur due to manufacturers' lax quality control over raw materials and components, as well as human error and equipment inaccuracies during production. This impacts product reliability. Therefore, environmental stress screening tests are necessary to eliminate potentially faulty products before shipment, thereby reducing the early failure rate and improving overall product reliability.

[0003] Currently, the environmental stress screening test commonly used by PCBA circuit board manufacturers is conventional environmental stress screening. This screening method does not establish a quantitative relationship between the screening results and the product's reliability requirements. At the same time, the stress intensity and screening time used for screening are empirical values ​​based on relevant standards, which are not clearly related to the PCBA circuit board products. This makes it difficult to quantify the screening results and control the screening costs.

[0004] Currently, publicly available technologies in China do not cover quantitative environmental stress screening for PCBA circuit board products, nor do they address environmental stress screening related to product reliability. Therefore, accurately screening PCBA circuit board products exhibiting early failure rates has become a pressing issue for industry professionals. Summary of the Invention

[0005] The purpose of this invention is to provide a PCBA circuit board product screening method based on reliability requirements, which solves the problem in the prior art that it is difficult to accurately screen PCBA circuit board products with early failure rates.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] This invention provides a PCBA circuit board product screening method based on reliability requirements, comprising the following steps:

[0008] S1. Assess the early failure rate of PCBA circuit board products;

[0009] S2. Generate the product's reliability target value based on the early failure rate and preset conditions of the PCBA circuit board product;

[0010] S3. Establish a functional relationship between the reliability target value and the product's early failure rate, the magnitude of the stress intensity used for screening, and the screening time, and determine the optimal screening stress intensity and screening time in conjunction with the preset conditions.

[0011] Furthermore, the early failure rate of PCBA circuit board products in step S1 is evaluated in three ways, and the occurrence time of all failures of the product within a specific time period is recorded in each method.

[0012] 1) For new product models, evaluate them by analyzing fault data from similar or older models during use;

[0013] 2) Evaluate based on the preliminary test data generated from the preliminary test of the new model product;

[0014] 3) For products already in use, evaluate the fault data reported by after-sales service during product use.

[0015] Further, step S1 specifically includes:

[0016] For repairable PCBA circuit board products, the mean time between failures (MTBF) is used to represent product reliability; the MTBF is calculated as follows:

[0017] Suppose a repairable PCBA circuit board product experiences Z failures during use. After each failure is repaired, it is put back into use. The duration of each operation is measured as t1, t2, ..., t. Z Then its mean time between failures (MTBF) is:

[0018]

[0019] (1) In the formula, t i ∈(t1, t2, ..., t Z T represents the total operating time of the product, and Z represents the total number of failures.

[0020] The reciprocal of the mean fault interval is used as the early failure rate of the repairable PCBA circuit board product.

[0021] Furthermore, assessing the early failure rate of PCBA circuit board products also includes:

[0022] For unrepairable PCBA circuit board products, the mean time to failure (MTBF) is used to represent product reliability; the MTBF is calculated as follows:

[0023] Suppose N0 unrepairable PCBA circuit board products are tested under the same conditions, and their total failure times are measured to be t1, t2, ..., t. N0 Then its mean time to failure (MTTF) is:

[0024]

[0025] (2) In the formula, t i ∈(t1, t2, ..., t N0 N0 represents the total number of unrepairable PCBA circuit board products; the failure time is the product's lifespan, and the MTTF is the average lifespan of the PCBA circuit board product.

[0026] The reciprocal of the mean time to failure is taken as the early failure rate of the unrepairable PCBA circuit board product.

[0027] Furthermore, the preset conditions include: the number of temperature cycles and the random vibration time accepted by the manufacturer.

[0028] Further, step S3 includes:

[0029] S31. Based on the early failure rate and reliability target values ​​of PCBA circuit board products, obtain the environmental stress screening probability of PCBA circuit board products:

[0030] λ1=(1-P)λ0 (4)

[0031] In the formula, λ1 is the reliability target value; λ0 is the early failure rate; and P is the probability of screening out early product failures using environmental stress screening.

