JP2010287844A - Power module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power module allowed to be inexpensively manufactured, having an excellent heat releasing property and for preventing electric insulation from being reduced even when a high voltage is applied for a long time under a high-temperature and high-humidity environment. <P>SOLUTION: In the power module including an organic insulating layer 2 between a Cu base substrate 1 and a Cu substrate 4, a Cu migration preventing layer is formed on a surface of the Cu base substrate and/or the Cu substrate to which a positive voltage is applied, which is brought into contact with the organic insulating layer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a power module that can be used even in a high-temperature and high-humidity environment.

  Power modules are required to efficiently dissipate heat generated from semiconductor elements while ensuring electrical insulation. In particular, in circuit boards for semiconductor mounting, in recent years, high density mounting and high performance have been demanded, and along with miniaturization and high performance of semiconductor elements, and miniaturization and high density of circuit wiring, The problem is how to dissipate the heat generated from the semiconductor element. Therefore, a power module using a highly thermally conductive organic insulating layer as an insulating layer between a Cu substrate (for example, a Cu circuit substrate or a Cu heat spreader) on which a semiconductor element is mounted and a metal base substrate, and excellent heat dissipation A power module having a different structure has been proposed. Here, the high thermal conductivity organic insulating layer is generally a layer in which a thermal conductive filler such as ceramics is dispersed in a thermosetting resin such as an epoxy resin.

  For example, Patent Document 1 proposes a power module in which a lead frame is provided on a metal base substrate via an organic insulating layer. Patent Document 2 proposes a power module in which predetermined heat dissipation members are provided on both sides of a semiconductor element. These power modules are excellent in heat dissipation as described in the literature.

On the other hand, the power module is often used in a situation where a high voltage of several hundred to several thousand volts is applied in a high-temperature moisture absorption environment, so that a deterioration phenomenon such as a leak or a short circuit occurs, and the power module may fail. is there.
Thus, several methods for preventing these deterioration phenomena have been proposed. For example, in Patent Document 3, an organic insulating layer between a metal base substrate and a lead frame is provided so that the organic insulating layer protrudes from the end portion of the metal base substrate. It has been proposed to prevent short circuits. Moreover, in patent document 4, by sealing using the sealing resin which added the additive combined with an ionic impurity, between lead frames when sealing resin peels, and between a lead frame and a metal base substrate It has been proposed to prevent the occurrence of leaks and shorts by preventing Cu migration in the meantime. Further, Patent Document 5 proposes a method for detecting timing at which the possibility that a short circuit occurs between a pair of electrodes to be insulated by using a special semiconductor chip.

JP 2001-196495 A JP 2001-156225 A JP-A-8-204098 JP 2003-92379 A JP 2008-177293 A

However, when a power module is used in a situation where a high voltage is applied in a high-temperature moisture-absorbing environment, it is between the lead frame and the metal base substrate end, between the lead frames when the sealing resin is peeled off, and between the lead frame and the metal. Leakage or short-circuiting occurs not only with the base substrate but also with deterioration of the organic insulating layer itself.
On the other hand, it is considered that deterioration of the organic insulating layer can be suppressed by increasing the filling of a thermally conductive filler such as ceramics with a high-pressure hot press or the like. Compared to power modules used in electrical appliances, the environment in which they are used has increased in temperature and humidity. Under such circumstances, the deterioration of the organic insulating layer cannot be sufficiently suppressed. As a result, a leak or a short circuit occurs, and the reliability of the power module is significantly reduced.

  Such deterioration of the organic insulating layer is considered to proceed due to the following phenomenon. First, when the power module sealed with resin is used in a state where a high voltage is applied in a high temperature moisture absorption environment, the power module gradually absorbs moisture, and moisture gradually diffuses from the periphery to the inside of the organic insulating layer. Then, moisture enters between the member in contact with the organic insulating layer, and Cu constituting the member is ionized and eluted ([1] dissolution of Cu). Next, Cu ions move due to application of voltage or the like ([2] movement of Cu ions), and the moved Cu ions are subjected to a reducing action and are precipitated as Cu or a Cu compound ([3] Cu precipitation). This phenomenon is generally referred to as Cu migration, and it is considered that these three processes occur sequentially. When this Cu migration occurs, the effective distance between the electrodes becomes small and an uneven electric field is generated. As a result, electric field concentration occurs, and the electrical insulation is significantly reduced.

