JPH10200015A - Ceramic board and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the reduction of the connection reliability due to the positional deviation on a ceramic board having recesses on the surface and external connecting electrodes located in the bottoms of the recesses. SOLUTION: Recesses having a diameter d meet the relation d<D<p; D is diameter of external connecting electrode and p is center-to-center distance between adjacent recesses. To form the recesses by laminating green sheets having through-holes, it suffices to meet the relation d'<D'<p'; d' is diameter of the through-hole of the green sheet, D' is diameter of the printed external connecting electrode and p' is center-to-center distance between adjacent recesses.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ceramic substrate and a method for manufacturing the same. More specifically, the present invention relates to a ceramic substrate having a structure having a concave portion on the surface and an external connection electrode located on the bottom surface of the concave portion, and a method of manufacturing the same.

[0002]

2. Description of the Related Art At present, multilayer ceramic substrates are mainly manufactured by a green sheet multilayer laminating method. In this method, a green sheet is formed by a doctor blade method from a slurry obtained by mixing a ceramic material with an organic resin binder, an organic solvent, a plasticizer, and the like, and a via hole (through hole) is formed in the green sheet.
After performing processing such as drilling holes, filling via holes with a conductive paste, and screen-printing the internal wiring or the external connection electrodes on the surface, a plurality of green sheets are laminated and thermocompression-bonded, and the obtained laminate is fired.

In recent years, for the purpose of increasing the mounting density by surface mounting, a BGA (Ball Grid Allay) connection method has been used for connecting a ceramic multilayer substrate to a printed wiring board, and the ceramic multilayer substrate for electronic components such as LSIs and chip capacitors has been used. The flip-chip connection method is becoming the mainstream for mounting. In this case, both surfaces of the substrate are connected using solder.

[0004] In the connection method using these solders, the solder at the connection portion is destroyed by the distortion caused by the difference in the coefficient of thermal expansion between the ceramic multilayer substrate and the printed wiring board or the electronic component, and especially the external connection on the ceramic multilayer substrate side. There is a problem that the electrode is easily broken near the interface of the electrode. To solve this problem, Japanese Patent Application Laid-Open Nos. 8-55928 and 8-55
Japanese Patent Publication No. 930 proposes an insulating substrate having a structure having a concave portion on the surface and an external connection electrode located on the bottom surface of the concave portion.

[0005] In addition, the BGA connection method and the flip chip connection method have a problem in that when solder is melted, the solders of adjacent connection portions are joined to each other, causing a short circuit. Regarding this problem, Japanese Utility Model Laid-Open No. 5-72177 discloses that
There has been proposed a wiring board having a structure having a concave portion on the surface and an external connection electrode located on the bottom surface of the concave portion.

[0006] In addition to the above, a solder dam structure in which a concave portion into which solder enters into the substrate surface to prevent the outflow of molten solder is disclosed in Japanese Unexamined Utility Model Publication No. 48-112955 and Japanese Patent Laid-Open No. 50-77862. It is also disclosed in the official gazette and JP-A-61-203648. However, the solder dams (concave portions) disclosed in these publications are formed of a polymer resin material completely different from the insulating layer constituting the substrate.

[0007]

SUMMARY OF THE INVENTION BGA using solder
In contrast to the connection method and flip-chip connection method, the structure of the ceramic substrate, in which a concave portion is formed on the surface and an external connection electrode is located on the bottom surface of the concave portion, as can be seen from the above-described conventional technology, the solder breakage of the connection portion And is very effective in preventing short circuits.

In a conventional insulating substrate having such a structure,
When the diameter of the external connection electrode is D and the diameter of the concave portion is d,
d = D. That is, the electrode diameter is equal to the concave diameter. Although the specifications of JP-A-8-55928, JP-A-8-55930, and JP-A-5-72177 do not describe that d = D, the drawings of the respective publications show that d = D. It is clear that

When a ceramic substrate having such a concave portion with d = D on the surface is manufactured by the above-described green sheet multilayer laminating method, the ceramic substrate is printed on the electrode printing surface of the green sheet on which the external connection electrode is printed. Another green sheet having a through hole having the same diameter as the electrode diameter (hereinafter, also referred to as a second green sheet) may be laminated, pressed, and fired. The through hole of the second green sheet becomes a concave portion on the surface of the ceramic substrate integrated after firing. Thus, ideally, as shown in FIG. 1B, a ceramic substrate is obtained in which the entire connection surface of the external connection electrode having the same diameter D is exposed on the bottom surface of the concave portion having the diameter d on the substrate surface.

