JP3499061B2 - Multilayer aluminum nitride circuit board - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer aluminum nitride circuit board having a surface conductor layer.

[0002]

2. Description of the Related Art In recent years, the demand for ceramic substrates has been increasing year by year with the development of semiconductor devices such as power ICs and high frequency transistors which require large currents. In particular, since the aluminum nitride substrate has features such as high thermal conductivity and excellent heat dissipation, it is attracting attention as a substrate that can cope with the increasing amount of heat dissipation from semiconductor elements.
When such an aluminum nitride substrate is used as a semiconductor package, a multilayer circuit board, or the like, it is common to simultaneously manufacture a multilayer aluminum nitride substrate and a conductor layer by simultaneous firing.

A general method for manufacturing a multilayer aluminum nitride substrate by simultaneous firing will be described. First, a through hole is formed in an aluminum nitride green sheet in accordance with a desired internal circuit pattern, and a conductor paste is filled in the through hole, and the conductor paste is applied in a desired circuit pattern on the green sheet. After laminating a plurality of such green sheets, the green sheet laminate is sandwiched between metal plates and pressed from above and below while being heated to produce an aluminum nitride compact.

At this time, the paste coating layer serving as the surface conductor layer is crushed and embedded in the underlying green sheet to form a substantially flat surface. That is, the upper surface of the paste coating layer, which is the surface conductor layer, is flush with the surrounding aluminum nitride green sheet. Thereafter, the aluminum nitride molded body is subjected to degreasing treatment and further fired at a predetermined temperature to simultaneously sinter the aluminum nitride base material and the conductor layer to obtain a multilayer aluminum nitride circuit board.

When the above-mentioned surface conductor layer is used as a bonding pad or the like, Ni / Au or the like is plated thereon, and a bonding wire is bonded onto this plating layer. By the way, when only such wire bonding property is taken into consideration, the flat surface conductor layer as described above generally leads to facilitation of bonding, improvement of bonding strength, and the like, and brings good results.

[0006]

However, in the multilayer aluminum nitride circuit board, there is a tendency that liquid phase components exuding from the aluminum nitride material during the firing step tend to collect in the conductor layer portion, and as a result, after firing, Many liquid phase components remain on the surface of the surface conductor layer. The liquid phase component existing on the surface conductor layer has a function of hindering plating, which causes a problem of non-uniform deposition of plating.

In wire bonding mounting, since the plating layer is formed relatively thick, it is apparently possible to carry out the plating satisfactorily even if there are some factors that hinder the plating. However, the non-uniform deposition at the beginning of plating causes blistering due to a heating test or the like, and causes a decrease in bonding strength of the bonding wire. And especially,
When the flip chip method is applied to the method of connecting the semiconductor chip and the package, it is desired to reduce the plating thickness, so that the non-uniform deposition at the beginning of plating directly causes a decrease in electrical characteristics.

As described above, in the conventional multilayer aluminum nitride circuit board, it has been a problem to improve the adherence of plating by reducing the amount of liquid phase component on the surface conductor layer. In the case of a multilayer alumina circuit board, etc., even if the liquid phase component exudes on the surface conductor layer, it can be easily removed by etching because the liquid phase is a glass component. XAl ₂ O
_Since there is no etchant capable of effectively removing the liquid phase component such as ₃ · yY ₂ O _3, it is impossible at present to remove only the liquid phase component by etching.

The present invention has been made in order to solve such a problem, and an object thereof is to provide a multilayer aluminum circuit board in which the plating adherence of the surface conductor layer is improved.

[0010]

A multilayer aluminum nitride circuit board of the present invention is a multilayer aluminum nitride substrate, an internal conductor layer formed by simultaneous firing of the multilayer aluminum nitride substrate, and the internal conductor layer electrically. Connected to the
A connection pad formed by co-firing on the surface of the multi-layer aluminum nitride substrate , wherein the multi-layer aluminum nitride substrate has only one surface before protruding from the surface;
A connection pad is formed , and a plating layer is formed on the connection pad.
Is provided . The plating layer is
On the Ni plating layer and the Ni plating layer on the connection pad
It may be an Au plating layer.

