Circuit board life estimation method

Abstract

To provide a circuit board life estimation method that can easily detect a deterioration state of a circuit board on which electronic components are mounted and appropriately estimate a life of the circuit board without providing a special detection circuit or detection device.SOLUTION: In a circuit board life estimation method for estimating a life of solder joints of a circuit board constituting an electric circuit of an electronic device mounted on a vehicle, multiple regression analysis is performed using a plurality of types of data including at least one of a voltage applied to the electric circuit, a current flowing through the electric circuit, a temperature around the electric circuit, and a vehicle speed as explanatory variables, and a temperature rise of the circuit board is estimated on the basis of results of the multiple regression analysis and travel record data collected from commercially available vehicles, and the life of the solder joints is estimated on the basis of the estimated temperature rise, the number of trips of the vehicle, and a predetermined life prediction formula.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for estimating the lifespan of a circuit board, which detects or estimates the deterioration state or lifespan of a circuit board on which electronic components are mounted. [Background technology]

[0002] Patent Document 1 describes an electronic device that can detect in advance the breakage of a solder joint connecting an electronic component to a circuit board, and a method for detecting connection defects of electronic components using this electronic device. In the method for detecting connection defects of electronic components described in Patent Document 1, a chip component composed of a dielectric base sandwiched between opposing external electrodes is mounted on a circuit board on which an electronic component to be detected is mounted using an electronic component solder joint. The resistance value of the chip solder joint is then measured to detect the breakage life of the electronic component solder joint.

[0003] Patent Document 2 describes a semiconductor device that aims to suppress the concentration of stress and strain at the soldered connection with the motherboard. The semiconductor device described in Patent Document 1 has a semiconductor chip mounted on a first main surface of a wiring board, and a connection electrode portion that forms a soldered connection with a double-sided mounting type motherboard is provided on a second main surface of the wiring board. The wiring board has at least a core region with a thickness of 100 μm to 320 μm and a Young's modulus of 1000 kgf / mm. 2 The wiring board is made of the following materials: The thickness t (μm) of the core region and the Young's modulus E (kgf / mm 2 The constant "t × E" based on the above equation is made of materials with specifications that are greater than or equal to 200,000 and less than or equal to 4,640,000. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-205821 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-257283 Summary of the Invention [Problem to be solved by the invention]

[0005] In the method for detecting connection defects in electronic components described in Patent Document 1, a circuit designed to break earlier than the component to be protected is installed around the component to be protected on a circuit board, and the lifespan of the component to be protected is detected by monitoring the circuit. As a result, the method for detecting connection defects in electronic components described in Patent Document 1 is said to be able to accurately detect damage to the joint between the circuit board and the electronic component in advance.

[0006] However, in order to implement the method for detecting connection defects in electronic components described in Patent Document 1, a separate circuit (measuring circuit, detection circuit, detection device, etc.) for detecting the lifespan of the component to be protected must be implemented. This results in issues such as an increase in the number of components, an increase in the board mounting area, and a decrease in the flexibility of board design. This results in an increase in the size and cost of the device. Furthermore, when applying this method to products that are already mass-produced, the configuration of the product's circuit board must be significantly modified. Therefore, it is not easy to apply the method for detecting connection defects in electronic components described in Patent Document 1 to existing mass-produced products.

[0007] This invention was devised with an eye on the technical challenges described above, and aims to provide a method for estimating the lifespan of a circuit board that can easily detect the deterioration state of a circuit board on which electronic components are mounted and appropriately estimate the lifespan of the circuit board without providing a special detection circuit or detection device, etc. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides a method for estimating the life of a solder joint of a substrate that constitutes an electrical circuit of an electronic device mounted on a vehicle, which method comprises performing a multiple regression analysis using multiple types of data as explanatory variables, including at least the voltage applied to the electrical circuit, the current flowing through the electrical circuit, the temperature around the electrical circuit (not a temperature measured directly on the substrate), and vehicle speed, estimating the rise in temperature of the substrate based on the results of the multiple regression analysis and actual driving data collected and obtained from commercially available vehicles of the same model or type as the vehicle, and estimating the life of the solder joint based on the estimated rise in temperature, the number of trips of the vehicle, and a predetermined life prediction formula obtained by applying a predetermined accelerated testing method.