[0032] S32. Based on the probability P of early product failure screening, the relationship between environmental stress screening degree P1 and failure detection degree P2 is: P = P1 P2, thus obtaining the environmental stress screening degree P1; the failure detection degree P2 is determined by the PCBA circuit board manufacturer based on its own failure detection level and product structural characteristics.

[0033] S33. Based on the screening degree P1 of the environmental stress, the optimal number of temperature cycles N and random vibration time t are obtained.

[0034] Further, step S33 includes:

[0035] S331. Based on the screening degree P1 of the environmental stress, substitute it into formula (6) to obtain the optimal number of temperature cycles N:

[0036] P 1T = 1 - exp{-0.0017(ΔT + 0.6)} 0.6 [ln(e+v)] 3 -N} (6)

[0037] In equation (6), P1 is taken as P 1T ΔT is the temperature change value, v is the rate of temperature change, and e is the natural constant, all of which are known values; N is the number of temperature cycles, which is a value to be determined.

[0038] S332. Based on the screening degree P1 of the environmental stress, substitute it into formula (7) to obtain the optimal random vibration time t:

[0039] P 1G =1-exp(-0.0046G 1.71 t) (7)

[0040] In equation (7), P1 is taken as P 1G G is the technical specification of random vibration stress, representing the root mean square value of acceleration, both of which are known values; t is the technical specification of random vibration stress, representing the vibration time, which is a value to be determined.

[0041] Furthermore, step S33 also includes:

[0042] S333. When the number of temperature cycles N or the vibration time t exceeds or falls below the manufacturer's acceptable range, step S2 is executed again to generate a larger or smaller reliability target value. This process is repeated until the number of temperature cycles N or the vibration time t just meets the manufacturer's requirements.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] This invention provides a PCBA circuit board product screening method based on reliability requirements:

[0045] PCBA circuit board manufacturers determine the early failure rate of PCBA circuit boards not included in the screening process through evaluation. Then, based on the early failure rate and their own conditions, manufacturers propose product reliability targets. A functional relationship is then established between the reliability targets and the early failure rate, the stress intensity used in screening, and the screening time. Considering the manufacturer's own conditions, the optimal screening stress intensity and time are determined, clarifying the screening results and costs. This approach controls screening costs while ensuring PCBA circuit board product reliability. It helps PCBA circuit board manufacturers accurately screen products with potential failures, improve product reliability, and optimize production efficiency. Attached Figure Description

[0046] Figure 1 A flowchart of a PCBA circuit board product screening method based on reliability requirements provided in an embodiment of the present invention;

[0047] Figure 2 This is a flowchart for setting a reliability target value using screening time as an example, provided for an embodiment of the present invention. Detailed Implementation

[0048] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0049] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," "front end," "rear end," "both ends," "one end," and "the other end," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0050] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0051] Reference Figure 1 As shown, the present invention provides a PCBA circuit board product screening method based on reliability requirements, comprising the following steps:

[0052] S1. Assess the early failure rate of PCBA circuit board products;

[0053] S2. Generate the product's reliability target value based on the early failure rate and preset conditions of the PCBA circuit board product;

[0054] S3. Establish a functional relationship between the reliability target value and the product's early failure rate, the magnitude of the stress intensity used for screening, and the screening time, and determine the optimal screening stress intensity and screening time in conjunction with the preset conditions.

[0055] In this embodiment, based on the given reliability target value of the PCBA circuit board product, the early failure rate of the product is quantitatively evaluated, and a functional relationship is established between the reliability target value and the early failure rate of the product, the stress intensity used for screening, and the screening time. The stress intensity used for screening and the screening time are quantitatively calculated through the reliability target value and the early failure rate, so as to have a clear understanding of the screening results and screening costs, and control the screening cost while ensuring the reliability level of the PCBA circuit board product.

[0056] The three steps described above will be explained in detail below:

[0057] The first step is for PCBA circuit board manufacturers to assess the early failure rate of their products.

[0058] For new product models, evaluation can be conducted by analyzing fault data from similar or older models during use; alternatively, preliminary tests can be carried out on the new model, and the data from these tests can be used for evaluation. For products already in use, evaluation can be conducted by analyzing fault data from after-sales feedback during product use. A common characteristic of these data is that they record the occurrence time of all faults within a specific timeframe.