[0011] In the multi-layer aluminum nitride circuit board of the present invention, since the surface conductive layer formed on the other hand the surface of the more protruding shape like substrate portions around the, the surface conductor layer in an aluminum nitride substrate Even if the liquid phase component permeates, the height of the surface conductor layer and the path for the liquid phase component to permeate can reduce the permeation of the liquid phase component to the surface. Further, as the surface area of the surface conductor layer increases, the reduction reaction of the liquid phase component on the surface of the surface conductor layer easily progresses, and this also suppresses the residual liquid phase component on the surface conductor layer. .

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Modes for carrying out the present invention will be described below.

FIG. 1 is a sectional view showing the structure of a multilayer aluminum nitride circuit board according to an embodiment of the present invention. The multilayer aluminum nitride circuit board 1 shown in the figure has a plurality of aluminum nitride layers integrated by firing, for example,
A multilayer aluminum nitride substrate 2 having four aluminum nitride layers 2a, 2b, 2c, 2d, an internal conductor layer 3 provided inside the multilayer aluminum nitride substrate 2, and a multilayer aluminum nitride substrate 2 provided on the surface thereof. And a surface conductor layer 4. Although FIG. 1 shows the multilayer aluminum nitride substrate 2 composed of four aluminum nitride layers, the multilayer aluminum nitride circuit board of the present invention is not particularly limited to the number of aluminum nitride layers.

The above-mentioned inner conductor layer 3 includes the conductor layer 3a filled in the through hole 5 provided in each of the aluminum nitride layers 2a to 2d and each of the aluminum nitride layers 2a to 2d.
It is composed of the circuit conductor layer 3b formed above.
The internal conductor layer 3 is formed according to a desired internal circuit pattern, and is a surface conductor layer as a connection pad or the like formed on one surface of the multilayer aluminum nitride substrate 2, specifically, the upper surface side. The upper surface conductor layer 4a is electrically connected to the other surface, specifically, the surface conductor layer (lower surface conductor layer) 4b as a connection pad or the like formed on the lower surface.

The multilayer aluminum nitride substrate 1 includes, for example, an aluminum nitride base material (multilayer aluminum nitride substrate 2) and a metal material for forming the internal conductor layer 3 and the surface conductor layer 4, specifically, a coating / filling layer of a conductor paste. It is produced by co-firing. The multilayer aluminum nitride substrate 2 is made of a general aluminum nitride sintered body. For example, a rare earth oxide powder such as yttrium oxide or an aluminum oxide powder is added to aluminum nitride powder as a sintering aid. An example is one obtained by sintering such mixed powder.

Examples of the metal material for forming the inner conductor layer 3 and the surface conductor layer 4 include refractory metals such as tungsten and molybdenum. These refractory metals may be used alone or as a mixture with an active metal such as titanium or zirconia. In particular, in the present invention,
It is preferable to use, as a main component, tungsten whose coefficient of thermal expansion is similar to that of aluminum nitride.

Of the surface conductor layers 4 described above, the surface conductor layer 4a on the upper surface side serving as a connection pad or the like has a convex shape protruding from the surface of the multilayer aluminum nitride substrate 2 around it. By thus forming the upper surface conductor layer 4 so as to project, it is possible to prevent the liquid phase component of the multilayer aluminum nitride substrate 2 from seeping out and remaining on the outermost surface thereof. As a result, good plating adherence can be obtained with good reproducibility, and the effect can be sufficiently obtained with a thin plating layer.

That is, the multilayer aluminum nitride circuit board 1 requires an aluminum nitride green sheet in which the through holes 5 are filled with a conductive paste and a coated layer of the conductive paste serving as the circuit conductive layer 3b and the surface conductive layer 4 is formed. It is formed by stacking a number of sheets, pressing the laminated body while heating to form a pressure-bonded body, disposing the pressure-bonded body on a setter made of an aluminum nitride sintered body, and degreasing and firing. The surface on the side not in contact with this setter is
It will be directly exposed to the firing atmosphere. A nitrogen atmosphere is usually applied as the firing atmosphere, but it is inevitable that carbon or carbon gas (CO _x ) evaporated from a firing jig or the like is included in the firing atmosphere.