[0009] The present invention may also be directed to a circuit board life estimation device that estimates the life of solder joints of a circuit board that constitutes an electrical circuit of an electronic device mounted on a vehicle, the device including a control unit that controls the vehicle and estimates the life of the solder joints, wherein the control unit performs a multiple regression analysis using multiple types of data including at least the voltage applied to the electrical circuit, the current flowing through the electrical circuit, the temperature around the electrical circuit (not a temperature measured directly on the circuit board), and vehicle speed as explanatory variables, estimates a rise in temperature of the circuit board based on the results of the multiple regression analysis and actual driving history data collected and acquired from commercially available vehicles of the same model or type as the vehicle, and estimates the life of the solder joints based on the estimated rise in temperature, the number of trips of the vehicle, and a predetermined life prediction formula obtained by applying a predetermined accelerated testing method.

[0010] The life prediction formula in the present invention may be an acceleration formula determined in advance by applying the modified Coffin-Manson law (or a modified formula of the Coffin-Manson law). [Effects of the Invention]

[0011] This invention estimates the deterioration state of solder joints in a circuit board constituting an electric circuit of an electronic device mounted on a vehicle (e.g., an inverter control device mounted on a hybrid vehicle or an electric vehicle) and predicts its lifespan. To this end, this invention first performs a multiple regression analysis using vehicle behavior data or component behavior data acquired through vehicle evaluation experiments during design as explanatory variables. The vehicle behavior data (component behavior data) includes at least data on the voltage and current of the electric circuit, the temperature of the circuit board (not directly measured), and vehicle speed. Multiple types of data including any of these are used as explanatory variables in the multiple regression analysis. By performing the multiple regression analysis, a correlation equation between the vehicle behavior data (component behavior data) and the temperature rise of the circuit board is calculated. The temperature rise of the circuit board is estimated based on the results of the multiple regression analysis, i.e., the correlation equation calculated by the multiple regression analysis, and actual driving data or market data collected from commercially available vehicles of the same model or type as the target vehicle. Then, by applying the estimated temperature rise of the board and the number of trips of the vehicle (or the number of ON-OFF cycles) to a lifespan prediction formula, the deterioration state of the solder joints is diagnosed, i.e., the lifespan of the board is estimated.

[0012] The life prediction formula used to estimate the life of a circuit board as described above can be determined in advance by applying a known accelerated testing method, such as the modified Coffin-Manson law (or a modified Coffin-Manson law). Therefore, in this invention, the deterioration state of solder joints can be estimated using previously acquired vehicle behavior data (component behavior data) and driving performance data of commercially available vehicles. In other words, the life of a circuit board can be predicted without providing a life detection circuit or detection device.

[0013] Therefore, according to this invention, it is possible to easily detect the deterioration state of the solder joints of the circuit board, which is affected by the number of vehicle cycles and temperature, without providing any special detection circuit or detection device, and to appropriately estimate the lifespan of the circuit board. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram showing an example of a vehicle equipped with an electric circuit (board) of an electronic device to which the present invention is applied. [Figure 2] FIG. 2 is a block diagram for explaining an example of a process for estimating the temperature rise of a board by performing multiple regression analysis using vehicle behavior data (or component behavior data) acquired in a vehicle evaluation experiment or the like during design as explanatory variables. [Figure 3] FIG. 3 is a block diagram for explaining an outline of a process for estimating the life (solder thermal life) of a solder joint based on an estimated value of the rise in temperature of the board (estimated rise in board temperature), the number of trips (or number of cycles), and a life prediction formula. [Figure 4] FIG. 4 is a block diagram for explaining the specific flow of the process for estimating the life (solder thermal life) of a solder joint based on the estimated value of the rise in temperature of the board (estimated rise in board temperature), the number of trips (or number of cycles), and a life prediction formula. DETAILED DESCRIPTION OF THE INVENTION

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following embodiments of the present invention will be described with reference to the accompanying drawings. Note that the following embodiments are merely examples of specific embodiments of the present invention and are not intended to limit the scope of the present invention.

