JP2013084657A - Semiconductor device and control method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device capable of relaxing a stress generated in a joint material layer between a semiconductor device and a mounting substrate, and a control method thereof.SOLUTION: A semiconductor device comprises: a mounting substrate 4; semiconductor elements 2 and 3 mounted on the mounting substrate via a thermoplastic joint material layer 5 having an electrical conduction property; and control means 6 for controlling the energization of the semiconductor elements. The control means performs stress relaxation control for softening at least the thermoplastic joint material layer under prescribed conditions.

Description

  The present invention relates to a semiconductor device and a control method thereof.

  A semiconductor device used as a power transistor or the like, comprising: a semiconductor chip; an insulating material that insulates current from the semiconductor chip; and a heat dissipating material that dissipates heat generated from the semiconductor chip. A thing provided with the buffer material for buffering the thermal stress by the thermal expansion difference with a heat radiating material is known (patent documents 1).

JP 2008-277317 A

  However, although the above-mentioned prior art can buffer the thermal stress due to the difference in thermal expansion between the insulating material and the heat dissipation material by the buffer material, the thermal stress is applied to the solder layer for mounting the semiconductor chip on the circuit board by the heat generated from the semiconductor chip. This acts as residual stress, which may cause cracks in the solder layer.

  The problem to be solved by the present invention is to provide a semiconductor device that can relieve stress generated in a bonding material layer between a semiconductor element and a mounting substrate, and a control method therefor.

  The present invention solves the above-described problem by at least softening the thermoplastic bonding material layer between the semiconductor element and the mounting substrate by controlling energization of the semiconductor element.

  According to the present invention, the residual stress accumulated in the thermoplastic bonding material layer can be relaxed by softening the thermoplastic bonding material layer.

1 is a perspective view showing a semiconductor device according to an embodiment of the present invention. It is sectional drawing which follows the II-II line of FIG. 1 is an equivalent circuit showing a semiconductor device according to an embodiment of the present invention. It is a flowchart which shows the control procedure of the controller of FIG. It is a top view (V arrow of FIG. 2) which shows the semiconductor device which concerns on other embodiment of this invention. It is a perspective view which shows the semiconductor device which concerns on further another embodiment of this invention. It is sectional drawing which follows the VII-VII line of FIG. It is a perspective view which shows the semiconductor device which concerns on further another embodiment of this invention. It is sectional drawing which follows the IX-IX line of FIG. It is a perspective view which shows the semiconductor device which concerns on further another embodiment of this invention. It is sectional drawing which follows the XI-XI line of FIG. It is a perspective view which shows the semiconductor device which concerns on further another embodiment of this invention. It is sectional drawing which follows the XIII-XIII line | wire of FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<< First Embodiment >>
The semiconductor device 1 according to this example has semiconductor elements that generate heat when energized, such as the transistor 2 and the diode 3 shown in FIG. 3, and these are soldered to the mounting substrate 4 as shown in FIGS. And a controller 6 that controls ON / OFF of the transistor 2 as shown in FIG. 3. This type of semiconductor device 1 is configured as a power module as shown in FIGS. 1 and 2 and can be used in an AC-AC, AC-DC, and DC-AC power conversion circuit.

  Hereinafter, the present invention will be described by giving an example in which a power conversion circuit (inverter circuit) including the semiconductor device 1 having the circuit configuration shown in FIG. 3 is applied to a power conversion device for an electric vehicle. However, the semiconductor device 1 of the present invention can be applied as long as a semiconductor element that generates heat is mounted on a substrate.

  The mounting substrate 4 shown in FIGS. 1 and 2 is a rigid substrate in which conductive patterns 4b are formed on the front and back sides of the insulating substrate 4a. Although not shown in the drawing, A heat radiating fin is attached or another power module is connected. On the other hand, a transistor 2 such as an IGBT and a diode 3 are mounted on a conductive pattern 4 b on the surface of the mounting substrate 4 via a thermoplastic bonding material layer 5.

  The thermoplastic bonding material layer 5 of this example is a layer made of a bonding material having electrical conductivity and thermoplasticity such as a solder material, and the transistor 2 and the diode 3 are formed on the surface of the mounting substrate 4 by a solder reflow process. Be joined. The thermoplastic bonding material layer 5 has a softening point (softening temperature) at which the material softens and a melting point at which the material melts in a higher temperature region. When the temperature of the thermoplastic bonding material layer 5 increases, the thermoplastic bonding material layer 5 softens at the softening point. After starting to melt, it melts into a liquid at the melting point, but when the temperature falls below the softening point, it returns to the original solid.

