JPH07309688A - Insulating heat radiating plate - Google Patents

Abstract

PURPOSE:To prevent cracks in a ceramic substrate or a solder layer from occurring due to thermal stress in a cryogenic cycle and to obtain an insulating heat radiating plate excellent in heat radiating property and reliability. CONSTITUTION:This insulating heat radiating plate is constituted so that a metallic foil is attached on each plane of an element mounting side and a heat sink side of a ceramic substrate. The insulating heat radiating plate has a copper foil of 0.075-0.2mm thickness on each plane of an element mounting side and heat sink side of an aluminum nitride substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulating heat dissipation plate having excellent heat dissipation and reliability, and is used for mounting devices such as power transistors, power diodes and power ICs.

[0002]

2. Description of the Related Art With the miniaturization of semiconductor devices, the power consumption per unit area is rapidly increasing, and circuit designers are struggling with heat dissipation measures. In particular, in order to dissipate large amounts of heat generated from elements such as power transistors, power diodes, and power ICs used for igniters and welding power sources, etc., conventionally, thick film metallization was performed on the surface of an alumina substrate by cofiring or the like. Used as an insulating heat sink, solder it to a heat sink made of metal such as copper or aluminum, and if necessary, use a copper heat spreader or a copper heat spreader on the surface where the element is mounted. The element was soldered through the foil.

However, since the thermal conductivity of alumina is not sufficiently high in the insulating heat dissipation plate in which the alumina substrate is subjected to thick film metallization, it is limited to use in a region where the element capacity has a spare capacity. was there. Therefore, it is possible to use an aluminum nitride substrate instead of the alumina substrate. Aluminum nitride has electrical characteristics equivalent to those of alumina, but has a thermal conductivity of 5 to 13 that of alumina.
It has a characteristic that the thermal expansion coefficient is close to that of Si.

The characteristic of the coefficient of thermal expansion close to that of Si enables direct mounting of a large-sized Si element, but has a problem that cracks occur in the aluminum nitride substrate and the solder layer due to the thermal stress caused by the thermal cycle. This is due to the difference in thermal expansion between aluminum nitride and a heat sink material, or when using a heat spreader, between aluminum nitride and a heat spreader material, and is due to generation of a larger stress than when alumina is used.

From the above, in an insulating heat dissipation plate obtained by subjecting an alumina substrate to thick film metallization, when the alumina substrate is replaced with an aluminum nitride substrate, a crack is generated in the aluminum nitride substrate to cause insulation failure. Also,
When the Si element is directly mounted on the insulating heat radiating plate with the thick film metallized on the aluminum nitride substrate without the use of a heat spreader, there is no difference in expansion between the Si element and the insulating heat radiating plate, so the thermal stress generated is extremely small. Although the board is less likely to break down, a large stress is generated on the heat sink side, and a horizontal crack is generated in the solder layer that joins the heat sink and the insulating heat sink to the joint surface. Progresses to peeling.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an insulating heat dissipation plate which is free from cracks in a ceramic substrate or a solder layer due to thermal stress due to a cooling / heating cycle and has excellent heat dissipation and reliability. .

[0007]

That is, according to the present invention, there is provided an insulating radiating plate and an aluminum nitride substrate, characterized in that a metal foil is provided on each of an element mounting side and a heat sink side of a ceramic substrate. 0.075-0.2mm thickness on each surface of element mounting side and heat sink side
The copper foil is provided on the insulating heat sink.

The present invention will be described in more detail below. The metal foil species formed on the surface of the ceramic substrate in the present invention are copper, aluminum, copper-aluminum alloy, iron-nickel alloy, etc. It is common. The thickness of the metal foil is not particularly limited, but is preferably 0.05 to 0.2 mm in order to cause the metal foil to function as a buffer layer for thermal stress.

In particular, when the metal foil type is copper, the thickness of the metal foil is set to 0.075 mm or more, particularly 0.1 mm or more, which occurs when the copper foil is bonded to the aluminum nitride substrate by the active metal method. Wrinkles on the copper foil can be prevented.

