JPH0763109B2 - Ceramic circuit board manufacturing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a ceramic circuit board such as a mounting mother board and a high frequency or high power board. 2. Description of the Related Art Usually, as a ceramic circuit board for the above-mentioned mother board, high frequency board or high power board, a paste containing conductors such as Ag / Pd, Ag / Pt and Au is used for insulation with a fired alumina plate. A substrate (hereinafter referred to as a thick film method substrate) on which a wiring pattern is formed by printing and baking the glass of No. 1 is used. Also, a ceramic circuit board obtained by printing a wiring pattern on the surface of the ceramic green sheet with a paste containing a conductor such as W or Mo and then laminating the ceramic green sheet and the wiring pattern at the same time (hereinafter referred to as a co-firing substrate Will be written)
Is also used. Further, a ceramic circuit board (hereinafter referred to as a hybrid board) produced by printing a paste for forming a low conductive resistance on the surface of a fired substrate formed by co-firing and firing it is also proposed. Of the above circuit boards,
In the thick film method substrate, when a conductor and glass are laminated, it is difficult to form a complicated circuit and a circuit element such as a capacitive element at low cost because the insulation resistance of the laminated layer portion is low. on the other hand,
Since the co-firing method substrate is printed and then fired after the wiring pattern is printed, the dimensional accuracy of the wiring pattern is poor, and the surface warps or undulates, so high-precision mounting, for example, a flip-chip type IC mounting substrate. Was difficult to apply to. Further, in the hybrid substrate, there is a problem that a highly accurate pattern cannot be obtained because the surface of the fired substrate is warped and undulated. Further, for any of the above-mentioned substrates, it was not possible to obtain a surface wiring having good dimensional accuracy and capable of passing a large current. SUMMARY OF THE INVENTION An object of the present invention is to provide a method of manufacturing a ceramic circuit board having a multi-layer structure in which surface wiring having high dimensional accuracy and flatness and high-density internal wiring can be mounted on devices for high frequency, large power, etc. The purpose is to provide. According to the method for manufacturing a ceramic circuit board of the present invention, a ceramic green sheet having an internal wiring pattern made of a conductor paste is laminated, and the obtained ceramic green sheet laminate is fired. In a method for manufacturing a ceramic circuit board, which comprises forming a fired body having internal wiring and then forming surface wiring on the surface of the fired body, the front and / or back surface of the fired body is polished to be flat, The surface wiring is formed by joining a copper plate to the flattened surface of 1 by a direct joining method. Further, in the above manufacturing method, the pattern to be the surface wiring is formed by etching a copper plate joined by the direct joining method. Further, in the above manufacturing method, a surface wiring pattern is formed in advance on the copper plate to be bonded by the direct bonding method. According to the method of the present invention, the internal wiring is formed by co-firing with the green sheet, and the surface wiring is formed by directly bonding the copper plate to be the surface wiring to the surface of the fired body by the direct bonding method. The surface wiring pattern is formed by etching the joined copper plates or by joining the copper plates on which the wiring patterns have been previously formed by etching or the like. In general, the laminate shrinks during firing, and the shrinkage varies widely, so a dimensional tolerance of about 1% occurs.
However, in the method of the present invention, the surface wiring is formed by firing the laminated body, polishing the surface and / or the back surface of the fired body to planarize the surface, and then joining a copper plate to the planarized surface. Therefore, the dimensional accuracy of the surface wiring pattern is extremely good. Furthermore, the surface wiring, compared to the thick film method substrate, co-firing method substrate, hybrid substrate, etc.,
Since it is formed of a thick copper plate, a large current can be applied to the surface wiring. (Embodiment 1) FIG. 1 is a diagram showing a process of manufacturing a ceramic circuit board by the method of the present invention. The circuit board obtained in the manufacturing process of FIG. 1 is an example of a circuit board obtained by laminating two green sheets. When manufacturing this circuit board, size 1
Two alumina green sheets 1 and 2 having a size of 50 mm × 150 mm and a thickness of 0.3 mm are prepared, and through holes 3 and 4 are formed in each sheet according to a target wiring pattern. Next, the through holes 3 and 4 of each sheet are filled with a paste containing a conductor such as W and Mo (hereinafter referred to as a conductor paste) (FIG. 1 (a)). Further, a wiring pattern having a thickness of about 20 μm to be the internal wiring 5 is printed on the sheet 2 with the above-mentioned conductor paste. A conductive paste is filled in the through holes 3 and 4, and a conductor pattern to be the internal wiring 5 is printed and laminated to obtain a laminated body 8. This laminated body 8 is heated to a temperature of 1600.