The controller 6 of this example controls energization of the transistor 2 or the diode 3, and specifically is a control device that outputs an ON / OFF signal to the transistor 2. Although shown as the dedicated controller 6 in FIG. 3, when applied to a power conversion circuit such as an inverter, it can be included in a controller that outputs an ON / OFF signal to the transistor of the inverter. The controller 6 of this example
Stress relaxation control is executed to at least soften the thermoplastic bonding material layer 5 under predetermined conditions. This will be described later.

  As shown in FIGS. 1 and 2, a temperature sensor 7 is mounted in the vicinity of the transistor 2 of the semiconductor device 1, and the temperature sensor 7 is a controller so that a detection signal from the temperature sensor 7 is output to the controller 6. 6 is connected. The temperature sensor 7 can directly detect the temperature of the thermoplastic bonding material layer 5 that fixes the transistor 2, but at the same time, the temperature of the thermoplastic bonding material layer 5 that fixes the diode 3 is also multiplied by a correction coefficient. And can be detected indirectly. Heat from the transistor 2 and the diode 3 is transmitted to the thermoplastic bonding material layer 5 and residual stress is generated by repeating the cooling / heating cycle. In order to detect the state of the cooling / heating cycle, the temperature detected by the temperature sensor 7 is detected. Used. However, the temperature sensor 7 is not essential in the semiconductor device of the present invention, and the temperature of the thermoplastic bonding material layer 5 may be estimated based on a control signal from the controller 6 or a control circuit of the power conversion circuit.

  As shown in FIG. 3, a signal related to the driving load state is input to the controller 6 from the controller 8 of the vehicle on which the semiconductor device 1 is mounted. The driving load state of the vehicle is a state in which the semiconductor device 1 of this example is stopped when the driving load is zero. In addition to the state where the vehicle is stopped or stopped, power conversion is performed in a hybrid vehicle or the like. This includes a state where the circuit is stopped. If the stress relaxation control of this example is executed when the driving load of the vehicle is large, the running performance of the vehicle is affected. Therefore, when the driving load of the vehicle is zero or low, the stress relaxation control is executed to determine a preferable timing. Therefore, the driving load state of the vehicle is detected.

Next, the control procedure of the controller 6 will be described.
As shown in FIG. 4, first, the output signal of the temperature sensor 7 is read (step S1), and it is determined whether or not the temperature of the thermoplastic bonding material layer 5 is equal to or higher than a predetermined threshold temperature _Tth (step S2). As the predetermined threshold temperature T _th , it is preferable to set a lower limit value of a temperature at which thermal stress is generated in the thermoplastic bonding material layer 5. If the temperature of the thermoplastic bonding material layer 5 is lower than the predetermined threshold temperature _{Tth, the} process returns to step S1 and the reading of the output signal from the temperature sensor 7 is repeated. If the temperature is higher than the predetermined threshold temperature _Tth, step S3 is repeated. to advances, as well as counting the number of times equal to or greater than a predetermined threshold temperature T _th, the number of times counted until now to determine whether or not a predetermined number N _th or more. The predetermined number N _th, it is preferable that the thermoplastic bonding material layer 5 is set with reference to whether the residual stress and it is repeated much time to be more than a predetermined threshold temperature T _th is generated. That is, in steps S2 and S3 of this example, the residual stress of the thermoplastic bonding material layer 5 is detected or estimated based on the integrated degree of temperature × time.

Number of equal to or greater than a predetermined threshold temperature T _th at step S3 is repeated from the reading of the temperature sensor 7 is returned to step S1 if it is less than the predetermined number N _th, but not less than the predetermined number N _th to step S4 The process proceeds to determine whether or not the vehicle is stopped based on a signal relating to the driving load state from the controller 8 of the vehicle on which the semiconductor device 1 of this example is mounted. If the vehicle is not stopped in step S4, the process returns to step S1 and repeats from the reading of the temperature sensor 7. If the vehicle is stopped, the process proceeds to step S5, and a control signal is output from the controller 6. Stress relaxation control is started by passing a current through the transistor 2 and the diode 3. Thereby, the transistor 2 and the diode 3 generate heat, and the temperature of the thermoplastic bonding material layer 5 starts to rise.

  In step S6, the output signal of the temperature sensor 7 is read, and in step S7, a control signal from the controller 6 is controlled in accordance with the temperature of the thermoplastic bonding material layer 5 detected by the temperature sensor 7, and flows to the transistor 2 and the diode 3. Adjust the current. That is, when the temperature difference between the temperature of the thermoplastic bonding material layer 5 and the softening point is large, energization control in which a large current flows through the transistor 2 and the diode 3 is performed, and conversely, the temperature and softening of the thermoplastic bonding material layer 5 are performed. When the temperature difference from the point is small, the current flowing through the transistor 2 and the diode 3 is suppressed.