In addition, the above-mentioned Cu migration is accelerated by various factors such as an increase in the moisture penetration rate in the organic insulating layer, mixing of ionic impurities, and a pH change due to dissolution of the thermally conductive filler. Even when the high voltage is applied, the deterioration of the organic insulating layer due to Cu migration becomes severe.
On the other hand, when the power module is used particularly for vehicles, electric railways and the like, it is desirable to adopt some fail-safe design because a failure of the power module may impair safety. However, when the method of providing a special detection circuit as in Patent Document 5 is adopted, there is a problem that the manufacturing cost increases.

  The present invention has been made to solve the above problems, and can be manufactured at a low cost, has excellent heat dissipation, and can be applied for a long time in a high temperature and high humidity environment. An object of the present invention is to provide a power module in which electrical insulation does not deteriorate.

Therefore, as a result of intensive studies to solve the above problems, the present inventors have formed a Cu migration prevention layer on the surface of the Cu-containing member to which a positive voltage is applied in contact with the organic insulating layer, thereby increasing the temperature and the temperature. It has been found that Cu migration from a Cu-containing member can be prevented even when a high voltage is applied for a long time in a wet environment, and the present invention has been completed.
That is, the present invention is a power module including an organic insulating layer between a Cu base substrate and a Cu substrate, and a Cu base substrate to which a positive voltage is applied and / or a surface of the Cu substrate in contact with the organic insulating layer is Cu. A power module characterized in that a migration prevention layer is formed.
In addition, the present invention is a power module including an organic insulating layer between a metal base substrate and a Cu substrate, and a Cu migration preventing layer is formed on a surface of the Cu substrate in contact with the organic insulating layer to which a positive voltage is applied. It is the power module characterized by the above.

  According to the present invention, there is provided a power module that can be manufactured at low cost, has excellent heat dissipation, and does not deteriorate in electrical insulation even when a high voltage is applied for a long time in a high temperature and high humidity environment. be able to.

FIG. 3 is a cross-sectional view of the basic structure of the power module according to Embodiment 1. FIG. 3 is a cross-sectional view of the power module in the first embodiment. FIG. 3 is a cross-sectional view of the power module in the first embodiment.

Embodiment 1 FIG.
The power module of the present embodiment includes an organic insulating layer between the base substrate and the Cu substrate.
When the power module is mounted on various products, a high voltage of several hundred to several thousand volts is applied by an external voltage or the like. The applied voltage varies depending on the circuit on which the power module is mounted, the product function, and the like, and a positive voltage may be applied to the base substrate or a positive voltage may be applied to the Cu substrate. In some cases, the voltage applied to the power module during use of the product may be reversed. The positive voltage applied to the power module causes Cu migration with respect to a member made of the Cu-containing material, and degrades the organic insulating layer.

The power module of the present embodiment has a Cu migration preventing layer on the surface in contact with the organic insulating layer of the Cu-containing member to which a positive voltage is applied in order to prevent the occurrence of Cu migration due to the application of a high voltage as described above. Is forming.
Hereinafter, the basic structure of the power module of the present embodiment will be described with reference to the drawings.
FIG. 1 is a cross-sectional view of the basic structure of the power module of the present embodiment. (A) is the basic structure of the power module when a positive voltage is applied to the Cu substrate, (b) is when the positive voltage is applied to the base substrate, and (c) is the case where the applied voltage is inverted. FIG.

