JP2016129178A - Crack detection device for an insulating plate and crack detection method, and manufacturing method of power module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crack detection device for insulating plate capable of detecting cracks on a single insulating plate.SOLUTION: A crack detection device includes: a stress application jig 2, which has an insulating plate 1a, a first conductive plate 1b on one plane of insulating plate 1a and a second conductive plate 1c on the other plane of the insulating plate 1a, applies a bending stress to an insulating plate 1; a power source 5 for applying a voltage across the first conductive plate 1b and the second conductive plate 1c; an ampere meter 8 for measuring a value of current flowing across the first conductive plate 1b and the second conductive plate 1c; and a determination device 9 that determines existence/absence of cracks in the insulating plate 1 based on the value measured by the ampere meter 8.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a crack detection apparatus and crack detection method for an insulating substrate, and a method for manufacturing a power module.

  Since a high voltage is applied to the power module on the insulating substrate used in the power module, high insulation reliability is required. However, cracks may occur in the insulating substrate during the manufacturing process. Such cracks in the insulating substrate can be detected by measuring partial discharge, leakage current, and the like in a state where a voltage is applied to the insulating substrate.

  In general, when a crack is detected by applying a voltage to an insulating substrate, it is necessary to increase the applied voltage in order to increase the sensitivity of detecting the crack of the insulating substrate. However, when the applied voltage is increased, dielectric breakdown occurs in the insulating substrate due to causes other than cracks. This dielectric breakdown is creepage breakdown caused by creeping discharge. Therefore, in detecting a crack in an insulating substrate, it is required to detect a crack with a low applied voltage.

  For this reason, there is a non-defective product determination device for a power module in which the power module is heated with a hot plate, the leakage current is increased, and the voltage capable of detecting a crack in the insulating substrate is lowered (for example, Patent Document 1).

JP 2009-224798 A

  Such a non-defective product determination device for a power module, which is a crack detection device for an insulating substrate, detects a crack in the insulating substrate assembled in the shape of the power module. Even if it is attempted to detect a crack in the insulating substrate before assembling into the shape of the power module by applying such an insulating substrate crack detecting device, it cannot be detected with the applied voltage kept low. If the applied voltage is increased in order to increase the sensitivity to detect cracks, dielectric breakdown may occur in the insulating substrate due to causes other than cracks. It was not possible to detect a crack in the insulating substrate by itself.

  If the cracks of the insulating substrate before assembling into the shape of the power module cannot be found by inspecting the insulating substrate alone, the insulating substrate with cracks will be assembled into the shape of the power module, which is a wasteful part Will come out.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an insulating substrate crack detection device capable of detecting a crack in an insulating substrate with a single insulating substrate.

  According to the present invention, there is provided a crack detection apparatus for an insulating substrate, comprising: an insulating substrate having a first conductive plate on one surface of the insulating plate and a second conductive plate on the other surface of the insulating plate; A stress applying jig for applying a voltage, a power source for applying a voltage between the first conductive plate and the second conductive plate, and a current flowing between the first conductive plate and the second conductive plate. An ammeter for measuring a value and a determination device for determining the presence or absence of a crack in the insulating substrate from the value measured by the ammeter are provided.

  According to the crack detection apparatus for an insulating substrate according to the present invention, it is possible to detect a crack in the insulating substrate with the insulating substrate alone. In the present invention, it was found that when a crack was detected by applying a voltage with a stress applied to the insulating substrate, the crack could be detected with the applied voltage being low, so the crack on the insulating substrate could be detected with the insulating substrate alone. The crack detection apparatus of the insulated substrate which can detect was able to be obtained.

It is the schematic which shows the structure of the crack detection apparatus of the insulated substrate concerning Embodiment 1 of this invention. It is the graph which showed the relationship between the voltage applied to the insulated substrate, and the electric current which flows into an insulated substrate for demonstrating the effect of the crack detection apparatus of the insulated substrate concerning Embodiment 1 of this invention. It is a process flowchart which shows the detection method of the crack of the insulated substrate using the crack detection apparatus of the insulated substrate concerning Embodiment 1 of this invention. It is the schematic which shows the structure of the crack detection apparatus of the insulated substrate concerning Embodiment 2 of this invention. It is the graph which showed the relationship between the voltage applied to the insulated substrate, and the electric current which flows into an insulated substrate for demonstrating the effect of the crack detection apparatus of the insulated substrate concerning Embodiment 2 of this invention. It is a process flowchart which shows the detection method of the crack of the insulated substrate using the crack detection apparatus of the insulated substrate concerning Embodiment 2 of this invention. It is the schematic which shows the structure of the crack detection apparatus of the insulated substrate concerning Embodiment 3 of this invention. It is a figure for demonstrating the crack detection apparatus of the insulated substrate concerning Embodiment 3 of this invention, and has shown the Paschen curve. It is the graph which showed the relationship between the voltage applied to the insulated substrate, and the electric current which flows into an insulated substrate for demonstrating the effect of the crack detection apparatus of the insulated substrate concerning Embodiment 3 of this invention. It is a process flowchart which shows the detection method of the crack of the insulated substrate using the crack detection apparatus of the insulated substrate concerning Embodiment 3 of this invention. It is the schematic which shows the structure of the crack detection apparatus of the insulated substrate concerning Embodiment 4 of this invention. It is the graph which showed the relationship between the voltage applied to the insulated substrate, and the electric current which flows into an insulated substrate for demonstrating the effect of the crack detection apparatus of the insulated substrate concerning Embodiment 4 of this invention. It is a process flowchart which shows the detection method of the crack of the insulated substrate using the crack detection apparatus of the insulated substrate concerning Embodiment 4 of this invention.

Embodiment 1 FIG.
A configuration of the crack detection apparatus for an insulating substrate according to the first embodiment of the present invention will be described. FIG. 1 is a schematic diagram illustrating the configuration of a crack detection apparatus for an insulating substrate according to a first embodiment of the present invention.