Examples of the ceramic substrate used in the present invention include an aluminum nitride substrate, a beryllia substrate, an alumina substrate, and a silicon nitride substrate. An aluminum nitride substrate is preferable, and its sintered density is mechanical. From the viewpoint of strength and electrical characteristics, it is desirable that the relative density be 95% or more.

Above all, the proportion Es of the grain boundary layer existing within 100 μm from the surface is 8 to 20%, and the proportion Ei of the grain boundary layer existing within ± 100 μm from the central portion in the thickness direction is 16%. An aluminum nitride substrate having an Es / Ei of 1.25 or more is preferable because it has a high durability against a cold heat cycle. Such an aluminum nitride substrate contains 3 to 5% by weight of a sintering aid with respect to the aluminum nitride powder, for example, a rare earth oxide such as yttria or ceria, or an alkaline earth oxide such as calcia or magnesia. The green sheet can be manufactured by firing the green sheet in a non-oxidizing atmosphere such as nitrogen or argon, and then cooling it up to a temperature of 1700 ° C. at a cooling rate of 8 ° C./minute or less.

The ratio Es or Ei of the grain boundary layer can be measured by taking a COMPO image of a cross section of the aluminum nitride substrate with a scanning electron microscope (SEM) and performing image processing. For example, when the molecular weight of the grain boundary component (sintering aid component) is larger than that of aluminum nitride, the grain boundary component looks white. Image processing is performed so that the grain boundary layer becomes white and the aluminum nitride particles become black in order to unify the contrast of the photograph. The chromaticity (L value) of the image-processed photograph is measured with a color difference meter, and the L value of the photograph is calculated by correcting the value so that 100 is obtained for all white and 0 for all black. The ratio Es or Ei of the grain boundary layer is determined from the L value according to a calibration curve prepared in advance.
If it is difficult to identify the difference in the molecular weight between the grain boundary component and aluminum nitride, perform a surface analysis using an EPMA device,
Similarly, it can be performed by obtaining the L value.

A scanning electron microscope or EPMA apparatus has a suitable magnification of about 500 times, and it is desirable to adjust the size of a photograph so that a circle having a diameter of about 100 μm can be accommodated as a measuring range of a color difference meter. For details of the above-mentioned grain boundary layer ratio Es or Ei and its measuring method, see Japanese Patent Application No. 6-17.
No. 640.

Regarding the thickness of the ceramic substrate, a thickness of 0.
It can be thinner than 635mm, 0.4m
There is no problem if m or more.

As a method for joining a metal foil to a ceramic substrate, an active metal method using an active metal solder and a DBC method are generally used.

In the active metal method, a paste-like active metal solder is applied to the surface of a ceramic substrate and then a metal foil is placed in contact with the metal substrate, or a metal foil is placed in contact with the active metal solder foil sandwiched between the metal foil and 1 × 10 ^{−. The} bonding treatment is performed in a vacuum of ⁴ torr or less at a temperature equal to or higher than the melting point of the active metal brazing, generally at a temperature about 50 ° C. higher than the melting point of the active metal brazing.

The active metal wax used in the active metal method is
There is no particular limitation as long as it has a melting point higher than that of the solder used for assembling the semiconductor component, but a silver-copper eutectic is generally used. As the active metal species, Ti, Zr, and Hf have a proven track record, but are not limited to these. Compounds such as hydrides of Hf, Hf, carbonates and oxides can also be used.

In order to form a pattern for mounting an element on a bonded body of a ceramic substrate and a metal foil, unnecessary metal foil and unnecessary wax are removed and patterned by a method such as chemical etching, and further, it is necessary. It can be carried out by applying a treatment such as plating accordingly. There are various methods for patterning.A method of arranging the active metal brazing only on the part to be joined and then joining the pre-patterned metal foil, and a method of arranging the active metal brazing only on the part to be joined and then joining the solid metal foil. There is a method of removing unnecessary metal foil by a chemical etching method.

The DBC method is used when the metal foil type is copper and the ceramic substrate is an alumina substrate or an aluminum nitride substrate. When the ceramic substrate is an aluminum nitride substrate, its surface is previously subjected to oxidation treatment before use. As the copper foil, one containing a little oxygen such as tough pitch copper is preferably used, and the temperature is 1063 to 1080.
Bonding is performed in a nitrogen stream containing a small amount of oxygen at ℃. D
Since the BC method does not apply a load when joining, 0.075 m
Even copper foil of m can be joined without causing wrinkles. The patterning of the copper foil can be performed by the method described above.

