Joint evaluation method, evaluation resistor, and joint evaluation device

Abstract

To enable non-destructive evaluation of an evaluation target.SOLUTION: A junction evaluation method for evaluating a junction (46, 48) between a resistor (14, 102) and a substrate 12 on which the resistor (14, 102) is mounted includes a temperature acquisition step P4 of acquiring the temperature of the resistor (14, 102) obtained when the resistor (14, 102) is energized, and an evaluation step P5. In the evaluation step P5, the joint state is evaluated on the basis of the temperature of the resistors (14, 102) acquired in the temperature acquisition step P4 and the temperature indicated by the resistor (14, 102) when the resistor (14, 102) is energized in the state of the reference junction (46, 48).SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a joint evaluation method, an evaluation resistor, and a joint evaluation device. [Background technology]

[0002] Patent Document 1 discloses a method for evaluating the state of soldered joints, which evaluates cracks in soldered joints that join chip components to a substrate.

[0003] The method for evaluating the solder joint condition involves polishing the chip component and then observing the polished cross section. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-133830 A Summary of the Invention [Problem to be solved by the invention]

[0005] The above-mentioned method for evaluating the solder joint condition is performed by destructive testing, and therefore, when performing evaluation using the method for evaluating the solder joint condition, the evaluation target cannot be maintained in its original state.

[0006] Therefore, an evaluation target that has been evaluated using the method for evaluating the state of soldered joints cannot be reused.

[0007] Therefore, an object of the present disclosure is to enable evaluation of an evaluation object in a non-destructive manner. [Means for solving the problem]

[0008] According to one aspect of the present disclosure, there is provided a joint evaluation method for evaluating a joint between a resistor and a substrate on which the resistor is mounted, the method comprising: a temperature acquisition step of acquiring a temperature of the resistor obtained when current is applied to the resistor; and an evaluation step of evaluating a joint state of the joint based on the temperature of the resistor acquired in the temperature acquisition step and a temperature exhibited by the resistor when current is applied to the resistor in a reference state of the joint; a reference acquisition step of acquiring a reference value indicating a temperature of the resistor obtained when a current is applied to the resistor in a reference state serving as a reference for the bonding state; A joint evaluation method comprising: The temperature acquisition step acquires a comparison value indicating the temperature of the resistor obtained with current flowing through the resistor in a comparison state in which the junction is compared with the reference state as a reference, and the evaluation step evaluates the state of the junction based on the reference value and the comparison value. The reference acquisition step determines a reference thermal resistance of the junction in the reference state using the reference value, the temperature acquisition step determines a comparative thermal resistance of the junction in the comparative state using the comparison value, and the evaluation step evaluates the junction state of the junction based on the reference thermal resistance and the comparative thermal resistance. Effect of the Invention

[0009] When a current is applied to a resistor mounted on a board, heat is generated in the resistor's resistive element. The generated heat is dissipated to the board through the joint that joins the resistor to the board. The temperature of the resistor stabilizes when the amount of heat generated by the resistive element and the amount of heat dissipated to the board are in balance.

[0010] Here, if the bonding condition of the joint changes, the amount of heat dissipated to the board also changes. Therefore, by using the temperature of the resistor acquired in the temperature acquisition step and the temperature indicated by the resistor when current is applied to the resistor in a reference bonding condition, it is possible to evaluate the change in the bonding condition that has occurred at the bonding part.

[0011] Therefore, it is possible to perform the evaluation of the evaluation object non-destructively, which makes it possible to reuse the evaluation object evaluated by this joint evaluation method. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view of an evaluation target used to explain the basic principle of the joint evaluation method. [Diagram 2] FIG. 2 is a perspective view showing an evaluation resistor and a substrate used in the bond evaluation method according to the first embodiment. [Diagram 3] FIG. 3 is a perspective view showing a state in which an evaluation resistor used in the bond evaluation method according to the first embodiment is mounted on a board. [Figure 4]FIG. 4 is a cross-sectional view of an evaluation object used in the bond evaluation method according to the first embodiment. [Diagram 5] FIG. 5 is a diagram showing each step of the bonded portion evaluation method according to the first embodiment. [Figure 6] FIG. 6 is an explanatory diagram showing how a current is passed through the evaluation resistor according to the first embodiment and a voltage is measured. [Figure 7] FIG. 7 is a graph showing changes in temperature and resistance value of the evaluation resistor according to the first embodiment when a constant current is applied to the evaluation resistor. [Figure 8] FIG. 8 is a graph showing changes in voltage when a constant current is applied to the evaluation resistor according to the first embodiment. [Figure 9] FIG. 9 is a conceptual diagram showing thermal characteristics of an evaluation target according to the first embodiment, and is a cross-sectional view showing a state before a reliability test. [Figure 10] FIG. 10 is a conceptual diagram showing the thermal characteristics of the evaluation target according to the first embodiment, and is a cross-sectional view showing the state after the reliability test. [Figure 11] FIG. 11 is an explanatory diagram showing a relational expression among the temperature, heat generation amount, and thermal resistance of the evaluation resistor to be evaluated according to the first embodiment. [Figure 12] FIG. 12 is a diagram showing the relationship between the crack rate and the rate of change in thermal resistance in the joints to be evaluated according to the first embodiment. [Figure 13] FIG. 13 is a block diagram showing an example of a hardware configuration of a bond evaluation device according to the second embodiment. [Figure 14] FIG. 14 is a functional block diagram showing an example of a functional configuration of a bond evaluation device according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] A substrate is provided inside electronic devices. A printed wiring board with integrated wiring and lands is used as the substrate. Electronic components such as ICs, capacitors, and resistors are mounted on this substrate to form an electronic circuit.

[0014] This board is subjected to a reliability test with electronic components mounted thereon. Examples of the reliability test include an overload test in which a voltage exceeding the rated voltage is repeatedly applied to the electronic components a predetermined number of times, and a rapid temperature change test in which the board is suddenly changed between low and high temperatures a predetermined number of times in a non-energized state. Other examples of the reliability test include a moisture resistance test in which the board is left in a humid environment for a certain period of time in a powered state, a rated terminal temperature test in which the terminals are heated to the maximum rated temperature and held there for a certain period of time in a powered state, and a high temperature exposure test in which the board is left in a high temperature environment for a certain period of time in a powered state.

[0015] Some of these reliability tests involve repeated thermal expansion and contraction between the electronic components and the board. In tests involving repeated thermal expansion and contraction, the bonding condition of the joints that join the electronic components to the board may change due to the thermal expansion and contraction.

[0016] One example of a change in the bonding state of a bonded portion is the occurrence of cracks, and therefore, after a reliability test, an evaluation is performed on the state of cracks that may occur in the bonded portion.

[0017] A known method for evaluating cracks is to polish the test object and inspect the cross section. This method destroys the test object, and therefore it is not possible to perform continuous reliability tests on the same test object.

