JP3244802B2 - Aluminum nitride heat sink - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum nitride radiator plate, and in particular, when formed by die press molding, can significantly reduce damage to a press die, and has little cracking or chipping and high reliability. It relates to a high aluminum nitride heat sink.

[0002]

2. Description of the Related Art Compared with conventional metal materials, ceramic sintered bodies having superior strength, insulation resistance, heat and corrosion resistance, wear resistance, light weight, etc. are used for semiconductors, electronic equipment materials, engine members, high-speed cutting tools. It is widely used as a component material used under severe conditions, such as materials for use, nozzles, and bearings.

[0003] In particular, an aluminum nitride (AlN) sintered body is an electric insulator having high thermal conductivity, and is made of silicon (S).
Since it has a thermal expansion coefficient close to i), it is used as a heat dissipation board of a highly integrated semiconductor device or a heat dissipation plate of a large capacity thyristor module.

FIG. 3 is a sectional view showing an example of the structure of a press-contact thyristor module as a silicon controlled rectifier (SCR). This press-contact thyristor module includes a silicon bonded body (thyristor chip) 3 interposed between a copper stud / heat sink 1 serving as an anode and a cathode wire 2,
A gate lead wire 4 connected to the silicon bonded body 3; a ceramic seal 5 and a case 6 for sealing the silicon bonded body 3 to block the air; and dissipating heat generated inside to the outside via the copper stud 1. And a disk-shaped heat radiating plate 7. A soft aluminum plate 8 is interposed between the radiator plate 7 and the copper stud 1, and the cathode conductor 2, the thyristor chip 3, the radiator plate 7, the soft aluminum plate 8 and the like are implanted in the copper stud 1. Pressed and fixed by the press-contact clamp 9. The inside of the ceramic seal 5 is filled with a resin 10 to seal the entire module.

A large current is controlled by switching between the positive and negative electrodes from an off (cut off) state to an on (starting) state by a gate current flowing through the gate conductor 4.

As a material for the heat radiating plate 7 of the press-contact thyristor module as described above, a conventional beryllia (B
eO), alumina (Al ₂ O ₃ ), silicon carbide (Si
A sintered body such as C) has been used. However, B
eO has drawbacks such as being toxic in the manufacturing process.

On the other hand, in order to cope with the recent increase in demand for electric power, a thyristor having a larger capacity has been demanded, and there is no possibility of inevitably causing dielectric breakdown due to heat generation, and more excellent heat radiation characteristics and insulation characteristics are obtained. A heat sink is desired.
For this reason, aluminum nitride sintered bodies that have no toxicity and have a much higher thermal conductivity than Al ₂ O _3, which is a conventional material, have become the mainstream of the heat dissipation plate material.

[0008] The shape of the radiator plate of the press-contact type module is determined by the shape of the thyristor chip to be applied and its required characteristics. Conventionally, a simple disk-shaped one is used and manufactured by the following procedure. It had been. That is, FIG.
After filling AlN powder finely pulverized into a mold (die) 11a of a press molding machine as shown in FIG.
A disc-shaped molded body 13a is prepared by pressing with an upper punch 12a at a molding pressure of about 200 kg / cm ² , and then this molded body 13a is degreased and sintered in a non-oxidizing atmosphere such as N ₂ gas. Had been manufactured.

[0009]

However, since the shape of the conventional heat sink is a simple disk shape, cracks (cracks) 14 and chipping are likely to occur at the peripheral corners of the heat sink as shown in FIG. However, there is a problem that the product yield is low. In particular, when trying to press the radiator plate with micro cracks generated during the forming and sintering operations against the thyristor module, the cracks expand due to the pressing force and the radiator plate is damaged, so the heat radiating function is lost. Dielectric breakdown is likely to occur due to heat generated in the module.

As a countermeasure for preventing the heat sink from cracking as described above, as shown in FIG.
Also, a structure in which a molded body 13b provided with the metal 5 is used is adopted.
In this case, a sharp edge 16 is formed on the periphery of the upper punch 12b of the mold. The edge portion 16 is easily broken at the time of handling, such as when replacing a mold or the like, and is liable to generate a chip 17 or a crack. Also, at the time of molding, the raw material powder is ejected from the chip 17 to make the molding operation substantially difficult. It is likely to be. In addition, there is a problem that the life of the mold is shortened, for example, when the molding operation is repeated for a short period of time, the life of the mold is shortened, such as the necessity of replacement.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is possible to prevent a mold of a press molding machine from being damaged, to prolong its life, and to generate cracks and chips. It is an object of the present invention to provide an aluminum nitride radiator plate which has low reliability and high reliability and product yield.