[0020]

A ceramic substrate such as an aluminum nitride substrate joined with a metal foil such as copper foil has been put into practical use as a circuit board for a power module such as an inverter. This has a circuit composed of at least 3 or 4 or more islands, and a current flows through the metal foil portion. Regarding the thickness of the metal foil, the circuit side tends to be thicker than 0.3 mm so far, in order to meet the recent demand for higher current, and the heat sink side has a warp of the circuit board in consideration. Should be the same thickness as the metal foil on the circuit side to balance it, or
It is thinner by about 0.05 to 0.1 mm than the metal foil on the circuit side. Such a structure has been shunned as an insulating heat dissipation plate from the viewpoint of the risk of peeling of the metal foil and cost, and the mainstream is a ceramic substrate provided with a thick film metallization.

On the other hand, in most cases, the insulating heat radiating plate of the present invention is composed of one island for mounting an element or a heat spreader (a large current may be passed through it), and is a metal foil. No current is passed through the section. When the element or the heat spreader is mounted on the insulating heat sink of the present invention, the metal foil acts as a buffer layer for thermal stress, and the life is extended as compared with the conventional aluminum nitride substrate having the thick film metallized. However, the life of the alumina substrate is shorter than that of an insulating heat sink having a thick film metallized, and the metal foil may be peeled off or the ceramic substrate may be cracked due to the thermal stress of the cooling / heating cycle. In order to eliminate such a problem, a ceramic substrate is an aluminum nitride substrate and a metal foil is 0.07 in thickness.
This is to use a copper foil of 5 to 0.2 mm, which allows it to withstand a minimum of 2000 cycles of heat and cold.

[0022]

EXAMPLES Hereinafter, examples and comparative examples will be described in more detail.

Example 1 97 parts of aluminum nitride powder ("parts" are "parts by weight"; the same applies hereinafter), 3 parts of yttria as a sintering aid, 8 parts of polyvinyl butyral as an organic binder, and 4 parts of butyl phthalate as a plasticizer. After defoaming a slurry composed of 1 part of glycerin trioleate as a dispersant and 50 parts of xylene as a solvent to adjust the viscosity, a sheet was formed by a doctor blade method. After drying, press punching to obtain 29 x 29 mm
And degreasing treatment in nitrogen at 700 ° C., followed by firing at 1850 ° C. for 2 hours to manufacture an aluminum nitride substrate. This substrate had a thermal conductivity of 150 W / mK, a relative density of 99.9%, and dimensions of 25 × 25 × 0.635 mm. In addition, Es value 6.5%, Ei value 6.3%, Es /
Ei was 1.03.

75 parts of silver powder, 25 parts of copper powder, 10 parts of zirconium powder, 15 parts of terpineol, and 1.5 parts of toluene solution of polyisobutylmethacrylate were kneaded in solid content to prepare an active metal brazing paste. did. This was applied by screen printing to the entire front and back surfaces of the aluminum nitride substrate at a rate of 10 mg / cm ² (application amount after drying).

Next, a 0.1 mm-thick copper foil is placed in contact, placed in a furnace, heat-treated at a temperature of 900 ° C. for 30 minutes under a vacuum of 1 × 10 ⁻⁴ torr, and then cooled at 2 ° C./minute. The assembly was manufactured by cooling at a speed.

A UV-curing type etching resist was applied on the copper foil of the obtained joined body by screen printing.
After applying in a shape of × 20 mm, the unnecessary copper foil portion is dissolved and removed using a cupric chloride solution, and the unnecessary brazing material and reaction products remaining outside the pattern are dissolved at 60 ° C. in a 10% ammonium fluoride solution. Removed. Then, the etching resist was peeled off with a 5% caustic soda solution to obtain an insulating heat sink having a target shape. Five pieces were subjected to Ni-P plating treatment for surface protection to prepare test pieces.

