JP2667486B2 - Ceramic circuit board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an aluminum nitride co-fired ceramics circuit board with improved bonding strength between ceramics layers.

(Prior Art) A semiconductor element is generally housed and used in a package made of a ceramic sintered body or the like for the purpose of mechanical protection of the semiconductor element itself or shielding from outside air. In the package, an internal wiring layer having a required circuit pattern is formed by simultaneous firing with the ceramic sintered body, and one end of the internal wiring is connected to an electrode portion of the semiconductor element, and an input / output is connected to the other end. By connecting the pins, the semiconductor element is electrically connected to an external device.

By the way, in a package for a high-frequency semiconductor device, it is indispensable that the internal wiring in the package is regarded as a transmission line and its characteristic impedance is made constant with an increase in circuit operation speed.

FIG. 3 shows an example of a semiconductor device package structure using a microstrip structure in a distributed constant circuit in order to control the characteristic impedance of internal wiring.

In the figure, the ground layer 2 in the microstrip structure is formed on the upper surface of the lowermost ceramics layer 1 by applying a conductor paste containing a refractory metal such as tungsten or molybdenum as a main component and simultaneously firing the ceramics layer. A metallized layer 4 for mounting a semiconductor element is formed on the upper surface of the second ceramic layer 3.
In the third ceramic layer 5, a semiconductor element housing 6 and an internal wiring layer 7 serving as a signal line or a power supply line radially from the semiconductor element housing 6 are similarly formed. The end 7a from the center of the internal wiring layer 7 on the upper surface of the third ceramic layer 5 is electrically connected to the mounted semiconductor element by a bonding wire, and the other end is through a through hole 9 provided in each layer. Lowermost ceramic layer 1
It is electrically connected to the input / output pin 10 joined to the lower surface.

As described above, when the microstrip structure is applied to the semiconductor element package, the ground layer 2 is formed so as to be substantially solid over almost the entire surface of the ceramic layer in order to sufficiently suppress the electric resistance.

By the way, recently, as a ceramic material of a ceramic circuit board used for such a semiconductor device package, aluminum nitride ceramics having excellent thermal conductivity and having a low coefficient of thermal expansion similar to that of a silicon chip has been attracting attention.

(Problems to be Solved by the Invention) However, since aluminum nitride ceramics has a larger thermal contraction rate than alumina or the like, when forming a conductor layer on one surface like a ground layer in a microstrip structure, an aluminum nitride layer is used. When the printed layer of the conductive paste serving as the ground layer and the ground layer are simultaneously fired, there is a problem that a sufficient bonding strength between the ground layer and the aluminum nitride layer laminated thereon cannot be obtained. If the bonding strength between the ground layer and the aluminum nitride layer is weak in this way, defects such as cracks are likely to occur due to the application of thermal stress even before the occurrence of peeling or the like, resulting in poor reliability. .

Such a problem occurs not only in the ground layer in the microstrip structure but also in a ground layer requiring various low resistances.

The present invention has been made to address such a problem of the conventional technique, and has a multi-layer structure with improved bonding strength during simultaneous firing of a grounding layer that requires low resistance and an adjacent aluminum nitride ceramic layer. It is an object of the present invention to provide a ceramic circuit board having:

[Structure of the Invention] (Means for Solving the Problems) That is, the ceramic circuit board of the present invention includes an aluminum nitride ceramic substrate having a multilayer structure in which semiconductor elements are housed, and an aluminum nitride ceramic substrate having this multilayer structure. An internal wiring layer formed at a desired position, and a ground layer having a blank portion for abutting the aluminum nitride layers adjacent to each other provided inside the aluminum nitride ceramic substrate of the multilayer structure, It is characterized in that the aluminum ceramic substrate, the internal wiring layer and the ground layer are simultaneously fired.

(Operation) In the ceramic circuit board of the present invention, a blank portion is provided in the ground layer. The blank area increases the contact area between the aluminum nitride layers adjacent to each other with the ground layer interposed therebetween, and the bonding strength is greatly improved, resulting in excellent reliability. Further, the electric resistance of the ground layer can be kept low by considering the formation position and formation area of the blank portion.

(Example) Hereinafter, an example of a ceramic circuit board of the present invention will be described with reference to the drawings.

FIG. 1 is an exploded perspective view showing a structure of a ceramic circuit board according to an embodiment in which the present invention is applied to a package for a semiconductor element, and FIG. 2 is a sectional view showing a state where a semiconductor element is mounted thereon.

This ceramic circuit board has a mesh-like ground layer 12
A lowermost first AlN ceramics layer 11 on which
The second AlN ceramics layer 13 on which the metallized layer 14 to be the semiconductor element mounting surface is formed, and the third AlN on which the semiconductor element housing 16 and the internal wiring layer 17 to be the input / output signal line and the power supply line are formed. It is mainly composed of a ceramic layer 15 and a fourth AlN ceramic layer 18 serving as a protective layer for the internal wiring layer 17, and these AlN ceramic layers 11, 13, 1
5, 18 and each conductor layer are multilayered by simultaneous firing.

The internal wiring layer 17 formed on the third AlN ceramic layer 15 includes a bonding portion, that is, a semiconductor element housing portion 16 formed in the center of the third AlN ceramic layer 15.
It is formed radially from the vicinity to the outer peripheral direction,
A bonding pad is formed at one end of the wiring pattern, and a through hole 19 is formed at the other end.