[0016] An example of a drive system and control system of a vehicle Ve that is the subject of an embodiment of the present invention is shown in Figure 1. In the example shown in Figure 1, the vehicle Ve is equipped with a hybrid drive unit 2 as a drive power source (POWER) 1. The vehicle Ve transmits torque output by the hybrid drive unit 2 to drive wheels 3, which then generate drive force.

[0017] The hybrid drive unit 2 is a drive unit made up of an engine (internal combustion engine) and a motor (not shown), and is equipped with an inverter 4, which is an "electronic device" for supplying power to the motor. The inverter 4 has a control circuit 4a, which is an "electrical circuit" for controlling the inverter 4, and a substrate 4b that constitutes the control circuit 4a. Furthermore, the substrate 4b has a "solder joint" (not shown) where electronic components (not shown) are joined to the substrate 4b by soldering.

[0018] The circuit board life estimation method and circuit board life estimation device in the embodiments of the present invention estimate the life of a "solder joint" of a "circuit board" that constitutes an "electric circuit" of an "electronic device," and the vehicle Ve targeted in the embodiments of the present invention may be equipped with a "circuit board" having a "solder joint" and an "electronic device." The "electronic device" is typically an "inverter" equipped with the above-mentioned "control circuit." Therefore, the vehicle Ve targeted in the embodiments of the present invention may be an "electric vehicle" or a "hybrid vehicle" equipped with a "motor" controlled by an "inverter" as a driving force source 1.

[0019] The drive wheels 3 generate driving force for the vehicle Ve by transmitting torque output from the drive power source 1. In the embodiment shown in Fig. 1, the drive wheels 3 are connected to the drive power source 1 (hybrid drive unit 2) via a transmission 5, a differential gear 6, and a drive shaft 7.

[0020] Furthermore, the vehicle Ve in the embodiment of the present invention is not limited to a front-wheel drive vehicle in which the output torque (driving torque) of the driving force source 1 is transmitted to the front wheels (driving wheels) 3, as in the example shown in FIG. 1 , and driving force is generated at the front wheels 3. For example, the vehicle Ve may be a rear-wheel drive vehicle in which driving torque is transmitted to the rear wheels 8 via a propeller shaft (not shown) or the like, and driving force is generated at the rear wheels 8. Alternatively, the vehicle Ve may be a four-wheel drive vehicle provided with a transfer mechanism (not shown) that transmits driving torque to both the front wheels 3 and the rear wheels 8, and generates driving force at both the front wheels 3 and the rear wheels 8.

[0021] In addition, the vehicle Ve in this embodiment of the present invention is equipped with a detection unit 9, a communication module (DCM) 10, and a control unit (ECU) 11 to estimate the life of the ``solder joint'' of the substrate 4b, as described below.

[0022] The detection unit 9 is a device or apparatus for acquiring various data and information required to control the vehicle Ve, and includes, for example, a power supply, a microcomputer, sensors, and an input / output interface. In particular, the detection unit 9 in this embodiment of the present invention detects various data for estimating the lifespan of the "solder joints" of the circuit board 4b. For example, the detection unit 9 includes a vehicle speed sensor (or wheel speed sensor) 9a for detecting the vehicle speed, a temperature sensor 9b for detecting temperature (e.g., the temperature around the control circuit 4a or the outside air temperature), a voltage sensor 9c for detecting the voltage applied to the control circuit 4a, and a current sensor 9d for detecting the current flowing through the control circuit 4a. The detection unit 9 also includes various sensors and measuring devices, such as a counter 9e for detecting the number of trips of the vehicle Ve or a switch sensor 9f for detecting the number of Ready ON-OFF cycles of the vehicle Ve. Furthermore, the detection unit 9 may include various sensors and measuring devices, such as an odometer 9g for calculating the accumulated mileage and a timer 9h for calculating the accumulated time, such as the control time and the driving time. The detection unit 9 is electrically connected to a control unit 11, which will be described later, and outputs an electrical signal corresponding to the detected or calculated values ​​of the various sensors, devices, and apparatuses described above to the control unit 11 as detection data.

