JPH08316373A - Resin sealed power module and production thereof - Google Patents

Abstract

PURPOSE: To prevent contamination of the inner surface of case with scattering gel or adhesion of gel to the inner surface of upper package structure at the time of low pressure defoaming by minimizing the quantity of get to be defoamed in the first stage and filling second and subsequent stage gels thereon without defoaming. CONSTITUTION: In a power module where a semiconductor element 1 is contained by means of an enclosure case 7 being set on a metal substrate 3 and a cover case 6, silicon gel 8a is injected through an injection hole 10 of the cover case 6 into the package up to a level slightly higher than a bonding wire 4. The silicon gel 8a is subjected to defoaming and thermally set. It is then cooled down to the room temperature and a second stage gel 8b is injected onto the first stage gel 8a. The second stage gel 8b is not subjected to defoaming and thermally set under same conditions as the first stage get 8a. By such a method, contamination of the inner surface of case with scattering gel or adhesion of gel to the inner surface of upper package structure can be prevented at the time of low pressure defoaming.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin-sealed power module device and a method for manufacturing the same.

[0002]

2. Description of the Related Art The configuration of a conventional power module device is
The configuration of a general IGBT module will be described as an example. FIG. 1 is a cross-sectional view of a general IGBT module. In the figure, 1 is a power chip such as an IGBT or a diode chip, and these are ceramic plates 2
And the ceramic plate is bonded to the metal substrate 3. An external lead-out terminal 5 fixed by soldering stands up from the ceramic plate 2. The external lead-out terminal 5 and the power chip 1 are electrically connected by the metal wire 4. An enclosure case 7 made of a thermoplastic resin such as polyphenylene sulfide (PPS) is adhered to the metal substrate 3. 6 is a lid made of the same resin. A silicon gel 8 having a very small elastic modulus is filled on the substrate on which the power chip is mounted for chip protection.
Furthermore, a hard resin 9 such as an epoxy resin composition is filled thereover in order to fix the terminals and keep the package airtight.

[0003]

The conventional power module device has a problem that the moisture resistance life is short. The main reason for this is that structural defects such as cracks and voids are likely to occur in the substrate, the outer case, and the silicone gel whose periphery is sealed with hard resin, and moisture condenses at these structural defects and / or Moisture can easily reach the power chip through these defective portions. Therefore, in order to improve the moisture resistance of the power module, it is very effective to prevent the occurrence of structural defects in the silicone gel part.

The reason why structural defects tend to occur in the silicone gel whose periphery is bound is that the large volume temperature change of the gel is inhibited. In particular, when the periphery of the gel is constrained during thermal contraction of the gel, it becomes impossible to absorb the volume reduction due to the shape change of the gel surface, and the volume of the gel must be reduced due to structural defects in the gel bulk. . This is the mechanism by which structural defects occur in the gel.

As a method for preventing the occurrence of structural defects in the gel part, it is effective to reduce the constraint on the gel. As a method from this point of view, a structure having a space on the upper surface of the gel is disclosed in Japanese Patent Application No. 6-179890. This structure is effective in preventing structural defects from occurring in the gel part, but the amount of gel to be filled must be strictly controlled. If the amount of the filled gel is too large, the upper surface of the gel adheres to the inner surface of the lid and rather restricts the gel, so that structural defects such as voids easily occur inside the gel. Adhesion on the top surface of the gel is an essential step not only when the amount of filled gel is too large, but also when high reliability is required. It is also generated when the formed gel adheres to the inner surface of the upper part of the package. Since the state of the gel scattering changes depending on the amount of the entrapped gas of the injected gel and the subtle difference in the manufacturing state of the substrate portion, it is usually very difficult to control the state of the gel scattering.

On the other hand, even in the conventional structure in which the hard resin is filled in the upper part of the gel, when the gel is subjected to the vacuum defoaming treatment, the gel scattered on the inner surface of the case hinders the adhesion with the hard resin, and external moisture is absorbed from this part. Will infiltrate, resulting in the adverse effect of reducing the moisture resistance of the module. An object of the present invention is to minimize the adhesion of the gel to the inner surface of the upper part of the package and the inner surface of the case by dividing the gel filling into a plurality of times, thereby causing a structural defect in the gel part and / or inhibiting the adhesion between the hard resin and the case. (EN) Provided are a resin-sealed type power module device excellent in moisture resistance in which the temperature is minimized and a manufacturing method thereof.

[0007]

The main purposes of filling a silicone gel on a substrate on which a semiconductor element is mounted are as follows.

(1) The external infiltration moisture is prevented from reaching the semiconductor element, the metal terminal, the wiring pattern on the substrate, the bonding wire, etc., and the malfunction due to the corrosion of these members and the infiltration moisture reached is prevented.

(2) By uniformly filling the periphery of the high voltage application portion such as the semiconductor element, the metal terminal, the wiring pattern on the substrate, and the bonding wire, the discharge at these portions is prevented and the insulation characteristics are maintained.