[0012]

Means for Solving the Problems In order to achieve the above object, the present inventor has prepared heat sink molded articles of various shapes, and has obtained a product obtained by sintering the molded article with the life of a molding die. The correlation with the defect rate was compared by experiments. As a result, by forming a step with a constant thickness on the periphery of the molded body,
It is not necessary to form a sharp edge on the upper punch of the press molding machine, and it is possible to greatly reduce damage to the mold equipment.On the other hand, by forming a chamfered inclined step from one end of the step toward the center of the molded body It was found that a product radiator plate with less cracks and chips could be obtained.

The present invention has been completed based on the above findings. That is, the aluminum nitride radiator plate according to the present invention has a stepped portion having a constant thickness formed on the outer peripheral edge of the plate-shaped aluminum nitride sintered body, and is chamfered from one end of the stepped portion toward the center of the aluminum nitride sintered body. A part is formed.

Further, the width of the step is set in the range of 0.01 to 0.15 mm, and the length of the chamfered inclined portion is set to 0.05.
It is good to set it in the range of 0.5 mm.

Further, the chamfer angle of the inclined portion is 30 to
It is good to set to 45 degrees.

The aluminum nitride radiator plate is manufactured by the following process. That is, as shown in FIG. 2, a mixture of the aluminum nitride powder and the sintering aid is placed in a mold such as an upper punch 12 or a die 11 machined into a predetermined shape to form a step 18 and a chamfered inclined portion 19. And pressurized with a molding pressure of about 750 to 1200 kg / cm ² to form a molded body 13. The obtained molded body 13 is sintered by a normal pressure sintering method or an atmospheric pressure sintering method. 1 is manufactured as a heat sink 7a.

Here, the reason why the width W of the step 18a of the heat sink 7a is set in the range of 0.01 to 0.15 mm as shown in FIG. 1 is as follows. That is, when the width W of the step is 0.
If it is less than 01 mm, a sharp edge (sharp edge) is formed at the tip of the upper punch of the mold, and the portion is very fragile, easily damaged, and a stable molding operation becomes difficult. On the other hand, when the width exceeds 0.15 mm, particularly when the heat sink 7a is mounted on a thyristor and resin sealing is performed, air bubbles (bubbles) are likely to be generated in the step portion, and the thermal resistance increases due to the bubbles. However, the withstand voltage characteristic of the thyristor is reduced and noise is likely to occur.

The length L of the chamfered inclined portion 19a is 0.0
If the thickness is less than 5 mm, the corners of the molded body become sharp, cracks and chips are easily generated, and the product yield of the heat sink decreases. On the other hand, if the length L exceeds 0.5 mm, the contact area of the radiator plate with respect to the thyristor shape decreases, and the heat radiation effect decreases. The same applies to the angle θ of the chamfered inclined portion 19a. When the angle θ is set to an acute angle of less than 30 degrees, a sharp portion is formed in the mold and the mold is easily damaged. On the other hand, if the angle exceeds 45 degrees, the contact area with the thyristor component decreases, and the heat radiation characteristics deteriorate, so the angle of the inclined portion is set in the range of 30 to 45 degrees.

Further, as the atmospheric gas in the normal pressure sintering method and the atmospheric pressure sintering method, a nitrogen gas or a mixed gas of a nitrogen gas and an inert gas is used. Atmospheric gas at normal pressure sintering method is about 1 kg / cm ^2, but in the atmosphere pressure sintering is set in the range of 1.5~100kg / cm ^2, is set to 5~6kg / cm ² Therefore, it is sufficient to use simple high-pressure gas equipment and pressure-resistant equipment. The atmospheric gas pressure is changed depending on the sintering temperature, and it is necessary to set the higher the higher the temperature, the higher the temperature. Normal 1750
1.5 to 10 kg / cm ² at １1800 ° C., temperature 1950
At ℃, it is about 20 to 30 kg / cm ² . Adjustment of the atmospheric gas pressure is performed by injecting a predetermined amount of gas from a gas cylinder connected to a pressure-resistant heating furnace.

The sintering temperature is 1750 to 185 by the normal pressure sintering method.
The temperature is about 0 ° C. and about 1800 to 1950 ° C. by an atmospheric pressure sintering method. When the temperature is lower than the lower limit of the above range, the sintering rate is low and the production efficiency is reduced. On the other hand, when the temperature is higher than the upper limit, the density is easily lowered due to thermal decomposition, evaporation and particle growth of the constituent materials.