The second AlN ceramics layer 13 is provided with a metallization layer 14 serving as a semiconductor element mounting surface corresponding to the semiconductor element accommodating portion 16 formed at the center of the third AlN ceramics layer 15, and A through-hole 20 corresponding to the position where the through-hole 19 is formed in the third AlN ceramic layer 15 is formed.

The first AlN ceramic layer 11 also has an internal wiring layer 17.
A through-hole 21 corresponding to one end position of the wiring pattern is formed, and an input / output pin bonding pad 22 is formed on the lower surface of the first AlN ceramic layer 11 corresponding to the position where the through-hole 21 is formed. This is the bond pad
Input / output pins 23 are joined via 22 and are electrically connected. The internal wiring layer 1 formed on the third AlN ceramic layer 15 is formed on the first AlN ceramic layer 11.
The ground layer 12 corresponding to the wiring pattern formation position 7 is formed, and the internal wiring layer 17 and the ground layer 12 form a microstrip structure.

This ground layer 12 has a mesh-like pattern,
The first AlN is formed by the blank portion 12a inside the mesh pattern.
The contact area between the ceramic layer 11 and the second AlN ceramic layer 13 is increased to increase the bonding strength.

Then, as shown in FIG. 2, the semiconductor element 24 is mounted on the metallized layer 14 of the second AlN ceramic layer 13 and formed on each electrode of the semiconductor element 24 and the third AlN ceramic layer 15. By connecting the bonding pads of the internal wiring layer 17 with the bonding wires 25, a semiconductor device is formed.

Such a ceramic circuit board is manufactured, for example, as follows.

First, the AlN to be each of the AlN ceramic layers 11, 13, 15, 18
Through holes and cavity openings are made in the green sheet according to the shape of each layer. Next, the internal wiring layer 17
A conductor paste is applied by screen printing or the like according to the pattern of the ground layer, the mesh-like pattern shape of the ground layer 12, and the pattern shape of the input / output pin joint pad 22, and the conductor paste is filled into the through holes 19, 20, and 21. . As the conductor paste to be used, for example, a paste obtained by adding an appropriate amount of AlN powder to tungsten powder, kneading the mixed powder with an organic binder, and the like is used.

Next, after laminating and integrating each AlN green sheet by thermocompression bonding, the AlN green sheet and each conductor paste coating layer are co-fired at a temperature condition of about 1700 ° C to 1900 ° C in an inert atmosphere to obtain an object. A ceramic circuit board serving as a semiconductor element package having a mesh-like ground layer is obtained.

Here, as the conductor paste for forming the mesh-shaped pattern of the ground layer, it is preferable to use a high melting point metal paste to which AlN powder is added as described above. By using a conductor paste to which AlN powder is added,
The joining strength with the AlN ceramic layer can be increased. However, if the addition amount of the AlN powder is too large, the electric resistance increases, so that the content is preferably set to 40% by weight or less.

As described above, in the ceramic circuit board of this example, since the ground layer has a mesh shape, the Al adjacent to the ground layer is formed by the blank portion inside the mesh pattern.
The contact area between the N ceramic layers is increased, the bonding strength is significantly improved, and the reliability against thermal stress can be significantly improved. Further, since the ground layer has a mesh shape in order to form the blank portion of the ground layer, it is possible to prevent the electric resistance from increasing as much as possible.

Further, in this embodiment, since the tungsten paste containing an appropriate amount of AlN powder is used as the ground layer forming conductor paste, the bonding strength is further improved.

When the resistance value of the ground layer is insufficient, the same effect as that of the solid ground layer can be obtained by providing a plurality of mesh ground layers.

In the above embodiment, the pattern shape of the ground layer is a mesh shape, but the present invention is not limited to this, and any shape may be used as long as a blank portion is formed inside. Good.

[Effects of the Invention] As described above, the ceramic circuit board of the present invention prevents reliability of thermal stress and the like by preventing the AlN ceramics layer from being defectively joined by the grounding layer while hardly preventing the resistance of the grounding layer from decreasing. Is greatly improved, whereby a highly reliable semiconductor device can be provided.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing the structure of a ceramic circuit board according to one embodiment of the present invention, FIG. 2 is a cross-sectional view showing a semiconductor device using the ceramic circuit board shown in FIG. 1, and FIG. FIG. 2 is an exploded perspective view showing a package structure of the device. 11, 13, 15, 18 ... AlN ceramics layer, 12 ... grounding layer, 12a ... blank space, 14 ... semiconductor element mounting part, 17 ...
Internal wiring layer.

Claims (1)

(57) [Claims] 1. A multi-layered aluminum nitride ceramic substrate that accommodates semiconductor elements, an internal wiring layer formed at a desired position in the multi-layered aluminum nitride ceramic substrate, and the multi-layered aluminum nitride substrate. And a ground layer having a blank portion provided inside the ceramic substrate made of aluminum and abutting the adjacent aluminum nitride layers to each other, and the ceramic substrate made of aluminum nitride, the internal wiring layer and the ground layer are simultaneously fired. Ceramic circuit board characterized by.