JPS6214943B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic device in which a semiconductor element is mounted on a metal support via an insulator.

In a high-output transistor, which is an example of a semiconductor device, a collector current of several amperes or more flows.
At this time, heat is generated inside the transistor pellet as a semiconductor element. In order to avoid instability of characteristics and accelerated deterioration of lifetime due to this heat generation, methods are used to prevent the temperature of the transistor pellet from rising beyond the allowable limit temperature. One method of preventing temperature rise has traditionally been to attach the stem, which serves as a support for the transistor pellet, to a radiator, and to release the heat generated by the transistor pellet to the outside via the stem and the radiator. It's here. However, in the case of high-output transistors, a large collector current flows as described above, so it is necessary to secure a current path and dissipate heat efficiently, so the transistor pellet is designed so that the collector region is directly attached to the stem. is listed. However, since this type of transistor is usually used with its emitter or base grounded, the collector terminal or stem cannot be directly attached to a heat sink (or chassis) etc. which is often grounded. For this reason, an insulating plate such as mica or polyester terephthalate (Mylar) is usually sandwiched between the stem and the heat sink to electrically insulate the stem and the heat sink. The stem and the radiator were fixed by using grease to fill the gap between the plate and the radiator, and by tightening screws using an insulating washer. However, even in this case, since the collector region is electrically connected to the stem (the stem cannot be grounded), it is difficult to avoid the effects of noise due to electromagnetic interference.

On the other hand, in an attempt to achieve electrical insulation, efficient heat dissipation, and prevention of electromagnetic interference, there are examples in which a semiconductor element is mounted on a metal support via beryllia porcelain or alumina porcelain. However, when Beryliya porcelain was used, the following problems specifically occurred. (1) Beryllium itself is highly toxic and requires extreme caution when handling, and is difficult to obtain and expensive. (2) The coefficient of thermal expansion of Beryliya porcelain is 7.6×
10 ^-6 /℃ and copper ( ¹⁸
℃) and aluminum ( ²⁵ It is difficult to
(3) In order to alleviate thermal fatigue at the joint, it is necessary to provide a buffer area for strain relief. For this purpose, for example, the solder layer at the joint may be made thicker, or molybdenum (5.2×10 ^-6 / °C) and tungsten (4.3×
It is necessary to insert a spacer such as 10 ^-6 /℃) in addition to the insulating plate, but in this case, there is a large loss in terms of the number of parts and processing steps required for integration, and it is also disadvantageous in terms of heat dissipation. (4) Molybdenum and tungsten, which are essential spacers when using beryllia porcelain as an insulating plate, are heavy metals (specific gravity of molybdenum: 10.27, specific gravity of tungsten: 19.3), so when trying to reduce the weight of semiconductor devices. It becomes an obstacle. On the other hand, even when alumina porcelain is used, the same problems as the above-mentioned Beryliya porcelain arise, except for the problem of toxicity.

As a result of various studies based on the above background, for example, the first
As shown in the figure, when placing the semiconductor element 1 on the copper support 2, the copper support 2 is integrated with the copper support 2 via the polyimide 3 and fluorinated ethylene 4, 4' as an adhesive. It has been found that the configuration consisting of the plate 5 is extremely effective as an electronic device. However, it has been difficult to apply it to higher output electronic devices for the following reasons.

(1) The fact that polyimide 3 itself has flexible properties and the fluorinated ethylene 4,4' layer as an adhesive is thin, combined with the fact that the adhesive layer
That is, gaps are locally formed between the support 2 and the polyimide 3 or between the polyimide 3 and the mounting plate 5, making uniform adhesion difficult.

(2) As a result of (1), the adhesion rate (area without voids/total contact area) is low.

(3) As a result of (1) and (2), the effective area contributing to heat conduction is small, and heat dissipation is inhibited.

(4) As a result of (1) and (2), it is difficult to expand the adhesive area.

The drawbacks of conventional electronic devices have been explained using transistors as an example, but the same problems apply not only to transistors but also to other semiconductor devices such as diodes and thyristors, or at least to hybrid integrated circuit devices that include semiconductor elements. I left a mark.

An object of the present invention is to provide an electronic device with improved heat dissipation by increasing adhesive efficiency.

The present invention provides a method for integrating a metal mounting body on which a semiconductor element is placed and a metal support body supporting the same through a metal layer consisting of a copper layer and a metal solder layer. This is what I did.

In this case, the copper layer plays the role of suppressing the flexibility of the polyimide and maintaining flatness even during high-temperature integration heat treatment, and the role of maintaining adhesion with the metal solder. The layer serves to achieve integration with the carrier or support and to fill voids caused by non-flatness of these surfaces.

