JP2008135595A - Power module - Google Patents

Abstract

A power module capable of achieving both high cooling performance and improved reliability against thermal stress generation.
A DBA substrate 16 in which a first Al layer 10, a ceramic plate 12, and a second Al layer 14 are laminated in this order, and a semiconductor chip 18 are provided on one main surface side of the semiconductor chip. The first Al layer 10 of the DBA substrate 16 is bonded via the solder 20, and a microchannel is formed in the second Al layer 14.
[Selection] Figure 1

Description

  The present invention relates to a power module.

  As miniaturization and capacity increase of power modules, the temperature rise of the semiconductor chip mounted in the module and the problem of thermal stress generated with the temperature rise and the temperature gradient become obvious. These problems will lead to a decrease in the reliability of the power module and should be overcome. Various types of power modules have been proposed (see, for example, Patent Document 1 and Non-Patent Document 1).

  In the power module proposed in Non-Patent Document 1, the substrate bonded to the semiconductor chip is a Cu layer / ceramic plate / Cu layer laminate (DBC substrate), and a cooling channel is provided in one Cu layer. It is characterized by being formed. This is intended to achieve high cooling performance.

  However, in this power module, there is a concern that the reliability is lowered due to the generation of thermal stress. This is because Cu has a larger coefficient of thermal expansion than semiconductor chips (Si) and ceramics, so that a large thermal stress may occur when there is a temperature rise or a temperature gradient. Therefore, it is difficult for this power module to achieve both high cooling performance and improved reliability against thermal stress generation.

  The power module proposed in Patent Document 1 is characterized by a double-sided cooling structure in which a semiconductor chip is sandwiched by Cu plates via solder from above and below, and a cooler is disposed via an insulating material. On the other hand, the generation of thermal stress due to the difference in thermal expansion coefficient between the Cu plate and the semiconductor chip (Si) is a concern as in the above example, but this problem has been overcome by resin molding. The effect of the resin mold is to constrain the deformation of each structural member caused by the thermal stress, thereby ensuring the reliability of the module against the thermal stress.

It can be considered that this module achieves both high cooling performance to some extent and improved reliability against thermal stress generation. In this way, resin molds are used to combat thermal stress. However, in large-area modules where a large number of chips, such as those found in automotive power modules, are placed in the module, this resin mold must be completely performed. Is impossible. Therefore, it is difficult to say that this module achieves both high cooling performance and improved reliability against thermal stress generation.
JP2003-110064 APEC2006 p885-p891

  As described above, it is considered that both the high cooling performance and the improvement in reliability against the generation of thermal stress are not realized in the conventional technology.

  An object of the present invention is to provide a power module capable of achieving both high cooling performance and improved reliability against thermal stress generation.

  The above object is achieved by the present invention described below. That is, the present invention includes a DBA substrate in which a first Al layer, a ceramic plate, and a second Al layer are laminated in this order, and a semiconductor chip, and solder is provided on one main surface side of the semiconductor chip. The first Al layer of the DBA substrate is bonded to the power module, and a microchannel is formed in the second Al layer. Since the microchannel is formed at a position closest to the semiconductor chip, the thermal resistance from the semiconductor chip to the microchannel can be greatly reduced by flowing the coolant through the microchannel. In addition, thermal stress can be relieved by the deformation of the microchannel due to the presence of the microchannel. As described above, both high cooling performance and low thermal stress can be achieved.

The power module of the present invention preferably includes at least one of the following first to third aspects.
(1) In the first aspect, the first Al layer of the DBA substrate is bonded to the other main surface side of the semiconductor chip via solder, and a microchannel is connected to the second Al layer. Is an aspect in which is formed. Thus, cooling performance can be made more excellent by cooling the upper and lower surfaces of the semiconductor chip. In addition, since stress relaxation can be achieved on both the upper and lower surfaces, deformation due to thermal stress can be efficiently suppressed.
(2) A 2nd aspect is an aspect with which the cooling member made from Al is provided in the said 2nd Al layer side of the said DBA board | substrate. By providing the Al cooling member, the cooling efficiency can be further increased.
(3) A third aspect is an aspect in which the Al purity in at least one of the first Al layer, the second Al layer, and the cooling member is 99.99% by mass or more. By setting the Al purity to 99.99% or more, the yield stress is low and deformation is easy, and the thermal stress can be further relaxed.

  The present invention also includes a semiconductor chip and a pair of substrates provided on both principal surface sides of the semiconductor chip, and one of the substrates is disposed on both principal surface sides of the semiconductor chip via solder. A DBA substrate in which the surfaces are bonded, a microchannel is formed on the other surface of the substrate, and the substrate is formed by laminating a first Al layer, a ceramic plate, and a second Al layer in this order; or The power module is a DBC substrate in which a first Cu layer, a ceramic plate, and a second Cu layer are laminated in this order. Due to the presence of the microchannel, it is possible to achieve both high cooling performance and low thermal stress as described above.