[0018] On the other hand, an evaluation method using X-ray CT is considered as a non-destructive inspection that does not destroy the evaluation target, but the evaluation method using X-ray CT takes time and makes it difficult to evaluate components placed in the center of the board.

[0019] Therefore, an example for solving at least one of these problems will be described below. The following will explain the example with reference to the drawings.

[0020] <Basic principle> First, the basic principle of the joint evaluation method will be explained with reference to the drawings.

[0021] Fig. 1 is a cross-sectional view of an evaluation target used to explain the basic principle of the bond evaluation method. The basic principle of the bond evaluation method will be explained using Fig. 1.

[0022] 1, an evaluation object 10 used in the bond evaluation method includes a substrate 12 and a resistor 14 mounted on the substrate 12. A printed wiring 18 is integrally formed on a surface 16 of the substrate 12, and a first land 20 and a second land 22 are formed on ends of the printed wiring 18.

[0023] The resistor 14 comprises a base 24 formed into a horizontally elongated plate, a first terminal 26 provided at one end of the base 24, a second terminal 28 provided at the other end of the base 24, a thin-film resistor 30 provided on the upper surface of the base 24, and a covering portion 32 covering the resistor 30.

[0024] The base 24 is made of an insulating ceramic. The first terminal 26 and the second terminal 28 are made of a conductor. The covering portion 32 is made of an insulating material.

[0025] The first terminal 26 and the second terminal 28 are composed of a metal plate bent along the end of the base 24. The first terminal 26 has a first upper surface portion 34 extending in close contact with the upper surface of the base 24, a first end surface portion 36 extending from the first upper surface portion 34 and extending in close contact with one end surface of the base 24, and a first lower surface portion 38 extending from the first end surface portion 36 and extending in close contact with the lower surface of the base 24.

[0026] The second terminal 28 has a second upper surface portion 40 extending in close contact with the upper surface of the base 24, a second end surface portion 42 extending from the second upper surface portion 40 and extending in close contact with the other end surface of the base 24, and a second lower surface portion 44 extending from the second end surface portion 42 and extending in close contact with the lower surface of the base 24.

[0027] A first upper surface portion 34 of the first terminal 26 is electrically connected to one end of the resistor 30. A second upper surface portion 40 of the second terminal 28 is electrically connected to the other end of the resistor 30. The covering portion 32 covers the entire surface of the resistor 30 and also covers the connection portions between the resistor 30 and each of the terminals 26, 28.

[0028] Each of the terminals 26, 28 of the resistor 14 is fixed to the substrate 12 by a joint (46, 48). The joint (46, 48) is made of a conductive material. Examples of the conductive material include a conductive adhesive or a solder. In this embodiment, the joint ( 46 , 48) made of solder will be used as an example.

[0029] Specifically, the first terminal 26 is joined to the first land 20 of the substrate 12 by a first bonding portion 46. The second terminal 28 is joined to the second land 22 of the substrate 12 by a second bonding portion 48.

[0030] The first joint portion 46 has a first fillet 50 formed between the first end surface portion 36 of the first terminal 26 and the first land 20, and a first intermediate layer 52 interposed between the first lower surface portion 38 of the first terminal 26 and the first land 20. The second joint portion 48 has a second fillet 54 formed between the second end surface portion 42 of the second terminal 28 and the second land 22, and a second intermediate layer 56 interposed between the second lower surface portion 44 of the second terminal 28 and the second land 22.

[0031] In such an evaluation object 10, when a current is applied to the resistor 14, heat is generated in the resistive element 30 of the resistor 14. The generated heat is dissipated to the substrate 12 via the joints 46, 48 that join the resistor 14 to the substrate 12. The temperature of the resistor 14 then stabilizes when the amount of heat generated by the resistive element 30 and the amount of heat dissipated to the substrate 12 are in balance.

[0032] Here, when the bonding state of each of the bonding portions 46, 48 changes, the amount of heat dissipated to the substrate 12 changes. One example of the bonding state of each of the bonding portions 46, 48 is the state of cracks occurring in each of the bonding portions 46, 48.

[0033] More specifically, when cracks occur in the joints 46, 48, the heat dissipation path to the substrate 12 narrows, and the amount of heat dissipation decreases. Then, the temperature of the resistor 14 in a state where cracks have occurred in the joints 46, 48 becomes higher than the temperature of the resistor 14 before cracks have occurred in the joints 46, 48. Also, the larger the cracks that occur in the joints 46, 48, the narrower the heat dissipation path becomes, and the higher the temperature of the resistor 14 becomes.

[0034] Therefore, by measuring the temperature of resistor 14 when current is applied to resistor 14, it is possible to evaluate the presence or absence of cracks and the size of the cracks.

[0035] In the embodiment described below, an evaluation device evaluates the bonding state of each of the bonding parts 46, 48 using an index called the amount of cracks. The amount of cracks is indicated by a crack rate (%), and when there are no cracks in both of the bonding parts 46, 48, the crack rate is set to 0%. Also, when cracks occur in both of the bonding parts 46, 48 and the terminals 26, 28 of the resistor 14 are disconnected from the lands 20, 22 of the substrate 12, resulting in a disconnection state, the crack rate is set to 100%.

[0036] Fig. 1 shows a state in which cracks have occurred in the second bonding portion 48. Fig. 1 shows, as examples of the cracks that may occur, a first crack 60 extending along the second land 22, a second crack 62 extending in a diagonal direction relative to the second land 22, and a third crack 64 extending along the second end surface portion 42.

[0037] The crack rate will be described by taking as an example a case where a first crack 60 occurs in the second bonded portion 48.

[0038] As an example, in a state where a first crack 60 occurs in the second bonding portion 48, if the bonding area between the second bonding portion 48 and the second land 22 is S0 and the area of ​​the first crack 60 is Sc, the crack rate is Sc / S0. The amount of cracks indicated by this crack rate is used to evaluate the bonding condition of the bonding portions (46, 48).

[0039] For this reason, the crack rate may be set by comparing a disconnection state in which the terminals 26, 28 of the resistor 14 and the lands 20, 22 of the substrate 12 are separated due to the occurrence of a crack with a state in which the two are not separated.

[0040] First Embodiment A joint evaluation method and an evaluation resistor according to the first embodiment will be described with reference to Fig. 2 to Fig. 11. First, an evaluation object 100 used in the joint evaluation method will be described.

[0041] Fig. 2 is a perspective view showing an evaluation resistor 102 used in the bond evaluation method according to the first embodiment and a substrate 12. Fig. 3 is a perspective view showing a state in which the evaluation resistor 102 used in the bond evaluation method according to the first embodiment is mounted on a substrate 12. Fig. 4 is a cross-sectional view of an evaluation object 100 used in the bond evaluation method according to the first embodiment.

[0042] As shown in FIGS. 2 and 3, an evaluation object 100 used in the bond evaluation method includes a rectangular substrate 12 and an evaluation resistor 102 mounted on the substrate 12.