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

As shown in FIG. 2, when a copper mounting plate 15 on which a silicon transistor pellet 11 as a semiconductor element is placed is integrated onto a copper support plate 12 via a polyimide 13, the support plate 12 and polyimide 13 are separated. In between, there is a copper layer 14 and a lead-tin solder layer 14'.
On the other hand, the polyimide 13 is integrated between the mounting plates 15 via a fluorinated ethylene layer 16. At this time, the emitter and base regions of the above integrated transistor pellet 11 are connected with aluminum wires 17 and 18, respectively.
The collector region is then electrically connected to the aluminum wire 19 via the copper mounting plate 15, and then the aluminum wires 17, 18, 19 are connected to copper leads (not shown) in a conventional manner, and the copper support plate 1
At least each of the above-mentioned parts except part 2 and the copper lead were molded with resin (not shown) so as to be completely isolated from the outside air.

The adhesion rate of the electronic device obtained with this configuration is about 75% between the polyimide 13 and the mounting plate 15, which is improved from about 60% in the conventional example of the structure shown in FIG. This was a significant improvement of approximately 96%. The reason for the significant improvement in the latter case was that the solder layer 14' melted and effectively filled the voids, and the reason for the small improvement in the former case was due to the presence of the copper layer 14, which caused the polyimide 13 This is because the flexibility, which is the essence of the material, is suppressed, and the generation of new voids is suppressed. As a result, the thermal resistance between the transistor pellet 11 and the support plate 12 is the first
The value was approximately 50% lower than that of the conventional structure shown in the figure. As described above, it was confirmed that according to this example, the voids in the bonded portion were reduced, so that heat dissipation was excellent. In addition, an insulation voltage of over 2000V can be obtained.
No abnormality was found in the bonded portion when thermal cycles between -20°C and +150°C were applied 1000 times. The reason why such a high dielectric strength voltage was obtained is that the excellent insulating properties of polyimide are effectively utilized.Polyimide and fluorine materials make it possible to form a robust structure that is less likely to cause thermal fatigue. Ethylene has a coefficient of thermal expansion that is almost the same as that of the copper support plate and copper mounting plate, and the solder layer is sandwiched between the copper layers, making it less susceptible to deformation due to thermal stress. to cause.

FIG. 3 is a front view showing a second embodiment of the invention.

As shown in FIG. 3, similar to the embodiment shown in FIG.
A copper layer 14 and a lead-tin solder layer 1 are placed between the support plates 12.
4' and also between the mounting plate 15 and the polyimide 13 via a solder layer 21' and a copper layer 21. Further, as in the first embodiment, a transistor pellet is placed thereon, and predetermined electrical wiring and molding are applied to form an electronic device.

The adhesion rate of the electronic device obtained with such a configuration is about 95% between the support plate 12 and the polyimide 13, which is almost the same as in the first embodiment, and about 93% between the polyimide 13 and the mounting plate 15. %, which was significantly improved compared to the case of Example 1. The reason why the adhesion rate improved on both the support plate 12 side and the mounting plate 15 side is because the structure in which polyimide 13 is sandwiched between copper layers 14 and 21 on both sides suppresses the flexibility, which is the essence of polyimide, and creates new voids. The outbreak was suppressed, and
This is because the solder layers 14' and 21' melted and effectively filled the voids. As a result, the transistor pellet support plate 12 of this electronic device
The thermal resistance between them was approximately 30% lower than that of Example 1. Thus, it was confirmed that according to this example, the heat dissipation performance could be further improved. Also,
As with the first example, excellent electrical insulation and thermal fatigue resistance were confirmed.

FIG. 4 is a front view showing a third embodiment of the present invention.

As shown in FIG.
In integrating the copper supporting plate 31 and the polyimide 34, a copper layer 35 and a lead-tin solder layer 36 are interposed between the copper support plate 31 and the polyimide 34, and the other polyimide 34, the copper mounting plates 32, 32', and the copper electrode plate are integrated. 33 and are integrated with a fluorinated ethylene layer 37 interposed therebetween. At this time, the thyristor 38, the diode 39,
40, a chip capacitor 41, and a chip resistor 42 are mounted, and a current control electronic device is obtained with predetermined wiring and molding.

The adhesion rate of the electronic device obtained with this configuration was almost the same as that of the first embodiment, and was significantly improved over the electronic device obtained by the conventional method. The reason for this is the same as in the first embodiment. Also, when 80W of power is applied to the current control electronic device and the temperature of the copper support plate 31 is maintained at 80℃, the thyristor 3
8. When the temperature of each of the diodes 39 and 40 was measured, it was only 115° C. at most, and the change in resistance value of the chip resistor 42 was only 5% at most. As described above, it has been confirmed that the embodiment shown in FIG. 4 can sufficiently function as an electronic device constituting a hybrid integrated circuit in which a large number of semiconductor elements, passive elements, etc. are mounted. The main reason for this is, as in the first embodiment, the improvement in heat dissipation accompanying the improvement in the adhesion rate. Furthermore, it was confirmed that the electrical insulation properties and thermal fatigue resistance were almost the same as those of the first example.