However, in consideration of the positional accuracy of the electrode pattern formed on the printing screen and the positional accuracy of the through-hole formed in the second green sheet laminated thereon, the former green sheet can be formed during the above lamination. It is extremely difficult to match the center of the external connection electrode printed on the surface with the center of the latter through hole formed in the second green sheet. Therefore, in the ceramic substrate obtained after firing, as shown in FIG. 1A, the center of the recess and the electrode for external connection are shifted, and the entire connection surface of the electrode is not exposed to the bottom of the recess. In other words, the insulating ceramic substrate is exposed on a part of the bottom surface of the concave portion. As a result, when the solder ball is welded to the electrode exposed on the bottom surface of the concave portion and the solder ball is connected to the outside, if the displacement is large, a connection failure may occur, and there is a problem in reliability of the external connection. It has been found.

An object of the present invention is to provide a ceramic substrate having a structure in which a concave portion is provided on the surface and an external connection electrode is located on the bottom surface of the concave portion, even if there is an unavoidable displacement due to positional accuracy. It is an object of the present invention to provide a ceramic substrate and a method for manufacturing the same, which can reliably prevent poor connection of the electrodes for use and thus have high connection reliability.

[0012]

According to the present invention, FIG.
As shown in (c), the above problem is solved by making the diameter D of the external connection electrode larger than the diameter d of the concave part and smaller than the pitch (distance between centers of adjacent concave parts) p of the concave parts. You. To do so, the diameter D 'of the electrode printed on the green sheet is larger than the diameter d' of the through hole of the second green sheet laminated thereon, and the pitch of the through holes is larger.
(Distance between centers of adjacent through-holes) It may be smaller than p ′.

By setting D> d and D ′> d ′, the positional accuracy of the pattern formed on the printing screen of the external connection electrode and the positional accuracy of the through hole formed in the second green sheet can be improved. Even if the center of the electrode and the through hole is displaced at the time of lamination, it is possible to expose the electrode to the entire bottom surface of the concave portion formed after firing, and therefore,
External connection reliability is ensured.

According to the present invention, there is provided a ceramic substrate having a conductor wiring incorporated therein and an electrode for external connection formed on a surface, wherein the surface of the substrate is positioned at a position corresponding to the electrode for external connection. The electrode is exposed on the bottom surface of the concave portion, and the diameter D of the electrode is such that the diameter of the concave portion is d,
A ceramic substrate characterized by satisfying d <D <p, where p is a distance between centers of adjacent concave portions.

From another aspect, the present invention relates to a method for manufacturing a ceramic substrate by a green sheet multi-layer laminating method, wherein one layer or two layers on which an internal wiring and a surface external connection electrode are printed with a conductive paste. Preparing a first ceramic green sheet comprising at least a layer, preparing a second ceramic green sheet having a through hole at a position corresponding to an electrode printing position on the surface of the green sheet;
Here, the diameter D ′ of the electrode printed on the surface of the first green sheet is represented by d ′ where the diameter of the through hole of the second green sheet is p ′ and the distance between the centers of adjacent through holes is p ′.
When d '<D'<p'is satisfied, one or more second green sheets are thermocompression-bonded on the electrode printing surface of the first green sheet to form a laminate, and the laminate is fired. A method for manufacturing a ceramic substrate.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The ceramic substrate of the present invention may be a multilayer substrate in which part of the internal wiring of the substrate extends in the horizontal direction (plane direction) (that is, has a so-called internal wiring). It may be a single-layer substrate in which the internal wiring is only in the vertical direction (generally formed by via holes). In the present invention, “internal wiring” means the entire wiring inside the substrate, and includes both horizontal and vertical wirings.