The sintering time is 0.5 to 5 hours, preferably 1 to 2 hours in each case at the above temperature and atmospheric gas pressure.

[0022]

According to the aluminum nitride heat radiating plate having the above-described structure, since a step portion having a constant thickness is formed on the outer peripheral edge, a punch or a die is required when a molded body of the heat radiating plate is manufactured by die pressing. No sharp edge is formed at the periphery of the mold. Therefore, the life of the mold can be greatly extended, and the molding operation can be stabilized.

Further, since the chamfered inclined portion is formed from one end of the step portion toward the center of the aluminum nitride sintered body, cracks and chips are less likely to occur during generation or sintering of the heat sink, and the product yield is reduced. It can be greatly improved. Further, the manufacturing cost of the aluminum nitride radiator plate can be significantly reduced by extending the life of the mold and improving the product yield.

[0024]

Next, the aluminum nitride heat sink according to the present invention will be described in more detail with reference to the following examples.

EXAMPLES 1-5 3% by weight of yttria (Y ₂ O ₃ ) as a sintering aid was added to aluminum nitride powder having a purity of 99% and an average particle size of 1.5 μm, and wet-processed in ethyl alcohol for 30 hours. Mixed. As shown in FIG. 2, the raw material mixture obtained by drying was filled into a molding die of a die molding machine, and compression-molded at a molding pressure of 1000 kg / cm ² to obtain a disk-shaped material according to Examples 1 to 5. 5000 heat-dissipating plate compacts were prepared. The dimensions of the molded body are as follows: the outer diameter is 40.5 mm, the width of the step portion is 0.125 to 0.19 mm, the thickness is 3.2 mm, and the length of the chamfered inclined portion is 0.13 to 0.6.
A die and an upper punch were used which were 5 mm, the angle of the inclined portion was 30 degrees or 45 degrees, and the thickness of the step portion was 3.1 mm.

Then, the molded body for heat sink according to each embodiment was
At the stage where 000 pieces were prepared, the amount of wear at the tip of the upper punch of the mold and the presence or absence of chipping of the upper punch were examined, and the results shown in Table 1 were obtained. Further, the number of continuous shots of the press die was measured until the shape error of the upper punch reached ± 5% or until the end of the upper punch was chipped or cracked.

Next, the compacts for the respective examples were placed in a heating furnace filled with nitrogen gas, and densified and sintered by high-frequency induction heating. The sintering conditions are as follows: atmosphere pressure in the furnace is 5 kg / cm.
^On the other hand, the temperature was set to 1815 ° C. and baked for 6 hours. The obtained sintered body is machined, and finally the outer diameter is 32 mm, the thickness of the entire sintered body is 2.5 mm, the thickness of the step is 2.46 mm, and the width of the step is common. In addition, 5000 pieces of heat sinks made of AlN sintered bodies according to Examples 1 to 5 each having the length and angle of the chamfered inclined portion having the dimensions shown in the left column of Table 1 were manufactured.

Next, the surfaces and corners of the obtained AlN heat radiating plates of the respective examples were examined, and those having defects such as cracks and chips, and defects other than the above-mentioned defects such as deformation and uneven color were generated. The yield of the final product as a thyristor heatsink was calculated and the results shown in the right column of Table 1 were obtained.

Comparative Example 1 On the other hand, the raw material mixture prepared in Examples 1 to 5 as Comparative Example 1 was charged into a mold of a mold molding machine shown in FIG.
A die (upper punch) was prepared at the time when 5000 compacts having the same dimensions as in Examples 1 to 5 were prepared except that they were compression-molded at the same molding pressure as in Examples 1 to 5 and no step portions and chamfered inclined portions were formed. ) Was measured, the defect occurrence rate and the product yield of the heat sink obtained by firing under the same conditions were measured, and the life of the upper punch was measured.

Comparative Example 2 The raw material mixture prepared in Examples 1 to 5 was
5,000 pieces of the same size as in Examples 1 to 5 except that no step is formed, and the upper punch is filled in a mold of a mold forming machine shown in FIG. Of the heat sink obtained by firing under the same conditions, the product yield and the life characteristics of the mold were measured.

The results of the above measurements are shown in Table 1 below.

[0032]

[Table 1]

The life of the mold (upper punch) was relatively indexed with the number of continuous shots in the conventional upper punch used in Comparative Example 1 as a reference value of 100.