FIG. 5 is a front view showing a fourth embodiment of the present invention.

In the electronic device of this embodiment, a first copper mounting plate 5 is placed on a copper support plate 57 in the same way as in the third embodiment.
1 and copper electrode plate 33 are integrated, and on the first copper mounting plate 51, a second copper is further placed via a laminate composed of fluorinated ethylene 53, polyimide 51, copper 55, and solder 56. The plate 52 is integrated. At this time, the diode 40, which generates a relatively small amount of heat, is mounted on the second copper mounting plate 52, and the other circuit elements are mounted in the same manner as in the third embodiment.
A current control electronic device having the same power capacity as the third embodiment is obtained.

Even when 80W of power is applied to such an electronic device and the temperature of the copper support plate 57 is maintained at 80°C, the temperature of the thyristor 38, diodes 39, 40, and chip resistor 42 does not exceed 115°C, and heat dissipation is prevented. No problems were found. Furthermore, no problems were found with regard to electrical properties and thermal fatigue resistance, as in the third example. Furthermore, in the case of this example, since the packaging density of the circuit elements was increased, the packaging area could be reduced by approximately 25% even though the electronic device had the same power capacity as the third example.

The present invention has been described above using each example, but
The present invention is not limited to this, and the effects and advantages of the present invention can be enjoyed even in the following cases, for example.

(1) When the support or mounting body that constitutes the electronic device is made of copper or aluminum whose surface is coated with gold, nickel, silver, etc.

(2) When the material for the metal solder layer constituting the electronic device is at least a gold-based alloy solder such as gold-germanium or gold-silicon, or a silver-based alloy solder such as silver-tin.

(3) When passive elements such as capacitors and resistors are placed on a mounting body that constitutes an electronic device.

As described above in detail, the embodiments of the present invention can provide the following advantages and effects.

(1) Since a copper layer and a metal solder layer are interposed between the polyimide and the support or mounting body, the metal solder melts and fills the voids, and the presence of the copper layer suppresses the flexibility of the polyimide. This prevents the formation of voids.

(2) As a result of (1), the adhesion rate improves.

(3) As a result of (1) and (2), heat dissipation is improved.

(4) As a result of (3), it is possible to increase the mounting density of circuit elements in an electronic device, thereby making the device smaller.

(5) Since polyimide has excellent insulation properties, it provides good insulation for electronic devices.

(6) A copper layer in which polyimide or fluorinated ethylene has a coefficient of thermal expansion almost equal to that of copper or aluminum, which is the base material of the support plate or mounting plate, and a metal solder layer has a coefficient of thermal expansion almost the same as that of copper or aluminum, which is the base material of the support plate or mounting plate. Since the structure is sandwiched between the support body or the copper layer and the mounting body, it is possible to realize an electronic device that is less prone to fatigue due to thermal stress.

In constructing the present invention, it is most desirable that the polyimide and the copper layer are directly integrated, but they may be integrated via an adhesive. In addition, lead-tin solder is preferable from the viewpoint of reliability against heat stress, cost, working temperature, etc., but for example, lead-tin solder is preferable. It may be an alloy solder containing at least one metal selected from the following.

As is clear from the above, according to the present invention, an electronic device with good heat dissipation performance can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a front view of a conventional electronic device, FIG. 2 is a front view of a first embodiment of the present invention, FIG. 3 is a front view of a second embodiment of the present invention, and FIG. 4 is a front view of the present invention. FIG. 5 is a front view of the third embodiment of the present invention, and FIG. 5 is a front view of the fourth embodiment of the present invention. 11...Silicon transistor pellet, 1
2, 31, 57...Copper support plate, 13, 34, 54
...Polyimide, 14,21,35...Copper layer, 1
4', 21', 36...Solder layer, 15, 32, 3
2'... Copper mounting plate, 16, 37, 53... Fluorinated ethylene layer, 33... Copper electrode plate, 38... Thyristor, 39, 40... Diode, 41... Chip capacitor, 42... Chip resistance, 51,5
2...First and second mounting plates.

Claims (1)

[Claims] 1. In an electronic device formed by integrally forming a metal mounting body on which a semiconductor element or the like is placed and a metal support body supporting the metal mounting body via polyimide,
An electronic device characterized in that a metal layer consisting of a copper layer and a metal solder is interposed between either the metal mounting body or the metal support and the polyimide.