  The insulating substrate crack detecting apparatus according to the first embodiment of the present invention includes a first conductive plate 1b on one surface of the insulating plate 1a and the second conductive surface on the other surface of the insulating plate 1a. A stress applying jig 2 for applying a bending stress to the insulating substrate 1 having the plate 1c and a power source 5 for applying a voltage between the first conductive plate 1b and the second conductive plate 1c are provided. Furthermore, the crack detection apparatus for an insulating substrate according to the first embodiment of the present invention includes an ammeter 8 that measures the value of the current flowing between the first conductive plate and the second conductive plate, and an ammeter 8. And a determination device 9 for determining the presence or absence of a crack in the insulating substrate 1 from the measured value.

  The crack detection device for an insulating substrate according to the first exemplary embodiment of the present invention is a device that determines a crack in the insulating substrate 1. The insulating substrate 1 in which the crack detection apparatus for an insulating substrate according to the first embodiment of the present invention detects a crack has a circuit pattern already formed on the insulating plate 1a by the first conductive plate 1b and the second conductive plate 1c. It is a thing.

  Furthermore, the insulating substrate crack detecting apparatus according to the first embodiment of the present invention is in contact with the sealed container 4 for arranging the insulating substrate 1 and the stress applying jig 2 and the insulating plate 1a of the second conductive plate 1c. The strain gauge 6 is applied to the insulating substrate 1 from the stress gauge 6 that is attached to the surface that is not attached and measures the strain generated in the insulating substrate 1 and generates an electric signal depending on the magnitude. And a stress monitor 7 for calculating and displaying the bending stress. Hereinafter, the crack detection apparatus for an insulating substrate according to the first embodiment of the present invention is simply referred to as a crack detection apparatus according to the first embodiment of the present invention.

  The stress application jig 2 supports both ends of the insulating substrate 1 and has a support jig 2a having a screw hole at the top, a screw-like screw jig 2b that can be fixed to the screw hole of the support jig 2a, and a second A block jig 2c is disposed between the conductive plate 1c and the screw jig 2b, and is pressed by tightening the screw jig 2b to push down the center of the insulating substrate 1. The stress applying jig 2 can apply bending stress to the insulating substrate 1 by supporting both ends of the insulating substrate 1 and pushing down the center of the insulating substrate 1.

  In FIG. 1, the support jig 2a has a shape that supports the left and right portions of the insulating substrate 1 from below, but the shape of the support jig 2a is a shape that supports the left and right portions of the insulating substrate 1 from above and below, The insulating substrate 1 may be sandwiched between both ends. Further, the block jig 2c has a cylindrical shape here, and in FIG. 1, bending stress can be applied almost evenly from the front side to the back side of the insulating substrate 1.

  The number of screw holes included in the support jig 2a, the screw jig 2b that can be fixed to the screw holes, and the number of block jigs 2c that apply bending stress to the insulating substrate 1 by tightening the screw jig 2b are particularly limited. Although not intended, the stress applying jig 2 must be configured so that bending stress can be applied to the insulating substrate 1.

  The insulating plate 1a of the insulating substrate 1 is made of ceramic, which is an inorganic material, such as alumina (Aluminum Oxide), aluminum nitride (Aluminum Nitride), silicon nitride (Silicon Nitride), or the like. The first conductive plate 1b and the second conductive plate 1c are made of a material having high electrical conductivity such as copper or aluminum.

  In FIG. 1, a power source 5 is directly connected to the first conductive plate 1b, and a voltage is applied between the first conductive plate 1b and the second conductive plate 1c. However, the power source 5 is not directly connected to the first conductive plate 1b, but an electrode is newly arranged and brought into contact with the surface of the first conductive plate 1b that is not in contact with the insulating plate 1a. A voltage may be applied from the power source 5 between the first conductive plate 1b and the second conductive plate 1c of the insulating substrate 1. That is, the crack detection apparatus according to the first exemplary embodiment of the present invention only needs to be able to apply a voltage between the first conductive plate 1b and the second conductive plate 1c, and is newly arranged. A voltage may be applied between the first conductive plate 1b and the second conductive plate 1c from the power source 5 via an electrode or the like.

  Similarly, in FIG. 1, the ammeter 8 is directly connected to the second conductive plate 1c, but an electrode is newly arranged on the surface side of the second conductive plate 1c that is not in contact with the insulating plate 1a. The current flowing between the first conductive plate 1b and the second conductive plate 1c via the electrodes may be measured by an ammeter 8 through the electrodes.

  Here, the first conductive plate 1b shown in FIG. 1 is patterned as a circuit pattern. Therefore, it has a plurality of divided conductive plates. In FIG. 1, wiring from the power source 5 is connected to all of the divided first conductive plates 1b. However, the voltage is applied as evenly as possible in the insulating substrate 1 so that the distribution of the voltage applied between the first conductive plate 1b and the second conductive plate 1c cannot be generated in the insulating substrate 1. Therefore, the connection between the power source 5 and the first conductive plate 1b is considered as appropriate according to the pattern of the first conductive plate 1b and the second conductive plate 1c. The wiring from the power source 5 is not necessarily connected to all of the first conductive plates 1b divided into two. When a voltage is applied between the first conductive plate 1b and the second conductive plate 1c, the plurality of divided conductive plates of the first conductive plate 1b are electrically shared. ing.

  The connection between the second conductive plate 1c and the ammeter 8 is also not shown here, but is not limited to this, so the first conductive plate 1b and the second conductive plate 1c are not limited thereto. This is considered according to the pattern.

  It should be noted that the first conductive plate 1b and the second conductive plate 1c may be integrated without being patterned, or may be patterned and have a plurality of divided conductive plates. 1 is a single unit of the insulating substrate 1 and can detect cracks in the insulating substrate 1. Only a slight difference occurs in the stress applied to the insulating substrate 1, and the effect of the present invention is not changed.

  In Embodiment 1 of the present invention, the power source 5 is connected so as to apply a negative DC voltage to the first conductive plate 1b. This is because creeping discharge that occurs when a large plate-like electrode is connected to one surface of an insulator and a small plate-like electrode is connected to the other surface and a voltage is applied between the two electrodes causes negative polarity to the small electrode. This is because it is generally known that applying a voltage is less likely to occur than applying a positive voltage. In Embodiment 1 of the present invention, the first conductive plate 1b is patterned, and the second conductive plate 1c is not patterned. Since it can be considered that the conductive plate 1c is replaced with the above-mentioned large electrode, the power source 5 is connected so as to apply a negative DC voltage to the first conductive plate 1b.