[0043] A printed wiring is integrally formed on the surface of the substrate 12. The printed wiring includes a first current path 104, a second current path 106, a first voltage detection path 108, and a second voltage detection path 110 that extend in the longitudinal direction of the substrate 12.

[0044] The first current path 104 extends from the center of the substrate 12 in the longitudinal direction toward one end side. The second current path 106 extends from the center of the substrate 12 in the longitudinal direction toward the other end side.

[0045] A rectangular first land 20 is formed at the other end of the first current path 104. A rectangular second land 22 is formed at one end of the second current path 106. The first land 20 and the second land 22 are spaced apart in accordance with the length dimension of the evaluation resistor 102.

[0046] The width dimension of the first voltage detection path 108 is narrower than the width dimension of the first current path 104. The width dimension of the second voltage detection path 110 is narrower than the width dimension of the second current path 106.

[0047] The first voltage detection path 108 extends from the first land 20 toward the second land 22, and then extends in the width direction of the substrate 12. The second voltage detection path 110 extends from the second land 22 toward the first land 20, and then extends in the width direction of the substrate 12. The first voltage detection path 108 and the second voltage detection path 110 extend in parallel.

[0048] 4, the evaluation resistor 102 includes a base 24 formed in a horizontally elongated plate shape, and a first terminal 26 provided at one end of the base 24. The evaluation resistor 102 also includes a second terminal 28 provided at the other end of the base 24, a resistive element 30 connecting the first terminal 26 and the second terminal 28, and a covering portion 32 covering the resistive element 30.

[0049] The resistor 30 may include a first resistor 112 that is disposed near the first terminal 26 and connected to the first terminal 26, and a second resistor 114 that is disposed near the second terminal 28 and connected to the second terminal 28. The resistor 30 also includes a connection portion 116 that electrically connects the first resistor 112 and the second resistor 114.

[0050] The base 24 is made of ceramic, which is an insulator, for example. The first terminal 26 and the second terminal 28 are made of a conductor. The first resistor 112 and the second resistor 114 are made of a thin film provided on the upper surface of the base 24, for example. The connection portion 116 is made of a conductor provided on the upper surface of the base 24. The covering portion 32 is made of an insulator.

[0051] The temperature coefficient of resistance (TCR) of the first resistor 112 and the second resistor 114 constituting the evaluation resistor 102 is set to a predetermined value larger than that of a general resistor, thereby increasing the amount of change in the resistance value of the evaluation resistor 102 that changes in response to a change in temperature.

[0052] As an example, the temperature coefficient of resistance (TCR) of the first resistor 112 and the second resistor 114 is set to 500 ppm / ° C. or more.

[0053] It is difficult to manufacture resistors whose temperature coefficient of resistance (TCR) exceeds 4000 ppm / ° C. For this reason, the temperature coefficient of resistance (TCR) of the first resistor 112 and the second resistor 114 is set in the range of 500 ppm / ° C. to 4000 ppm / ° C.

[0054] Furthermore, if the temperature coefficient of resistance (TCR) of the resistor exceeds 3000 ppm / ° C., it becomes difficult to control the accuracy. For this reason, it is preferable that the temperature coefficient of resistance (TCR) of the first resistor 112 and the second resistor 114 is set to 500 ppm / ° C. or more and 3000 ppm / ° C. or less.

[0055] Here, the temperature coefficient of resistance (TCR) indicates the rate of change in resistance value associated with a change in temperature, and is calculated based on the rate of change in resistance value and the amount of temperature change.

[0056] For example, in an object that exhibits a first resistance value R1 at a first temperature T1 and a second resistance value R2 at a second temperature T2, the temperature coefficient of resistance TCR [ppm / °C] can be calculated using the following formula:

[0057] TCR={(R2-R1) / R1} / {(T2-T1)×1000000}

[0058] The first terminal 26 and the second terminal 28 are composed of a metal plate bent along the end of the base 24. The first terminal 26 has a first upper surface portion 34 extending in close contact with the upper surface of the base 24, a first end surface portion 36 extending from the first upper surface portion 34 and extending in close contact with one end surface of the base 24, and a first lower surface portion 38 extending from the first end surface portion 36 and extending in close contact with the lower surface of the base 24.

[0059] The second terminal 28 has a second upper surface portion 40 extending in close contact with the upper surface of the base 24, a second end surface portion 42 extending from the second upper surface portion 40 and extending in close contact with the other end surface of the base 24, and a second lower surface portion 44 extending from the second end surface portion 42 and extending in close contact with the lower surface of the base 24.

[0060] The first upper surface portion 34 of the first terminal 26 is electrically connected to one end of the first resistor 112. The other end of the first resistor 112 is electrically connected to one end of the connection portion 116. The other end of the connection portion 116 is electrically connected to one end of the second resistor 114. The other end of the second resistor 114 is electrically connected to the second upper surface portion 40 of the second terminal 28. The covering portion 32 covers the entire surfaces of both resistors 112, 114 and the connection portion 116, and covers the connection portions between the resistors 112, 114 and the terminals 26, 28.

[0061] The terminals 26, 28 of the evaluation resistor 102 are fixed to the substrate 12 by a first bonding portion 46 and a second bonding portion 48. The bonding portions 46, 48 are made of a conductive material. Examples of the conductive material include a conductive adhesive or solder. In this embodiment, a case where the bonding portions 46, 48 are made of solder will be described as an example.

[0062] Specifically, the first terminal 26 is joined to the first land 20 of the substrate 12 by a first bonding portion 46. The second terminal 28 is joined to the second land 22 of the substrate 12 by a second bonding portion 48.

[0063] The first joint portion 46 has a first fillet 50 formed between the first end surface portion 36 of the first terminal 26 and the first land 20, and a first intermediate layer 52 interposed between the first lower surface portion 38 of the first terminal 26 and the first land 20. The second joint portion 48 has a second fillet 54 formed between the second end surface portion 42 of the second terminal 28 and the second land 22, and a second intermediate layer 56 interposed between the second lower surface portion 44 of the second terminal 28 and the second land 22.

[0064] In such an evaluation object 100, when a current is applied to the evaluation resistor 102, heat is generated in each of the resistive elements 112, 114 of the evaluation resistor 102. The generated heat is dissipated to the substrate 12 via each of the joints 46, 48 that join the evaluation resistor 102 to the substrate 12 and each of the lands 20, 22 to which the joints 46, 48 are joined.

[0065] Each of the lands 20, 22 is disposed in the center of the substrate 12. Therefore, heat transferred to each of the lands 20, 22 can be dissipated radially from the center of the substrate 12 to the periphery.

[0066] The temperature of the evaluation resistor 102 becomes stable when the amount of heat generated by the resistor 30 and the amount of heat dissipated to the substrate 12 are in balance.

[0067] The resistive element 30 of the evaluation resistor 102 is divided into a first resistive element 112 and a second resistive element 114, and the central part of the evaluation resistor 102 is composed of a connection part 116 made of a conductor that does not easily generate heat. Furthermore, the first resistive element 112 and the second resistive element 114, which generate heat when current is applied, are located near the terminals 26, 28 at both ends.