The basic structure of the power module (a) includes a base substrate 1, an organic insulating layer 2 formed on the base substrate 1, and a Cu substrate 4 formed on the organic insulating layer 2. A Cu migration preventing layer 3 is formed on the surface in contact with the organic insulating layer 2. In this basic structure, the base substrate 1 may be a Cu base substrate or a metal base substrate.
According to this basic structure, even if a positive voltage is applied to the Cu substrate 4, the presence of the Cu migration prevention layer 3 prevents Cu from being ionized and eluted from the Cu substrate 4, thereby preventing Cu migration. it can. As a result, the deterioration of the organic insulating layer 2 due to Cu migration does not occur, and a decrease in electrical insulation can be prevented.

The basic structure of the power module (b) includes a base substrate 1, an organic insulating layer 2 formed on the base substrate 1, and a Cu substrate 4 formed on the organic insulating layer 2. A Cu migration preventing layer 3 is formed on the surface in contact with the organic insulating layer 2. In this basic structure, the base substrate 1 is a Cu base substrate.
According to this basic structure, even if a positive voltage is applied to the base substrate 1, the presence of the Cu migration preventing layer 3 prevents Cu from being ionized and eluted from the base substrate 1, thereby preventing Cu migration. it can. As a result, the deterioration of the organic insulating layer 2 due to Cu migration does not occur, and a decrease in electrical insulation can be prevented.

The basic structure of the power module (c) includes a base substrate 1, an organic insulating layer 2 formed on the base substrate 1, and a Cu substrate 4 formed on the organic insulating layer 2. The Cu migration preventing layer 3 is formed on the surface of the Cu substrate 4 in contact with the organic insulating layer. In this basic structure, the base substrate 1 is a Cu base substrate.
According to this basic structure, even if the applied voltage is reversed (that is, even if a positive voltage is applied to both the base substrate 1 and the Cu substrate 4), the presence of the Cu migration preventing layer 3 makes the base substrate 1 And Cu does not ionize and elute from Cu substrate 4, and Cu migration can be prevented. As a result, the deterioration of the organic insulating layer 2 due to Cu migration does not occur, and a decrease in electrical insulation can be prevented.

The Cu migration preventing layer 3 is not particularly limited as long as ion migration is difficult to occur. In general, the ease of ion migration is related to various factors such as ionization tendency, pH, reaction rate, etc., and it is difficult to define uniquely, but for example, the standard electrode potential is higher than Cu. A layer formed of a metal (for example, Au, Pt, Pd, Fe, etc.) or an alloy thereof can be used as the Cu migration preventing layer 3.
Further, as shown in Table 1, the standard electrode potential of each metal is in a range of ± several V, and is lower than Cu in an environment of a high voltage of several hundred to several thousand V applied to the power module. Even if it is a metal, if it is a metal which forms an oxide on the surface and is passivated (for example, Ni, Sn, Al, etc.), ion migration hardly occurs. Therefore, a layer formed from these metals and alloys may be used as the Cu migration preventing layer 3.

Furthermore, even if a metal such as Ag is prone to ion migration, it can be used as the Cu migration preventing layer 3 if Pd, Cu or the like is added to form an alloy that hardly causes ion migration.
In FIG. 1, the Cu migration preventing layer 3 is a single layer, but may be a plurality of layers.

The formation method of the Cu migration preventing layer 3 is not particularly limited, and can be formed using a known surface treatment method. Examples of the surface treatment method include thermal spraying, electroplating, and electroless plating.
The thickness of the Cu migration preventing layer 3 is not particularly limited, but is preferably 0.05 μm or more, more preferably 0.5 μm or more and 5 μm or less. When the thickness of the Cu migration preventing layer 3 is less than 1 μm, the Cu migration preventing layer 3 is damaged by the heat conductive filler contained in the organic insulating layer 2 when bonded to the organic insulating layer 2 by hot pressing. , Cu migration prevention effect may not be sufficiently obtained.