  Therefore, the shape of the first conductive plate 1b and the second conductive plate 1c, whether any electrode is interposed when a voltage is applied between the first conductive plate 1b and the second conductive plate 1c, etc. Depending on various conditions, the type of voltage applied to the first conductive plate 1b is changed.

  The determination device 9 compares the value measured by the ammeter 8 with the crack determination current threshold value X input to the determination device 9 in advance, and the value measured by the ammeter 8 is equal to or greater than the crack determination current threshold value X. In this case, it is determined that the insulating substrate 1 has a crack, and when it is less, it is determined that there is no crack. The crack determination current threshold value X is determined from the first conductive plate 1b to the first conductive plate 1b when a voltage is applied between the first conductive plate 1b and the second conductive plate 1c when there is no crack in the insulating substrate 1. It is the electric current value which calculated the electric current which flows into the 2 conductive plate 1c.

  In general, a crack in the insulating substrate 1 can be detected by measuring a leakage current with a voltage applied to the insulating substrate 1. Here, the leakage current is a current measured by the ammeter 8, and is a current that flows through the insulating plate 1a between the first conductive plate 1b and the second conductive plate 1c. When a current value measured by the ammeter 8 is rapidly increased in a state where a voltage is applied to the insulating substrate 1, that is, when the leakage current increases rapidly, the insulating substrate 1 has a crack. If the leakage current increases rapidly with voltage applied to the insulating substrate 1, the value of the current flowing through the insulating substrate 1 exceeds the crack determination current threshold value X.

  Here, the bending stress applied to the insulating substrate 1 from the stress applying jig 2 is set so as to be a stress applied to the insulating substrate 1 when the insulating substrate 1 is assembled into the shape of the power module. The stress applied to the insulating substrate 1 when the insulating substrate 1 is assembled into the shape of the power module varies depending on the size of the insulating substrate 1 and the shape of the power module. Therefore, the bending stress applied from the stress applying jig 2 to the insulating substrate 1 is appropriately determined depending on the size of the insulating substrate 1 and the shape of the power module in which the insulating substrate 1 is assembled thereafter.

  For example, the bending stress applied to the insulating substrate 1 from the stress applying jig 2 can be determined by a stress simulation when the insulating substrate 1 is assembled into the shape of a power module. In addition, when a bending stress is applied to the insulating substrate 1, it can be derived from an actual measurement value at which the insulating substrate 1 breaks.

  Even if it tries to detect the crack of the insulating substrate 1 before assembling into the shape of the power module by applying the non-defective product judgment device of the conventional power module that detects the crack of the insulating substrate after assembling into the shape of the power module, it cannot be detected. It was. This is because the cracks of the insulating substrate 1 before assembling into the shape of the power module can be detected only by increasing the applied voltage and increasing the sensitivity for detecting cracks, except for cracks that can be visually confirmed. It was thought that this was caused by a crack called a latent crack. A potential crack is a crack that does not penetrate completely in the thickness direction of the insulating plate 1a, and is a crack in which the insulating plates 1a on both sides of the crack are in close contact. In addition, even if the insulating plate 1a is completely penetrated in the thickness direction, the insulating plates 1a on both sides of the crack are in close contact with each other, and a crack that does not create a space in the insulating substrate 1 is also included in the potential crack. However, such cracks are rare.

  A crack is detected when the leakage current of the insulating substrate 1 increases rapidly. The sudden increase in leakage current is triggered by a discharge in the crack. In order for discharge to occur in the crack, there must be a minute space filled with air to some extent in the crack. Although the potential crack is a crack, since the insulating plates 1a on both sides of the crack are in close contact with each other, there is no minute space filled with air to some extent. Therefore, the crack detection apparatus according to the first exemplary embodiment of the present invention applies a bending stress to the insulating substrate 1 to generate a minute space in the potential crack.

  That is, the crack detection apparatus according to the first exemplary embodiment of the present invention applies a bending stress to the insulating substrate 1 to generate a minute space in the potential crack so that electric discharge easily occurs in the potential crack. It was. By doing so, it was considered to detect cracks in the insulating substrate 1 with a low applied voltage without increasing the applied voltage and increasing the sensitivity to detect cracks in the insulating substrate 1. The bending stress applied to the insulating substrate 1 by the stress applying jig of the crack detection apparatus according to the first embodiment of the present invention is the stress applied to the insulating substrate 1 when the insulating substrate 1 is assembled into the shape of the power module. Therefore, the stress is applied to the insulating substrate 1 and does not apply a stress enough to destroy the insulating substrate 1.

  FIG. 2 is a graph showing the relationship between the voltage applied to the insulating substrate 1 and the current flowing through the insulating substrate 1 for explaining the effect of the crack detection apparatus for the insulating substrate according to the first embodiment of the present invention. In FIG. 2, a solid line A indicates a relationship between a voltage applied to the insulating substrate 1 in an atmospheric pressure / room temperature environment without applying a bending stress to the insulating substrate 1 and a current flowing through the insulating substrate 1 at this time (V−I Characteristic). A broken line L1 indicates the voltage applied to the insulating substrate 1 under the atmospheric pressure / room temperature environment by applying a bending stress to the insulating substrate 1 using the crack detection apparatus according to the first embodiment of the present invention, and the insulating substrate 1 at that time. The relationship (VI characteristic) of the electric current which flows into is shown.

These are Paschen that the discharge start voltage V _S [V] of the gas in the crack in an equal electric field is expressed as a function of the product of the pressure P [Pa] in the crack and the gap distance d [m] in the crack. It is derived from the law. It is calculated that the thickness of the insulating plate 1a is 1 mm and there is a potential crack in the insulating plate 1a. In FIG. 2, the voltage applied to the insulating substrate 1 and the value of the current flowing through the insulating substrate 1 are shown as absolute values. Both the solid line A and the broken line L1 are not the evaluation results performed on the insulating substrate 1 assembled in the shape of the power module, but the evaluation results performed on the insulating substrate 1 alone not assembled in the shape of the power module. . A one-dot chain line X represents a line of the crack determination current threshold value X.