[0068] This allows the hot spot HS1, which is the center of the heat generating portion of the first resistor 112, to be brought closer to the first terminal 26. Also, the hot spot HS2, which is the center of the heat generating portion of the second resistor 114, can be brought closer to the second terminal 28.

[0069] Furthermore, compared to when the resistor hot spot is located away from the first terminal 26, the difference between the distance from the hot spot HS1 of the first resistor 112 to the first end surface portion 36 of the first terminal 26 and the distance to the first lower surface portion 38 can be made smaller.

[0070] In addition, compared to when the hot spot of the resistor 30 is located away from the second terminal 28, the difference between the distance 200 from the hot spot HS2 of the second resistor 114 to the second end surface portion 42 and the distance 202 to the second lower surface portion 44 can be made smaller.

[0071] Here, when the bonding state of each of the bonding parts 46, 48 that bond the evaluation resistor 102 to the substrate 12 changes, the amount of heat dissipated to the substrate 12 changes. One example of the bonding state of each of the bonding parts 46, 48 is the state of cracks occurring in each of the bonding parts 46, 48.

[0072] (Joint evaluation method) Next, the bond evaluation method according to the present embodiment will be described with reference to the drawings. Fig. 5 is a diagram showing each step of the bond evaluation method according to the first embodiment.

[0073] [Mounting process] In the mounting step P1 shown in FIG. 5, the evaluation resistor 102 is mounted on the substrate 12 as shown in FIG.

[0074] The substrate 12 may be a dedicated substrate 12 used in the bond evaluation method, or a mounting substrate to be mounted on an electronic device. When a mounting substrate is used, an evaluation resistor 102 is mounted on the mounting substrate instead of an actual resistor to be used. In this embodiment, the case where a dedicated substrate 12 is used is described as an example.

[0075] The resistor mounted on the substrate 12 may be the resistor 14 configured with a single resistive element 30 as described in the basic principle, or the evaluation resistor 102 described above. In this embodiment, the case where the evaluation resistor 102 is used will be described as an example.

[0076] [Standard acquisition process] In the reference acquisition step P2 shown in FIG. 5, a reference value indicating the temperature of the evaluation resistor 102 obtained when current is passed through the evaluation resistor 102 in a reference state that serves as a reference for the bonding state is acquired.

[0077] Here, obtaining a reference value indicating the temperature of the evaluation resistor 102 may be achieved, for example, by measurement, calculation, or simulation.

[0078] The reference stage is a stage for obtaining a reference value that serves as a reference for evaluating changes in the bonding state of each of the bonded portions 46, 48. An example of the reference stage is a stage before a load is applied to each of the bonded portions 46, 48. In this embodiment, an example will be described in which the reference stage is a stage before a reliability test is performed.

[0079] In the reference acquisition process P2, a reference thermal resistance is obtained using a voltage applied to the evaluation resistor 102 while the evaluation resistor 102 is energized in this reference stage. Specifically, in the reference acquisition process P2, a reference thermal resistance of each of the junctions 46, 48 in the reference stage is obtained using a reference value.

[0080] More specifically, in the reference acquisition process P2, while current is applied to the evaluation resistor 102 in the reference stage, a reference value is obtained from the current flowing through the evaluation resistor 102, the voltage applied to the evaluation resistor 102, and the temperature coefficient of resistance (TCR) of the evaluation resistor 102.

[0081] This reference obtaining step P2 will be specifically described with reference to the drawings.

[0082] Fig. 6 is an explanatory diagram showing how a current is passed through the evaluation resistor 102 according to the first embodiment to measure the voltage. Fig. 7 is a diagram showing changes in temperature and resistance value of the evaluation resistor 102 when a constant current is passed through the evaluation resistor 102 according to the first embodiment. Fig. 8 is a diagram showing changes in voltage when a constant current is passed through the evaluation resistor 102 according to the first embodiment.

[0083] 6, a constant current I0 is applied to the evaluation resistor 102 on the substrate 12 by a constant current circuit connected to the first current path 104 and the second current path 106 of the substrate 12. In this state, a voltage V0 applied to the evaluation resistor 102 is measured by a voltmeter connected to the first voltage detection path 108 and the second voltage detection path 110.

[0084] In this embodiment, a case will be described in which a constant current is passed through the evaluation resistor 102 and a change in voltage applied to the evaluation resistor 102 is observed, but the present invention is not limited to this. As an example, a constant voltage may be applied to the evaluation resistor 102 and a change in current flowing through the evaluation resistor 102 may be observed.

[0085] Each resistive element 112, 114 of the evaluation resistor 102 generates heat when current is applied. As shown in Fig. 7, when the temperature T0 of the evaluation resistor 102 rises, the resistance value R0 of the evaluation resistor 102 increases in accordance with the temperature coefficient of resistance (TCR) characteristics. Then, as shown in Fig. 8, the voltage V0 applied to the evaluation resistor 102 increases as the resistance value R0 increases.

[0086] Then, the temperature T0 of the evaluation resistor 102 stabilizes when the amount of heat generated by each of the resistive elements 112, 114 and the amount of heat dissipated to the substrate 12 are in balance, and the voltage V0 applied to the evaluation resistor 102 also stabilizes. The resistance value R0 of the evaluation resistor 102 is calculated from the product of this stabilized voltage V0 and the current I0 passed through the evaluation resistor 102.

[0087] Here, the temperature coefficient of resistance (TCR) of the evaluation resistor 102 is set to a predetermined value, and the temperature coefficient of resistance (TCR) characteristics of the evaluation resistor 102 are known. Therefore, the temperature T0 of the evaluation resistor 102 is calculated using the temperature coefficient of resistance (TCR) characteristics and the resistance value R0 calculated from the voltage V0 and current I0.

[0088] This allows the current I0 flowing through the evaluation resistor 102 when current is applied to the evaluation resistor 102 in the reference stage, the voltage V0 applied to the evaluation resistor 102, and the temperature T0 indicating the reference value from the temperature coefficient of resistance (TCR) of the evaluation resistor 102.

[0089] Fig. 9 is a conceptual diagram showing the thermal characteristics of the evaluation object 100 according to the first embodiment, and is a cross-sectional view showing the state before a reliability test. Fig. 10 is a conceptual diagram showing the thermal characteristics of the evaluation object 100 according to the first embodiment, and is a cross-sectional view showing the state after a reliability test. Fig. 11 is an explanatory diagram showing a relational expression among the temperature T0, the heat generation amount Q0, and the thermal resistance of the evaluation resistor 102 of the evaluation object 100 according to the first embodiment.

[0090] 9 and 10 show a state in which the substrate 12 of the evaluation object 100 is placed in close contact with a temperature constant plate 120. The temperature constant plate 120 is maintained at a temperature Ta. The temperature Ta is set to a temperature equal to the ambient temperature, for example.

