JPH0730244A - Bump electrode, and method of forming bump electrode - Google Patents

Abstract

PURPOSE:To provide a multilayered ceramic substrate with a close spacing of bump electrodes, which can be mounted on a motherboard at a given height. CONSTITUTION:A multilayered ceramic substrate includes via conductors 2, each connected with a bump that is formed, directly above the conductor, of a metallic core electrode 3 having a higher melting point than solder. The bump has a solder coating 4, and if necessary, it may have a gold plating 5 on the solder coating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bump electrode formed on a ceramic multilayer wiring board and a method for forming the bump electrode.

[0002]

2. Description of the Related Art Hitherto, as a bump electrode formed on a ceramic multilayer wiring board, a method of forming it by using cream solder or solder ball has been generally used.

In such a bump electrode forming method, first, a conductor pattern is formed on a bump electrode forming portion on a ceramic multilayer wiring substrate, cream solder is printed or applied on the conductor pattern, and a solder ball is formed on the surface. It was a method of mounting and heating and melting in the atmosphere.

Since most of the bump electrode formed by the above method is composed of solder, the size of the bump electrode depends on the amount of the cream solder printed or applied and the size of the solder ball. The shape of the bump electrode was almost spherical as shown in FIG. 5 due to the surface tension of the solder when melted.

[0005]

However, when the ceramic multilayer wiring substrate 102 having the bump electrodes 101 formed by the above-described conventional method is mounted on the mother board 103, the bump electrodes 101 are formed as described above. Since most of it is composed of solder, the entire body melts at the time of reheating for mounting on the mother board 103, and the shape cannot be maintained. As shown in FIG. 6, the structure is such that problems such as short-circuiting between adjacent bump electrodes due to oblique joining of the two substrates or poor connection between the two substrate electrodes are likely to occur. It was

Further, the size and shape of the bump electrode formed by the above-mentioned conventional method depends on the printing or application amount of the cream solder and the size of the solder ball as described above, and It is difficult to obtain a bump electrode having a uniform height and width because it largely changes due to sagging during melting.
As shown in FIG. 3, even when the ceramic multilayer wiring substrate 102 having the bump electrodes 101 and the mother board 103 can be joined with a constant space therebetween, the bump electrodes adjacent to each other due to the unevenness in height and width. Short between,
Alternatively, problems such as connection failure between both substrate electrodes are still likely to occur.

Further, the above-mentioned problems are more remarkable when mounting these ceramic multi-layer wiring boards on a mother board in the future as the modules using the ceramic multi-layer wiring boards are highly integrated and highly densified. Appeared in
It was feared that the yield of products would deteriorate.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object thereof is to keep a constant space between both substrates when mounting a ceramic multilayer wiring substrate having bump electrodes on a mother board. The present invention provides a novel bump electrode formed on a ceramic multilayer wiring substrate that can be connected by a high-density bump electrode, and a method for forming the bump electrode.

[0009]

In order to achieve the above object, the present invention is capable of electrically connecting to a via conductor formed directly on a ceramic multilayer wiring substrate and having a higher melting point than solder. A core electrode formed of a metal was provided, and a solder electrode was provided on the surface of the core electrode to form a bump electrode.

Further, according to the present invention, an Ag-based or Cu-based conductor paste is screen-printed directly on the via conductor formed on the ceramic multilayer wiring board by using a metal mask having a through hole having a predetermined shape, and then the screen printing is performed. A method of forming a bump electrode is described in which a desired core electrode is formed by drying and firing, and a solder layer is formed on the surface of the core electrode by a melt dipping method.

According to the above-mentioned bump electrode of the present invention, when the ceramic multilayer wiring board having the bump electrode is mounted on the mother board, the core electrode which does not melt at the heating temperature for mounting serves as a spacer. It becomes possible to bond both substrates while keeping them at regular intervals, and the solder that contributes to the bonding of both substrates is a small amount provided as a layer on the surface of the core electrode,
Even if the bump electrodes are formed in close proximity to each other, a structure such as a short circuit is unlikely to occur, and a high-density bump electrode can be connected.