Firing is performed under a reducing atmosphere at a temperature of around ℃ to produce a fired body 8. In this state, inside the fired body 8, the internal wiring 5 made of a conductor such as W or Mo and having a thickness of about 12 μm is formed. On the surface of the fired body 8, the conductor of the through hole portion is exposed, and there may be warpage or undulation (FIG. 2 (b)). To remove this warp and swell,
The front and / or back of the fired body is polished and flattened by buffing or the like using an abrasive. Next, the conductor portion of the through hole exposed on the surface may be N
After plating i, Cu, etc., on the entire flattened surface,
Copper plates 6 and 7 having a thickness of 0.3 mm for forming a surface wiring pattern are joined by a direct joining method (FIG. 7C). The plating on the conductor part of the through hole is
This is to enhance the bondability between the conductor such as W and Mo and the copper plate, and it is possible to bond even without plating.
Tough pitch copper or oxygen-free copper having an oxide film formed on its surface is suitable for the copper plate used in the direct bonding method. Direct bonding is performed in a state where the above copper plate is arranged on the surface of the fired body, in an inert gas atmosphere such as nitrogen gas or argon gas,
It may be heated at a temperature of 5 ° C to 1083 ° C. By this heat treatment, the copper plate is bonded to the alumina, which is a fired body, and the conductor in the through hole portion. At the time of joining by heating, some oxygen is required, but since tough pitch copper contains oxygen, it is not necessary to supply oxygen to others. Further, in the case of oxygen-free copper, by forming an oxide film on the surface as described above, oxygen is supplied to the joint portion, so that it is not necessary to supply oxygen other than this. Next, the copper plate directly bonded to the fired body is etched using a photoresist to form a surface wiring pattern. The specific steps of etching are as follows. First, a liquid photoresist is uniformly applied to the surface of a copper plate, and then a pattern mask corresponding to the wiring pattern is placed on the photoresist application surface and exposure is performed. By developing this, the resist is left only on the wiring pattern portion. In this state, for example, the non-wiring pattern portion is dissolved and removed with a ferric chloride solution. After that, the resist remaining on the wiring pattern portion is removed using a stripping solution. The surface wiring patterns 9 and 10 thus formed have through holes 3 and 4, respectively.
It is electrically connected to the internal wiring 5 by the inner conductor ((d) of the same figure). (Embodiment 2) FIG. 2 is a diagram showing another manufacturing process of the present invention. In the same process as in the example, a fired body 8 having internal wirings and conductors of through holes connected to the internal wirings and having its surface planarized by polishing is obtained ((a) and (b) in the same figure). Next, a thickness of 0.3 which was previously processed into the shape of the surface wiring pattern
A mm copper plate is bonded to the surface of the fired body 8 by the direct bonding method. The conditions of the copper plate and the direct joining were the same as those in Example 1.
Is the same as in. The surface wiring patterns 9 and 10 thus formed are electrically connected to the internal wiring 5 by the conductors in the through holes 3 and 4 (FIG. 7C). The surface wiring pattern obtained in Example 1 or 2 may be Ni-plated with a thickness of about 3 μm and further Au-plated with a thickness of about 1.5 μm, if necessary. The Au plating as the upper layer plating is for improving the bonding property when performing the bonding wiring with the element, and the Ni plating as the plating lower layer is for increasing the adhesion strength between the copper and the Au plating. .
