JPH0621288A - Ceramic package - Google Patents

Abstract

PURPOSE:To provide a ceramic package where excellent heat radiation is exhibited and the reliability of jointed heat sink fitting screw is high. CONSTITUTION:A heat sink fitting screw 3 is jointed in an area other than just above semiconductor element mounting part on a ceramic base 1, with a joint metallic layer 2 with no fillet interposed, and a heat sink 10 is fitted on the base 1 by the screw 3 to furnish a ceramic package.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic package having a ceramic base such as AlN, and more particularly to a ceramic package having a heat sink mounting screw for mounting a heat sink such as a radiation fin on the ceramic base.

[0002]

2. Description of the Related Art A package is a container that mainly protects a semiconductor device having low mechanical strength from various stresses and atmospheres that are applied during a manufacturing process and a transportation operation. But,
With the recent development of semiconductor technology, that is, the high integration of semiconductor devices, the increase in the number of pins of semiconductor elements, the increase in speed, and the increase in the size of chips, the demand for packages is mainly to protect the semiconductor elements from mechanical stress. There is a shift from what is protected to what is protected electrically and thermally.

Resins, metals, ceramics, etc. are used as the package material depending on the application. Among them, ceramics are comprehensively excellent in heat dissipation, electrical characteristics, and reliability. Particularly in recent packages, heat dissipation of semiconductor elements is large, so that heat dissipation is important.
Ceramics such as 1N, SiC and SiN are often used.

Regarding the heat radiation from the package, in addition to the use of ceramic as the package material, the use of a heat sink or heat pipe has been used to improve the characteristics. In particular, the heat pipe is effective in radiating heat from a semiconductor element having high heat generation. However, since the heat pipe has a large accommodation area, miniaturization is impossible. In addition, using a heat pipe increases the cost and is not practical.

On the other hand, heat sinks such as heat radiating fins have been improved in heat radiating property by conventionally improving the structure and the like. Usually, a metal such as aluminum is used as the material of the heat sink. When joining such a metal to the ceramic package, a brazing material or a solder material is used. However, when a metal heat sink is attached to a ceramic package by joining with a brazing material or a solder material, in a reliability test such as a thermal cycle test, peeling occurs at the joint portion between the two due to the difference in thermal expansion coefficient between the two.
At the same time, since the structure of the heat sink is becoming complicated, the method of brazing and directly attaching to the ceramic package is not practical because of high manufacturing cost. Further, it is required from the mounting surface that the heat sink can be removed for the purpose of repairing the die-bonded semiconductor element.

From the above, the heat sink mounting screw is joined to the surface of the conventional ceramic base opposite to the semiconductor element mounting portion surface, and the heat sink is detachably mounted by the heat sink mounting screw. At this time, there are the following three methods of joining the heat sink mounting screw to the ceramic base. One of them is simultaneous firing (C
This is a method in which a W conductor layer is formed on a ceramic substrate by o-fired), and then a heat sink mounting screw is joined by plating with Ni and Au. Another method is to form a thin film conductor layer on the ceramic substrate and then To the ceramic base by the active metal method. In this case, the heat sink mounting screw is usually joined directly above the semiconductor element mounting portion of the ceramic base from the viewpoint of facilitating heat dissipation to the heat sink therethrough.

[0007]

However, the above three methods have the following problems.

In the method of forming the W conductor layer on the ceramic substrate by co-firing, a fillet is usually formed in the joining metal layer, and the heat radiation effect is reduced. Furthermore, cracks are likely to occur at the hem of the joining metal layer, and the reliability of joining the heat sink mounting screws is not sufficient.

Further, the method of forming a thin film conductor layer on a ceramic substrate requires a double-sided thin film, which is costly, and the heat dissipation effect is similarly reduced due to the fillet formed in the joining metal layer, and the reliability is high. A crack is generated at the hem of the joining metal layer after the property test.

Similarly, in the case of direct joining by the active metal method, if fillet is formed in the joining metal layer to maintain the adhesion strength of the heat sink mounting screw,
There is a problem that the heat dissipation effect is reduced and cracks are generated at the hem of the joining metal layer after the reliability test.