When firing is performed in such an atmosphere, the upper surface conductor layer 4a not in contact with the setter is sintered while being exposed to the atmosphere containing carbon. Further, at the time of sintering, the liquid phase component in the aluminum nitride layer 2 a to 2 d, for example a liquid phase component comprising _{xAl 2 O 3 · yY 2 O} 3 comes seeps slowly on the surface side of the multilayer aluminum nitride substrate 2. At this time, it is considered that the liquid phase component mainly passes through the conductor layer 3a filled in the through hole 5 and reaches the upper surface side conductor layer 4a which is directly exposed to the firing atmosphere, and exudes to the surface thereof. . This is xAl ₂ O ₃ · yY ₂ O
_Since the liquid phase component such as ₃ has a property of moving to a place where a large amount of carbon is present and the reduction reaction progresses, finally, the upper surface conductor layer 4a of the upper surface conductor layer 4a exposed directly to the firing atmosphere containing carbon is used. It is thought to exude to the surface.

At this time, as in the conventional multilayer aluminum nitride circuit board shown in FIG. 3, the upper surface side conductor layer 4a exposed to the firing atmosphere is embedded in the uppermost aluminum nitride layer 2a to form the same plane. If there is xAl ₂ O ₃ ·
The liquid phase component such as yY ₂ O ₃ is easily exposed or left on the outermost surface of the upper surface-side conductor layer 4a which is directly exposed to the firing atmosphere containing carbon, and the liquid phase component existing on this surface causes plating. It inhibits adherence. The arrow in the figure indicates the exudation path of the liquid phase component, and the X indicates the liquid phase component exuding on the surface.

On the other hand, in the multilayer aluminum nitride circuit board of the present invention, as shown in FIG. 2, the upper surface side surface conductor layer 4a exposed to the firing atmosphere is formed so as to protrude from the uppermost aluminum nitride layer 2a. Therefore, even if the liquid phase component soaks into the upper surface side conductor layer 4a, the exudation to the outermost surface is reduced. This is because the bleeding distance resulting from the height h of the upper surface-side conductor layer 4a is increased, and the bleeding path of the liquid phase component is limited (the liquid phase component due to only the conductor layer 3a filled in the through hole 5 is Exudation)
Etc. Furthermore, when the liquid phase component exudes on the surface of the upper surface side conductor layer 4a, the liquid phase component is reduced by the firing atmosphere (Al ₂ O ₃ + CO + N ₂ → 2AlN + 2C
O ₂₎ is although, since the aim to increase the surface area by protruding the upper side surface conductor layer 4a of aluminum nitride layer 2a, the reduction reaction tends to proceed. It is considered that this also suppresses the liquid phase component from remaining on the surface of the upper surface conductor layer 4a.

As described above, by forming the upper surface side conductor layer 4a so as to project, it is possible to suppress the exudation and residue of the liquid phase component of the multilayer aluminum nitride substrate 2 on the surface of the upper surface side conductor layer 4. It will be possible. As a specific shape of the upper surface-side conductor layer 4a, it is preferable that the height h (after firing) be 3 μm or more in order to sufficiently obtain the above-described effect of suppressing exudation and residual of the liquid phase component. . It is more preferable that the height h is 7 μm or more.

As described above, the exudation of the liquid phase component is basically a problem only on the side directly exposed to the firing atmosphere. Therefore, the surface conductor layer on the upper surface side directly exposed to the firing atmosphere. By making only 4a convex, the effect of improving plating adherence can be sufficiently obtained. Therefore, the lower surface conductor layer 4b that is in direct contact with the setter or the like may have the same planar shape as the conventional one, that is, the shape embedded in the aluminum nitride layer 4d.

The multilayer aluminum nitride circuit board 1 of the above-described embodiment is manufactured, for example, as follows. The manufacturing process of the multilayer aluminum nitride circuit board 1 will be described with reference to FIG.

First, a plurality of aluminum nitride green sheets 2a 'to 2d' are prepared, and through holes 5 are formed in each of them according to a desired circuit pattern. Next, the conductive paste is filled in the through holes 5 (3a ').
At the same time, a conductor paste is applied (3a ', 4a', 4b ') on each of the green sheets 2a'-2b' according to the shapes of the circuit conductor layer 3a of the inner conductor layer 3 and the surface conductor layer 4. At this time, the paste coating layer 4 that becomes the upper surface side during firing
It is preferable that a'is applied relatively thickly. Although the specific thickness of the paste coating layer 4a 'varies depending on the metal content in the conductor paste and the like, it is usually preferably 10 μm or more. Then, these aluminum nitride green sheets 2a 'to 2d' are laminated (FIG. 4A).