  The Cu substrate 4 is not particularly limited, and a known Cu substrate can be used. This Cu substrate 4 is a substrate (Cu heat spreader) on which a circuit for the purpose of heat diffusion is not formed even if it is a circuit substrate (Cu circuit substrate) on which various circuit patterns are formed according to the application. There may be. Here, the Cu substrate 4 includes not only a substrate composed only of Cu but also a substrate composed of a compound (alloy) containing Cu or the like.

The base substrate 1 is not particularly limited, and a known base substrate can be used. Examples of the base substrate 1 include a Cu base substrate and an Al base substrate. Here, the Cu base substrate includes not only a base substrate composed of only Cu but also a base substrate composed of a compound (alloy) containing Cu or the like. Similarly, the Al base substrate includes not only a base substrate composed of only Al but also a base substrate composed of a compound (alloy) containing Al or the like.
When a Cu base substrate is used as the base substrate 1 and a positive voltage is applied to the base substrate 1, Cu migration occurs. Therefore, it is necessary to form the Cu migration prevention layer 3 on the Cu base substrate. On the other hand, when a metal base substrate other than Cu (for example, an Al base substrate) is used as the base substrate 1, Cu migration is slight in the metal base substrate, so the Cu migration prevention layer 3 is formed on the metal base substrate. There is no need.

  Further, when the Cu migration preventing layer 3 is formed on the Cu substrate 4, the adhesion between the organic insulating layer 2 and the Cu substrate 4 tends to be lowered, and peeling may occur after the heat cycle. The stress that causes the peeling is related to the thickness of the base substrate 1. If the base substrate 1 is too thick, peeling between the organic insulating layer 2 and the Cu substrate 4 occurs, and the reliability of the power module is increased. May decrease. Therefore, the thickness of the base substrate 1 is preferably 5 mm or less, more preferably 0.01 mm or more and 3 mm or less.

The organic insulating layer 2 is not particularly limited, and a known organic insulating layer (organic insulating sheet) can be used. Examples of the organic insulating layer 2 include a layer or sheet in which a heat conductive filler is dispersed in a thermosetting resin. Examples of the thermally conductive filler include fused silica (SiO ₂ ), crystalline silica (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), boron nitride (BN), aluminum nitride (AlN), silicon carbide (SiC), and the like. It is done. Moreover, as a thermosetting resin, an epoxy resin, an unsaturated polyester resin, a phenol resin, a melamine resin, a silicone resin, a polyimide resin, etc. are mentioned. The manufacturing method of this organic insulating layer (organic insulating sheet) is not particularly limited, and a known method can be used.
The thickness of the organic insulating layer 2 is not particularly limited, but is generally 10 μm or more and 1000 μm or less.

  The method for producing the basic structure of the power module is not particularly limited, and can be performed according to a known method. For example, after forming the Cu migration preventing layer 3 on the base substrate 1 and / or the Cu substrate 4, the base substrate 1, the organic insulating layer 2, and the Cu substrate 4 are laminated and bonded by hot pressing. If necessary, a desired circuit pattern may be formed on the Cu substrate 4 by etching or the like. What is necessary is just to set suitably about the conditions of hot press according to the magnitude | size, thickness, etc. of the material to be used.

The power module of the present embodiment has the above basic structure. An example of this power module will be described with reference to the drawings.
2 and 3 are cross-sectional views of the power module of the present embodiment. 2 and 3 show only the power module having the basic structure of FIG. 1 (a), it may have the basic structure of FIGS. 1 (b) and (c).
In FIG. 2, in addition to the basic structure of FIG. 1, the power module includes a semiconductor element 5 and external electrode terminals 9 arranged on a Cu substrate 4, and the semiconductor elements 5 are connected via metal wires 7. ing. Then, the case 10 provided around the structure body is sealed with a sealing resin 8 except for the external connection portion of the external electrode terminal 9 and the external heat dissipation portion of the base substrate 1.