As described above, no matter what method is used, heat can not be effectively radiated from the heat sink mounting screw to the heat sink, and the reliability of the joining of the heat sink mounting screw is low. The present invention has been made in view of such circumstances, and an object thereof is to provide a ceramic package having excellent heat dissipation.

[0012]

In order to solve the above problems, the present invention firstly provides a ceramic base having a semiconductor element mounting portion in a predetermined region, and a semiconductor element mounting portion of the ceramic base. A ceramic package comprising a heat sink mounting screw bonded to the opposite surface through a bonding metal layer, and a heat sink mounted to the semiconductor element mounting portion of the ceramic base on the opposite surface by the heat sink mounting screw. A heat sink mounting screw is joined to a region of the ceramic base other than directly above the semiconductor element mounting portion, to provide a ceramic package.

Secondly, a ceramic base having a semiconductor element mounting portion in a predetermined region, and a heat sink mounting screw bonded to a surface of the ceramic base opposite to the semiconductor element mounting portion via a bonding metal layer. A heat sink mounted on the surface of the ceramic base opposite to the semiconductor element mounting portion by the heat sink mounting screw, wherein the wetting area of the bonding metal layer with respect to the ceramic base is equal to that of the heat sink mounting screw. Provided is a ceramic package characterized by having an area equal to or smaller than that of a bonding surface.

The inventors of the present invention have made repeated studies on the cause of ineffective heat radiation to the heat sink in the ceramic package in which the heat sink mounting screw is joined to the ceramic base. It has been found that fillets are formed in the layers, and when a heat sink such as a radiation fin is attached, a gap is created between the ceramic substrate and the heat sink. In addition, at this time, it was found that cracks are likely to occur at the skirt of the fillet, and there is a problem in terms of bonding strength. Further, in the case of the method of directly bonding using an active metal, there is a problem that the wettability between the ceramic and the metal is poor and a gap is more likely to be formed between the ceramic base and the heat sink.

Based on such knowledge, the inventors of the present invention provided a hole in the heat radiation fin as a heat sink with a width corresponding to the formed fillet, and provided a gap between the ceramic base and the heat radiation fin in other regions. I tried to lose it. However, since the portion provided with the hole is a region directly above the semiconductor element mounting portion such as an IC and contributes most to heat dissipation, it has been found that heat dissipation is still insufficient.

Therefore, as a result of further studies by the present inventors, firstly, if a heat sink mounting screw is joined to a region of the substrate other than directly above the semiconductor element mounting portion, a fillet is formed in the joining metal layer. It has been found that it is possible to avoid the influence of the gap caused by the above, and by this, even if the heat dissipation through the heat sink mounting screw is not achieved, the direct heat dissipation from the ceramic substrate is sufficient.

Secondly, for example, by reducing the amount of brazing material used so that the wetting area of the joining metal layer with respect to the ceramic substrate is equal to or less than the area of the joining surface of the heat sink mounting screw, the brazing in the joining metal layer is prevented. The fillet of the material is not formed, so that the generation of the gap between the ceramic base and the heat sink and the generation of the crack at the skirt of the fillet due to the formation of the fillet can be eliminated, and sufficient heat radiation can be obtained. At the same time, it was found that the joint strength of the heat sink mounting screw is improved. The present invention having the above-mentioned configuration is made based on such knowledge of the present inventors. Hereinafter, the principle of the present invention will be described in more detail.

In the ceramic package, the heat generated in the semiconductor element passes through the ceramic substrate and is further radiated to the air through the I / O pin, and the heat is further radiated through the heat sink such as the heat radiation fin. Heat is released in a total of three directions, that is, the one released into the inside and the one released from the ceramic substrate into the air. Among these, most of the ceramic packages to which a heat sink is attached are released into the air via the I / O pins and the heat sink. In addition, the amount of heat generated in the vicinity of the active surface of the semiconductor element is determined in consideration of the distance from the heat generating portion to the heat radiating portion and the heat radiation efficiency of heat sinks such as I / O pins and heat radiating fins serving as radiators. . Further, in the ceramic package of the type in which the heat sink is attached to the surface of the ceramic base opposite to the semiconductor element mounting portion, which is the subject of the present invention, the main heat dissipation path is via the heat sink.