[0023] The communication module 10 transmits and receives data between a control unit 11 (described later) and a server (not shown) installed outside the vehicle Ve. The communication module 10 is, for example, equipped with a wireless dedicated communication system (not shown) called a DCM (Data Communication Module) in the vehicle Ve, and transmits and receives various data between the control unit 11 and the external server using a dedicated communication line. Note that in an embodiment of the present invention, data may be transmitted and received using a general-purpose communication device (not shown) and a general mobile communication line. Alternatively, data may be transmitted and received using dedicated or general-purpose communication device installed in, for example, a dealer or repair shop of the vehicle Ve.

[0024] The control unit 11 is an electronic control device mainly composed of, for example, a microcomputer, and in this embodiment of the present invention, the control unit 11 controls the overall operation of the vehicle Ve. In particular, it estimates the lifespan of the "solder joints" of the substrate 4b in the control circuit 4a of the inverter 4. The control unit 11 receives various data detected or calculated by the detection unit 9 and various data for linking with the communication module 10. The control unit 11 performs calculations using the input data, pre-stored data, calculation formulas, etc. The control unit 11 then outputs the calculation results as control command signals to control the vehicle Ve. Note that while FIG. 1 shows an example in which one control unit 11 is provided, multiple control units 11 may be provided, one for each device or equipment to be controlled, or for each control content.

[0025] As described above, the circuit board life estimation method and circuit board life estimation device according to the embodiment of the present invention estimate the temperature of the circuit board 4b from information about surrounding vehicles ("commercially available vehicles") and calculate the life (solder thermal life) of the "solder joints" of the circuit board 4b without providing a life detection circuit or detection device to the circuit board 4b of the control circuit 4a or directly measuring the temperature of the circuit board 4b. In this case, the "commercially available vehicle" is, for example, a "general vehicle" of the same model or type as the vehicle Ve, already on the market and running on public roads. It may also be a "general vehicle" equipped with a "board" of the same model or type as the inverter 4 and the circuit board 4b of the control circuit 4a.

[0026] The lifespan of the "solder joints" of the circuit board 4b in the control circuit 4a varies mainly due to the influence of heat on the "solder joints." The lifespan of such "solder joints" is the solder thermal life of the circuit board 4b, and the main factors that determine the solder thermal life are the temperature of the circuit board 4b and the number of cycles. The number of cycles is the number of Ready ON-OFF cycles of the vehicle Ve and can be determined by detecting the number of trips of the vehicle Ve. The temperature of the circuit board 4b is determined by heat received from other surrounding components and devices and by its own heat generation. Therefore, it is possible to measure the temperature in advance (e.g., during the design stage) through evaluation tests of an actual vehicle and determine a correlation equation between the temperature of surrounding components and the temperature of the circuit board 4b. Then, by estimating the temperature of the circuit board 4b using information (driving performance data) monitored by a "commercial vehicle," the lifespan of the "solder joints" of the circuit board 4b can be estimated without installing a detection circuit or device.

[0027] Specifically, the control unit 11 of the vehicle Ve in the embodiment of the present invention is configured to execute the controls shown in the block diagrams of FIGS. 2, 3 and 4 below, for example.

[0028] The block diagram in Figure 2 shows an image of the process of estimating the temperature rise of the circuit board 4b by performing multiple regression analysis using component behavior data or vehicle behavior data acquired in vehicle evaluation experiments during the design of the vehicle Ve as explanatory variables. As shown in Figure 2, the vehicle behavior data (component behavior data) includes at least the voltage (voltage value) applied to the control circuit 4a, the current (current value) flowing through the control circuit 4a, the temperature around the control circuit 4a (not the temperature measured directly on the circuit board 4b), and the vehicle speed.