The semiconductor element 5, the metal wire 7, the external electrode terminal 9, and the case 10 are not particularly limited, and known ones can be used. Also, these arrangement methods are not particularly limited, and can be performed according to known methods.
The sealing resin 8 is a known potting sealing material such as an epoxy resin, silicone gel, or rubber.
The method for manufacturing the power module in FIG. 2 is not particularly limited. For example, in addition to the basic structure, the semiconductor element 5, the metal wire 7, the external electrode terminal 9, and the case 10 are arranged and then sealed in the case 10 from above. What is necessary is just to seal the inside of a case by potting the stop resin 8 and making it heat-harden. What is necessary is just to set the conditions of heat curing suitably according to the sealing resin 8 to be used.

3, in the power module, in addition to the basic structure of FIG. 1, a semiconductor element 5 is disposed on a Cu substrate 4, a lead frame 6 is directly connected to the Cu substrate 4, and a metal wire 7 It is connected to the semiconductor element 5 via. The portions other than the external connection portion of the lead frame 6 and the external heat dissipation portion of the base substrate 1 are sealed with a sealing resin 8.
The semiconductor element 5, the lead frame 6, and the metal wire 7 are not particularly limited, and known ones can be used. Also, these arrangement methods are not particularly limited, and can be performed according to known methods.
The sealing resin 8 is a known transfer mold sealing material such as a thermosetting resin such as an epoxy resin.

The method for manufacturing the power module in FIG. 3 is not particularly limited. For example, in addition to the basic structure, after the semiconductor element 5, the lead frame 6, and the metal wire 7 are arranged, the external connection portion of the lead frame 6 and What is necessary is just to seal other than the external heat dissipation part of the base substrate 1. What is necessary is just to set the conditions of transfer molding suitably according to the sealing resin 8 to be used.
In particular, the transfer module sealed power module shown in FIG. 3 is more productive than the power module shown in FIG. 2, so that the cost can be reduced and it is advantageous for high-mix low-volume production.

  In the power module according to the present embodiment, the Cu migration preventing layer 3 is formed on the surface of the base substrate 1 and / or the Cu substrate 4 that is in contact with the organic insulating layer 2 to which a positive voltage is applied. Even when a voltage of several hundred to several lines V is applied, Cu migration from the base substrate 1 and / or the Cu substrate 4 can be prevented, and deterioration of the organic insulating layer 2 can be suppressed. As a result, no leakage or short circuit due to deterioration of the organic insulating layer 2 occurs, and the electrical insulation does not deteriorate, so that the reliability of the power module is improved.

Hereinafter, although an Example and a comparative example demonstrate the detail of this invention, this invention is not limited by these.
Example 1
About 1 μm thick Au plating (Cu migration prevention layer) was applied to one surface of a 3 mm thick Cu substrate. Next, an organic insulating layer (0.2 mm) in which boron nitride is dispersed in an epoxy resin is formed on a 0.1 mm thick copper foil (base substrate), and then a Cu substrate on which Au plating is formed is laminated. It was. This laminate was vacuum hot pressed at 180 ° C. to produce a basic structure of the power module shown in FIG.
(Comparative Example 1)
A basic structure of the power module was produced in the same manner as in Example 1 except that the Cu substrate was not subjected to Au plating.

The basic structure of the power module obtained in Example 1 and Comparative Example 1 was placed in a high-temperature and high-humidity tank, and wiring from a power source was applied so that the Cu substrate was a positive electrode and the base substrate was a cathode. Then, the high-temperature and high-humidity tank was adjusted to 85 ° C. and 85 RH, and when the temperature and humidity were stabilized, a DC voltage of 1000 V was applied from the power source, and a bias test was performed.
In this bias test, the current flowing between the two electrodes was measured by a current detector, and the time during which this current rose discontinuously was evaluated as the dielectric breakdown lifetime. Moreover, the dielectric breakdown lifetime was evaluated using four samples, and the average value of the breakdown lifetime was obtained.
As a result, the basic structure of the power module of Example 1 has a dielectric breakdown lifetime of 10 times or more compared with the basic structure of the power module of Comparative Example 1, and a high voltage is applied in a high temperature moisture absorption environment. It was also found that the electrical insulation does not deteriorate.