According to the first aspect of the present invention, as described above, the heat sink mounting screw is joined to a region of the ceramic substrate other than directly above the semiconductor element mounting portion, so that even if a fillet is formed in the joining metal layer. In the region directly above the semiconductor element mounting portion, there is no gap between the ceramic base and the heat sink. Therefore, the heat generated near the active surface of the semiconductor element is directly transmitted to the heat sink,
The heat from the semiconductor element can be quickly released into the air, and the thermal resistance of the entire semiconductor device including the ceramic package and the semiconductor element can be significantly reduced.

In the first aspect, the heat sink is attached by, for example, joining the heat sink attaching screws to the four corners of the ceramic base, and forming a hole having a diameter corresponding to a fillet formed at a position corresponding to the heat sink attaching screw of the heat sink. This is done by opening, inserting a heat sink mounting screw into the hole, and fixing with a female screw.

The surface roughness and warpage of the ceramic substrate are preferably 20 μm or less. By using such a ceramic base, it is possible to further reduce the gap between the ceramic base and the heat sink. Further, in consideration of heat dissipation, it is preferable to interpose silicone grease or the like between the ceramic base and the heat sink.

Furthermore, as the material of the ceramic substrate, those having high thermal conductivity such as AlN, SiC, and Si ₃ N ₄ are preferable. Al as the material of the ceramic substrate
When N is used, its coefficient of thermal expansion is 4.5 × 10 ^-6 ℃
(RT to 600 ° C.), which is the thermal expansion coefficient of Si 3
Since it is close to × 10 ^-6 ° C, it is particularly preferable because it is well matched thermally with the semiconductor element and does not cause any problem in reliability.

As described above, according to the first aspect, the conventional problem of the heat radiation limit in the ceramic package is eliminated, and it becomes possible to mount a semiconductor element having a larger heat generation amount.

On the other hand, the magnitude σ of the thermal stress generated in the brazed portion between the ceramic as the base material and the metal as the heat sink material is proportional to the actual elongation of the coupling system. It is known that the elongation L is represented by the following formula (1). L = (λ _b A _b E _b + λ _c A _c E _c + λ _k A _k E _k ) / (A _b E _b + A _c E _c + A _k E _k ) ... (1)

Here, λ is the amount of free expansion and expansion, A is the cross-sectional area, E is the longitudinal elastic modulus, and the subscripts b are brazing filler metal, c is ceramic, and k is metal (kovar). Furthermore, λ is expressed by λ = αlT (where α is the linear expansion coefficient, l is the length, and T is the temperature rise), and the linear expansion coefficient of the brazing filler metal is much larger than that of ceramics and Kovar. Since the coefficient difference is large, it is understood that the elongation L of the coupled dynamic system is mainly caused by the elongation of the brazing material. Therefore, from the formula (1), it is clear that as the cross-sectional area of the brazing material increases, the magnitude of the elongation and the thermal stress proportional to the elongation increase. Further, as a result of the research conducted by the present inventors, it was confirmed that this thermal stress is concentrated at the hem after the brazing material flows at the joint, in other words, at the hem of the fillet formed in the joint metal layer. There is.

On the other hand, in the second aspect of the present invention, as described above, since the heat sink mounting screw is joined to the ceramic base in a state where the fillet is not formed in the joining metal layer, the ceramic base is formed by the presence of the fillet. The gap between the heat sink and the heat sink can be eliminated, and the thermal stress generated at the joint can be significantly reduced.