[0059] For repairable PCBA circuit board products, the Mean Time Between Failures (MTBF, in hours) can be used to represent product reliability. It is measured as the ratio of the total number of product lifespan units to the number of failures under specified conditions and within a specified time. Suppose a repairable PCBA circuit board product experiences Z failures during use, and is returned to use after each repair. The duration of each failure is measured as t1, t2, ..., t... Z Then its mean time between failures (MTBF) is:

[0060]

[0061] (1) In the formula, t i ∈(t1, t2, ..., t Z T represents the total working time of the product, and Z represents the total number of failures.

[0062] For irreparable PCBA circuit board products, the Mean Time To Failure (MTTF, in hours) can be used to represent product reliability. It is measured as the ratio of the total number of product lifespan units under specified conditions and within a specified time to the total number of failed products. Let N0 irreparable PCBA circuit board products be tested under the same conditions, and their total failure times be measured as t1, t2, ..., t... N0 Then its mean time to failure (MTTF) is:

[0063]

[0064] (2) In the formula, t i ∈(t1, t2, ..., t N0 Since the failure time is the lifespan of an unrepairable PCBA circuit board, the MTTF is the average lifespan of the PCBA circuit board.

[0065] The failure time of PCBA circuit board products follows an exponential distribution. After calculating the MTBF or MTTF of the PCBA circuit board products using equation (1) or equation (2), the early failure rate λ0(h) of the PCBA circuit board products can be calculated using the following formula. -1 )

[0066] or

[0067] The second step is for PCBA circuit board manufacturers to propose a reliability target value for their products, taking into account the early failure rate of the products and their own conditions.

[0068] After calculating the early failure rate λ0 of the PCBA circuit board product using equation (3), it is necessary to reduce the early failure rate to an acceptable level λ1(h) through environmental stress screening. -1 ), where λ1 is less than the early failure rate λ0, but cannot be less than 0. For example... Figure 2 As shown, if PCBA circuit board manufacturers do not have a specific concept of setting the value of λ1, they can first set an empirical value that is greater than 0 and less than λ1. If they find that the screening time exceeds their own acceptable range, they can appropriately increase the value of λ1; if they find that the screening time is within their own acceptable range, they can appropriately decrease the value of λ1 until the screening time just meets their own requirements. At this point, the optimal product reliability target value can be determined.

[0069] The third step is to establish a functional relationship between the reliability target value and the early failure rate of the product, the stress intensity used for screening, and the screening time. PCBA circuit board manufacturers, based on their own conditions, determine the optimal screening stress intensity and screening time, and clarify the screening results and screening costs.

[0070] The early failure rate λ0 and the reliability target value λ1 of PCBA circuit board products have the following mathematical relationship:

[0071] λ1=(1-P)λ0 (4)

[0072] Where P represents the probability of identifying early product failures using environmental stress screening.

[0073] The environmental stress screening probability P of PCBA circuit board products can be calculated using equation (4). P is related to the environmental stress screening degree P1 and the fault detection degree P2, and the relationship is as follows:

[0074] P = P1P2 (5)

[0075] Among them, the fault detection degree P2 is determined by the PCBA circuit board product manufacturer based on its own fault detection level and the structural characteristics of the product.

[0076] At this point, the screening degree P1 of the environmental stress can be obtained by equation (5).

[0077] For PCBA circuit board products, commonly used screening stresses include temperature cycling and random vibration. Manufacturers can choose either one as the screening stress based on the product's sensitivity to stress.

[0078] The main technical indicators of temperature cyclic stress are: temperature change range ΔT (°C), number of temperature cycles N, and temperature change rate v (°C / min).

[0079] The formula for calculating the screening degree of temperature cyclic stress is as follows:

[0080] P 1T = 1 - exp{-0.0017(ΔT + 0.6)} 0.6 [ln(e+v)] 3 -N} (6)

[0081] In equation (6), P1 is taken as P 1T ΔT is the temperature change value, v is the rate of temperature change, and e is the natural constant, all of which are known values; N is the number of temperature cycles, which is a value to be determined.