In order to achieve these objects, it is necessary to eliminate structural defects such as voids in the filled gel, particularly in the gel in the vicinity of the contact with the member. This is because, in the structural defect portion in the gel, infiltrated water is condensed and easily discharged. For this reason, in the gel filling process when various types of high reliability are required, a reduced pressure defoaming process is required to remove the entrapped gas and bubbles in the gel under reduced pressure after injecting the gel onto the substrate. .

However, during the defoaming process, the gel is scattered, so that the gel adheres to the inner surface of the case. In the case of a structure in which the hard resin is filled in the upper part of the gel, the scattered gel hinders the adhesion between the hard resin and the case, and this part becomes the entry path for external moisture, which reduces the moisture resistance of the module. . On the other hand, in the case of a structure where the space above the gel is aimed at reducing the restraint of the gel, which is effective in preventing the occurrence of structural defects in the gel part, the gel is scattered and adhered to the inner surface of the package top, so It may adhere. In this case, the gel is pulled upward to exert a restraining force on the gel, so that structural defects easily occur inside the gel. Therefore, it is absolutely necessary to establish a gel filling method that can minimize the amount of gel scattered on the inner surface of the outer case and the inner surface of the lid case. In the present invention, as this method, it was found that it is very effective to fill the gel in a plurality of times.

The effect of performing the gel filling in a plurality of times will be described below. For the purpose of filling the gel, it is necessary to remove the entrapped gas and bubbles in the vicinity of the chip, the substrate, and the bonding wire. For this reason, it is sufficient to perform decompression defoaming on the gel filled up to the height at which the bonding wire is hidden. On the other hand, since the scattering of gel during defoaming under reduced pressure causes the above-mentioned adverse effect, the amount (or thickness) of gel to be subjected to this treatment needs to be made as small as possible. Considering these facts, it is appropriate to reduce the pressure-defoaming gel to the maximum height at which the bonding wire is hidden, and possibly reduce the pressure-defoaming gel more than this. Since the height at which the bonding wire is hidden is usually about 10 mm or less, the gel injection in the first step may be performed within this range. After injecting the gel, a vacuum defoaming process is performed and then heat curing is performed. Then, the second-stage gel is poured on the cured first-stage gel. The injection amount in this case is such that, when there is a package structure with a space above the gel, the entire gel layer including the first-stage gel and the second-stage gel expands at the maximum temperature during heat curing. In doing so, it is necessary to keep the amount below the amount that does not adhere to the inner surface of the structure. The volume expansion coefficient of the gel is
It is usually about 900 ppm / ° C. When the maximum temperature during gel hardening, which is a general condition, is 150 ° C., the gel thermal expansion amount is about 11% of the volume at room temperature. Therefore, when injecting gel into a normal rectangular box-shaped package space,
It is necessary to control the injection amount of the second-stage gel so that the gel upper portion does not adhere to the inner surface of the package structure even if the thickness of all gel layers increases by about 11%. Further, after the injection of the second-stage gel, heat curing may be performed without defoaming under reduced pressure. For the above reasons, the effect of vacuum defoaming is sufficient if it is performed on the first-stage gel, and if this treatment is performed on the second-stage gel, the scattered gel may adhere to the inner surface of the case or the inner surface of the upper package structure, or This is because, depending on the situation, adverse effects such as generation of voids in the first-stage cured gel may occur.

As described above, the amount of the first-stage gel to which vacuum defoaming is applied is suppressed to a required minimum amount, and after the gel is filled and cured, the second-stage gel is filled without vacuum defoaming. By performing the gel filling a plurality of times, it is possible to prevent the contamination of the inner surface of the case and the attachment of the gel to the inner surface of the package structure above the gel due to the scattered gel during defoaming under reduced pressure. As a result, in the case of filling the hard resin on the gel, it is possible to suppress the inhibition of adhesion between the hard resin and the case, which becomes the external moisture infiltration route, and in the case of the gel upper space structure which is very effective in reducing the gel constraint. In addition, it is possible to prevent the occurrence of structural defects in the gel caused by the adhesion on the upper surface of the gel. As a result, the moisture resistance of the module is greatly improved.

[0014]

According to the present invention, in the resin-sealed power module device, it is possible to prevent the occurrence of structural defects such as voids inside the gel, which hinders the adhesion between the hard resin and the case, which causes a decrease in moisture resistance. Therefore, the humidity resistance reliability of the power module device can be significantly improved.

[0015]

EXAMPLES Next, the present invention will be specifically described by way of examples. FIG. 2 is a schematic cross-sectional view of the module device according to this embodiment.
Shown in

By soldering 1, 2 and 3 in order, a substrate having a semiconductor chip mounted thereon was manufactured. Next, the metal terminal 5 fixed to the lid-shaped case 6 having the resin injection hole 10 was bonded onto a predetermined metal wiring pattern on the substrate by cream solder. Next, in the groove-shaped structure portion provided around the lid-shaped case 6, up to about half the groove depth,
An acid-curable alicyclic epoxy resin 9a was injected. Then, the outer case 7 was mounted on the substrate so as to cover it from above. At this time, a silicone-based adhesive was previously applied to the contacting portions of both the case and the substrate. After set, 1
Both the epoxy resin and the silicone-based adhesive were cured by heating at 50 ° C. for 4 hours. In this way, the periphery of the lid-like case and the outer case were sealed, and the outer case and the substrate were bonded. Then, the groove portion of the lid-like case seal portion was further filled with the same resin 9b as the epoxy resin to reinforce the sealing property and strength of this portion.