The external connection electrodes are formed on both surfaces of most ceramic substrates, but may be formed on only one surface. When the external connection electrodes are formed on both sides of the ceramic substrate, it is not necessary to follow the present invention on both sides.
According to the present invention, only the external connection electrode on the surface to be connected to the outside with the solder may be located in the recess.
In addition, it is preferable that all of the external connection electrodes on one surface are positioned in the concave portion according to the present invention, but this is not necessarily essential, and some of the external connection electrodes are not positioned in the concave portion, Alternatively, even if it is located in the concave portion, the condition of the present invention may be deviated.

Hereinafter, the ceramic substrate of the present invention having a structure having external connection electrodes positioned in the concave portions on both surfaces of the ceramic multilayer substrate and a method of manufacturing the same will be described with reference to FIG. As is clear from the above, the present invention is not limited to this embodiment.

The ceramic substrate of the present invention can be manufactured according to the well-known green sheet multilayer lamination method.
First, the ceramic raw material powder is used as the binder organic resin,
A green sheet is obtained by mixing with an organic solvent and further other additives such as a plasticizer to form a slurry, forming the resulting slurry into a sheet by a doctor blade method, and drying the sheet.

The type and mixing ratio of the ceramic raw material powder may be selected according to the characteristics required for the substrate. The “ceramics” of the present invention also includes glass ceramics that can be fired at a low temperature of 1000 ° C. or lower. In this case, the ceramic raw material powder contains glass powder in addition to the ceramic powder, and the blending amount of the glass powder may be larger. In some cases, the ceramic raw material powder may consist only of crystallized glass powder.

On a plurality of green sheets cut to the same size, predetermined via holes are formed, and a conductor paste mainly composed of metal powder is screen-printed.
Filling of via holes and printing of internal wiring (these correspond to internal wiring) or printing of electrodes for external connection (for the outermost green sheet) [Fig. 2 (a)]. The green sheet on which these conductor pastes are printed is referred to as a first green sheet in the present invention.

The plurality of (two or more) first green sheets need not all be the same. For example, green sheets made of different ceramic materials may be used for the inside and the surface. However, since they are fired together,
The sintering temperature must be close.

Separately, two second green sheets to be laminated on both sides of the first green sheet to form a concave portion are prepared. In each of the second green sheets, a through hole is formed at a position corresponding to the external connection electrode printed on the surface of the first green sheet on the surface on which the second green sheets are laminated [FIG. 2 (a)]. When a single layer of the second green sheet cannot form a recess having a sufficient depth for each surface, two or more layers of the second green sheet may be used.

The second green sheet may have the same composition as the first green sheet, or may have a different composition. For example, in order to increase the strength of the substrate surface, the second green sheet may be made of a ceramic material having a higher strength than that used for the first green sheet. However, since it is fired at the same time as the first green sheet, it is preferable that the shrinkage ratio does not greatly differ from that of the first green sheet. In order to match the shrinkage ratios, it is convenient to use the same composition as the first green sheet for the second green sheet.

The first green sheet is laminated so that the external connection electrodes are located on the outer surfaces on both sides thereof, and the second green sheets provided with the corresponding through holes on the outer surfaces on both sides are overlapped. The laminate is formed by thermocompression bonding according to a method [FIG. 2 (b)].

Thereafter, the laminate is fired to remove organic components in the green sheet, and the ceramic material is sintered to integrate the whole. The firing conditions may be selected according to the ceramic material constituting the green sheet. In order to suppress warpage and shrinkage in the planar direction during firing, firing may be performed under pressure.

In this manner, the conductor wiring (formed by filling the via hole with the conductor paste and printing the inner layer wiring) is provided inside, the external connection electrode is provided on the surface, and the surface recess is provided at a position corresponding to the external connection electrode. Is formed, and the ceramic substrate according to the present invention is obtained in which the electrodes are exposed on the bottom surfaces of the concave portions [FIG. 2 (c)]. Electronic components are connected to the external connection electrodes on the upper surface of the substrate shown by a flip-chip connection method, and the external connection electrodes on the lower surface are connected to a printed wiring board by the BGA method.