Next, the laminated body of the aluminum nitride green sheets 2a 'to 2d' is subjected to heating / pressurizing treatment.
In this pressure treatment, as shown in FIG. 4B, the lower surface side may be a normal metal plate 11, but the upper surface side uses a metal plate 13 provided with a flexible layer such as a rubber sheet 12 on the surface. . As described above, by applying a pressing force to the paste coating layer 4a 'on the upper surface side through the rubber sheet 12, it is possible to prevent the paste coating layer 4a' from being embedded in the aluminum nitride green sheet 2a 'as shown in FIG. . That is, even after the heating / pressurizing process, the paste coating layer 4a 'on the upper surface side has a convex shape.

After degreasing the green sheet pressure-bonded body 2 ', it is fired in a non-oxidizing atmosphere such as a nitrogen atmosphere to simultaneously sinter the aluminum nitride base material and the conductor layer metal. Even after the heating / pressurizing treatment, the paste coating layer 4a 'on the upper surface side has a convex shape, so that a convex upper surface side surface conductor layer 4a is obtained after firing, and the convex shape is also maintained during firing. Since it is maintained, it is possible to suppress the exudation and residual of the liquid phase component of the multilayer aluminum nitride substrate 2 on the surface of the upper surface side conductor layer 4a as described above. This makes it possible to obtain the multilayer aluminum nitride circuit board 1 having good plating adherence with good reproducibility.

The multilayer aluminum nitride circuit board 1 shown in FIG. 1 has a semiconductor package 2 as shown in FIG. 5, for example.
It is used as a 0 package base. With reference to FIG. 5, a semiconductor package 20 which is a specific example of use of the multilayer aluminum nitride circuit board of the present invention will be described.
Note that the basic structure of the multilayer aluminum nitride circuit board 1 is duplicated and therefore omitted.

That is, on the surface conductor layer 4 of the multilayer aluminum nitride circuit board 1, that is, on the upper surface-side surface conductor layer 4a and the lower surface-side surface conductor layer 4b having the convex shape, the Ni / Au plating layer 21 (upper surface side) is formed. A plating layer (not shown) or the like is formed on the surface conductor layer 4a. On the lower surface conductor layer 4b as an electrode pad, the plating layer 21 is formed.
The bump terminals 22, which serve as external connection terminals, are bonded to each other via the.

On the upper surface side of the multilayer aluminum nitride circuit board 1, a semiconductor element 24 is mounted in a state of being bonded to the lid 23, and the electrode (bump electrode) 25 of this semiconductor element 24 is a multilayer aluminum nitride. It is electrically connected to the upper surface conductor layer 4a as a connection pad of the circuit board 1. The lid 23 is bonded to the outer peripheral portion of the multilayer aluminum nitride circuit board 1 via a sealing material 26. As the lid 23, an aluminum nitride lid, a metal lid, or the like is used.

In the semiconductor package 20 having such a structure, the surface conductor layer 4 and particularly the surface conductor layer 4a on the upper surface side serving as the connection pad have good plating adherence, so that the plating thickness can be reduced. A sound plating layer can be obtained. Further, since the upper surface conductor layer 4a is suppressed from seeping out the liquid phase component, which causes a resistance increase, to the surface, a low connection resistance with the plating layer can be realized. Therefore, when the package and the semiconductor element 24 are connected by the flip chip method as described above, good electrical connection can be obtained with a thin plating layer. Further, it is possible to avoid the occurrence of abnormalities such as blistering of the plating layer due to heat treatment and the like. As a result, the connection reliability of the semiconductor element 24 can be improved and the connection resistance can be reduced. As a result, the operating characteristics of the semiconductor element 24 can be improved.

[0032]

EXAMPLES Next, specific examples of the present invention will be described.

Examples 1 to 3 and Comparative Examples 1 to 3 First, four aluminum nitride green sheets were prepared, and through holes were formed in each aluminum nitride green sheet. Then, while filling the through holes with the tungsten paste, the tungsten paste was printed on each aluminum nitride green sheet. In addition, in Example 1 and Comparative Example 1, the thickness of the paste coating layer to be the upper surface conductor layer was 7 μm,
For Example 2 and Comparative Example 3, the thickness of the paste coating layer to be the upper surface conductor layer was 15 μm, and for Example 3 and Comparative Example 3, the thickness of the paste coating layer to be the upper surface conductor layer. Was set to 25 μm.