  In FIG. 2, when the applied voltage is Y in the solid line A and the applied voltage is Q1 in the broken line L1, the current flowing through the insulating substrate 1 increases rapidly and exceeds the crack determination current threshold value X. ing. The fact that the current flowing through the insulating substrate 1 suddenly increases and exceeds the crack determination current threshold value X means that when the applied voltage is Y on the solid line A and when the applied voltage is Q1 on the broken line L1. This means that the leakage current has increased rapidly. That is, when the applied voltage is Y in the solid line A and the applied voltage is Q1 in the broken line L1, a crack in the insulating substrate 1 is detected. Y at this time is called the discharge start voltage Y of the solid line A, and Q1 is called the discharge start voltage Q1 of the broken line L1.

  That is, when detecting a crack in the insulating substrate 1 under the condition of the solid line A, the crack in the insulating substrate 1 cannot be detected unless a voltage higher than the discharge start voltage Y is applied to the insulating substrate 1. On the other hand, when detecting a crack in the insulating substrate 1 under the condition of the broken line L1, if a voltage higher than the discharge start voltage Q1 is applied to the insulating substrate 1, the crack in the insulating substrate 1 can be detected. When the crack of the insulating substrate 1 is detected under the conditions, the voltage applied to the insulating substrate 1 can be made lower than when the crack of the insulating substrate 1 is detected under the condition of the solid line A. The difference in detection conditions between the solid line A and the broken line L1 is whether or not bending stress is applied to the insulating substrate 1.

  As described above, in the first embodiment of the present invention, the bending stress is applied to the insulating substrate 1 with respect to the single insulating substrate 1 using the crack detection device for the insulating substrate according to the first embodiment of the present invention. Thus, it was found that the voltage applied to the insulating substrate 1 can be reduced when detecting cracks in the insulating substrate 1. Therefore, the crack detection apparatus according to the first embodiment of the present invention is a state in which the applied voltage is low and the applied voltage is increased without increasing the sensitivity for detecting the cracks of the insulating substrate 1. It can be seen that That is, the insulating substrate crack detecting apparatus according to the first embodiment of the present invention can detect a crack in the insulating substrate 1 with the insulating substrate 1 alone.

  Next, a method for detecting cracks in the insulating substrate using the crack detection apparatus according to the first embodiment of the present invention will be described. Here, the case where the crack detection apparatus concerning Embodiment 1 of this invention is used at the time of the acceptance inspection of the purchased insulated substrate 1 is demonstrated. That is, when the purchased insulating substrate 1 is received, the presence or absence of a crack in the insulating substrate 1 is determined, and the insulating substrate 1 that should not be assembled into the shape of the power module is found. And it prevents that the insulating substrate 1 which has a crack is assembled in the shape of a power module, and a wasteful part is taken out.

  In the method for detecting cracks in an insulating substrate using the crack detection apparatus according to the first embodiment of the present invention, the voltage applied between the first conductive plate 1b and the second conductive plate 1c is determined here as crack determination. Called voltage. Here, since the crack detection apparatus according to the first embodiment of the present invention will be described when used at the time of acceptance inspection of the purchased insulating substrate 1, the crack determination voltage is determined to be one value. In this case, since the crack determination voltage must first be determined before the crack detection of the insulating substrate using the crack detection apparatus according to the first embodiment of the present invention is started, the crack determination voltage will be described.

  The crack determination voltage can be determined as follows, for example. 100 insulating substrates 1 with potential cracks are prepared. And about the 100 insulating substrates 1, when a voltage is applied to the insulating substrate 1 in a state where bending stress is applied to the insulating substrate 1 using the crack detection apparatus according to the first embodiment of the present invention, The value of the current flowing through the insulating substrate 1 increases rapidly, and a discharge start voltage exceeding the crack determination current threshold value X is acquired. Then, one discharge start voltage is derived using statistical processing such as Weibull distribution, and a value slightly higher than that is used as a crack determination voltage.

  In addition, it is slightly higher than the discharge start voltage that can be theoretically calculated using the characteristics of the material of the insulating substrate 1, the structural parameters, the bending stress applied to the insulating substrate 1 when assembled into the shape of the power module, and the like. The value may be a crack determination voltage. In the method for detecting cracks in an insulating substrate using the crack detection apparatus according to the first embodiment of the present invention, the crack determination voltage surely increases the leakage current reliably when there is a crack in the insulating substrate 1. Since the value needs to be a value, the value is slightly higher than the discharge start voltage.

  FIG. 3 is a process flow diagram illustrating a method for detecting cracks in an insulating substrate using the crack detection apparatus for insulating substrates according to the first embodiment of the present invention. As shown in FIG. 3, the method for detecting a crack in the insulating substrate 1 using the insulating substrate crack detecting apparatus according to the first embodiment of the present invention includes seven steps from step S0 to step S6.

  First, an insulating substrate 1 is prepared in step S0, a stress gauge 6 is attached to the insulating substrate 1 in step S1, a bending stress is applied by fixing the insulating substrate 1 with the stress applying jig 2 in step S2, and step S3. In step S4, the insulating substrate 1 fixed by the stress applying jig 2 and applied with bending stress is placed in the sealed container 4, and a crack determination voltage is applied to the insulating substrate 1 in step S4. In step S5, the current flowing through the insulating substrate 1 is measured by the ammeter 8, and the current value obtained in step S5 is compared with the crack determination current threshold value X in step S6.

  In step S6, if the current value obtained in step S5 is equal to or greater than the crack determination current threshold value X, it is determined that the insulating substrate 1 has a crack, resulting in R1. On the other hand, if the current value obtained in step S5 is less than the crack determination current threshold value X, it is determined that there is no crack in the insulating substrate 1, resulting in R2.

  The details of the seven steps from Step S0 to Step S6 in FIG. 3 will be described. First, in step S0, an insulating substrate 1 having a first conductive plate 1b on one surface of the insulating plate 1a and the insulating plate 1a and a second conductive plate 1c on the other surface of the insulating plate 1a is prepared. . In step S1, the stress gauge 6 is attached to the surface of the second conductive plate 1c that is not in contact with the insulating plate 1a.