In the present invention, on each surface of the ceramic substrate, the diameter D of the external connection electrode is expressed as d <d, where d is the diameter of the recess and p is the pitch of the recess (the distance between the centers of adjacent recesses). Satisfies D <p. If the pitch of the concave portions is not constant, it is sufficient that the above relationship is satisfied between the concave portions on both sides.

After the diameter d of the concave portion is determined, the external connection is performed in consideration of the positional accuracy of the pattern formed on the printing screen of the electrode for external connection and the positional accuracy of the through hole formed in the second green sheet. The diameter D of the electrode for external connection is determined so that the electrode for external connection is exposed on the entire bottom surface of the concave portion even when the displacement of the electrode for connection becomes maximum. Specifically, the electrode diameter D may be a numerical value obtained by adding twice the maximum value of the electrode misalignment expected from the accuracy to the concave diameter d. Thus, no matter what direction the displacement occurs, the entire bottom surface of the concave portion is always covered with the external connection electrode, and the insulating ceramic material does not appear on the bottom surface. Further, in order to avoid a short circuit between adjacent external connection electrodes, the diameter D of the external connection electrodes must be smaller than the concave pitch p.

The final amount of displacement depends on the accuracy of punching of a punching machine for punching, the accuracy of positioning of a screen printing machine, the accuracy of positioning of a screen, the accuracy of lamination of a laminating machine, and the like. And in any respect,
Preferably, D is at least 20 μm larger than d and at least 20 μm smaller than p.

In the fired ceramic substrate, d <D
In order to satisfy the relationship of <p, the diameter D ′ of the external connection electrode printed on the first green sheet before firing is the diameter d ′ of the through hole of the second green sheet and the pitch of the through hole (adjacent through hole). For the distance between the centers of the holes) p ', d'<D'
<P '. Since the conductive paste and the second green sheet used for printing the external connection electrodes are thermocompressed before firing and then fired, they shrink together during firing, so the shrinkage may be considered to be the same. . Therefore, if d ′ <D ′ <p ′ is satisfied before firing, d <D <p
Is obtained. In addition,
The actual values of d 'and D' are calculated by taking into account the shrinkage during firing.
The values of d and D may be determined after firing.

[0032]

【Example】

(Embodiment 1) Organic resin (acrylic resin), organic solvent, and dispersion were mixed in raw material powder in which glass powder and ceramic (alumina) powder each having a particle size of 0.1 to 10 μm were mixed at a weight ratio of 60:40. After adding an agent and a plasticizer, mixing and slurrying, a green sheet having a constant thickness was produced by a doctor blade method.

After a predetermined via hole is formed in a plurality of green sheets cut to a predetermined size, the inner layer wiring, the filling of the via hole, and the flip chip connection electrode and the BGA connection electrode are screened using Ag paste. Printed. The screen printing machine used was LS-25TVA manufactured by Neurong, and the punching machine used for punching was MP-715 manufactured by UHT.
It was 0.

Green sheet 2 prepared separately as above
In each of the sheets, a through hole having a diameter smaller than that of the corresponding electrode was punched by the above-mentioned punching machine at one position corresponding to the printing position of the flip chip connection electrode, and at the other position corresponding to the printing position of the BGA connection electrode.

The electrode printing diameter D ' _f for flip-chip connection,
The diameter d _'f and pitch p' _f of the through holes of the green sheets to be laminated to the flip chip bonding surface, and the electrode printing diameter D for BGA connection _'b, the diameter d of the through holes of the green sheets to be laminated to the BGA connection surface' specific dimensions _b and the pitch p _'b were as follows. D ' _f = 180 µm, d' _f = 150 µm, p ' _f = 300 µm D' _b = 1.2 mm, d ' _b = 1.08 mm, p' _b = 1.56 mm.

