JPH0136998B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing a multilayer ceramic substrate for mounting input/output electrical connection pins in a package substrate.

(Prior Art and its Problems) With the recent trend towards higher density, smaller size, higher speed, and higher performance of computer systems, the requirements for package boards at the mounting level are becoming more and more stringent. Specifically, there are demands for increasing the wiring density and miniaturizing the signal line width on package substrates, lowering the resistance value of signal line conductors, and lowering the dielectric constant of insulating materials. Package board technology has been developed.

For example, multilayer ceramic substrates using alumina green sheets, low-temperature sintered multilayer ceramic substrates that can be sintered at around 900℃ using glass-ceramic green sheets, and can use gold and silver-palladium conductors, and even ceramic substrates. There are package substrates that use thin film techniques such as sputtering and vapor deposition, and package substrates that use organic insulating materials (polyimide, etc.) in combination with thin film conductors. On such high-density, miniaturized mounting boards,
A large number of VLSI chips will be mounted, and the number of input and output terminals for electrical connection to the outside of the board will therefore be extremely large. Therefore, a technique has been developed in which input and output terminals are formed using pins on the back surface of a multilayer board.

As a conventional technique for attaching electrical connection pins to a substrate, for example, in an alumina multilayer substrate, electrical connection pins made of a material such as Kovar or 4.2 alloy were attached using silver solder.

Figure 1 is a diagram for explaining the conventional method of attaching to an alumina multilayer board, in which conductor pads made of molybdenum or tungsten formed on an alumina green sheet and conductors in through holes are used.
The ceramic substrate 1 and the conductor 2, such as molybdenum or tungsten, are shown after sintering in a hydrogen reducing atmosphere at temperatures above 1500°C. A nickel layer 3 is formed on this conductor pad part by plating, and then an electrical connection pin 5 of Kovar or 4.2 alloy is formed.
is attached with silver solder 4. The composition of silver solder is generally a eutectic alloy of 60 mol% silver and 40 mol% copper, and its melting point is 779°C. Therefore, the appropriate brazing temperature is about 810°C, and the brazing process is carried out in a hydrogen-reducing atmosphere to prevent oxidation of the conductor such as molybdenum. The electrical connection pins and conductors attached to the board are then gold plated to prevent deterioration.

FIG. 2 shows a cross-sectional view of a substrate with electrical connection pins on which a gold plating layer 6 is formed. This method requires a high brazing temperature, and it is difficult to heat a fine thin film pattern formed on a substrate to this temperature.
On the other hand, even when forming fine thin film patterns such as signal lines after attaching pins to a substrate in advance, the precision in forming various patterns on the pin-equipped substrate deteriorates, and the workability also deteriorates. The same applies to packaging technology in which a pattern is formed on a multilayer ceramic substrate using an organic insulating film (polyimide or the like). Furthermore, a process of gold plating the connection pins and conductor pads after brazing is included, resulting in poor workability.

Next, in order to lower the processing temperature, Au was used as a brazing material.
-Sn or Au-Si, Au-Sn-Pd, Au-Sn-Ag
Figures 3 and 4 show a specific example where such issues were considered.
As shown in the figure.

In FIG. 3, a molybdenum layer 12 is attached to the surface of a ceramic substrate 11, and a nickel coating 13 is formed on the molybdenum layer by means such as plating.
form. Next, a gold coating 14 is formed on the nickel coating using gold paste, and a gold/nickel solid solution is formed by heat treatment. Next, gold plating 1
Connecting pins 16 coated with No. 7 are connected by Au--Sn brazing material 15. In this method, the gold-nickel solid solution is formed at a temperature of approximately 700°C under hydrogen reduction. Further, in FIG. 4, a molybdenum layer 2 is formed on the surface of the ceramic substrate 21.
2, a nickel coating 23 is formed on the molybdenum layer, and a barrier gold coating 24 is formed on the nickel coating. On the gold film, a connecting pin 27 which has been coated with a metal layer 25 of the group 25 serving as a source of Sn gettering metal and then plated with gold 28 is bonded by an Au--Sn brazing material 26. In both of these methods, the alumina multilayer ceramic substrate is sintered at high temperatures, and the pads to which the connection pins are attached must be made of metal pads such as molybdenum that can withstand high temperatures, making the process cost-effective. It is also disadvantageous. Further, with respect to the problem of oxidation of the conductor, careful attention must be paid and the heat treatment must be carried out in a hydrogen reducing atmosphere. Furthermore, in order to provide good adhesion between the molybdenum pad and the ceramic substrate, additives such as glass frit must be included in the paste, resulting in an increase in conductor resistance.

On the other hand, glass-ceramic multilayer ceramic substrates can be fired at temperatures below 1000°C, so conductors such as gold, silver, and silver-palladium with high conductivity can be used, and they have the advantage of being able to be fired in an oxidizing atmosphere.
Although much development is being carried out in various fields, the adhesion between the glass ceramic and the metal is not sufficient for attaching pins, which is a major problem in achieving high density.