As shown in FIG. 1, 30 is provided on the back surface of the test piece.
X30x4mm heatsink copper plate, 2 on the surface
When a heat spreader made of a 0.times.20.times.1 mm copper plate was soldered and a cooling / heating cycle test was carried out, no abnormality was observed in any of the five test bodies up to 2500 cycles.

The thermal cycle test is -40 ° C in the atmosphere.
After holding for 30 minutes x 25 ° C, leave for 10 minutes, then 125
After holding at 30 ° C. for 30 minutes, leaving at 25 ° C. for 10 minutes as one cycle, and even if one of the five test pieces had a crack in the aluminum nitride substrate (substrate crack),
Alternatively, when the test body peeled from the solder layer (solder peeling), the number of cooling / heating cycles at that time was evaluated as resistance to cooling / heating cycle.

Examples 2 to 9 Test pieces were prepared and evaluated in the same manner as in Example 1 except that the thickness of the copper foil bonded to the aluminum nitride substrate was changed variously. Note that in Examples 2, 3, 7 and 9, 25, 15, 17 and 1 of the 50 sheets of the joined body, respectively.
Since there were wrinkles in the copper foil on 5 sheets, 5 wrinkles without wrinkles
A sheet was selected and used as a test piece.

Comparative Example 1 100 parts of tungsten powder (average particle size: 1.5 μm) and a toluene solution of polyisobutyl methacrylate were solidified on each of the front and back surfaces of a 29 × 29 mm molded body punched by press in Example 1. A metallized paste prepared by diluting 2 parts with terepineol into a metallized paste was applied by screen printing to a 23 × 23 mm shape, degreased in nitrogen at 700 ° C., and then baked at 1850 ° C. for 2 hours to obtain aluminum nitride. An insulating radiator plate having a thick metallized substrate was manufactured. The thermal conductivity of this insulating heat sink is 150 W / mK, the relative density is 99.9%, and the size is 25 ×.
25 × 0.635 mm, thick film metallized area is 20 × 20
It was mm. Five pieces were subjected to Ni-P plating treatment for surface protection to prepare test pieces.

A heat sink copper plate and a heat spreader made of a copper plate similar to those used in Example 1 were soldered to this test piece and a cooling / heating cycle test was carried out.
Through cracks were generated in the aluminum nitride substrates on all of the sheets, causing insulation failure.

Comparative Example 2 Dimensions 25 × 25 × 0.635 mm, thermal conductivity 20 W / m
A commercially available aluminum oxide substrate, which is K, is coated with Mo—Mn paste on each of the front and back surfaces by screen printing.
It was applied to × 20 mm and subjected to thick film metallizing treatment at 1450 ° C. in a wet forming gas (nitrogen-hydrogen). Ni-P plating was applied to this to manufacture five test bodies.

A heat sink copper plate and a heat spreader made of a copper plate similar to those used in Example 1 were soldered to this test piece and a cooling / heating cycle test was carried out. But had sufficient strength. But 1
When 500 cycles had passed, all five sheets were peeled off from the heat sink copper plate.

The results of Examples 1 to 9 and Comparative Examples 1 and 2 are summarized in Table 1.

[Table 1]

Example 10 A cooling / heating cycle test was conducted in the same procedure as in Example 1 except that an aluminum plate of 30 × 30 × 2 mm was used as the heat sink material. No abnormality was found at 2500 cycles. It was

Examples 11 to 18 Specimens were prepared in the same manner as in Example 10 except that the thickness of the copper foil bonded to the aluminum nitride substrate was variously changed, and the same evaluation as in Example 1 was performed. In addition, Example 11,
In 12 and 16, some of the copper foils had wrinkles, so 5 sheets each having no wrinkles were selected as test pieces.

Comparative Example 3 A test piece was prepared and evaluated in the same manner as in Comparative Example 1 except that a 30 × 30 × 2 mm aluminum plate was used as the heat sink material. Cracks occurred, causing insulation failure.

Comparative Example 4 A test piece was prepared in the same manner as in Comparative Example 2 except that an aluminum plate of 30 × 30 × 2 mm was used as the heat sink material, and the same evaluation was performed. All five were peeled from the heat sink aluminum plate.