Next, silicone gel 8a was injected into the package from the resin injection hole 10 of the lid-like case 6 to a position slightly higher than the height of the bonding wire 4 (gel thickness 6 mm). Then, defoaming treatment was performed for 30 minutes at a reduced pressure of 1 torr. Then, it was cured by heating at 80 ° C./3 hours and 150 ° C./2 hours. After cooling to room temperature, the first stage gel 8
The second stage gel 8b was injected on top of a. Here, a package in which the distance between the substrate and the innermost lower end of the lid-like case is 16 mm is used. Assuming that the gel expands by about 11% at 150 ° C., the injection amount of the second stage gel was set so that the total thickness of the first stage gel and the second stage gel would be 14 mm. After injecting the second-stage gel, it was cured under the same conditions as the first-stage gel without defoaming under reduced pressure. After cooling to room temperature, a cap 11 made of silicone rubber was fitted into the resin injection hole 10 of the lid-shaped case.

As a result of disassembling the module assembled by this method and observing the state of the gel, there was no place where the upper surface of the gel adhered to the inner surface of the lid-like case, and there was no occurrence of structural defects such as voids inside the gel.

Regarding the six modules produced here,
A high temperature and high humidity bias test was performed. The module was left in an atmosphere of 85 ° C./85% RH while applying a bias voltage of 80% of the rated voltage (here, 2 kV). It was taken out at predetermined time intervals and the leakage current and voltage characteristics at room temperature were measured. The case where there was a variation of 10% or more as compared with the initial value was regarded as defective. As a result, the total number of evaluation modules is 10
It was normal after 00 hours.

(Comparative Example) A module was prepared in the same manner as in the Example except for the gel filling method. Here, the amount of gel filled in the package is the same as in the example, but the total amount was injected once instead of dividing into two as in the example. Then, defoaming under reduced pressure and heat curing were performed under the same conditions as in the example.

When the gel state was observed by disassembling the module produced here, the upper surface of the gel near the outer case adhered to the inner surface of the lid-like case at all points, and further inside the gel bulk immediately below the adhered part. In many cases, void-like structural defects occurred in the area near the chip. Furthermore, the same high-temperature and high-humidity bias test as in the example was carried out on the six modules produced here. As a result, three defects occurred after 1000 hours.

[0022]

In the resin-sealed power module device of the present invention, the amount of the first-stage gel to be degassed under reduced pressure is set to a necessary minimum, and after the first-stage gel is filled, degassing without degassing is performed on the gel. Second
Since the gel after the step is filled, it is possible to prevent the contamination of the inner surface of the case and the attachment of the gel to the inner surface of the package structure above the gel due to the gel that scatters during defoaming under reduced pressure. As a result, it becomes possible to prevent the adhesion between the hard resin and the case, which is the place where the external moisture penetrates, or to suppress the occurrence of structural defects such as voids inside the gel, which is the place where the external moisture condenses. Can be greatly improved.

[Brief description of drawings]

FIG. 1 is a sectional view of a conventional example.

FIG. 2 is a sectional view of an embodiment of the present invention.

[Explanation of symbols]

 10 ... Resin injection hole, 11 ... Silicone rubber cap.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideo Shimizu Inventor Hideo Shiba, 1-1 1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. (72) Inventor Hiroshi Suzuki 7-chome, Omika-cho, Hitachi-shi, Ibaraki No. 1 Hitachi Ltd., Hitachi Research Laboratory (72) Inventor Shin Morishima 7-1, 1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. (72) Inventor Ryuichi Saito Hitachi Mita, Ibaraki Prefecture 7-1-1, Machi, Hitachi Co., Ltd. Hitachi Research Laboratory

Claims (4)

[Claims] 1. An insulating substrate having a semiconductor element and an external lead-out terminal electrically connected to the outside is attached on a metal substrate, and an outer case and a lid-like case are provided on the metal substrate. According to the power module device in which the semiconductor element is accommodated, a plurality of layers of silicone gel are filled on the metal substrate on which the semiconductor element is mounted, the resin-sealed power module device. 2. The metal substrate according to claim 1, wherein 2 is formed on the metal substrate.
A resin-sealed power module device in which a layer of silicone gel is filled, and the thickness of the first silicone gel layer directly above the metal substrate is 10 mm or less. 3. A resin-encapsulated power module device according to claim 1, wherein the silicone gel uppermost layer is filled with a silicone resin or an epoxy resin. 4. An outer case is attached to a substrate on which a semiconductor element is mounted, a silicone gel having a thickness of 10 mm or less is filled on the substrate, and the silicone gel is further filled on the silicone gel. Method for manufacturing a resin-sealed power module device.