  According to the present invention, it is possible to provide a power module capable of achieving both high cooling performance and improved reliability against thermal stress generation.

[First embodiment]
As shown in FIG. 1, the power module according to the first embodiment of the present invention includes a DBA substrate 16 in which a first Al layer 10, a ceramic plate 12, and a second Al layer 14 are laminated in this order, The first Al layer 10 of the DBA substrate 16 is bonded to one main surface side of the semiconductor chip 18 via the solder 20, and the second Al layer 14 is connected to the second Al layer 14. A microchannel is formed. Further, the second Al layer 14 is joined to the cooling member 22. The “main surface” means a surface having the largest surface area in a semiconductor chip or the like.

  Since the power module has excellent cooling performance, the temperature rise of the semiconductor chip 18 can be reduced. On the other hand, regarding the problem of thermal stress generated in the module structural member, it is possible to reduce the thermal stress generated by temperature rise or temperature gradient because of its excellent stress relaxation function. That is, the present invention has the effect of achieving both high cooling performance and low thermal stress.

  Here, the reason why such cooling performance is excellent is that (1) the semiconductor chip 18 is cooled from one surface side, and (2) the second A1 layer 14 on one surface side of the DBA substrate 16 is microchanneled. This is thought to be because the semiconductor chip 14 is cooled by forming the thermal resistance from the semiconductor chip 14 to the microchannel. In addition, the thermal resistance can be greatly reduced from the point that the microchannel is formed closest to the semiconductor chip 18.

  The reason why the stress relaxation function is excellent is that the second A1 layer 14 in which the microchannel is formed in the DBA substrate 16 is less rigid and easily deformed than in the case without the microchannel, so that the thermal stress is relaxed. It is thought that it is possible.

  The power module according to the first embodiment may have a configuration in which DBA substrates 16 are provided on both surfaces of a semiconductor chip 18 as shown in FIG. 2 in which members that are the same as those in FIG. That is, the first Al layer 10 of the DBA substrate 16 is bonded to both main surface sides of the semiconductor chip 18 via the solder 20, and a microchannel is formed in the second Al layer 14.

  In this way, by cooling the upper and lower surfaces of the semiconductor chip 18, the cooling performance can be further improved. In addition, stress relaxation can be achieved on both the upper and lower surfaces, so that deformation due to thermal stress can be suppressed more efficiently.

  In the power module according to the first embodiment, as shown in FIGS. 1 and 2, an Al cooling member 22 may be further provided on the second Al layer 14 side of the DBA substrate 16. By providing the cooling member 22 made of Al, the cooling efficiency can be further increased. As the cooling member 22 made of Al, it is preferable to employ a configuration in which fins that enhance cooling efficiency are provided.

  The Al purity in at least one of the first Al layer 10, the second Al layer 14, and the cooling member 22 is preferably 99.99% or more. By setting it as 99.99% or more, the yield stress is low and it becomes easy to deform, and the thermal stress can be more relaxed. In particular, when A1 is 99.99% or more, A1 has a very low yield stress and is easy to creep. Therefore, the stress relaxation effect more than expected can be expected by using this material. The Al purity of all the members is more preferably 99.99% or higher.

The thicknesses of the first Al layer 10 and the second Al layer 14 are each preferably 0.3 to 3 mm. Each thickness is preferably the same. The groove depth, groove width, and groove pitch of the microchannel provided in the second Al layer 14 are preferably 0.3 to 3 mm, 0.3 to 3 mm, and 0.6 to 6 mm, respectively. . As the ceramic plate 12, AlN, Al ₂ O ₃ , SiN, or the like can be used, but AlN is preferable in consideration of thermal conductivity. The ceramic plate 12 is preferably 0.2 to 2 mm.

  Here, examples of the semiconductor chip 18 include IGBTs (elements in which MOS FETs and bipolar transistors are combined into one chip), transistors such as power MOSs and power transistors, diodes, and the like.

[Second form]
A power module according to a second aspect of the present invention includes a semiconductor chip and a pair of substrates provided on both main surfaces of the semiconductor chip, and solder is provided on both main surfaces of the semiconductor chip. The one surface of the substrate is joined to each other, and the microchannel is formed on the other surface of the substrate, and the substrate connects the first Al layer, the ceramic plate, and the second Al layer to each other. The structure is a DBA substrate that is sequentially laminated or a DBC substrate in which a first Cu layer, a ceramic plate, and a second Cu layer are laminated in this order.