More specifically, when the ceramic base and the heat sink mounting screw made of metal are directly joined using the brazing filler metal containing the active metal, the brazing filler metal containing the active metal has a comparatively wettability to the ceramic base. Bad Therefore, the oxygen content in the nitrogen atmosphere in the belt furnace is reduced,
In vacuum processing, operations such as increasing the degree of vacuum are required, making mass production difficult. However, if the amount of brazing filler metal is reduced and the wettability of the brazing filler metal to the ceramic substrate is less than the area of the joint surface of the heat sink mounting screw, fillets are not formed and conversely cracking occurs. The occurrence of cracking is suppressed, and high strength and highly reliable bonding becomes possible. Similarly, when joining the ceramic substrate and the heat sink mounting screw via the thin film conductor layer, the land diameter formed by the thin film conductor layer is made equal to or smaller than the diameter of the heat sink mounting screw, and the amount of brazing material is reduced to form a fillet. By not allowing it, cracks can be suppressed. The same applies to a case where a W conductor layer is formed on ceramics by co-firing, and Ni and Au plating is applied to join metals.

In the second aspect, the area A of the joint surface of the heat sink mounting screw and the wetting area B of the joint metal layer, which contributes to the joint of the ceramic base and the heat sink mounting screw, on the ceramic base side further satisfy 1 < (A / B)
It is preferable to satisfy <4. By defining in this way, it is possible to surely prevent the fillet from being formed in the joining metal layer.

The reliable joining by not forming the fillet in the joining metal layer is not limited to the joining of the ceramic base and the heat sink mounting screw as described above, but the ceramic cap in the ceramic package. Generally, it can be widely applied to join a ceramic and a metal, such as when joining a heat sink mounting screw to the substrate or when directly joining a heat sink to a ceramic substrate.

Also in this embodiment, as in the first embodiment, the material of the ceramic substrate is AlN, SiC, S.
i ₃ N ₄ is preferred. Further, it is preferable that the heat sink mounting screw and the heat sink are formed of a high melting point metal such as W or Mo or an alloy of W and Cu. These materials are suitable as heat sink mounting screws or heat sinks because they have a thermal expansion coefficient close to that of the above-mentioned ceramic base material and high thermal conductivity. As described above, also in the second aspect, it is possible to obtain a ceramic package having excellent heat dissipation and high reliability.

[0031]

Embodiments of the present invention will be specifically described below with reference to the drawings.

FIG. 1 is a schematic diagram showing an example of a ceramic package according to the first aspect of the present invention. Reference numeral 1 in the drawing indicates a ceramic substrate. On one surface of the ceramic base 1, heat sink mounting screws 3 for mounting the heat radiation fins 10 as a heat sink by brazing using a brazing material containing an active metal are provided at four corners via the bonding metal layers 2. It is joined. I / O pins 4 and weld rings 5 are bonded to the surface of the ceramic substrate 1 on the opposite side. These are heat sink mounting screws 3
At the same time as brazing, it is joined by brazing.

The actual brazing is performed in a vacuum at 83
It was carried out under the condition of holding at 0 ° C. for 30 seconds. The I / O pin 4 and the weld ring 5 are formed on the ceramic substrate 1 in advance by Ti.
-Ni-Au is used to form a thin film conductor layer, and 72
Bonding was performed using a brazing filler metal 6 of wt% Ag-Cu.

As the material of the ceramic substrate 1, AlN or SiC having high thermal conductivity is desirable as described above, and here, AlN having a thermal conductivity of 170 W / m · K was used.
Further, both surfaces of the ceramic substrate 1 were ground so that the surface roughness Ra was 10 μm. The ceramic base 1
Has an internal wiring made of W, and each bonding pad and I / O pad electrically connected to each other are formed on the surface.

As the active metal in the brazing material used for joining the heat sink mounting screw 3, Ti, Zr, Hf or the like is desirable, and Ti is used here. As a material for the heat sink mounting screw 3, a material having a high thermal conductivity and a coefficient of thermal expansion close to that of the ceramic base 1 is preferable, and as described above, a high melting point metal such as W or Mo or an alloy of W and Cu is desirable. , Mo was used here. Then, as the heat sink mounting screw 3, a header having a diameter of 8 mmφ is used, while the diameter is 6 mmφ and the thickness is 0.05 mm.
The heat sink mounting screw 3 was brazed and bonded to the ceramic base 1 using an Ag—Cu brazing material containing 2 wt% of Ti in mm.