Next, these aluminum nitride green sheets were laminated to form six green sheet laminates. For each of Examples 1 to 3, these green sheet laminates were pressed while being heated while being heated by the press device with the rubber sheet 12 interposed therebetween, and Comparative Examples 1 to 3.
In regard to, the upper and lower sides were pressed while being heated by a pressing device using a metal plate. The applied pressure was 100 MPa in all cases.

After degreasing each of the above pressure-bonded bodies in a nitrogen stream, they are placed on an aluminum nitride setter and fired at 2073 K in nitrogen, and aluminum nitride and tungsten are fired at the same time to obtain multilayers. An aluminum nitride circuit board was obtained. Table 1 shows the height of the upper surface conductor layer of each of the multilayer aluminum nitride circuit boards.

[Table 1] Next, Ni / Au plating was applied on the upper surface conductor layer of each of the above-mentioned multilayer aluminum nitride circuit boards. The plating is Ni plating thickness 1.5 μm / Au plating thickness 0.1 μm (plating No1), Ni plating thickness 5 μm / Au plating thickness 1.5 μm
Two types of (plating No2) were implemented. The adherence of the plating during each plating was evaluated. The results are shown in Table 2.

[0036]

[Table 2] As is clear from Table 2, in each of the examples in which the upper surface-side surface conductor layer has a convex shape, good plating adherence is obtained even when the plating thickness is thin (plating No. 1).
On the other hand, in each of the comparative examples, when the plating thickness was made thin, uneven adhesion of the plating occurred, and by making the plating thickness thick, an apparently good plating layer was finally obtained. However, the plating layer (N
o2 *) was then subjected to a heating test at 673K, and swelling occurred in the plating layer. It is considered that this is because a cavity was formed at the beginning of the plating and the cavity was expanded by the heating test. A similar heating test was performed on the plated layers according to Examples 1 to 3, but no blister of the plated layers was observed.

[0037]

As described above, according to the multilayer aluminum nitride circuit board of the present invention, it is possible to greatly improve the plating adherence of the surface conductor layer. As a result, when the surface conductor layer is plated and used as a package substrate or the like, it is possible to reduce the plating thickness and obtain a good plating layer. Therefore, it is possible to provide a multilayer aluminum circuit board having low resistance and excellent connection reliability.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a main configuration of a multilayer aluminum nitride circuit board according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the action of suppressing the exudation of liquid phase components in the multilayer aluminum nitride circuit board of the present invention.

FIG. 3 is a diagram for explaining the exudation state of a liquid phase component in a conventional multilayer aluminum nitride circuit board.

FIG. 4 is a cross-sectional view showing the main parts of one manufacturing process example of the multilayer aluminum nitride circuit board of the present invention.

5 is a cross-sectional view showing a configuration example of a semiconductor package manufactured using the multilayer aluminum nitride circuit board shown in FIG.

[Explanation of symbols]

1 ... Multilayer aluminum nitride circuit board 2 ... Multilayer aluminum nitride substrate 2a to 2d ... Aluminum nitride layer 3 ... Inner conductor layer 4 ... Surface conductor layer 4a ... Upper surface conductor layer (connection pad) 4b ... Lower surface conductor layer (electrode pad) 5: Through hole

Front page continuation (56) References JP-A-5-191049 (JP, A) JP-A-7-94625 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 23 / 12-23/15 H05K 3/46

Claims (2)

(57) [Claims] 1. A multilayer aluminum nitride substrate, an internal conductor layer formed by simultaneous firing of the multilayer aluminum nitride substrate, and an internal conductor layer that is electrically connected to the internal conductor layer and is simultaneously fired on the surface of the multilayer aluminum nitride substrate. Formed connection pad
; And a de, the multilayer aluminum nitride substrate is the connection pad projecting from its surface only on one surface is formed, the contact
A multilayer aluminum nitride circuit board , wherein a plating layer is provided on the continuous pad . 2. The plating layer is a Ni film on the connection pad.
That it is the Au plating layer on the Ni layer and the Ni plating layer
A multilayer aluminum nitride circuit board according to claim 1, characterized in that
Board.