[0082] PCBA circuit board manufacturers can determine the temperature change range ΔT and temperature change rate v based on the product's ultimate working stress and environmental stress screening equipment technical parameters. Substituting these into equation (6) will yield the number of temperature cycles N, which can be used as the determination of the intensity of the temperature cycle stress.

[0083] In addition, the main technical indicators of random vibration stress are: root mean square acceleration G(g) and vibration time t(min). The formula for calculating the screening degree of random vibration stress is as follows:

[0084] P 1G =1-exp(-0.0046G 1.71 t) (7)

[0085] In equation (7), P1 is taken as P 1G G is the technical specification of random vibration stress, representing the root mean square value of acceleration, both of which are known values; t is the technical specification of random vibration stress, representing the vibration time, which is a value to be determined.

[0086] PCBA circuit board manufacturers can determine the root mean square value of acceleration G based on the product's ultimate working stress and environmental stress screening equipment technical parameters. Substituting this value into equation (7) will yield the vibration time t, at which point the intensity of random vibration stress and screening time can be determined.

[0087] Specifically, if PCBA circuit board manufacturers do not have a specific understanding of the value of λ1 and the previously set λ1 is an empirical value, if the calculated number of temperature cycles N or vibration time t exceeds the manufacturer's acceptable range, it is necessary to return to step two, reset a larger λ1 value, and repeat step three. If the calculated number of temperature cycles N or vibration time t is within the manufacturer's acceptable range, it is necessary to return to step two, reset a smaller λ1 value, and repeat step three. This process of repeating steps two to three continues until the calculated number of temperature cycles N or vibration time t exactly meets the manufacturer's requirements.

[0088] This invention establishes a functional relationship between the early failure rate and reliability target value of PCBA circuit board products, the early failure rate of the product, the magnitude of the stress intensity used for screening, and the screening time, by determining the early failure rate and reliability target value of the product. Based on the manufacturer's screening capability and the product's ultimate operating stress, the screening stress intensity and screening time are determined, and the optimal environmental stress screening scheme is generated under the premise of meeting the product reliability requirements.

[0089] For example:

[0090] Prior to implementing environmental stress screening, some usage data existed for a certain model of PCBA circuit board. The data showed that this model experienced 20 repairable early failures within 10,000 hours of operation. The manufacturer aimed to reduce this early failure rate to 10% through temperature cycling stress screening. -6 The known technical parameters of the screening equipment are: temperature range 80℃ (-20℃~60℃), temperature change rate 10℃ / min, and root mean square acceleration value 10g. These parameters are all less than the ultimate working stress of this model of product. The screening fault detection rate is 1.

[0091] The mean time between failures (MTBF) for this product model is:

[0092] MTBF = 10000 / 20 = 500h

[0093] The early failure rate for this product model was:

[0094]

[0095] The probability that environmental screening stress will detect early failures of this product model is:

[0096]

[0097] The screening degree of environmental screening stress is:

[0098] P1 = P / P2 = 0.995 / 1 = 0.995

[0099] The equation for solving the number of temperature cycles N is:

[0100] 0.995 = 1 - exp{-0.0017(80+0.6)} 0.6 [ln(e+10)] 3 -N}

[0101] Solving for the given information, we get:

[0102] N = 5

[0103] The equation for solving the random vibration time t is:

[0104] 0.995 = 1 - exp(-0.0046 × 10 1.71 t)

[0105] Solving for the given information, we get:

[0106] t = 22.46 min

[0107] Therefore, the optimal temperature cycling stress screening scheme for this model of PCBA circuit board product is: temperature change range 80℃, temperature change rate 10℃ / min, temperature cycle number 5 times; the optimal random vibration stress screening scheme is: root mean square acceleration value 10g, vibration time 22.46min.