The size of the semiconductor element 7 is 15.5 × 15.5.
× 0.35 mm, the semiconductor element 7 is mounted on the semiconductor element mounting portion of the ceramic substrate 1 in a nitrogen atmosphere using an Au—Si thin film, and the bonding wire 8 is used to separate the semiconductor element 7 and the ceramic substrate 1. Electrical connection was made. Then, the lid 9 was used for sealing with solder.

The heat radiation fins 10 as heat sinks were attached to the heat sink attachment screws 3 joined as described above. At this time, silicone grease 11 was applied to the surface of the ceramic substrate 1 to maintain good heat transfer between the ceramic substrate 1 and the heat radiation fins 10 and to impart high heat radiation. Further, the heat sink mounting screws 3 were respectively inserted into the holes at the four corners of the heat radiation fin 10, and the heat radiation fin 10 was fixed by the nut 12.

When the thermal characteristics of the ceramic package obtained as described above were measured, it was 3.3 ° C./W without forced convection and 1.5 at 2 m / s of convection.
It was confirmed that excellent heat dissipation of ℃ / W was achieved.

Further, in this embodiment, the heat sink mounting screw 3 joined to the ceramic substrate 1 has a joining strength of 30 cm · kg or more at the initial torque strength, and the breaking portion of the joining is thread breakage of the female screw used for strength measurement. It was confirmed that the strength was high. As a result of SEM observation of the cross section, no crack was observed. Furthermore, in the reliability test, 100 cycles of TST test and TCT
As a result of each of 1000 cycles of the test, no decrease in the bonding strength was observed. Next, the second aspect of the present invention will be described. FIG. 2 is a schematic configuration diagram showing an example of a ceramic package according to the second aspect of the present invention.

Reference numeral 21 in the drawing denotes a ceramic substrate. On one surface of the ceramic base 21, a heat sink mounting screw 23 is joined to the center portion of the ceramic base 21 through a joining metal layer 22 by brazing using a brazing material containing an active metal. I / O is provided on the surface opposite to the ceramic base 21.
The pin 24 and the weld ring 25 are joined. These are joined by brazing at the same time as the heat sink mounting screw 23 is brazed.

The actual brazing was carried out in vacuum using the same thin film conductor layer and brazing material as in the first embodiment under the same conditions as in the first embodiment. Further, the I / O pin 24 and the weld ring 25 are joined in the same manner.

As the material of the ceramic base 21, AlN or SiC having high thermal conductivity is desirable as described above,
Here, AlN having a thermal conductivity of 170 W / m · K was used. As the active metal in the brazing material used for joining the heat sink mounting screw 23, Ti was used as in the first embodiment, and as the material of the heat sink mounting screw 23, Mo was used as in the first embodiment. . Then, as the heat sink mounting screw 23, a header having a diameter of 8 mmφ is used, while the diameter is 6 mmφ and the thickness is 0.05 mm.
The heat sink mounting screw 23 was brazed to the ceramic base 21 using an Ag—Cu brazing material containing 2 wt% of Ti of mm.

Although not shown, the same semiconductor element as in the first embodiment is mounted on the semiconductor element mounting portion on the surface of the ceramic base 21 opposite to the heat sink mounting screw 23. The heat sink mounting screw 23 is inserted into a screw hole at the center of the heat radiating fin 30, the heat radiating fin 30 is mounted on the heat sink mounting screw 23, and silicone grease is applied to the gap between the ceramic base 21 and the heat radiating fin 30. .