The above Examples 10 to 18 and Comparative Examples 3 to 4
The results are collectively shown in Table 2.

[Table 2]

Example 19 A cooling / heating cycle test was conducted in the same manner as in Example 1 except that a heat sink copper plate of 30 × 30 × 4 mm was soldered only on the back surface of the test body, and no abnormality was found until 2500 cycles. I couldn't do it.

Examples 20 to 28 Test pieces were prepared and evaluated in the same manner as in Example 19 except that the thickness of the copper foil bonded to the aluminum nitride substrate was variously changed. Incidentally, Examples 20, 21 and 25
Since there were some wrinkles on the copper foil, five wrinkle-free copper foils were selected as test pieces.

Comparative Example 5 A cooling / heating cycle test was conducted in the same manner as in Comparative Example 1 except that a heat sink copper plate of 30 × 30 × 4 mm was soldered only on the back surface of the test piece. All five were peeled from the heat sink copper plate.

Comparative Example 6 A cooling / heating cycle test was conducted in the same manner as in Comparative Example 2 except that a heat sink copper plate of 30 × 30 × 4 mm was soldered only on the back surface of the test piece. All five were peeled from the heat sink copper plate.

The above Examples 19 to 28 and Comparative Examples 5 to 6
The results are summarized in Table 3.

[Table 3]

Example 29 An Es value of 8.2%, an Ei value of 5.5%, and an Es / Ei of 1.4 were produced by the following method as an aluminum nitride substrate.
A test piece was prepared in the same manner as in Example 1 except that the sample No. 9 was used, and the conditions were severer than those in Example 1.
In the air, the temperature was kept at -60 ° C for 30 minutes, left at 25 ° C for 15 minutes, further held at 150 ° C for 30 minutes, and left at 25 ° C for 15 minutes to evaluate the thermal cycle resistance as 2500 cycles. No abnormality was found. In addition, in the test body of Example 1, under these conditions, 2000
Substrate cracks occurred during the cycle.

To a total of 100 parts by weight of 97 parts by weight of aluminum nitride powder and 3 parts by weight of sintering aid (yttria),
8 parts by weight of polyvinyl butyral as an organic binder, 4 parts by weight of butyl phthalate as a plasticizer, 1 part by weight of glycerin trioleate as a dispersant, and xylene 5 as a solvent.
0 part by weight was mixed in a nylon pot for 24 hours. After adjusting the viscosity of the obtained slurry, it was spread into a PET film by doctor blading and forcedly dried to form a green sheet having a predetermined thickness. This green sheet was punched out into a size of 60 × 35 mm, 10 sheets of it were stacked and a weight of tungsten was placed on the green sheet, and the organic binder was removed by heating in air at 500 ° C. for 1 hour. After firing at 1950 ° C, the temperature up to 1700 ° C is 1 ° C
Cooled at a rate of / min.

[0047]

According to the present invention, it is possible to provide an insulating radiating plate which is excellent in radiating property and reliability without causing cracks in the ceramic substrate or the solder layer due to the thermal stress caused by the cold heat cycle.

[Brief description of drawings]

FIG. 1 is a diagram for explaining that a heat sink copper plate is soldered to the back surface of a test body manufactured in Example 1 and a copper plate heat spreader is soldered to the front surface thereof.

[Explanation of symbols]

 1 heat sink copper plate 2 solder layer 3 copper foil on heat sink side 4 aluminum nitride substrate 5 copper foil on element mounting side 6 solder layer 7 heat spreader made of copper plate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Miyai 1 Shinkai-cho, Omuta-shi, Fukuoka Electric Chemical Industry Co., Ltd. Omuta factory (72) Inventor Yoshihiko Tsujimura 1 Shinkai-machi, Omuta-shi, Fukuoka Electric-type industrial company Omuta Factory

Claims (2)

[Claims] 1. An insulating radiating plate, characterized in that a metal foil is provided on each of an element mounting side and a heat sink side of a ceramic substrate. 2. A thickness of 0.075 to 0.2 on each of the element mounting side and the heat sink side of the aluminum nitride substrate.
An insulating heat sink, characterized in that a copper foil of mm is provided.