[0029] A multiple regression analysis is performed using multiple types of data including any of the above vehicle behavior data as explanatory variables, and a correlation equation between the vehicle behavior data and the temperature rise of the substrate 4b is calculated by this multiple regression analysis.

[0030] Then, based on the result of the above multiple regression analysis, that is, the correlation equation calculated by the multiple regression analysis, the estimated value of the temperature rise of the substrate 4b (estimated substrate temperature rise) ΔT PCB The estimated substrate temperature rise ΔT is calculated. PCB teeth, ΔT PCB =A1×X1+A2×X2+ … +A n ×X n Here, A(A1,A2,...A n ) is the gain obtained by multiple regression analysis, and X(X1,X2,…X n ) are multiple types of explanatory variables.

[0031] The block diagram in Figure 3 shows the estimated substrate temperature rise ΔT PCB 1 shows an outline of a process for estimating the life (solder thermal life) of the "solder joint" of the substrate 4b based on the number of trips (or number of cycles) of the vehicle Ve and a life prediction formula.

[0032] Based on the results of the multiple regression analysis as described above, the estimated substrate temperature rise ΔT PCBis calculated, and the number of trips (or the number of cycles) of the vehicle Ve is calculated. The number of trips is detected, for example, by the counter 9e of the detection unit 9. From the number of trips, the number of Ready ON-OFF cycles of the vehicle Ve is calculated.

[0033] And the estimated substrate temperature rise ΔT PCB The solder thermal life is estimated by applying the number of cycles and the number of cycles to the life prediction formula. The life prediction formula is an accelerated formula determined in advance by applying a predetermined accelerated test method. In the example shown in Figures 3 and 4, the life prediction formula is determined in advance by applying the modified Coffin-Manson law (or a modified formula of the Coffin-Manson law). In the life prediction formulas shown in Figures 3 and 4, N1 is the number of actual uses (number of cycles), N2 is the number of tests (number of cycles), ΔT1 is the actual use temperature difference (i.e., the estimated board temperature rise ΔT PCB ), ΔT2 is the test temperature difference (temperature rise), T 1max is the maximum temperature in actual use (i.e., the estimated temperature rise of the board ΔT PCB ), T 2max is the maximum temperature (maximum temperature rise) during the test. a is the activation energy (a constant depending on the solder material), and k is Boltzmann's constant.

[0034] The block diagram in Figure 4 shows the estimated substrate temperature rise ΔT PCB 1 shows a specific flow of the process of estimating the life (solder thermal life) of the "solder joint" of the substrate 4b based on the number of trips (or number of cycles) of the vehicle Ve and a life prediction formula.

[0035] First, as shown in Figure 2 above, the estimated substrate temperature rise ΔT PCB is calculated (PCU single item evaluation). At this time, as shown in the example in Figure 4, the estimated substrate temperature rise ΔT PCB may be calculated.

[0036] Next, the maximum temperature rise ΔT of the substrate 4b (i.e., the estimated temperature rise ΔTPCB The maximum temperature rise ΔT of the circuit board 4b is calculated based on the vehicle behavior data (component behavior data) and the results of the multiple regression analysis. PCB For example, the estimated substrate temperature rise ΔT PCB The maximum value, that is, the maximum temperature rise ΔT, is found from the above.

[0037] At the same time, the number of trips or cycles of the vehicle Ve can be calculated (market data). The number of trips (cycles) can be calculated using the logic of the cumulative number of Ready ON-OFFs of the vehicle Ve, which is recorded. Also, as shown in the example in Figure 4, As shown in the example of FIG. 4, the lifetime of the vehicle Ve (a predetermined period before the data acquisition date) and seasonal temperature cycles (such as the average annual temperature data in the main driving area) may also be taken into consideration.