(Object of the Invention) The present invention eliminates such conventional drawbacks and problems, and also provides a multilayer ceramic pin with sufficient adhesive strength for electrical connection pins even to low-temperature sintered glass-ceramic multilayer substrates. An object of the present invention is to provide a method for manufacturing a substrate.

(Structure of the Invention) According to the present invention, a metal film of group a of the periodic table is formed on the side of the raw ceramic sheet on which the electrical connection pin is attached, and a metal film of group a of the periodic table is formed on the metal film of group a of the periodic table. a step of forming a metal film of group B, and forming a layer of a mixture containing a single element or a part of a metal of group b of the periodic table on the metal film of group b; A multilayer ceramic board with pins, comprising the steps of laminating raw ceramic sheets and then firing them, and attaching electrical connection pins using a brazing material onto a group B metal or metal layer on the fired board. A manufacturing method is obtained.

(Detailed Description of Configuration) The present invention solves the problems of the conventional method by employing the above-mentioned manufacturing method. First, by forming a Group A metal film on a raw ceramic sheet, after sintering, the adhesion between the glass ceramic and the Group A metal becomes good, and as a result, a metallic bond is formed between the Group A metal and the glass ceramic. It is no longer necessary to form thick film conductor pads such as molybdenum on alumina multilayer substrates or gold, silver, silver-palladium, etc. on glass ceramic multilayer substrates.
It has become possible to attach electrical connection pins with sufficient adhesive strength. In addition, by forming a group metal of the periodic table, it is alloyed and integrated with a group B metal during firing, and also acts as a source of tin geckling in the gold-tin brazing material. It is possible to raise the melting point of the tin brazing material, resulting in better results for thermal cycling of the pinned part. Furthermore, in the case of a group B metal layer, there is an effect of increasing the melting point of the gold-tin brazing material, and a similar effect can be expected. Another effect of forming the group B metal layer is to prevent oxidation of the group a metal film and the group metal film during firing of the multilayer substrate.

(Example) Examples of the present invention will be described in detail below with reference to the drawings. 5 to 12 are cross-sectional views showing the method for manufacturing a multilayer ceramic substrate with pins according to the present invention, and FIG. 13 is a schematic diagram of a multilayer ceramic substrate with pins manufactured in an example. Moreover, FIGS. 14 to 18 are sectional views for explaining other embodiments.

FIG. 5 shows a raw ceramic sheet 31 made from a mixture of alumina powder and lead borosilicate crystallized glass powder. A through hole 32 is formed in this sheet to provide conduction between layers.

A conductor 33 shown in FIG. 6 is embedded in this through hole by screen printing or the like. The conductor is gold,
Although silver, silver-palladium, etc. can be used, silver-palladium was used here. Next, as shown in FIG. 7, a mask 34 with an open pin attachment portion formed by etching a thin metal plate is superimposed on the raw ceramic sheet in which conductors are embedded in the through holes. Next, as shown in Figure 8, a layer of 300 Å ~
A chromium thin film 35 with a thickness of 1000 Å is formed.

As shown in FIG. 9, a palladium layer 36, which is a metal from Group 3 of the periodic table, is formed on the chromium film. The palladium layer was formed to a thickness of 1000 Å to 3000 Å by sputtering similar to that used for forming a chromium thin film.

In addition to palladium used here, nickel,
Metals such as iron can also be formed. After reducing the vacuum to about 10 ^-5 torr or less, spatsuta uses Ar gas.
The experiment was carried out by introducing up to about 10 ^-2 torr. Subsequently, as shown in FIG. 10, silver-palladium 37 is formed as a conductor containing a single element or a part of a metal belonging to Group B on the thin film of palladium.
Although the formation method was carried out by a screen printing method using a conductor paste, a sputtering method, a vapor deposition method, etc. may also be used. Figure 11 shows chromium thin film, palladium film,
A cross-sectional view when the mask is removed after forming the silver-palladium layer is shown. As can be seen from FIG. 8, in this method, a chromium film is directly formed on the surface of the raw ceramic sheet, and this is one of the features that is significantly different from other methods. FIG. 12 shows an embodiment in which the conductor layer is formed by another method. That is, as shown in FIG. 9, after forming a chromium thin film and a palladium film, the mask is removed and a silver-palladium layer is formed on the formed thin film by screen printing or the like. The raw ceramic sheet having the pin pad portion thus obtained and the raw ceramic sheet having various electrical wiring patterns formed thereon are laminated in an appropriate number and heat pressed at 250 kg/cm ² at about 110°C to produce a laminate. do. After sufficiently removing organic residues from the obtained laminate at a temperature of about 450°C, it is sintered at a temperature of 850°C to 950°C. If copper, one of the Group B metals, is used as a conductor, it is necessary to select an organic compound that can be decomposed and removed in a neutral atmosphere during binder removal, as well as an atmosphere where copper will not be oxidized during firing. It is necessary to do so.