As is apparent from the results shown in Table 1, Examples 1 to 5 in which a step portion and a chamfered inclined portion having predetermined dimensions were formed.
According to the AlN heat radiating plate according to the above, the rate of occurrence of cracks and chips in the heat radiating plate itself was as small as 5 to 6%, and a high quality heat radiating plate was obtained with a high yield. In addition, since it has a shape that forms a step, a sharp edge is not formed on the upper punch, the tip of the punch is not damaged during molding and when changing the mold, and the molding operation is stabilized and the mold equipment is installed. Was able to extend the life of about three times.

On the other hand, according to the conventional AlN heatsink shown in Comparative Example 1 in which the step portion and the chamfered inclined portion are not formed, cracks and chips are generated in the corners at about 10 to 15%, and the final yield is 8%.
The value was as low as about 0%.

According to the AlN heat sink of Comparative Example 2 in which only the chamfered inclined portion is formed and no step is formed, a weak sharp edge is formed at the tip of the upper punch. Was remarkably worn, and in some cases chipping occurred. Although the incidence of defects such as cracks and chips in the heat sink itself tends to decrease as compared with Comparative Example 1, the mold life was short and the production cost was expected to increase.

[0037]

As described above, according to the aluminum nitride radiator plate of the present invention, since a step having a constant thickness is formed on the outer peripheral edge, a molded body of the radiator plate is manufactured by die pressing. At this time, a sharp portion (a sharp edge) is not formed at the periphery of the die such as a punch or a die. Therefore, the life of the mold can be greatly extended, and the molding operation can be stabilized.

Further, since the chamfered inclined portion is formed from one end of the step portion toward the center of the aluminum nitride sintered body, cracks and chips are less generated at the time of generation or sintering of the heat sink, and the product yield is reduced. It can be greatly improved. Further, the manufacturing cost of the aluminum nitride radiator plate can be significantly reduced by extending the life of the mold and improving the product yield.

[Brief description of the drawings]

FIG. 1 is a front view showing one embodiment of an aluminum nitride radiator plate according to the present invention.

FIG. 2 is a cross-sectional view of a press forming machine showing a state of forming an aluminum nitride radiator plate according to the present invention.

FIG. 3 is a sectional view showing a structural example of a thyristor module.

FIG. 4 is a cross-sectional view of a press forming machine showing a state of forming a conventional flat heat sink.

FIG. 5 is a sectional view of a press molding machine showing a molding state of a conventional heat sink having a chamfered portion.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Copper stud (heat sink) 2 Cathode conductor 3 Thyristor chip (silicon joined body) 4 Gate conductor 5 Ceramic seal 6 Case 7, 7a Heat sink 8 Soft aluminum plate 9 Clamp for pressure welding 10 Sealing resin 11, 11a, 11b Mold ( Dies) 12, 12a, 12b Upper punch 13, 13a, 13b Molded body 14 Crack 15 Chamfer 16 Edge 17 Chipping 18, 18a Step 19, 19a Chamfer slope

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-254475 (JP, A) JP-A-2-289302 (JP, A) JP-A-61-88250 (JP, U) Japan Powder Metallurgy Association Ed., “Sintering machine parts-design and manufacture-”, 1st edition, Technical Publishing Co., Ltd., Oct. 20, 1987, pp. 173-178, p. 341-344 (58) Field surveyed (Int.Cl. ⁷ , DB name) C04B 33/22 B28B 3/00-3/26 C04B 35/58 C04B 35/64

Claims (4)

(57) [Claims] 1. A step having a constant thickness is formed on an outer peripheral edge of a plate-shaped aluminum nitride sintered body, and a chamfered inclined part is formed from one end of the step toward the center of the aluminum nitride sintered body. An aluminum nitride radiator plate, wherein a chamfered inclined portion and a step portion are formed on both surfaces of an aluminum nitride sintered body. 2. The step width is set in the range of 0.01 to 0.15 mm, and the length of the chamfered inclined portion is set to 0.05 to 0.15 mm.
2. The method according to claim 1, wherein the distance is set to 0.5 mm.
The aluminum nitride radiator plate as described in the above. 3. The chamfer angle of the chamfered inclined portion is 30 to 45.
2. The aluminum nitride radiator plate according to claim 1, wherein the heat sink is set at a predetermined temperature. 4. The aluminum nitride radiator plate according to claim 1, which is used as a radiator plate of a thyristor module.