(Example 2)
In Example 2, the experiment was performed by changing the thickness of the Cu migration prevention layer formed on the Cu substrate.
The basic structure of the power module of Example 2 was produced in the same manner as Example 1 except that Ni plating of 0.05 μm to 2.0 μm was applied to the Cu substrate instead of about 3 μm of Au plating. did.
With respect to the basic structure of the obtained power module, the dielectric breakdown lifetime was evaluated in the same manner as in Example 1. Moreover, the dielectric breakdown lifetime was evaluated using four samples, and the average value of the breakdown lifetime was obtained. The results are shown in Table 2. In addition, the result of Table 2 was represented by the ratio on the basis of the dielectric breakdown lifetime of the comparative example 1.

  As shown in the results of Table 2, an improvement in the dielectric breakdown lifetime was observed when the thickness of the Ni plating (Cu migration treatment layer) was in the range of 0.05 μm to 2.0 μm. In particular, when the thickness was 2.0 μm, the result that the dielectric breakdown lifetime was 5 times or more that of Comparative Example 1 was observed with good reproducibility.

(Example 3)
In Example 3, the experiment was performed by changing the thickness of the base substrate.
The basic structure of the power module of Example 3 was obtained by applying a 3 μm thick Ni plating to a Cu substrate instead of an approximately 3 μm thick Au plating, and using a 0.1 to 5.0 mm thick base substrate. Except for the above, it was produced in the same manner as in Example 1.
About the basic structure of the obtained power module, the heat cycle test was performed 300 times between -40 degreeC-125 degreeC, and the presence or absence of peeling in a basic structure was observed visually. In this peeling observation, the case where there was no peeling at all was evaluated as 一部, the portion where there was peeling, ○ which was practical, and the case where there was much peeling as x. The results are shown in Table 3.

表３の結果に示されるように、ベース基板の厚さが０．１〜５．０ｍｍの範囲において、剥離は観察されないか、又は一部に剥離があっても実用可能なレベルであった。特に、その厚さが３．０ｍｍ以下の範囲では、剥離が全くなかった。

As shown in the results of Table 3, in the range where the thickness of the base substrate is in the range of 0.1 to 5.0 mm, no peeling was observed, or even if there was some peeling, it was at a practical level. In particular, there was no peeling at all when the thickness was 3.0 mm or less.

  As can be seen from the above results, according to the present invention, it can be manufactured at low cost, has excellent heat dissipation, and the electrical insulation is reduced even when a high voltage is applied for a long time in a high temperature and high humidity environment. A power module can be provided.

  DESCRIPTION OF SYMBOLS 1 Base substrate, 2 Organic insulating layer, 3 Cu migration prevention layer, 4 Cu substrate, 5 Semiconductor element, 6 Lead frame, 7 Metal wire, 8 Sealing resin, 9 External electrode terminal, 10 Case.

Claims (7)

  A power module including an organic insulating layer between a Cu base substrate and a Cu substrate, wherein a Cu migration preventing layer is formed on a surface of the Cu base substrate to which a positive voltage is applied and / or a surface of the Cu substrate in contact with the organic insulating layer. A power module characterized by   A power module comprising an organic insulating layer between a metal base substrate and a Cu substrate, characterized in that a Cu migration preventing layer is formed on a surface of the Cu substrate in contact with the organic insulating layer to which a positive voltage is applied. Power module to do.   The Cu migration prevention layer is a layer formed of at least one selected from the group consisting of Au, Pt, Pd, Fe, Ni, Sn, Al, and alloys thereof. 2. The power module according to 2.   The power module according to claim 1, wherein a thickness of the Cu migration preventing layer is 0.05 μm or more.   The power module according to claim 1, wherein a thickness of the base substrate is 5 mm or less.   The power module according to claim 1, wherein the power module is potted and sealed with silicone gel or rubber.   The power module according to claim 1, wherein the power module is sealed by transfer molding with a thermosetting resin.

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