The multilayer ceramic substrate having the metal pad portion obtained as described above is made of a plurality of materials such as Kovar or 4.2 alloy, to which are each attached approximately 1 to 3 mg of alloy brazing filler metal 38 with a weight ratio of 80% gold and 20% tin. and bonded onto the silver-palladium surface. The surface of the metal pin 39 is coated in advance with a gold coating layer 40 formed by plating or the like. The processing temperature for brazing was 300°C to 500°C for 10 to 30 minutes since the melting point of the 80% gold-20% tin alloy brazing material was 280°C. Group metals are
It forms compounds with Group B metals and also acts as a getter for the tin in the gold-tin brazing filler metal, resulting in a higher apparent proportion of gold to tin in the filler metal and thus after cooling or condensation of the filler metal. It has the effect of raising the melting point of the brazed joint. This is effective in cases where there is a step of applying a thermal cycle after attaching the pin. Furthermore, the gold coating applied to Group B metals and pins will partially melt together with the gold-tin brazing material during the brazing process, resulting in a similar effect by raising the melting point of the joint. .

Next, another example will be shown. As shown in FIG. 14, a chromium film 41 is formed by sputtering over the entire surface of a raw ceramic sheet in which conductors are buried in through holes. The thickness of the chromium film is 300Å to 1000Å
range, and is formed directly on the sheet. Subsequently, as shown in FIG. 15, a palladium film 42, which is a metal from Group 3 of the periodic table, is formed on the chromium thin film by sputtering in the same manner as the chromium thin film.

Next, the pad shape for attaching the electrical connection pin is etched to remove the excess portion as shown in FIG. 16. Thereafter, a conductor layer as described in the explanation of FIG. 12 above is formed.

In yet another embodiment, as shown in FIG. 17, a silver-palladium layer is formed as a conductive layer 43 containing a Group B metal in the shape of a pad for attaching an electrical connection pin on the palladium layer shown in FIG. form. The ceramic raw sheet thus formed and the ceramic raw sheet on which patterns such as other wirings have been formed are laminated and hot pressed under the aforementioned conditions of 250 kg/cm ² and about 110° C. to obtain a laminate. This raw laminate was debindered and then heated to 850°C in an oxidizing atmosphere.
When sintering is performed at a temperature of ~950°C, the palladium film on which the conductor layer 43 is not formed and the underlying chromium film are oxidized and become electrical insulators 44 and 45 as shown in FIG. 18. Electrical connection pins are then attached using gold-tin braze in the manner described above.

In this example, chromium was used as the group a metal, palladium was used as the group metal, and silver-palladium was used as the group b metal, but the present invention is not limited to these examples. do not have. In addition to sputtering, methods such as screen printing, vapor deposition, and plating can be used as a method for forming the metal layer.

(Effects of the Invention) The adhesive strength between the input/output electrical connection pins attached by this method and the multilayer ceramic substrate was 4.0 Kg/mm ² or more, indicating sufficient strength as input/output pins of a mounting board.

As described above, by employing the method for manufacturing a multilayer ceramic substrate with pins of the present invention, the brazing process can be performed at an extremely low temperature of 500°C or less, and a thick film of metal (molybdenum) for pin pads can be applied to the surface of the ceramic substrate. , tungsten, gold, silver,
It is now possible to obtain a pinned substrate with sufficient adhesive strength without the need to previously form a layer (silver-palladium, etc.).

[Brief explanation of drawings]

1 to 4 are schematic diagrams showing conventional pinned ceramic substrates, FIGS. 5 to 12 and 14 to 18 are diagrams showing the method of the present invention, and FIG. FIG. 1 is a schematic diagram of a pin-equipped substrate produced by the method of the present invention. In the figure, 1...ceramic substrate, 2...conductor pad layer, 3...nickel layer, 4...silver solder,
5... Pin, 6... Gold coating layer, 11... Ceramic substrate, 12... Conductor pad layer, 13... Nickel layer, 14... Gold coating, 15... Gold-tin wax, 1
6...Pin, 17...Gold coating layer, 21...Ceramic substrate, 22...Conductor pad layer, 23...Nickel layer, 24...Gold coating, 25...Group metal layer, 26...Gold- Tin wax, 27...Pin, 28...
...Gold coating layer, 31...Ceramic raw sheet, 32
...Through hole, 33...Conductor, 34...Mask, 35...Chromium layer, 36...Palladium layer,
37... Silver-palladium layer, 38... Brazing metal, 3
9... Pin, 40... Gold coating layer, 41... Chromium layer, 42... Palladium layer, 43... Silver-palladium layer, 44... Chromium oxide layer, 45... Palladium oxide layer.

Claims (1)

[Claims] 1. In a method of manufacturing a multilayer ceramic substrate to which metal electrical connection pins are attached, the connection pin attachment side of the raw ceramic sheet is marked with item a of the periodic table.
forming a metal film of Group A of the Periodic Table on the metal film of Group A, and forming a metal film of Group B of the Periodic Table on the metal film of Group A; a step of forming a partially-containing metal layer; a step of laminating and pressing a plurality of raw ceramic sheets including the ceramic raw sheet and firing the ceramic raw sheets; and connecting the group B metal layer of the fired substrate with a brazing material. 1. A method for manufacturing a multilayer ceramic substrate with pins, the method comprising the step of brazing the pins.