[0038] As shown in Figure 3 above, the estimated substrate temperature rise ΔT PCB The solder thermal life is estimated by applying the number of cycles and the number of cycles to a life prediction formula. The estimated solder thermal life is compared with a design guaranteed value (design guaranteed life), for example, as a "life rate" relative to the design guaranteed value. Then, when the "life rate" determined from the solder thermal life reaches the design guaranteed value, or when the "life rate" exceeds a predetermined threshold, an alert may be issued or displayed indicating that the "solder joints" of the board 4b have deteriorated.

[0039] As described above, the circuit board life estimation method and circuit board life estimation device according to the embodiment of the present invention estimate the deterioration state of the "soldered joints" of the circuit board 4b constituting the "electric circuit" (in the above example, the control circuit 4a of the inverter 4) of the "electronic device" mounted on the vehicle Ve (in the above example, the inverter 4 mounted on the electric vehicle) and predict its life. Specifically, first, a multiple regression analysis is performed using vehicle behavior data or component behavior data acquired during vehicle evaluation experiments or the like during design as explanatory variables. The vehicle behavior data (component behavior data) includes at least data on the voltage, current, temperature (not directly measured on the circuit board), and vehicle speed of the electric circuit, and multiple types of data including any of these are used as explanatory variables. By performing the multiple regression analysis, a correlation equation between the vehicle behavior data (component behavior data) and the temperature rise of the circuit board 4b is calculated. The temperature rise of the circuit board 4b is estimated based on the correlation equation and actual driving data or market data collected from commercially available vehicles of the same model or type as the vehicle Ve. Then, by applying the estimated temperature rise of the board 4b (specifically, the maximum temperature rise ΔT) and the number of trips of the vehicle Ve (or the number of ON-OFF cycles) to a life prediction formula, the deterioration state of the "solder joints" is diagnosed, i.e., the life of the board is estimated.

[0040] The life prediction formula used to estimate the life of the substrate 4b as described above can be determined in advance by applying a known accelerated testing method, such as the modified Coffin-Manson law (or a modified Coffin-Manson law). Therefore, the substrate life estimation method and substrate life estimation device according to the embodiment of the present invention can estimate the deterioration state of the "solder joints" using previously acquired vehicle behavior data (component behavior data) and driving performance data of commercially available vehicles. In other words, the life of the substrate 4b can be predicted without providing a life detection circuit or detection device.

[0041] Therefore, according to the substrate life estimation method and substrate life estimation device in the embodiment of the present invention, it is possible to easily detect the deterioration state of a substrate on which electronic components are assembled without providing a special detection circuit or detection device, and to appropriately estimate the life of the substrate. [Explanation of symbols]

[0042] 1. Power source 2 Hybrid drive unit 3 Drive wheels (front wheels) 4. Inverter (INV) (electronic device) 4a (Inverter) control circuit (electrical circuit) 4b (control circuit) board 5-speed 6 Differential gear 7 Drive shaft 8 rear wheels 9. Detection unit 9a (detection part) vehicle speed sensor 9b (detection part) temperature sensor 9c (detection part) voltage sensor 9d Current sensor (detection section) 9e (detection part) counter 9f (detection part) switch sensor 9g (detector) odometer 9h (detector) timer 10 Communication Module (DCM) 11 Control Unit (ECU) Vehicle

Claims

[Claim 1] A method for estimating the lifespan of a solder joint of a substrate constituting an electric circuit of an electronic device mounted on a vehicle, comprising: performing multiple regression analysis using a plurality of types of data including at least one of the voltage applied to the electric circuit, the current flowing through the electric circuit, the temperature around the electric circuit, and the vehicle speed as explanatory variables; estimating the temperature rise of the substrate based on the results of the multiple regression analysis and driving performance data collected from commercially available vehicles; A life of the solder joint is estimated based on the estimated temperature rise, the number of trips of the vehicle, and a predetermined life prediction formula. A method for estimating the life of a substrate.

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