[0108] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for screening PCBA circuit board products based on reliability requirements, characterized in that, Includes the following steps: S1. Assess the early failure rate of PCBA circuit board products; S2. Generate the product's reliability target value based on the early failure rate and preset conditions of the PCBA circuit board product; S3. Establish a functional relationship between the reliability target value and the product's early failure rate, the stress intensity used for screening, and the screening time, and determine the optimal screening stress intensity and screening time based on the preset conditions; step S3 includes: S31. Based on the early failure rate and reliability target values ​​of PCBA circuit board products, obtain the environmental stress screening probability of PCBA circuit board products: （4） In the formula, λ 1 represents the reliability target value; λ 0 represents the early failure rate; P This represents the probability of identifying early product failures using environmental stress screening. S32. Based on the probability of early product failures. P Screening degree with environmental stress P 1 and fault detection rate P The relation for 2: P = P 1 P 2. Determine the screening degree of environmental stress. P 1; The fault detection degree P 2. Determined by the PCBA manufacturer based on its own fault detection capabilities and product structure characteristics; S33, Based on the screening degree of the environmental stress. P 1. Determine the optimal number of temperature cycles N and the random vibration time t.

2. The PCBA circuit board product screening method based on reliability requirements according to claim 1, characterized in that, The early failure rate of PCBA circuit board products in step S1 is evaluated in three ways, and the occurrence time of all failures of the product is recorded within a specific time period. 1) For new product models, evaluate them by analyzing fault data from similar or older models during use; 2) Evaluate based on the preliminary test data generated from the preliminary test of the new model product; 3) For products already in use, evaluate the fault data reported by after-sales service during product use.

3. The PCBA circuit board product screening method based on reliability requirements according to claim 1, characterized in that, Step S1 specifically includes: For repairable PCBA circuit board products, the mean time between failures (MTBF) is used to represent product reliability; the MTBF is calculated as follows: Suppose a repairable PCBA circuit board product experiences an accident during use. Z Each time the fault occurred, the device was repaired and then put back into use. The duration of each operation was measured to be [duration missing]. t 1, t 2, ..., t Z Then its mean time between failures (MTBF) is: （1） (1) In the formula, t i ∈（t 1, t 2, ..., t Z ），T This represents the total working time of the product. Z This represents the total number of failures. The reciprocal of the mean fault interval is used as the early failure rate of the repairable PCBA circuit board product.

4. The PCBA circuit board product screening method based on reliability requirements according to claim 3, characterized in that, Assessing the early failure rate of PCBA circuit board products also includes: For unrepairable PCBA circuit board products, the mean time to failure (MTBF) is used to represent product reliability; the MTBF is calculated as follows: set up N Zero irreparable PCBA circuit board products were tested under the same conditions, and their total failure time was measured to be [time value missing]. t 1, t 2, ..., t N0 Then its mean time to failure (MTTF) is: （2） (2) In the formula, t i ∈（t 1, t 2, ..., t N0 ），N 0 represents the total number of irreparable PCBA circuit board products; failure time is the product's lifespan. MTTF This refers to the average lifespan of PCBA circuit board products; The reciprocal of the mean time to failure is taken as the early failure rate of the unrepairable PCBA circuit board product.

5. The PCBA circuit board product screening method based on reliability requirements according to claim 4, characterized in that, The preset conditions include: the number of temperature cycles and the random vibration time accepted by the manufacturer.

6. The PCBA circuit board product screening method based on reliability requirements according to claim 1, characterized in that, Step S33 includes: S331, Based on the screening degree of the environmental stress. P 1. Substitute into formula (6) to obtain the optimal number of temperature cycles N: （6） In formula (6), P 1 as P 1T ;Δ T This represents the temperature change value. v Here, is the rate of temperature change, and e is the natural constant; both are known values. N Let be the number of temperature cycles, and be the value to be determined. S332, Based on the screening degree of the environmental stress. P 1. Substitute into formula (7) to obtain the optimal random vibration time t: （7） In formula (7), P 1 as P 1G ; G The technical specifications for random vibration stress are represented by the root mean square value of acceleration, both of which are known values. t is the technical specification of random vibration stress, represents the vibration time, and is the value to be determined.

7. The PCBA circuit board product screening method based on reliability requirements according to claim 6, characterized in that, Step S33 further includes: S333. When the number of temperature cycles N or the vibration time t exceeds or falls below the manufacturer's acceptable range, step S2 is executed again to generate a larger or smaller reliability target value. This process is repeated until the number of temperature cycles N or the vibration time t just meets the manufacturer's requirements.

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