According to the bump electrode forming method of the present invention described above, since the core electrode is formed using a so-called mold, the height and width of the formed core electrode are uniform. It is possible to form a bump electrode having a highly reliable core electrode as a spacer, and a solder layer is formed on the core electrode by a melt dipping method. It is possible to easily form a uniform thin-film solder layer on the surface of the core electrode with less sagging during mounting on the core electrode.

Here, the size and shape of the core electrode provided right above the via conductor are such that the height is 50 to 500 μm, the bottom diameter is 100 to 1000 μm, and the aspect ratio of the height to the bottom diameter is 0.25 to 1.0. It is desirable to use a trapezoidal core electrode as described in 1. This is because the core electrode having such a size and shape has such strength that the core electrode can effectively function as a spacer when mounted on a mother board, and can be used for high-density connection. This is because it becomes a core electrode.

Further, it is desirable to further provide a gold plating layer on the surface of the solder layer provided on the surface of the core electrode. This is because the gold plating layer can prevent the surface oxidation of the solder, and can maintain good solder wettability when mounting on the board even after long-term storage, and provide a bump electrode with high bonding reliability. Because you can.

Further, in forming the core electrode,
It has a height of about 1.0 to 1.3 times the desired height of the core electrode formed on the metal by the additive method, and about 0.8 to 1.2 times the desired bottom diameter of the core electrode. It is desirable to use a metal mask in which a film of a fluorine compound having self-lubricating property is formed on the processed surface of the through hole having the diameter of. This is because the presence of the above-mentioned self-lubricating fluorine compound coating on the processed surface of the metal prevents sagging of the paste on the back surface of the metal mask during printing of the Ag-based or Cu-based conductor paste, and This is because good results can be obtained regarding the detachability from the metal mask.

Regarding the sagging of the paste after printing and during drying, an effect of suppressing sagging can be obtained by improving the thixotropy of the paste and by not using a resinous binder in forming the paste.

Flux is applied to the surface of the core electrode described above, and a uniform solder layer is formed on the surface of the core electrode by immersing it in a solder melting bath, and, if necessary, on the surface of the solder layer, Further, a gold plating layer is formed by a method of immersing it in an electroless gold plating solution. Here, generally commercially available flux, solder and electroless gold plating solution can be used.

[0018]

EXAMPLES Hereinafter, the bump electrode according to the present invention described above,
And, an embodiment of the forming method thereof will be described with reference to the drawings.

FIG. 1 is a cross-sectional view after forming high-density bump electrodes on a ceramic multilayer wiring substrate according to an embodiment of the present invention. Such bump electrodes have a bump diameter of 300 μm and a bump height of 300 μm. It is a bump electrode having a thickness of 250 μm and a bump pitch of 500 μm.

In FIG. 1, 1 is a ceramic multilayer wiring board, 2 is a via conductor (Ag), 3 is a core electrode (20% P).
d-Ag), 4 is a solder layer (62Sn / 36Pb / 2A)
g) and 5 are gold plating layers.

A method of forming the bump electrode will be described below.

First, a core electrode forming paste (20% P
d-containing Ag paste, BPM-105: manufactured by Nippon Cement Co., Ltd., using a metal mask 7 made by an additive method with a metal thickness of 300 μm and a bottom diameter of the through hole 6 of 280 μm shown in FIG. Directly on the via conductor formed on the substrate, screen-printed using a square squeegee having a hardness of 70, dried at 70 ° C. for 10 minutes, and then held in a belt baking furnace in the atmosphere at a peak temperature of 850 ° C. for 10 minutes, Moreover, the firing was performed in a profile of 60 minutes in all steps. A film 8 of a fluorine-based compound is formed on the processed surface of the metal mask 7.

Next, flux (R5003: manufactured by Nippon Alpha Metals Co., Ltd.) was applied to the surface of the core electrode after firing, and preheating was performed at 150 ° C. for 30 seconds,
Solder melted at 230 ° C (62Sn / 36Pb /
2Ag solder, S-2062: Senju Metal Co., Ltd.) The core electrode was immersed in a bath for 5 seconds to form a solder layer on the surface of the core electrode. The above-mentioned applied flux cleaning was carried out by dipping and stirring for 30 seconds in a mixed solution of ethanol + butyl acetate.