  Step S2 is the first step of the method for detecting cracks in the insulating substrate according to the present invention, and the first conductive plate 1b and the other surface of the insulating plate 1a on one surface of the insulating plate 1a and the insulating plate 1a. This is a step of applying a bending stress to the insulating substrate 1 having the second conductive plate 1c thereon. In step S2, the insulating substrate 1 is fixed by the support jig 2a, and the screw jig 2b is tightened in the direction of the first conductive plate 1b of the insulating substrate 1. The block jig 2c is pushed by tightening the screw jig 2b, and a bending stress is applied to the insulating substrate 1 by the block jig 2c.

  In step S <b> 3, the insulating substrate 1 fixed by the stress applying jig 2 and applied with bending stress is placed in the sealed container 4.

  Step S4 is the second step of the method for detecting cracks in an insulating substrate according to the present invention, and is between the first conductive plate 1b and the second conductive plate 1c of the insulating substrate 1 to which bending stress is applied. This is a step of applying a voltage. In step S4, a crack determination voltage is applied between the first conductive plate 1b and the second conductive plate 1c of the insulating substrate 1 disposed in the sealed container 4.

  Step S5 is a third step of the method for detecting cracks in an insulating substrate according to the present invention, and is a second step of the method for detecting cracks in an insulating substrate according to the present invention, that is, the first conductive plate 1b and step S4. This is a step of measuring the current flowing between the second conductive plate 1c. In step S5, the ammeter 8 measures the value of current flowing between the first conductive plate 1b and the second conductive plate 1c of the insulating substrate 1.

  Step S6 is the fourth step of the method for detecting cracks in an insulating substrate according to the present invention, and is the third step of the method for detecting cracks in an insulating substrate according to the present invention, that is, the insulating substrate from the current value measured in step S5. 1 is a step of determining the presence or absence of a crack. In step S6, the determination device 9 compares the current value obtained in step S5 with the crack determination current threshold value X input in advance to the determination device 9, and determines the presence or absence of a crack.

  Through the above steps, as described above, if the current value obtained in step S5 is greater than or equal to the crack determination current threshold value X in step S6, it is determined that the insulating substrate 1 has a crack. When the current value obtained in step S5 is less than the crack determination current threshold value X, it is determined that the insulating substrate 1 has no crack.

  In addition, among the insulating substrates 1 determined to have cracks in this way, the insulating substrate 1 determined to have no cracks is rotated 90 degrees, and the steps S1 to S6 are performed again. Furthermore, the presence or absence of a crack in the insulating substrate 1 can be determined more precisely. This is because the process from step S1 to step S6 is performed again after being rotated by 90 degrees, so that the presence or absence of cracks in a state where the direction of the bending stress applied to the insulating substrate 1 is rotated by 90 degrees is further determined. Because it becomes.

  As described above, in the first embodiment of the present invention, it is possible to detect the cracks in the insulating substrate 1 alone with respect to the presence or absence of cracks in the insulating substrate 1 used in power equipment such as a power module.

  In the above description, the crack detection device according to the first exemplary embodiment of the present invention has been described in the case of using the purchased insulating substrate 1 during an acceptance inspection. However, the use of the crack detection apparatus according to the first embodiment of the present invention is not limited to this. For example, when a voltage is applied to the insulating substrate 1 in step S4, the bending stress applied to the insulating substrate 1 is gradually increased. It can also be used in the development stage of the insulating substrate 1 by examining whether it is possible to prevent the generation of cracks.

Embodiment 2. FIG.
In the second embodiment of the present invention, portions that are different from the first embodiment of the present invention will be described, and descriptions of the same or corresponding portions will be omitted. The second embodiment of the present invention is different from the first embodiment of the present invention in that the crack detection device for an insulating substrate further includes a heater.

  FIG. 4 is a schematic diagram showing the configuration of an insulating substrate crack detection apparatus according to the second embodiment of the present invention. In the crack detection apparatus for an insulating substrate according to the second embodiment of the present invention, a heater 3 for heating the insulating substrate 1 is further added to the crack detection apparatus for the insulating substrate according to the first embodiment of the present invention. Hereinafter, the crack detection apparatus for an insulating substrate according to the second embodiment of the present invention is simply referred to as a crack detection apparatus according to the second embodiment of the present invention.

  The heater 3 heats the insulating substrate 1 by setting the inside of the sealed container 4 to a high temperature. The heater 3 raises the temperature inside the sealed container 4 so that the temperature of the insulating substrate 1 becomes the maximum temperature applied to the insulating substrate 1 when the insulating substrate 1 is assembled in the shape of the power module and the power module is driven. Yes.

  FIG. 5 is a graph showing the relationship between the voltage applied to the insulating substrate 1 and the current flowing through the insulating substrate 1 for explaining the effect of the crack detection apparatus for an insulating substrate according to the second embodiment of the present invention. In FIG. 5, the solid line A is the same as the solid line A in FIG. 2, and the voltage applied to the insulating substrate 1 in an atmospheric pressure / room temperature environment without applying bending stress to the insulating substrate 1, The relationship (V-I characteristic) of the flowing electric current is shown. The long broken line B shows the relationship between the voltage applied to the insulating substrate 1 in an atmospheric pressure / high temperature environment without applying a bending stress to the insulating substrate 1 and the current flowing through the insulating substrate 1 at that time (V-I characteristic). Show. A broken line L2 applies a bending stress to the insulating substrate 1 using the crack detection apparatus according to the second embodiment of the present invention, heats the insulating substrate 1, and applies it to the insulating substrate 1 under an atmospheric pressure / high temperature environment. The relationship between the voltage and the current flowing through the insulating substrate 1 at that time (VI characteristic) is shown.

  These are derived from Paschen's law, as in the first embodiment of the present invention. In FIG. 5, the voltage applied to the insulating substrate 1 and the value of the current flowing through the insulating substrate 1 are shown as absolute values. The solid line A, the long broken line B, and the broken line L2 are not evaluation results performed on the insulating substrate 1 assembled in the shape of the power module, but performed on the insulating substrate 1 alone not assembled in the shape of the power module. It is an evaluation result. A one-dot chain line X represents a line of the crack determination current threshold value X.

  In FIG. 5, when the applied voltage is Y in the solid line A, the applied voltage is W in the long broken line B, and the applied voltage is Q2 in the broken line L2, in FIG. Furthermore, it rapidly increases and exceeds the crack determination current threshold value X. The fact that the current flowing through the insulating substrate 1 suddenly increases and exceeds the crack determination current threshold value X means that when the applied voltage is Y in the solid line A and W is applied in the long broken line B. In addition, the broken line L2 indicates that when the applied voltage becomes Q2, the leak current increases rapidly and a crack in the insulating substrate 1 is detected. Y at this time is called the discharge start voltage Y of the solid line A, W is called the discharge start voltage W of the long broken line B, and Q2 is called the discharge start voltage Q2 of the broken line L2.

Here, the relationship between the discharge start voltage and the temperature will be described. The density ρ [kg / m ³ ] is inversely proportional to the absolute temperature T [K] under the constant atmospheric pressure environment from the gas equation of state, so that the relational expression ρT = constant can be said. Therefore, at a high temperature, the discharge start voltage decreases due to a change in gas density. That is, by setting the insulating substrate 1 to a high temperature, the gas density in the crack changes, and the discharge start voltage can be lowered. This is indicated by the solid line A and the long broken line B in FIG. 5, and the crack of the insulating substrate 1 is detected under the condition of the long broken line B rather than the crack of the insulating substrate 1 detected under the condition of the solid line A. However, the voltage applied to the insulating substrate 1 can be lowered.

  The crack detection apparatus according to the second embodiment of the present invention uses the above-described relationship between the discharge start voltage and the temperature to start the discharge of cracks in the insulating substrate 1 than the crack detection apparatus according to the first embodiment of the present invention. The voltage can be lowered. This is because the crack detection apparatus according to the second embodiment of the present invention further includes the heater 3 for heating the insulating substrate 1 in addition to the crack detection apparatus according to the first embodiment of the present invention. This is because the temperature of the gas in the crack can be raised. Needless to say, the discharge start voltage Q2 is smaller than the discharge start voltage Q1.

  Next, a crack detection method for an insulating substrate using the crack detection apparatus according to the second embodiment of the present invention will be described. FIG. 6 is a process flow diagram illustrating a method for detecting cracks in an insulating substrate using the crack detection apparatus for insulating substrates according to the second embodiment of the present invention. The method for detecting a crack in the insulating substrate 1 using the insulating substrate crack detecting apparatus according to the second embodiment of the present invention is the same as that of the insulating substrate 1 using the insulating substrate crack detecting apparatus according to the first embodiment of the present invention. Before step S4 of the crack detection method, step S3-1 is performed in which the inside of the sealed container 4 is heated to a high temperature by the heater 3. That is, step S4 is performed with the insulating substrate 1 heated. The other steps are the same or correspond to each other, and thus description thereof is omitted.

  As described above, in the second embodiment of the present invention, the presence or absence of cracks in the insulating substrate 1 used in power equipment such as a power module is detected with the insulating substrate 1 alone, and the cracks in the insulating substrate are detected with a low applied voltage. Can do.

Embodiment 3 FIG.
In the third embodiment of the present invention, portions that are different from the first embodiment of the present invention will be described, and descriptions of the same or corresponding portions will be omitted. The third embodiment of the present invention is different from the first embodiment of the present invention in that the crack detection device for an insulating substrate further includes a pressure regulator.

  FIG. 7 is a schematic diagram showing a configuration of a crack detection apparatus for an insulating substrate according to a third embodiment of the present invention. The crack detection apparatus for an insulating substrate according to the third embodiment of the present invention further includes a pressure regulator 10 for reducing the atmosphere in which the insulating substrate 1 is present in the crack detection apparatus for the insulating substrate according to the first embodiment of the present invention. ing. Hereinafter, the crack detection apparatus for an insulating substrate according to the third embodiment of the present invention is simply referred to as a crack detection apparatus according to the third embodiment of the present invention.

  The pressure regulator 10 adjusts the atmospheric pressure of the atmosphere in which the insulating substrate 1 exists, that is, the atmospheric pressure in the sealed container 4 to a reduced pressure value. The pressure regulator 10 includes a pressure gauge, a vacuum pump, and a valve, and is configured to be able to adjust the valve so that the air pressure in the sealed container 4 becomes a specified reduced pressure value. The pressure regulator 10 is not limited to the above-described configuration because it only needs to have a configuration capable of adjusting the atmospheric pressure of the atmosphere with the insulating substrate 1 to a reduced pressure value.

Here, the discharge start voltage will be further described. As described above, the discharge start voltage V _S [V] of the gas in the crack in the equal electric field is a function of the product of the pressure P [Pa] in the crack and the gap distance d [m] in the crack according to Paschen's law. Can be expressed as Since the atmospheric pressure P can be replaced by the gas density ρ, it can be expressed by a relational expression of V _S = f (Pd) = f (ρd). FIG. 8 is a view for explaining the crack detection apparatus for an insulating substrate according to the third embodiment of the present invention, and shows a Paschen curve. As shown in FIG. 8, the discharge start voltage V _S of the gas in the crack depends on the atmospheric pressure P of the gas in the crack and has a minimum value. This minimum value is called the Paschen minimum. It can be seen from the Paschen curve that the discharge start voltage can be minimized by bringing the product of the pressure P of the gas in the crack and the gap distance d in the crack closer to the Paschen minimum.

  When the gas in the crack is air, assuming that the thickness of the insulating plate 1a is 1 mm and the gap distance d in the crack is 1 mm, the atmospheric pressure in the crack realizing the Paschen minimum is 660 Pa. Therefore, the pressure regulator 10 of the crack detection apparatus according to the third embodiment of the present invention preferably sets the pressure in the crack of the insulating substrate 1 to a value that realizes the Paschen minimum, where the gap in the crack When the distance d is 1 mm, the inside of the sealed container 4 is preferably decompressed so that the pressure inside the sealed container 4 is about 660 Pa.