When the thermal characteristics of the ceramic package obtained as described above were measured, it was confirmed that the excellent heat dissipation characteristics similar to those of the first embodiment were achieved. Moreover, the radiation fin 3
Before actually mounting 0, the joint strength of the heat sink mounting screw 23 joined to the ceramic base 21 was measured, and as a result, the initial torque strength was 30 cm · kg or more. It was confirmed that the mountain was cut off and the strength was high. Also, a cross-section SEM
As a result of observation, no crack was observed in the ceramic substrate. In the reliability test, the TST test was carried out for 100 cycles and the TCT test was carried out for 1000 cycles, respectively, and as a result, no decrease in bonding strength was observed.

In addition, as a reference example, an example in which the radiation fin is directly joined to the ceramic substrate without forming a fillet will be shown. That is, here, the radiation fin was joined to the ceramic substrate by using the same joining method as described above.

As a result of similarly conducting a joint strength test on this ceramic package, the initial torque strength was 30 c.
It was confirmed that the strength was more than m · kg and the strength was high. As a result of SEM observation of the cross section, no crack was observed in the ceramic substrate. In the reliability test, TST
As a result of carrying out the test for 100 cycles and the TCT test for 1000 cycles, respectively, no decrease in bonding strength was observed.

Next, a comparative example will be described. Here, with respect to the diameter of the header of the heat sink mounting screw of 8 mmφ, 2 wt% of 10 mmφ and 0.10 mm thick Ti is used.
A heat sink mounting screw was brazed and bonded to the central portion of the ceramic substrate, that is, the region directly above the semiconductor element mounting portion, using the Ag-Cu brazing material contained therein. Other than that, the conditions were set to be the same as those in the above-mentioned embodiment. When the thermal characteristics of the ceramic package obtained as described above were measured, in the case of no forced convection, the same 3.3 ° C /
Although it was W, at a convection of 2 m / s, 1.7 ° C /
W was inferior in heat dissipation. Also, the heatsink mounting screw joined in this way has an initial torque strength of 20
In cm · kg, the joint breakage was cracking of the ceramic substrate. As a result of SEM observation of the cross section, it was confirmed that cracks were generated in the ceramic substrate.

[0048]

As described above, according to the present invention, a ceramic package having excellent heat dissipation is provided.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of a ceramic package according to a first aspect of the present invention.

FIG. 2 is a schematic configuration diagram showing an example of a ceramic package according to a second aspect of the present invention.

[Explanation of symbols]

1, 21 ... Ceramic substrate, 2, 22 ... Bonding metal layer,
3, 23 ... Heat sink mounting screw, 7 ... Semiconductor element,
10, 30 ... Radiating fins.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kyoaki Yasumoto 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Toshiba Research Institute Ltd. (72) Inventor Nobuo Iwase Komukai-Toshiba, Kawasaki-shi, Kanagawa Town No. 1 Incorporated company Toshiba Research Institute (72) Inventor Masako Nakahashi Komukai-shi, Kawasaki-shi, Kanagawa No. 1 Toshiba Town Incorporated company (72) Inventor Mitsuyoshi Endo Sumihiro Tsurumi-ku, Yokohama-shi, Kanagawa 2-4 Machi, Keio, Toshiba Corp. (72) Keiichi Yano 2-4, Suehiro-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Toshiba Keihin, Ltd.

Claims (2)

[Claims] 1. A ceramic base having a semiconductor element mounting portion in a predetermined region, a heat sink mounting screw bonded to a surface of the ceramic base opposite to the semiconductor element mounting portion via a bonding metal layer, and the heat sink mounting. A ceramic package comprising a heat sink attached to the surface of the ceramic base opposite to the semiconductor element mounting portion by a screw, wherein the heat sink mounting screw has a region other than directly above the semiconductor element mounting portion of the ceramic base. A ceramic package characterized by being bonded to. 2. A ceramic base having a semiconductor element mounting portion in a predetermined region, a heat sink mounting screw bonded to a surface of the ceramic base opposite to the semiconductor element mounting portion via a bonding metal layer, and this heat sink mounting. A ceramic package comprising a heat sink attached to a surface of the ceramic base opposite to the semiconductor element mounting portion by a screw, wherein a wetting area of the bonding metal layer to the ceramic base is an area of a bonding surface of the heat sink mounting screw. A ceramic package characterized by: