JP2669033B2 - Manufacturing method of ceramic circuit board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a method for manufacturing a ceramic circuit board on which a semiconductor chip is mounted. And the main component,
A step of forming a green sheet made of a glass-ceramic composite material, a step of cutting the green sheet into a predetermined size, and a step of punching a hole for a via and a hole for mounting a semiconductor chip; A step of printing a copper paste to form a conductor circuit, aligning and laminating the plurality of green sheets, and then firing to form a glass-ceramic substrate; and forming the glass-ceramic substrate and a hole for mounting a semiconductor chip. Manufacturing a ceramic circuit board including a step of applying a glass paste to an aluminum nitride substrate having the same shape and bonding the two via the glass paste, and a step of firing and integrating in an inert gas atmosphere Configure the method.

[Industrial applications]

The present invention relates to a method for manufacturing a ceramic circuit board on which a semiconductor chip is mounted.

Due to the need to process a large amount of information at high speed, information processing technology has made remarkable progress, and optical communication has come into wide use.

Here, the feature of optical communication is that high-speed transmission can be performed together with multiplexing. To take advantage of this feature, it is needless to say that semiconductor chips such as LSI and VLSI are configured to be suitable for high-speed signals. The circuit board on which the semiconductor chip is mounted also needs to have low signal attenuation and low loss.

That is, it is necessary that the circuit board made of the multilayer ceramic has low loss and good thermal conductivity, and the conductor line is made of a metal material having a low conductor resistance.

[Conventional technology]

Alumina (Al ₂ O ₃ ) is used as a substrate material of a conventional multilayer ceramic circuit board, and tungsten (W) or the like is used as a conductor line.

This is because the melting point of alumina is as high as 2015 ° C, so a sintering temperature of about 1600 ° C is necessary. This is because only metals having a high melting point (3387 ° C.) can be used.

However, the thickness of the unit substrate that constitutes the multilayer ceramic circuit substrate is as thin as several tens to several hundreds of μm, and the conductor circuit is 50 to 100 μm.
Since the fine patterns with a width of μm are provided close to each other, if the dielectric constant of the substrate is large, the transmission loss increases and the signal propagation delay also increases.

That is, since alumina has a large dielectric constant of 8 to 10, signal leakage (cross-talk) is likely to occur, and the signal delay time (τ) also increases.

Further, the conductor resistance of W is as large as 10 mΩ / □, which results in a large power loss and a large heat generation of the substrate.

FIG. 3 shows the structure of a conventional ceramic circuit board 1. After punching holes for forming vias in a green sheet made of alumina, conductor paste and vias are formed by screen printing of W paste. After stacking such green sheets, they are fired and integrated at a temperature of about 1600 ° C.

Here, the conductor circuit 3 made of W is patterned on the alumina substrate 2, and the conductor circuits 3 of the respective layers are circuit-connected by the vias 4.

The semiconductor chip 5 is mounted on the alumina substrate 2 of the uppermost layer by eutectic bonding or an adhesive, and the electrode terminals provided around the semiconductor chip 5 and the bonding terminals provided on the alumina substrate 2 are bonded. Pad 6
Is wire-bonded using a gold (Au) wire or an aluminum (Al) wire.

As described above, the semiconductor chip 5 is mounted on the ceramic circuit board and is connected to the bonding pads 6 provided on the board, and the bonding is performed because the chip surface is higher than the circuit board surface. The long distance also causes an increase in transmission loss.

[Problems to be solved by the invention]

As described above, in optical communication, a ceramic circuit board on which a semiconductor chip is mounted needs to have a small signal propagation delay, a small transmission loss, a good heat dissipation property, and a conductor circuit having a low resistance.

However, alumina is used as the substrate material and the conductor circuit is made of W
It is a problem that the conventional ceramic circuit board constructed from the above does not satisfy these requirements.

[Means for solving the problem]

The above-mentioned problem is a process of forming a green sheet made of a glass-ceramic composite material using alumina powder and borosilicate glass powder as main components, and cutting the green sheet into a predetermined size to form a via hole. A process of punching holes for mounting semiconductor chips, and printing a copper paste on each cut green sheet to form a conductor circuit, aligning and stacking the plurality of green sheets, and firing the glass / ceramic substrate. And a step of applying a glass paste to the glass / ceramic substrate and an aluminum nitride substrate of the same shape without a hole for mounting a semiconductor chip, and bonding the two via the glass paste, A ceramic circuit board manufacturing method including a step of firing and integrating in a gas atmosphere is solved. Can.

[Action]

In the present invention, a glass / ceramic composite material is used instead of alumina, the conductor line is formed using copper (Cu) instead of W, the substrate portion on which the semiconductor chip is mounted is formed as a recess, and the semiconductor chip is formed of aluminum nitride ( (AlN) is mounted on a substrate.

In order to put a ceramic circuit board with low transmission loss and excellent high-frequency characteristics into practical use, the inventors have found that the dielectric constant of the ceramic board is low, that Cu is used as a component of the conductor circuit, and that the heat dissipation of the board is excellent. And that the distance for wire bonding is small.

Here, borosilicate glass and Al ₂ O ₃
And a composite dielectric consisting of

The reason is that the dielectric constant of borosilicate glass varies depending on the composition ratio, which is 4.1 to 4.8, which is far less than that of alumina. I can't.

Also, borosilicate glass alone has poor mechanical strength.

Thus, a composite dielectric with alumina was used to increase the softening temperature and mechanical strength.

This slightly increases the composite permittivity to about 5.6,
The softening temperature becomes 1000 ° C. or higher, and it becomes possible to use Cu having a conductor resistance as small as 1.5 mΩ / □ as a constituent material of the conductor line.

Next, as a method of improving the heat dissipation of the semiconductor chip, the semiconductor chip was directly mounted on an aluminum nitride (AlN) substrate.

That is, the thermal conductivity of AlN is 260 W / mK (theoretical value is 320 W / mK).
The thermal conductivity of K) and α-Al ₂ O ₃ is much better than that of 20 W / mK.

Also, as a method of shortening the wire bonding distance, a hole necessary for the semiconductor chip to be loosely fitted in the glass ceramic substrate is made, and the height of the semiconductor chip mounted on the AlN substrate is approximately equal to the surface of the glass ceramic substrate. did.

FIG. 1 is a perspective view of a ceramic circuit board according to the present invention,
FIG. 2 shows a sectional view.

That is, a composite material of borosilicate glass and alumina is used as a dielectric material, Cu is used as a conductor line, and a glass / ceramic green sheet having a hole 7 for mounting a semiconductor chip in the center is laminated, and the glass / green sheet is fired. A ceramic substrate 8 is made and bonded to an AlN substrate 10 via a glass adhesive layer 9 formed by applying a glass paste.

Here, in order to fuse the glass-ceramic substrate 8 to the AlN substrate 10 by using the glass paste, it is necessary to perform it in an inert atmosphere in order to prevent the oxidation of Cu.

The thermal expansion coefficient of the glass-ceramic substrate is 4.5 × 10 ^-6 / ℃, while the thermal expansion coefficient of AlN is 4.2 ×
Since it is slightly different from 10 ⁻⁶ / ° C., it is necessary to match the thermal expansion coefficient of the glass adhesive layer 9 with both in order to obtain sufficient bonding strength. Is the most important issue.

〔Example〕

Example 1: Alumina powder (particle diameter 1 μm) 50 parts by weight Borosilicate glass (particle diameter 1 μm) 50 μ Polymethyl methacrylate (binder) 70 parts by weight Dibutyl phthalate (plasticizer) 30ア セ ト ン Acetone (solvent) 110 110 メ チ ル Methyl ethyl ketone (solvent) 530 530 、 and kneaded using a ball mill for 24 hours, and using this slurry, the thickness is 0.3 μm by doctor blade method.
Green sheet was formed.

Next, Cu powder (particle size: 1 μm) ... 100 parts by weight Polymethyl methacrylate (binder) ... 3 parts by weight Titanium (Ti) coupling agent ... 1 テ ル Terpineol (solvent) ... 10 〃 Methyl ethyl ketone (solvent) ...... 100〃 was ball-milled and subsequently kneaded using a three-roll mill to make a Cu paste.

Next, the created green sheet was cut into a 150 mm square by using a mold, and a via hole and a hole for mounting a semiconductor chip were punched out.

A pattern was formed on this green sheet using a Cu paste to fill the via hole, followed by drying and alignment to form a four-layer laminate.

The laminated body was debindered at 850 ° C. in a nitrogen (N ₂ ) atmosphere and then fired at 1000 ° C. to form a glass / ceramic substrate.

Next, the coefficient of thermal expansion is 4.2 × 10 ^-6 / ° C and the softening temperature is 470 ° C
Using glass (product name 7593, manufactured by Corning Incorporated), glass powder (particle size: 3 μm) ... 100 parts by weight PMMA (binder) ... 2 ２ terpineol (solvent) ... 8 メ チ ル methyl ethyl ketone (solvent) ... 80 をThe mixture was mixed using a ball mill and then kneaded using a three-roll mill to prepare a glass paste.

This glass paste is applied to a glass-ceramic substrate and AlN
Screen printing was performed on the substrate, dried and then aligned and joined, and this was fired and integrated in a N ₂ atmosphere at a temperature of 640 ° C. for 30 minutes.

As a result of the measurement, the adhesive strength between the glass / ceramic substrate and the AlN substrate was 10 Kg / mm ² , which was excellent.

Comparative Example 1: The glass constituting the glass adhesive layer has a coefficient of thermal expansion of 3.
A glass paste having a particle size of 3 μm and a softening temperature of 620 ° C. (product name: ASF-1460, manufactured by Asahi Glass Co., Ltd.) was prepared in the same direction as in Example 1 using 6 × 10 ⁻⁶ / ° C.

This glass paste was applied to the glass paste in the same manner as in Example 1.
Screen printed on the ceramic substrate and the AlN substrate, and joined aligned after drying, the temperature 75 this in an atmosphere of N ₂
It was baked at 0 ° C for 30 minutes to be integrated.

As a result of the measurement, the adhesive strength between the glass-ceramic substrate and the AlN substrate was as small as 5 kg / mm ² .

 This is due to a mismatch in the coefficient of thermal expansion.

Comparative Example 2: The glass constituting the glass adhesive layer has a coefficient of thermal expansion of 6.
A glass paste having a particle size of 3 μm and a softening temperature of 513 ° C. (product name: 7586, manufactured by Corning Incorporated) at 6 × 10 ⁻⁶ / ° C. was used to prepare a glass paste in the same direction as in Example 1.

This glass paste was applied to the glass paste in the same manner as in Example 1.
Screen printed on the ceramic substrate and the AlN substrate, aligned after drying by bonding, the temperature this in an atmosphere of N ₂
They were fired and integrated at 750 ° C for 30 minutes.

As a result of the measurement, the adhesive strength between the glass / ceramic substrate and the AlN substrate was as low as 1 kg / mm ² .

 This is due to a mismatch in the coefficient of thermal expansion.

Comparative Example 3: The glass constituting the glass adhesive layer has a coefficient of thermal expansion of 4.
A glass paste having a particle size of 3 μm and a softening temperature of 415 ° C. (product name CF-5, manufactured by Nippon Electric Glass) at 7 × 10 ⁻⁶ / ° C. was used to prepare a glass paste in the same direction as in Example 1.

This glass paste was applied to the glass paste in the same manner as in Example 1.
Screen printed on the ceramic substrate and the AlN substrate, aligned after drying by bonding, the temperature this in an atmosphere of N ₂
They were fired and integrated at 650 ° C for 30 minutes.

As a result of the measurement, the adhesive strength between the glass / ceramic substrate and the AlN substrate was 8 kg / mm ² .

Comparative Example 4: The glass constituting the glass adhesive layer has a coefficient of thermal expansion of 1
A glass paste having a particle size of 3 μm and a softening temperature of 337 ° C. (product name 8473, manufactured by Corning Incorporated) at 0.3 × 10 ⁻⁶ / ° C. was used in the same direction as in Example 1 to prepare a glass paste.

This glass paste was applied to the glass paste in the same manner as in Example 1.
Screen printed on the ceramic substrate and the AlN substrate, aligned after drying by bonding, the temperature this in an atmosphere of N ₂
It was baked at 600 ° C for 30 minutes to be integrated.

As a result of the measurement, the adhesive strength between the glass / ceramic substrate and the AlN substrate was as low as 1 kg / mm ^2, and the glass / ceramic substrate was broken.

Next, when the signal propagation delay time was measured for the glass-ceramic circuit board obtained in Example 1 and the conventional ceramic circuit board, the latter was 11 ns / m, whereas the former was as small as 7.5 ns / m. It was

Table 1 compares the high frequency characteristics of the glass-ceramic circuit board prepared in Example 1 with that of the conventional product.

[Advantages of the Invention] As described above, according to the present invention, it is possible to put into practical use a ceramic circuit board having excellent heat dissipation and excellent high-frequency characteristics, which enables high-speed transmission with low loss.

[Brief description of the drawings]

1 is a perspective view of a ceramic circuit board according to the present invention, FIG. 2 is a cross-sectional view of the ceramic circuit board according to the present invention, and FIG. 3 is a cross-sectional view showing a configuration of a conventional ceramic circuit board. In the figure, 1 is a ceramic circuit substrate, 2 is an alumina substrate, 3 is a conductor circuit, 5 is a semiconductor chip, 7 is a hole for mounting a semiconductor chip, 8 is a glass / ceramic substrate, 9 is a glass adhesive layer, 10 is an AlN substrate, Is.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Koichi Niwa 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited

Claims (1)

(57) [Claims] 1. A step of forming a green sheet made of a glass / ceramic composite material using alumina powder and borosilicate glass powder as main constituents, and cutting the green sheet into a predetermined size to form a green sheet. A step of punching holes and holes for mounting semiconductor chips, and printing a copper paste on each of the cut green sheets to form a conductive circuit, aligning and stacking the plurality of green sheets, and then firing the glass / glass. A step of forming a ceramic substrate, a step of applying a glass paste to the glass-ceramic substrate and an aluminum nitride substrate having the same shape without a hole for mounting a semiconductor chip, and bonding the two via the glass paste, And a step of firing in an inert gas atmosphere to integrate the ceramic circuit board.