  FIG. 9 is a graph showing the relationship between the voltage applied to the insulating substrate 1 and the current flowing through the insulating substrate 1 for explaining the effect of the crack detection apparatus for an insulating substrate according to the third embodiment of the present invention. In FIG. 9, the solid line A is the same as the solid line A in FIG. 2, and the voltage applied to the insulating substrate 1 under the atmospheric pressure / room temperature environment without applying bending stress to the insulating substrate 1, The relationship (V-I characteristic) of the flowing electric current is shown. The long broken line C shows the relationship between the voltage applied to the insulating substrate 1 in a reduced pressure / room temperature environment without applying bending stress to the insulating substrate 1 and the current flowing through the insulating substrate 1 at that time (V-I characteristics). ing. A broken line L3 applies a bending stress to the insulating substrate 1 using the crack detection apparatus according to the second embodiment of the present invention, depressurizes the atmosphere in which the insulating substrate 1 is present, and moves to the insulating substrate 1 under a reduced pressure / room temperature environment. The relationship (V-I characteristic) of the applied voltage and the electric current which flows into the insulated substrate 1 at that time is shown.

  In FIG. 9, when the applied voltage is Y in the solid line A, the applied voltage is V in the long broken line C, and the applied voltage is Q3 in the broken line L3 in FIG. Furthermore, it rapidly increases and exceeds the crack determination current threshold value X. The fact that the current flowing through the insulating substrate 1 suddenly increases and exceeds the crack determination current threshold value X means that when the applied voltage becomes Y on the solid line A and when the applied voltage becomes V on the long broken line C. In addition, the broken line L3 indicates that when the applied voltage becomes Q3, the leakage current increases rapidly and a crack in the insulating substrate 1 is detected. Y at this time is called the discharge start voltage Y of the solid line A, V is called the discharge start voltage V of the long broken line C, and Q3 is called the discharge start voltage Q3 of the broken line L3.

  The crack detection apparatus according to the third embodiment of the present invention uses the Paschen's law described above to lower the crack discharge start voltage of the insulating substrate 1 than the crack detection apparatus according to the first embodiment of the present invention. Can do. Because, the crack detection apparatus according to the second embodiment of the present invention is further added to the crack detection apparatus according to the first embodiment of the present invention, a pressure regulator 10 that depressurizes the atmosphere with the insulating substrate 1. This is because the atmospheric pressure in the crack can be reduced by reducing the atmosphere in which the insulating substrate 1 is present. Needless to say, the discharge start voltage Q3 is smaller than the discharge start voltage Q1.

  Next, a crack detection method for an insulating substrate using the crack detection apparatus according to the third embodiment of the present invention will be described. FIG. 10 is a process flow diagram illustrating a method for detecting cracks in an insulating substrate using the crack detection apparatus for insulating substrates according to the third embodiment of the present invention. The method for detecting a crack in the insulating substrate 1 using the insulating substrate crack detecting apparatus according to the third embodiment of the present invention is the same as that of the insulating substrate 1 using the insulating substrate crack detecting apparatus according to the first embodiment of the present invention. Before step S4 of the crack detection method, step S3-2 for reducing the pressure in the sealed container 4 by the pressure regulator 10 is provided. That is, step S4 is performed in a state where the atmosphere in which the insulating substrate 1 is present is decompressed. The other steps are the same or correspond to each other, and thus description thereof is omitted.

  As described above, in the third embodiment of the present invention, the presence or absence of cracks in the insulating substrate 1 used in power equipment such as a power module is detected with the insulating substrate 1 alone, and the cracks in the insulating substrate are detected at a lower applied voltage. be able to.

Embodiment 4 FIG.
In the fourth embodiment of the present invention, parts different from the first to third embodiments of the present invention will be described, and description of the same or corresponding parts will be omitted. The fourth embodiment of the present invention is a combination of the second embodiment of the present invention and the third embodiment of the present invention. The first embodiment is different from the first embodiment in that a crack detecting device for an insulating substrate is further provided with a heater and a pressure regulator. Is different.

  FIG. 11 is a schematic diagram illustrating a configuration of a crack detection apparatus for an insulating substrate according to a fourth embodiment of the present invention. Insulating substrate crack detection apparatus according to the fourth embodiment of the present invention is an atmosphere in which insulating substrate crack detecting apparatus according to the first embodiment of the present invention includes a heater 3 for heating insulating substrate 1 and insulating substrate 1. And a pressure regulator 10 for reducing the pressure. Hereinafter, the crack detection apparatus for an insulating substrate according to the fourth embodiment of the present invention is simply referred to as a crack detection apparatus according to the fourth embodiment of the present invention.

  Since the heater 3 is the same as that described in Embodiment 2 of the present invention and the pressure regulator 10 is the same as that described in Embodiment 3 of the present invention, the description thereof is omitted here.

  FIG. 12 is a graph showing the relationship between the voltage applied to the insulating substrate 1 and the current flowing through the insulating substrate 1 for explaining the effect of the crack detection apparatus for an insulating substrate according to the fourth embodiment of the present invention. In FIG. 12, the solid line A is the same as the solid line A in FIG. 2, and the voltage applied to the insulating substrate 1 under the atmospheric pressure / room temperature environment without applying a bending stress to the insulating substrate 1, and the insulating substrate 1 at that time. The relationship (V-I characteristic) of the flowing electric current is shown. The long broken line D shows the relationship between the voltage applied to the insulating substrate 1 in a reduced pressure / high temperature environment without applying bending stress to the insulating substrate 1 and the current flowing through the insulating substrate 1 at that time (V-I characteristics). ing. A broken line L4 applies a bending stress to the insulating substrate 1 using the crack detection apparatus according to the fourth embodiment of the present invention, heats the insulating substrate 1, and further reduces the atmosphere in which the insulating substrate 1 is present, thereby reducing the pressure. The relationship between the voltage applied to the insulating substrate 1 in a high temperature environment and the current flowing through the insulating substrate 1 at that time (VI characteristics) is shown.