[0091] The thermal characteristics of the evaluation object 100 will be described with reference to Fig. 9. Here, thermal resistance indicates the magnitude of the force that prevents heat from flowing in an object. Thermal resistance is a value obtained by dividing the temperature difference between any two points by the amount of heat flowing between the two points.

[0092] In other words, if the temperature of an arbitrary first point is T1, the temperature of an arbitrary second point is T2, and the heat flow between the two points is P, the thermal resistance Rth can be calculated using the following formula.

[0093] Rth = (T1-T2) / P

[0094] In an evaluation object 100 in which an evaluation resistor 102 is mounted on a substrate 12, as shown in FIG. 9, thermal resistance exists between a resistor 30 that generates heat and a constant temperature plate 120 from which the heat of the resistor 30 is dissipated.

[0095] For convenience of explanation, only the second resistor 114 is shown in Fig. 9. In the following, with regard to the resistor 30, only the second resistor 114 will be explained. In addition, with regard to the joint, only the second joint 48 will be explained.

[0096] The thermal resistance of the evaluation resistor 102 can be divided into a thermal resistance Rtha of the base 24, a thermal resistance Rth1 of the second bonding portion 48, and a thermal resistance Rthb of the substrate 12. The thermal resistance Rtha of the base 24 and the thermal resistance Rthb of the substrate 12 are steady. On the other hand, the thermal resistance Rth1 of the second bonding portion 48 changes when the bonding state of the second bonding portion 48 changes before and after the reliability test.

[0097] The thermal resistance Rth1 of the second junction 48 indicates a reference thermal resistance. The thermal resistance Rth1 indicating the reference thermal resistance indicates a reference thermal resistance obtained using a voltage V1 applied to the evaluation resistor 102 in a state in which a current is applied to the evaluation resistor 102 in a reference stage.

[0098] The relationship between the surface temperature T0 of the evaluation resistor 102 and the temperature Ta of the temperature plate 120 and each thermal resistance is expressed by a first formula 130 shown in Fig. 11. Using this first formula 130, the thermal resistance Rth1 of the second bonding portion 48 is calculated from the temperature difference between the temperature T0 of the evaluation resistor 102 and the temperature Ta of the temperature plate 120.

[0099] In this embodiment, the thermal resistance Rth1 of the second bonding portion 48 is calculated by the first formula 130, but the present invention is not limited to this. As an example, the thermal resistance Rth1 of the second bonding portion 48 may be obtained by a transient thermal measurement method.

[0100] One example of a measurement using the transient thermal measurement method is a measurement using the "Transient Thermal Tester T3Ster" manufactured by Siemens AG. Using the transient thermal tester T3Ster, measurements can be performed that comply with the Transient Thermal Measurement Method (JESD51-14), a standard set by the JEDEC (Joint Electron Devices Committee).

[0101] [Reliability testing process] 5, a reliability test is performed on the evaluation object 100 for which the reference value, temperature T0, has been acquired in the reference acquisition process P2. The reliability test is a test in which a load is applied to the evaluation object 100, and a load is also applied to each of the bonding portions 46, 48. Examples of the reliability test include the tests described above.

[0102] Based on the results of this reliability test, the design of the evaluation object 100 and the materials and joining methods of each of the joining portions 46, 48 are reviewed.

[0103] [Temperature acquisition process] In the temperature acquisition step P4 shown in FIG. 5, the temperature of the evaluation resistor 102 obtained in a state where a current is applied to the evaluation resistor 102 in the comparison stage is acquired as a comparison value.

[0104] Here, obtaining the temperature of the evaluation resistor 102 as a comparison value may be achieved, for example, by obtaining the reference value through measurement, calculation, or simulation.

[0105] The comparison stage is a stage for determining whether or not the bonding state of each of the bonded portions 46, 48 has changed from the reference stage. An example of the reference stage is a stage after a load is applied to each of the bonded portions 46, 48. In this embodiment, an example will be described in which the comparison stage is a stage after a reliability test is performed.

[0106] The temperature acquisition process P4 obtains a comparative thermal resistance using the voltage applied to the evaluation resistor 102 with current flowing through the evaluation resistor 102 in the comparison stage. Specifically, the temperature acquisition process P4 obtains a comparative thermal resistance of each of the junctions 46, 48 in the comparison stage using the comparison value. More specifically, the temperature acquisition process P4 obtains a comparative value from the current flowing through the evaluation resistor 102, the voltage applied to the evaluation resistor 102, and the resistance temperature coefficient of the evaluation resistor 102 with current flowing through the evaluation resistor 102 in the comparison stage.

[0107] 6, in this temperature acquisition process P4, a constant current I0 is applied to the evaluation resistor 102 on the substrate 12 after the reliability test by a constant current circuit connected to the first current path 104 and the second current path 106 of the substrate 12. In this state, the voltage Vc applied to the evaluation resistor 102 is measured by a voltmeter connected to the first voltage detection path 108 and the second voltage detection path 110.

[0108] At this time, each of the resistive elements 112, 114 of the evaluation resistor 102 generates heat due to the passage of current. As shown in Fig. 7, when the temperature Tc of the evaluation resistor 102 rises, the resistance value Rc of the evaluation resistor 102 increases in accordance with the characteristics of the temperature coefficient of resistance (TCR). Then, as shown in Fig. 8, as the resistance value Rc increases, the voltage Vc applied to the evaluation resistor 102 increases.

[0109] Then, the temperature Tc of the evaluation resistor 102 stabilizes when the amount of heat generated by each of the resistive elements 112, 114 and the amount of heat dissipated to the substrate 12 are in balance, and the voltage Vc applied to the evaluation resistor 102 also stabilizes. The resistance value Rc of the evaluation resistor 102 is calculated from the product of this stabilized voltage Vc and the current I0 passed through the evaluation resistor 102.

[0110] Here, the temperature coefficient of resistance (TCR) of the evaluation resistor 102 is set to a predetermined value, and the temperature coefficient of resistance (TCR) characteristics of the evaluation resistor 102 are known. Therefore, the temperature Tc of the evaluation resistor 102 is calculated using the temperature coefficient of resistance (TCR) characteristics and the resistance value Rc calculated from the voltage Vc and the current I0.

[0111] As a result, a temperature Tc indicating a comparison value is obtained from the current I0 flowing through the evaluation resistor 102 when current is applied to the evaluation resistor 102 during the comparison stage, the voltage Vc applied to the evaluation resistor 102, and the temperature coefficient of resistance (TCR) of the evaluation resistor 102.

[0112] In the evaluation object 100 in which the evaluation resistor 102 is mounted on the substrate 12, as shown in FIG. 10, a thermal resistance exists between the second resistor 114 which generates heat and the constant temperature plate 120 from which the heat of the second resistor 114 is dissipated.

[0113] For convenience of explanation, only the second resistor 114 side is shown in FIG.

[0114] This evaluation resistor 102 can be divided into a thermal resistance Rtha of the base 24, a thermal resistance Rth2 of the second junction, and a thermal resistance Rthb of the substrate 12. The thermal resistance Rtha of the base 24 and the thermal resistance Rthb of the substrate 12 are steady.

[0115] Here, if the bonding state of the second bonding portion 48 changes before and after the reliability test, the thermal resistance of the second bonding portion 48 also changes. Fig. 10 shows a state in which the thermal resistance of the second bonding portion 48 has changed from thermal resistance Rth1 to thermal resistance Rth2 before and after the reliability test.

[0116] The thermal resistance Rth2 of the second joint 48 indicates a comparative thermal resistance. The thermal resistance Rth2 indicating the comparative thermal resistance indicates a comparative thermal resistance obtained using the voltage Vc applied to the evaluation resistor 102 in a state in which current is applied to the evaluation resistor 102 in the comparison stage.

[0117] The relationship between the surface temperature Tc of the evaluation resistor 102 and the ambient temperature Ta, which is the temperature of the substrate 12, and each thermal resistance is expressed by the second formula 132 shown in Fig. 11. Therefore, using this second formula 132, the thermal resistance Rth2 of the second bonding portion 48 is calculated from the temperature difference between the temperature Tc of the evaluation resistor 102 and the temperature Ta of the thermostatic plate 120.

[0118] As a result, the thermal resistance Rth2, which is the comparative thermal resistance of the junctions (46, 48) in the comparison stage, is found using the temperature Tc indicating the comparative value.

[0119] Here, in this embodiment, the thermal resistance Rth2 of the second bonding portion 48 is calculated by the second formula 132, but the present invention is not limited to this. As an example, the thermal resistance Rth2 of the second bonding portion 48 may be obtained by a transient thermal measurement method. As an example of the measurement by this transient thermal measurement method, there is a measurement using a "transient thermal tester T3Ster" manufactured by Siemens AG.

[0120] [Evaluation process] As shown in FIG. 5, in the evaluation step P5, the bonding state of each of the bonding portions 46, 48 is evaluated using a thermal resistance Rth1 indicating a reference thermal resistance and a thermal resistance Rth2 indicating a comparative thermal resistance.

[0121] Here, the bonding state of each of the bonding portions 46, 48 can be, for example, the state of cracks occurring in each of the bonding portions 46, 48.

[0122] The thermal resistance Rth1 indicating the reference thermal resistance is obtained using the temperature T0 which is the reference value as described above. The thermal resistance Rth2 indicating the comparative thermal resistance is obtained using the temperature Tc which is the comparative value as described above. Therefore, in the evaluation process P5, the bonding state of each of the bonding parts 46, 48 is evaluated using the temperature T0 which is the reference value and the temperature Tc which is the comparative value.

[0123] In the evaluation process P5, the bonding state of each of the bonding portions 46, 48 is evaluated based on data indicating the relationship between the change in thermal resistance of each of the bonding portions 46, 48 and the bonding state of each of the bonding portions 46, 48.

[0124] FIG. 12 is a correlation diagram 140 showing the correlation between the crack rate and the rate of change in thermal resistance at each of the joints 46, 48 of the evaluation object 100 according to the first embodiment.

[0125] The crack rate at each of the joints 46, 48 indicates the bonding state of each of the joints 46, 48. As explained with reference to Fig. 1, when the bonding area between each of the joints 46, 48 and each of the lands 20, 22 is S0 and the area of ​​the crack is Sc, the crack rate is Sc / S0. The rate of change in thermal resistance indicates the difference between thermal resistance Rth1 indicating the reference thermal resistance and thermal resistance Rth2 indicating the comparative thermal resistance.

[0126] The correlation diagram 140 showing this correlation is obtained by a simulation carried out in advance. Alternatively, the correlation diagram 140 showing the correlation may be created using results obtained by an experiment.

[0127] By using correlation diagram 140 showing this correlation, it is possible to evaluate the amount of cracks that have occurred in each of the joints 46, 48 due to the reliability test from the rate of change in thermal resistance before and after the reliability test. Alternatively, it is possible to evaluate how far the cracks in each of the joints 46, 48 have progressed through the reliability test.

[0128] (Action and Effects) Next, the effects of the first embodiment will be described.

[0129] The bond evaluation method of the present embodiment is a bond evaluation method for evaluating a bond (46, 48) between a resistor (14, 102) and a substrate 12 on which the resistor (14, 102) is mounted. The bond evaluation method includes a temperature acquisition step P4 for acquiring a temperature of the resistor (14, 102) obtained when electricity is applied to the resistor (14, 102), and an evaluation step P5. The evaluation step P5 evaluates the bond state based on the temperature of the resistor (14, 102) acquired in the temperature acquisition step P4 and the temperature indicated by the resistor (14, 102) when electricity is applied to the resistor (14, 102) in a reference state of the bond (46, 48).

[0130] In this configuration, when a current is applied to the resistor (14, 102) mounted on the substrate 12, the resistive element of the resistor (14, 102) 30 The generated heat is dissipated to the substrate 12 through the joints (46, 48) that join the resistors (14, 102) to the substrate 12. The temperature of the resistors (14, 102) is then calculated as 30 The amount of heat generated and the amount of heat dissipated to the substrate 12 are balanced and stable.

[0131] Here, a change in the bonding state of the joints (46, 48) changes the amount of heat dissipated to the substrate 12. Therefore, by using the temperature of the resistors (14, 102) acquired in the temperature acquisition step P4 and the temperature indicated by the resistors (14, 102) in a reference state of the joints (46, 48), it is possible to evaluate the change in the bonding state of the joints (46, 48).

[0132] Therefore, it becomes possible to perform non-destructive evaluation of the evaluation objects 10 and 100. This makes it possible to reuse the evaluation objects 10 and 100 evaluated by this joint evaluation method.

[0133] The bond evaluation method further includes a reference acquisition step P2 for acquiring a reference value indicating a temperature T0 of the resistor (14, 102) obtained when current is applied to the resistor (14, 102) in a reference state that serves as a reference for the bonded state. A temperature acquisition step P4 acquires a comparison value indicating a temperature Tc of the resistor (14, 102) obtained when current is applied to the resistor (14, 102) in a comparison state in which the bonded portion (46, 48) is compared with the reference state. An evaluation step P5 evaluates the state of the bonded portion (46, 48) based on the reference value and the comparison value.

[0134] In this configuration, a reference value indicating the temperature T0 of the resistor (14, 102) in a reference stage, which is a reference state, and a comparison value indicating the temperature Tc of the resistor (14, 102) in a comparison stage are used for evaluation. This makes it possible to evaluate the change in the bonding state of the bonding parts (46, 48) that occurs between the reference stage and the comparison stage.

[0135] Specifically, by using the joint evaluation method of the present embodiment, it is possible to evaluate the state of cracks that may occur in the joints (46, 48) through a reliability test. As a result, it is possible to review the material and joining method of the joints (46, 48), for example.

[0136] In addition, the bonding condition of the bonding parts (46, 48) can be evaluated each time a different reliability test is performed, which makes it possible to know in which reliability test the bonding condition of the bonding parts (46, 48) deteriorated.

[0137] In the bond evaluation method of this embodiment, a reference acquisition process P2 obtains a reference thermal resistance (Rth1) of the bonded parts (46, 48) in a reference state using a reference value (T0). A temperature acquisition process P4 obtains a comparative thermal resistance (Rth2) of the bonded parts (46, 48) in a comparative state using a comparative value (Tc). An evaluation process P5 evaluates the bonded state of the bonded parts (46, 48) based on the reference thermal resistance (Rth1) and the comparative thermal resistance (Rth2).

[0138] According to this configuration, the bonding condition of the joints (46, 48) can be evaluated from a change in thermal resistance occurring at the joints (46, 48).

[0139] Furthermore, in the bond evaluation method of the present embodiment, a reference acquisition process P2 acquires a reference thermal resistance (Rth1) using a voltage applied to the resistor (14, 102) with current flowing through the resistor (14, 102) in a reference state. A temperature acquisition process P4 acquires a comparison thermal resistance (Rth2) using a voltage applied to the resistor (14, 104) with current flowing through the resistor (14, 102) in a comparison state.

[0140] According to this configuration, the heat values ​​Q0 and Qc of the resistors (14, 102) can be calculated from the current I0 and voltages V0 and Vc passing through the resistors (14, 102). This makes it possible to calculate the thermal resistances (Rth1, Rth2) by a calculation using the calculated heat values ​​Q0 and Qc.

[0141] In the bond evaluation method of the present embodiment, the reference acquisition process P2 acquires a reference temperature (T0) of the resistor (14, 102) using the following values: a current I0 flowing through the resistor (14, 102) when current is applied to the resistor (14, 102), a voltage V0 applied to the resistor (14, 102), and a temperature coefficient of resistance (TCR) of the resistor (14, 102) in a reference stage. A temperature acquisition process P4 acquires a comparison value (Tc) from the current I0 flowing through the resistor (14, 102) when current is applied to the resistor (14, 102), a voltage Vc applied to the resistor (14, 102), and a temperature coefficient of resistance (TCR) of the resistor (14, 102) in a comparison stage.

[0142] According to this configuration, the reference value (T0) and the comparison value (Tc) are obtained from the current I0 flowing through the resistor (14, 102), the voltages V0 and Vc applied to the resistor (14, 102), and the temperature coefficient of resistance (TCR) of the resistor (14, 102). This eliminates the need to measure the temperature of the resistor (14, 102).

[0143] This allows the reduction of the temperature sensor that measures the temperature of the resistors (14, 102).

[0144] Furthermore, in the bonded portion evaluation method of the present embodiment, the reference acquisition process P2 is performed before a load is applied to the bonded portions (46, 48), and the temperature acquisition process P4 is performed after a load is applied to the bonded portions (46, 48).

[0145] This configuration makes it possible to evaluate changes that occur in the joints (46, 48) before and after a load is applied to the joints (46, 48).

[0146] The evaluation resistor 102 of this embodiment is an evaluation resistor 102 used in a joint evaluation method. The evaluation resistor 102 includes a first terminal 26 joined to the substrate 12 by a joint (46), a second terminal 28 joined to the substrate 12 by a joint (48), and a resistor 30 connecting the first terminal 26 and the second terminal 28. The resistor 30 includes a first resistor 112 arranged in a position close to the first terminal 26 and connected to the first terminal 26, and a second resistor 114 arranged in a position close to the second terminal 28 and connected to the second terminal 28. The resistor 30 also includes a connection portion 116 that electrically connects the first resistor 112 and the second resistor 114.

[0147] With this configuration, compared to a resistor 14 having a single resistive element 30, it is possible to reduce the temperature difference that may occur depending on the location of each terminal 26, 28 when heat from each resistive element 112, 114 is transferred to the corresponding terminal (26, 28).

[0148] Moreover, the evaluation resistor 102 of this embodiment has a temperature coefficient of resistance (TCR) of 500 ppm / ° C. or more.

[0149] This configuration allows for a larger change in resistance value in response to temperature changes compared to a typical resistor with a temperature coefficient of resistance (TCR) set to less than 50 ppm / ° C. This makes it possible to improve the accuracy of evaluations that utilize changes in resistance value.

[0150] Second Embodiment A bond evaluation device for implementing a bond evaluation method according to the second embodiment will be described with reference to Figures 13 and 14. Note that parts that are the same as or equivalent to those in the first embodiment will be denoted by the same reference numerals as in the first embodiment and will not be described again, and only parts that differ from the first embodiment will be described.

[0151] Fig. 13 is a block diagram showing an example of a hardware configuration of a bonded portion evaluating device 150 according to the second embodiment. Fig. 14 is a functional block diagram showing an example of a functional configuration of the bonded portion evaluating device 150 according to the second embodiment.

[0152] (Hardware configuration) The bond evaluation device 150 is a device for evaluating the bond (46, 48) between the resistor (14, 102) and the substrate 12 on which the resistor (14, 102) is mounted. In this embodiment, a case where the evaluation resistor 102 described above is used will be described.

[0153] 13, the bond evaluation device 150 is configured around a processor 160 that constitutes a computer. Connected to the processor 160 are a current supply unit 162, a current measurement unit 164, a voltage measurement unit 166, and a temperature measurement unit 168. Also connected to the processor 160 are a memory unit 170, an input unit 172, a display unit 174, a notification unit 176, a clock unit 178, and a communication unit 180.

[0154] The current supplying unit 162 supplies a constant current to the current paths 104, 106 of the substrate 12 in accordance with instructions from the processor 160, and energizes the evaluation resistor 102. The current measuring unit 164 measures the current flowing through the evaluation resistor 102 via the current paths 104, 106, and outputs the result to the processor 160. The voltage measuring unit 166 measures the voltage applied to the evaluation resistor 102 via both voltage detection paths 108, 110, and outputs the result to the processor 160. The temperature measuring unit 168 measures the temperature of the thermostatic plate 120, and outputs the result to the processor 160.

[0155] The storage unit 170 stores data so that the data can be read by the processor 160. The input unit 172 sends data input by a user to the processor 160. The display unit 174 performs display in accordance with the data from the processor 160.

[0156] The notification unit 176 issues notifications in accordance with data from the processor 160. The clock unit 178 outputs the current date and time to the processor 160. The communication unit 180 enables data transmission and reception between the processor 160 and an external device.

[0157] (Function Block) 14, the bond evaluation device 150 includes a reference thermal resistance acquisition unit 190, a comparative thermal resistance acquisition unit 192, and an evaluation unit 194. The units 190, 192, and 194 are realized by the processor 160 operating in accordance with a program stored in the storage unit 170.

[0158] The reference thermal resistance acquisition unit 190 performs the above-mentioned reference thermal resistance acquisition step. The comparative thermal resistance acquisition unit 192 performs the above-mentioned comparative thermal resistance acquisition step. The evaluation unit 194 performs the above-mentioned evaluation step P5.

[0159] The reference thermal resistance acquiring unit 190 obtains the reference temperature (T0) of the evaluation resistor 102 using the following values: a current I0 flowing through the evaluation resistor 102 when current is applied to the evaluation resistor 102 in the reference stage, a voltage V0 applied to the evaluation resistor 102, and a temperature coefficient of resistance (TCR) of the evaluation resistor 102. The reference thermal resistance acquiring unit 190 acquires a reference thermal resistance (Rth1) of the junctions (46, 48) using the reference temperature (T0) and the temperature (Ta) of the thermostatic plate 120 on which the substrate 12 is placed.

[0160] The comparative thermal resistance acquisition unit 192 obtains a comparative temperature (Tc) of the evaluation resistor 102 using the following values: a current I0 flowing through the evaluation resistor 102 when current is applied to the evaluation resistor 102 in the comparison stage, a voltage Vc applied to the evaluation resistor 102, and a temperature coefficient of resistance (TCR) of the evaluation resistor 102. The comparative thermal resistance acquisition unit 192 acquires a comparative thermal resistance (Rth2) of the junctions (46, 48) using the comparative temperature (Tc) and a temperature (Ta) of the thermostatic plate 120 on which the substrate 12 is placed.

[0161] The evaluation unit 194 evaluates the bonding state of the bonding parts (46, 48) based on the reference thermal resistance (Rth1) and the comparative thermal resistance (Rth2).

[0162] (Action and Effects) A bond evaluation method can be implemented by using the bond evaluation device 150 of the present embodiment. Therefore, the present embodiment can also achieve the same effects as the first embodiment.

[0163] In each embodiment, the bonding state of the joints (46, 48) is evaluated from the rate of change in thermal resistance before and after the reliability test, but this is not limited to this. As an example, the temperature change of the resistors (14, 102) before and after the reliability test may be measured by a thermocouple or a thermograph, and the bonding state of the joints (46, 48) may be evaluated from the temperature change.

[0164] In addition, in the present embodiment, the joints (46, 48) are made of solder, but the present invention is not limited to this. As an example, even if the joints (46, 48) are made of a conductive adhesive, the joints (46, 48) can be evaluated. [Explanation of symbols]

[0165] 10, 100 rated 14 resistor 26 First terminal 28 Second terminal 30 Resistor 46 First joint 48 Second joint 102 Evaluation resistor 112 First resistor 114 Second resistor 150 Joint evaluation device 160 processors 190 Standard thermal resistance acquisition section 192 Comparative thermal resistance acquisition section 194 Evaluation Department P2 standard acquisition process P4 Temperature acquisition process P5 Evaluation process Rth1 thermal resistance Rth2 thermal resistance TCR Temperature Coefficient of Resistance T0 temperature Ta Ambient temperature Tc temperature V0 Voltage V1 Voltage

Claims

1. A joint evaluation method for evaluating a joint between a resistor and a substrate on which the resistor is mounted, comprising the steps of: a temperature acquisition step of acquiring a temperature of the resistor obtained in a state where the resistor is energized; an evaluation step of evaluating a bonding state of the joint based on the temperature of the resistor acquired in the temperature acquisition step and a temperature of the resistor when a current is passed through the resistor in a reference state of the joint; a reference acquisition step of acquiring a reference value indicating a temperature of the resistor obtained when a current is applied to the resistor in a reference state serving as a reference for the bonding state, The temperature acquisition step includes acquiring a comparison value indicating a temperature of the resistor obtained in a comparison state in which the joint is compared with the reference state, while current is being applied to the resistor; The evaluation step evaluates a state of the joint based on the reference value and the comparison value, the reference obtaining step obtains a reference thermal resistance of the junction in the reference state by using the reference value; the temperature acquisition step uses the comparison value to obtain a comparative thermal resistance of the junction in the comparative state; The evaluation step evaluates the bonding state of the bonding portion based on the reference thermal resistance and the comparative thermal resistance. Joint evaluation methods.

2. The bond evaluation method according to claim 1, The reference obtaining step obtains the reference thermal resistance by using a voltage applied to the resistor in a state where a current is applied to the resistor in the reference state; The temperature acquisition step determines the comparative thermal resistance using a voltage applied to the resistor when a current is applied to the resistor in the comparison state. Joint evaluation methods.

3. The bond evaluation method according to claim 2, The reference value obtaining step obtains the reference value from a current flowing through the resistor in a state where a current is applied to the resistor in the reference state, a voltage applied to the resistor, and a temperature coefficient of resistance of the resistor; The temperature acquisition step determines the comparison value from a current flowing through the resistor in a state where current is applied to the resistor in the comparison state, a voltage applied to the resistor, and a resistance temperature coefficient of the resistor. Joint evaluation methods.

4. The bond evaluation method according to any one of claims 1 to 3, The reference obtaining step is performed before applying a load to the joint; The temperature acquisition step is performed after applying a load to the joint. Joint evaluation methods.

5. An evaluation resistor for use in a joint evaluation method for evaluating a joint between a resistor and a board on which the resistor is mounted, the method including: a temperature acquisition step of acquiring a temperature of the resistor obtained when current is passed through the resistor; and an evaluation step of evaluating a joint state of the joint based on the temperature of the resistor acquired in the temperature acquisition step and the temperature exhibited by the resistor when current is passed through the resistor in a reference joint state, a first terminal joined to the substrate by the joining portion; a second terminal joined to the substrate by the joining portion; a resistor connecting the first terminal and the second terminal; Equipped with The resistor includes a first resistor that is disposed near the first terminal and connected to the first terminal, a second resistor that is disposed near the second terminal and connected to the second terminal, and a connection portion that electrically connects the first resistor and the second resistor. Evaluation resistor.

6. The evaluation resistor according to claim 5 , The temperature coefficient of resistance is 500 ppm / °C or more. Evaluation resistor.

7. A joint evaluation device for evaluating a joint between a resistor and a substrate on which the resistor is mounted, comprising: a reference thermal resistance acquisition unit that determines a reference temperature of the resistor from a current flowing through the resistor, a voltage applied to the resistor, and a resistance temperature coefficient of the resistor in a reference state that is a reference for the bonding state of the bonding portion when current is applied to the resistor, and acquires a reference thermal resistance of the bonding portion using the reference temperature and a temperature of a thermostatic plate on which the substrate is placed; a comparative thermal resistance acquisition unit that, in a comparison state in which the joint is compared with the reference state, determines a comparative temperature of the resistor from a current flowing through the resistor, a voltage applied to the resistor, and a resistance temperature coefficient of the resistor when current is applied to the resistor, and acquires a comparative thermal resistance of the joint using the comparative temperature and the temperature of the thermostatic plate; an evaluation unit that evaluates a state of the joint based on the reference thermal resistance and the comparative thermal resistance; A joint evaluation device equipped with the above.

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