After that, electroless gold plating (K24N: manufactured by Kojundo Chemical Co., Ltd.) was used on the surface of the solder layer of the obtained core electrode, and the plating solution was immersed for 1 minute at a temperature of 90 ° C. ± 5 ° C. A gold plating layer having a film thickness of about 100 angstrom was formed.

As described above, the dimensional data of the bump electrode obtained by the bump electrode forming method according to the present invention is
As shown in FIG.

As is clear from FIG. 4, the bump electrode forming method according to the present invention makes it possible to form the bump electrode within a variation range of ± 5% in diameter and height.

Next, in order to compare the performance of the bump electrode obtained in the present invention with the bump electrode obtained by the conventional method, 900 bumps having a bump diameter of 300 μm, a bump height of 250 μm and a bump pitch of 500 μm. After the ceramic multilayer wiring board having the above-mentioned structure was manufactured by the conventional method and the above-described method of the present invention, 30 substrates each were manufactured, and these substrates were aligned and mounted on the alumina multilayer wiring board (motherboard) on which the Au electrode was formed. Both substrates were mounted by melting the solder on the bumps.

In the mounting board thus obtained, the yield ratio for connecting bumps of the board manufactured by the conventional method and the method of the present invention was determined, and the mounting yield of the bump electrode-formed substrate formed by the conventional method was 67%. The mounting yield of the bump electrode-formed substrate formed by the method of the present invention was 93%.

[0029]

As described above, according to the bump electrode and the method for forming the bump electrode according to the present invention, the mounting yield of the ceramic multilayer wiring board having the bump electrode on the mother board is improved and the high density bump is provided. It is possible to form bump electrodes on the ceramic multilayer wiring substrate that can be connected to electrodes.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a ceramic multilayer wiring board having bump electrodes formed thereon according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a ceramic multilayer wiring board having bump electrodes formed thereon according to an embodiment of the present invention after being mounted on a mother board.

FIG. 3 is a cross-sectional view of a metal mask used for forming bump electrodes in the present invention.

FIG. 4 is a graph showing dimensional data of bump electrodes obtained according to an example of the present invention.

FIG. 5 is a cross-sectional view of a ceramic multilayer wiring substrate having bump electrodes formed by a conventional method.

FIG. 6 is a cross-sectional view after mounting a ceramic multilayer wiring substrate on which bump electrodes are formed in a conventional method on a mother board.

FIG. 7 is a cross-sectional view after mounting a ceramic multilayer wiring substrate on which bump electrodes are formed in a conventional method on a mother board.

[Explanation of symbols]

 1 Ceramic Multilayer Wiring Board 2 Via Conductor 3 Core Electrode 4 Solder Layer 5 Gold Plated Layer 6 Through Hole 7 Metal Mask 8 Fluorine Compound Coating 9 Motherboard

Claims (5)

[Claims] 1. A ceramic multi-layer wiring board is directly above the via conductor, and can be electrically connected to the via conductor,
A bump electrode comprising a core electrode formed of a metal having a melting point higher than that of solder, and a solder layer provided on the surface of the core electrode. 2. The bump electrode according to claim 1, wherein a gold plating layer is further provided on the surface of the solder layer. 3. An Ag-based or Cu-based conductor paste is screen-printed directly on the via conductor formed on the ceramic multilayer wiring board by using a metal mask having through holes of a predetermined shape formed, and then dried and baked. A bump electrode is formed by forming a desired core electrode by a melt dipping method on the surface of the core electrode. 4. The method of forming a bump electrode according to claim 3, wherein a film of a fluorine-based compound having self-lubricating property is formed on the processed surface of the metal mask. 5. The bump electrode forming method according to claim 3, wherein a gold plating layer is formed on the surface of the solder layer by a method of further immersing the solder layer in an electroless gold plating solution.