  In other words, the DBC substrate is used instead of the DBA substrate in the embodiment shown in FIG. 2 or the embodiment shown in FIG. As a mode in which a DBC substrate is used instead of the DBA substrate, high cooling performance and low thermal stress can be achieved at the same time as in the power module according to the first embodiment. However, considering relaxation of thermal stress, the first aspect may be preferable.

  The present invention will be specifically described by the following examples, but the present invention is not limited thereto.

(Example 1)
Two semiconductor chips (IGBT and diode) were prepared, and a DBA substrate (AlN (0.635 mm) was used for the ceramic plate) was joined to the lower surface of these semiconductor chips via solder to produce a power module. (See Figure 1 for structure). Regarding the bonded DBA substrate, one having an Al layer (second Al layer (1 mm)) on one side formed with a microchannel (a flow path for flowing a cooling medium having a stripe pattern) was used. Further, an Al cooler (cooling member) was joined to the outside of the DBA substrate by brazing. The microchannel formed in the A1 layer of the DBA substrate and the cooler provided outside the DBA substrate are designed so that the cooling water flows, so that the semiconductor chip is cooled twice from the lower surface. become. The purity of each A1 layer of the DBA substrate and the A1 constituting the cooler was 99.99%. The groove depth, groove width, and groove pitch of the microchannel were 1 mm, 1 mm, and 2 mm, respectively.

(Example 2)
Two semiconductor chips (IGBT and diode) are prepared, and a DBA substrate (AlN (0.635 mm) is used for the ceramic plate) is joined via solder from both the upper and lower sides of these semiconductor chips. Was made. Regarding the two DBA substrates bonded up and down, a substrate in which a microchannel (a flow path for flowing a cooling medium having a stripe pattern) is formed in the A1 layer (second Al layer (1 mm)) on one side is used. . A cooler (cooling member) made of A1 was joined to the outside of each of the two DBA substrates by brazing. The cooling channel is designed to flow through the microchannel formed in the A1 layer of the DBA substrate and the cooler provided outside the DBA substrate, and the semiconductor chip is cooled twice from both the upper and lower surfaces. become. The purity of each A1 layer of the DBA substrate and the A1 constituting the cooler was 99.99%. The groove depth, groove width, and groove pitch of the microchannel were 1 mm, 1 mm, and 2 mm, respectively.

  Here, the stress-strain characteristic of A1 is shown in FIG. From this result, it can be seen that A1 has a very low yield stress compared to Cu and exhibits remarkable creep, and is excellent in stress relaxation.

  FIG. 4 shows the stress-strain characteristics when the Al purity is different. As can be seen from FIG. 4, as the purity of Al increases, the stress decreases and an excellent stress relaxation effect is exhibited.

  From the above, the power modules of Example 1 and Example 2 are expected to exhibit an excellent stress relaxation effect. In addition, since the microchannel is formed at a position closest to the semiconductor chip, it is expected that the thermal resistance from the semiconductor chip to the microchannel can be significantly reduced by flowing a coolant through the microchannel.

It is sectional drawing which shows the structure of a power module. It is sectional drawing which shows the structure of a power module. It is a figure which shows the stress-strain characteristic of A1 and Cu. It is a figure which shows the stress-strain characteristic at the time of making Al purity different.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... 1st Al layer 12 ... Ceramic plate 14 ... 2nd Al layer 16 ... DBA substrate 18 ... Semiconductor chip 20 ... Solder

Claims (5)

A DBA substrate in which a first Al layer, a ceramic plate, and a second Al layer are laminated in this order, and a semiconductor chip;
The first Al layer of the DBA substrate is bonded to one main surface side of the semiconductor chip via solder,
A power module in which a microchannel is formed in the second Al layer. The first Al layer of the DBA substrate is bonded to the other main surface side of the semiconductor chip via solder,
A power module in which a microchannel is formed in the second Al layer.   The power module according to claim 1, wherein an Al cooling member is provided on the second Al layer side of the DBA substrate.   The power module according to any one of claims 1 to 3, wherein an Al purity in at least one of the first Al layer, the second Al layer, and the cooling member is 99.99 mass% or more. . A semiconductor chip, and a pair of substrates provided on both main surface sides of the semiconductor chip,
The one surface of the substrate is bonded to both main surface sides of the semiconductor chip via solder, and a microchannel is formed on the other surface of the substrate,
The substrate is a DBA substrate in which a first Al layer, a ceramic plate, and a second Al layer are laminated in this order, or a DBC in which a first Cu layer, a ceramic plate, and a second Cu layer are laminated in this order. A power module that is a substrate.

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