  If the temperature of the thermoplastic bonding material layer 5 is raised to at least the softening point, the thermoplastic bonding material layer 5 is softened. Therefore, in the stress relaxation control of this example, the thermoplastic bonding material layer 5 is set to the softening point or higher. Although the residual stress is reduced by raising the temperature, the temperature may be raised to the melting point of the thermoplastic bonding material layer 5 or higher. Residual stress is further reduced or eliminated by raising the temperature to the melting point or higher.

  In step S8, it is determined whether or not the temperature of the thermoplastic bonding material layer 5 detected by the temperature sensor 7 has reached the softening point. If not, the process returns to step S6 and steps S7 and S8 are repeated. On the other hand, when the temperature of the thermoplastic bonding material layer 5 reaches the softening point, the process proceeds to step S9, and the stress relaxation control of the thermoplastic bonding material layer 5 by the controller 6 is ended.

  In step S10, the thermoplastic bonding material layer 5 is cooled and re-solidified by a control signal from the controller 6. At this time, natural cooling may be performed, but it is preferable to adjust the control signal of the controller 6 to cool with the same temperature profile as the reflow process when the transistor 2 and the diode 3 are mounted. When the re-solidification of the thermoplastic bonding material layer 5 is completed, the number of times counted in step S3 is reset, and then the process returns to step S1 to repeat the above processing.

  As described above, according to the semiconductor device 1 of this example, when residual stress is generated in the thermoplastic bonding material layer 5, the stress relaxation control is executed at a timing that does not affect the running state of the vehicle. The layer 5 is softened, and the residual stress accumulated so far can be reduced or removed. As a result, the mounting part of the transistor 2 and the diode 3 can be extended.

  Further, according to the semiconductor device 1 of this example, the control accuracy of the controller 6 is improved by using the temperature detection value from the temperature sensor 7 and can be softened at an optimal temperature for an optimal time.

  Further, according to the semiconductor device 1 of this example, the residual stress is detected or estimated based on the actual operating environment such as the temperature of the thermoplastic bonding material layer 5 × the integrated degree of time, and the residual stress becomes a predetermined threshold or more. In this case, since the stress relaxation control is executed, it is possible to avoid softening the thermoplastic bonding material layer 5 at an unnecessary timing.

  Further, according to the semiconductor device 1 of the present example, the driving load state is detected such as when the vehicle is stopped, and the stress relaxation control is executed when the driving load is small, which may adversely affect the running performance of the vehicle. Is prevented.

  Moreover, according to the semiconductor device 1 of this example, the temperature profile when the thermoplastic bonding material layer 5 is re-solidified in the cooling process of step S10 has the same characteristics as the temperature profile of the reflow process at the time of mounting. It is possible to make the size of the particles of the thermoplastic bonding material layer 5 having the same as that immediately after the initial mounting.

<< Second Embodiment >>
A semiconductor device 1 according to another embodiment of the present invention will be described. 5 is a perspective plan view of the thermoplastic bonding material layer 5 as viewed from the top of the transistor 2 or the diode 3 as viewed from the direction of arrow V in FIG. Between the mounting substrate 4 of this example and the semiconductor element 2 or 3, the thermoplastic bonding material layer 5 of the first embodiment described above and the second heat provided in a portion other than the thermoplastic bonding material layer 5. It is comprised from 5 A of plastic joining material layers. Specifically, as shown in FIG. 5, the softening point T ₁ (or the thermoplastic bonding material layer 5) is formed on the portion excluding the end of the transistor 2 or the diode 3, that is, on the central portion of the thermoplastic bonding material layer 5. A second thermoplastic bonding material layer 5 having a higher softening point T ₂ (or melting point) and electrical conductivity is provided.

Then, in step S5 and subsequent stress relief control of FIG. 4, the controller 6, at least the power supply control transistor 2 or diode 3 so that the temperature of the second thermoplastic bonding material layer 5A is a temperature below the softening point T ₂ To do.

  According to the semiconductor device 1 of this example, even if the thermoplastic bonding material layer 5 having electrical conductivity having a low softening point (or melting point) is softened or liquefied, the second thermoplastic bonding material layer 5A is softened or liquefied. Therefore, the inclination of the semiconductor element such as the transistor 2 or the diode 3 can be prevented. As a result, it is possible to prevent an electrical short circuit from occurring due to execution of stress relaxation control. Moreover, since it can prevent that the thickness of the thermoplastic joining material layer 5 varies when it softens or liquefies, it can also prevent that the part where stress concentrates arises.