In the above embodiment, an example in which two green sheets are stacked is shown, but the number of stacked green sheets is not particularly limited. Further, the internal wiring may include a capacitive element, a resistive element, or the like. The ceramic circuit board obtained by the method of the present invention,
Since the copper plate is joined after the surface of the fired body is flattened, the adhesion between the fired body and the copper plate is good, and the non-bonded portion (void) is present in the joint.
Does not occur. Further, it is possible to obtain a ceramic circuit board having a multilayer structure including high-density internal wiring and surface wiring made of a copper plate connected through through holes. Therefore, this circuit board has the following features. First of all, since the surface is flat and the dimensional accuracy of the surface wiring is extremely good, it can be applied to applications where dimensional accuracy is required, such as application to IC mounting substrates by flip chip method. . Second, since the surface wiring having a thickness larger than that of the surface wiring formed by the thick film method or the like can be formed, the surface wiring has a lower conduction resistance than the internal wiring. Therefore, it can be used as a high frequency or high power substrate. By the way, the surface wiring having a thickness of 18 to 35 μm is effective when used at a current of 5 mA or less and a frequency of 1 to 4 GHz, whereas the surface wiring having a thickness of 0.3 mm (Example of the present invention) is , A circuit through which a current of up to 25 A flows can be configured. Similarly, the surface wiring having a thickness of 0.5 mm or more can be applied to a circuit in which a current of 30 A or more flows. On the other hand, the internal wiring is formed by depositing a wiring pattern on a green sheet by a printing method, stacking a plurality of sheets, and then firing them. Suitable for wiring. Therefore, it is possible to obtain a circuit board in which the surface wiring for large current and the internal wiring for small current are combined.
A compact circuit board can be obtained. In addition, since the surface wiring obtained by the method of the present invention is formed of copper, it has characteristics that it has better electric characteristics than aluminum and the like and is cheaper than gold and silver. Further, there is also an advantage that mounting such as soldering and bonding can be performed without surface treatment. According to the method of the present invention, it is possible to obtain a ceramic circuit board having a multilayer structure including internal wiring formed by a printing method and surface wiring made of a flat copper plate having a high dimensional accuracy. Therefore, this circuit board can be utilized for applications requiring dimensional accuracy, such as application to a flip-chip type IC mounting board. Further, since the conduction resistance of the surface wiring is low, it can be used as a substrate for high frequency or large power, and a circuit board in combination with high-density internal wiring for small current can be obtained. A compact circuit board can be obtained even for large currents. In addition to this, the surface wiring obtained by the method of the present invention is
Since it is made of copper, it has the advantages of good electrical characteristics and low cost.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view showing a process of manufacturing a ceramic circuit board by the method of the present invention. FIG. 2 is a cross-sectional view showing another process for manufacturing a ceramic circuit board by the method of the present invention. Explanation of symbols 1, 2: Ceramic green sheet, 3, 4: Through hole 5: Internal wiring, 6, 7: Copper plate, 8: Laminated body, 9, 1
0: Surface wiring

Claims (1)

(1) A ceramic green sheet having a pattern for internal wiring made of a conductor paste is laminated, and the obtained ceramic green sheet laminate is fired to form a fired body having internal wiring. After that, in a method for manufacturing a ceramic circuit board in which surface wiring is formed on the surface of the fired body, the front surface and / or the back surface of the fired body is polished and flattened, and then a direct bonding method is applied to the flattened surface of the fired body. A method of manufacturing a ceramic circuit board, wherein the surface wiring is formed by joining a copper plate with each other. (2) The method of manufacturing a ceramic circuit board according to claim 1, wherein the copper wiring plates joined by the direct joining method are subjected to etching to form surface wiring. (3) The method of manufacturing a ceramic circuit board according to claim 1, wherein a surface wiring pattern is formed in advance on the copper plate to be bonded by the direct bonding method.