  In FIG. 12, when the applied voltage is Y in the solid line A, the applied voltage is U in the long broken line D, and the applied voltage is Q4 in the broken line L4 in FIG. Furthermore, it rapidly increases and exceeds the crack determination current threshold value X. The fact that the current flowing through the insulating substrate 1 suddenly increases and exceeds the crack determination current threshold value X means that when the applied voltage is Y in the solid line A and U is applied in the long broken line D. In addition, the broken line L4 indicates that when the applied voltage becomes Q4, the leakage current increases rapidly and a crack in the insulating substrate 1 is detected. Y at this time is called the discharge start voltage Y of the solid line A, U is called the discharge start voltage U of the long broken line D, and Q4 is called the discharge start voltage Q4 of the broken line L4.

  The crack detection apparatus according to the fourth embodiment of the present invention utilizes the relationship between the discharge start voltage and the temperature described in the second embodiment of the present invention and the Paschen's law described in the third embodiment of the present invention. As compared with the crack detection device according to the first embodiment of the present invention, the second embodiment of the present invention, or the third embodiment of the present invention, the discharge start voltage in the crack of the insulating substrate 1 can be lowered. This is because the crack detection apparatus according to the fourth embodiment of the present invention is the same as the crack detection apparatus according to the first embodiment of the present invention, except that the heater 3 that heats the insulating substrate 1 and the pressure that depressurizes the atmosphere in which the insulating substrate 1 is present. This is because the regulator 10 is further added, so that the insulating substrate 1 can be heated, and the atmosphere in which the insulating substrate 1 is present can be reduced to reduce the pressure in the crack. Needless to say, the discharge start voltage Q4 is smaller than any one of the discharge start voltage Q1, the discharge start voltage Q2, and the discharge start voltage Q3.

  Next, a crack detection method for an insulating substrate using the crack detection apparatus according to the fourth embodiment of the present invention will be described. FIG. 13 is a process flow diagram illustrating a method for detecting cracks in an insulating substrate using the insulating substrate crack detecting apparatus according to the fourth embodiment of the present invention. The method for detecting a crack in the insulating substrate 1 using the insulating substrate crack detecting apparatus according to the fourth embodiment of the present invention is the same as that of the insulating substrate 1 using the insulating substrate crack detecting apparatus according to the first embodiment of the present invention. Prior to step S4 of the crack detection method, step S3-1 in which the inside of the sealed container 4 is heated to a high temperature by the heater 3 and step S3-2 in which the inside of the sealed container 4 is depressurized by the pressure regulator 10 are provided. . That is, step S4 is performed in a state where the insulating substrate 1 is heated and the atmosphere in which the insulating substrate 1 is present is decompressed. The other steps are the same or correspond to each other, and thus description thereof is omitted. The order of step S3-1 and step S3-2 may be interchanged, and step S4 may be performed in a state where the insulating substrate 1 is heated and the atmosphere where the insulating substrate 1 is present is decompressed.

  As described above, in the fourth embodiment of the present invention, the presence or absence of cracks in the insulating substrate 1 used in power equipment such as a power module is detected by the insulating substrate 1 alone with the cracks in the insulating substrate being in a lower applied voltage state. be able to.

  In the present invention, it is further determined that there is no crack in the method for detecting a crack in an insulating substrate using the crack detecting device for an insulating substrate according to any one of the first to third embodiments of the present invention. A power module can be manufactured by disposing a semiconductor element based on Si, SiC or the like on the insulating substrate 1 and sealing the insulating substrate 1 and the semiconductor element with a resin.

  The power module in this specification is a so-called case-type power module in which an insulating substrate is mounted, a semiconductor element based on Si, SiC, or the like is mounted and sealed with a sealing resin such as silicone gel, All semiconductor devices, such as what is called a mold type power module, sealed by transfer molding with a mold resin such as an epoxy resin are shown.

  In the present invention, each embodiment can be appropriately modified or omitted within the scope of the invention.

  DESCRIPTION OF SYMBOLS 1 Insulation board | substrate, 1a Insulation board, 1b 1st electroconductive board, 1c 2nd electroconductive board, 2 Stress application jig, 2a Support jig, 2b Screw jig, 2c Block jig, 3 Heater, 4 Airtight container, 5 power source, 6 stress gauge, 7 stress monitor, 8 ammeter, 9 judgment device, 10 pressure regulator.

Claims (7)

A stress applying jig for applying a bending stress to an insulating substrate having an insulating plate and a first conductive plate on one surface of the insulating plate and a second conductive plate on the other surface of the insulating plate;
A power source for applying a voltage between the first conductive plate and the second conductive plate;
An ammeter for measuring a value of a current flowing between the first conductive plate and the second conductive plate;
From the value measured by the ammeter, a determination device that determines the presence or absence of cracks in the insulating substrate,
Insulating substrate crack detection device comprising: A heater for heating the insulating substrate;
The crack detection apparatus for an insulating substrate according to claim 1, further comprising: A pressure regulator for adjusting the atmospheric pressure of the atmosphere with the insulating substrate to a reduced pressure value;
The crack detection apparatus of the insulated substrate of Claim 1 or Claim 2 further provided. Applying a bending stress to an insulating substrate having an insulating plate and a first conductive plate on one surface of the insulating plate and a second conductive plate on the other surface of the insulating plate;
A second step of applying a voltage between the first conductive plate and the second conductive plate of the insulating substrate to which bending stress is applied;
A third step of measuring a current flowing between the first conductive plate and the second conductive plate by the second step;
A fourth step of determining the presence or absence of cracks in the insulating substrate from the current value measured in the third step;
A method for detecting cracks in an insulating substrate comprising: Performing the second step in a state where the insulating substrate is heated;
The method for detecting cracks in an insulating substrate according to claim 4. The second step is performed in a state where the atmosphere with the insulating substrate is decompressed;
The method for detecting cracks in an insulating substrate according to claim 4 or 5, wherein: A semiconductor element is disposed on the insulating substrate that is determined to have no cracks by the crack detection method for an insulating substrate according to any one of claims 4 to 6, and the insulating substrate and the semiconductor element are made of resin. A method for manufacturing a power module that is sealed with

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