<< Third Embodiment >>
A semiconductor device 1 according to still another embodiment of the present invention will be described. 6 to 13 are perspective views showing respective embodiments in which outflow prevention means 9, 10, 11, and 12 for damming the molten material of the thermoplastic bonding material layer 5 are provided around the thermoplastic bonding material layer 5. FIG. FIG. Explaining each, the first example shown in FIGS. 6 and 7 is provided with a resin frame 9 on the surface of the mounting substrate 4 so as to surround the periphery of the transistor 2 and the diode 3.

  In the second example shown in FIGS. 8 and 9, the range including the transistor 2 and the diode 3 is sealed with a resin sealing body 10 using a resin mold. In the third example shown in FIGS. 10 and 11, a resin resist film 11 surrounding the thermoplastic bonding material layer 5 is provided. In the fourth example shown in FIGS. 12 and 13, an annular recess 12 is provided around the thermoplastic bonding material layer 5.

  In any form of the first example to the fourth example, even if the thermoplastic bonding material layer 5 is liquefied when the stress relaxation control is executed, the resin frame 9, the resin sealing body 10, and the resin resist The outflow of the liquefied material can be blocked by the film 11 or the annular recess 12, and the performance of the semiconductor device 1 can be prevented from being deteriorated when re-solidified.

  The transistor 2 and the diode 3 correspond to a semiconductor element according to the present invention, the controller 6 corresponds to a control means according to the present invention, the temperature sensor corresponds to a temperature detection means according to the present invention, and the vehicle controller 8 Corresponds to the load detection means according to the present invention, and the resin frame body 9, the resin sealing body 10, the resin resist film 11 and the annular recess 12 correspond to the outflow prevention means according to the present invention.

DESCRIPTION OF SYMBOLS 1 ... Semiconductor device 2 ... Transistor 3 ... Diode 4 ... Mounting board 5 ... Thermoplastic joining material layer 5A ... 2nd thermoplastic joining material layer 6 ... Controller 7 ... Temperature sensor 8 ... Vehicle controller 9 ... Resin frame 10 ... Resin sealing body 11 ... resin resist film 12 ... annular recess

Claims (8)

A mounting board;
A semiconductor element mounted on the mounting substrate via a thermoplastic bonding material layer having electrical conductivity;
In a semiconductor device comprising a control means for controlling energization of the semiconductor element,
The said control means is a semiconductor device which performs stress relaxation control which at least softens the said thermoplastic joining material layer on predetermined conditions. A temperature detecting means for directly or indirectly detecting the temperature of the thermoplastic bonding material layer;
The semiconductor device according to claim 1, wherein the control unit controls energization to the semiconductor element according to a temperature detected by the temperature detection unit.   3. The semiconductor device according to claim 1, wherein the control unit executes the stress relaxation control when a time or number of times when the temperature detected by the temperature detection unit is equal to or higher than a predetermined threshold reaches a predetermined threshold. Load detecting means for detecting a driving load state of a vehicle on which the semiconductor device is mounted;
The semiconductor device according to claim 1, wherein the control unit performs the stress relaxation control when a driving load state of the vehicle by the load detection unit is a predetermined threshold value or less. A second layer provided at a portion other than the thermoplastic bonding material layer between the mounting substrate and the semiconductor element and having a softening point T ₂ higher than a softening point T ₁ of the thermoplastic bonding material layer and electrical conductivity. Further comprising a thermoplastic bonding material layer,
Said control means, a temperature of at least the second thermoplastic bonding material layer according to any one of claims 2-4 to perform the stress relaxation controlled to a temperature of less than said softening point T ₂ Semiconductor device.   The control means according to any one of claims 1 to 5, wherein when the thermoplastic bonding material layer is melted, the temperature profile at the time of cooling is set equal to the temperature profile of the cooling process at the time of mounting the semiconductor element. The semiconductor device described.   The semiconductor device according to claim 1, further comprising an outflow prevention unit that dams up a molten material of the thermoplastic bonding material layer around the thermoplastic bonding material layer. For a semiconductor device in which a semiconductor element is mounted on a mounting substrate via a thermoplastic bonding material layer having electrical conductivity,
Detecting a residual stress of the thermoplastic bonding material layer;
A method of controlling a semiconductor device, comprising: energizing the semiconductor element to soften at least the thermoplastic bonding material layer when the residual stress is equal to or greater than a predetermined threshold.

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