These green sheets are laminated in a predetermined order, and integrated by thermocompression bonding (100 ° C., 70 kgf / cm ² ). The laminated body is placed on a setter and is pressed in an electric furnace without pressure. The resultant was fired at 900 ° C. for 1 hour under atmospheric conditions to obtain a ceramic multilayer substrate having a structure in which both surfaces have a concave portion on the surface and an electrode for external connection is located on the bottom surface of the concave portion. Electrode diameter of flip-chip bonding side and BGA connection side of the ceramic multilayer substrate D _f and D _b, recess diameter d _f and d _b and the recess pitch p _f and p _b, were as follows. _{D f = 150 μm, d f} = 125 μm, p f = 250μm D b = 1.0 mm, d b = 0.9 mm, p b = 1.3 mm.

When the cross sections of the bottom surfaces of the concave portions on both sides of the ceramic substrate were observed by SEM, the bottom surfaces of the concave portions on both surfaces were completely covered with the external connection electrodes, and the insulating ceramic did not appear on the bottom surfaces of the concave portions.

Comparative Example 1 Flip Chip Connection Electrode and B
A ceramic multilayer substrate was produced in the same manner as in Example 1, except that the printing diameter of the GA connection electrode was changed so that the diameter became the same as the diameter of the corresponding through hole. The dimensions before firing in this case were as follows. _{D 'f = d' f =} 150 μm, p 'f = 300 μm D' b = d 'b = 1.08mm, p' b = 1.56mm.

The corresponding dimensions of the ceramic substrate obtained after firing were as follows. D _f = d _f = 125 μm, p _f = 250 μm D _b = d _b = 0.9 mm, p _b = 1.3 mm.

When the cross section of the bottom surface of the concave portion on both sides of this ceramic substrate was observed by SEM, the exposed bottom surface of the ceramic insulator having a maximum width of about 10 μm was replaced with the concave portion on the surface of the BGA connection side. Exposed portions of the ceramic insulator having a maximum width of about 10 μm were also observed on the bottom surface, and were not completely covered with the external connection electrodes.

As can be seen from the above, if the printing diameter of the external connection electrode and the diameter of the through hole of the green sheet for forming the surface concave portion are made the same, the positional deviation necessarily occurs due to the printing accuracy and the drilling accuracy. It is very difficult to expose the external connection electrode to the entire bottom surface of the surface recess formed after firing, and in most cases, the insulating ceramic substrate material is exposed to a part of the bottom surface of the recess. As a result, the reliability of the external connection is impaired.

[0042]

According to the present invention, there is provided a ceramic substrate having a structure in which an external connection electrode is exposed on the bottom surface of a concave portion formed by laminating a green sheet having a through hole formed on a surface by a green sheet multilayer laminating method. When manufacturing, even if the center of the printing position of the electrode and the center of the position of the through hole are shifted due to the printing accuracy and drilling accuracy of the conductor paste, the entire bottom surface of the surface recess is surely covered with the external connection electrode. be able to.

As a result, the following effects can be obtained for the ceramic substrate having this structure. (1) External connection reliability is improved. (2) The tolerance of the manufacturing error is expanded. (3) Connection to the outside becomes easy.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an external connection electrode located on the bottom surface of a surface concave portion according to the related art and the present invention.

FIG. 2 is an explanatory view showing a process of manufacturing the ceramic substrate of the present invention.

Claims (2)

[Claims] 1. A ceramic substrate having a conductor wiring incorporated therein and an electrode for external connection formed on a surface thereof, wherein the surface of the substrate has a recess at a position corresponding to the electrode for external connection. The electrode is exposed on the bottom surface of the concave portion, and the diameter D of the electrode satisfies d <D <p, where d is the diameter of the concave portion, and p is the distance between the centers of adjacent concave portions. , Ceramic substrates. 2. A method of manufacturing a ceramic substrate by a green sheet multi-layer lamination method, comprising: one or more first ceramics on which an internal wiring and an external connection electrode on a surface are printed with a conductive paste.・ Preparing a green sheet, preparing a second ceramic green sheet having a through hole at a position corresponding to an electrode printing position on the surface of the green sheet, wherein a second ceramic green sheet is printed on the surface of the first green sheet. The diameter D ′ of the electrode is defined as d ′, the diameter of the through hole of the second green sheet, and p ′, the distance between the centers of adjacent through holes.
d '<D'<p'is satisfied, and one or more second green sheets are thermocompression-bonded on the electrode printing surface of the first green sheet to form a laminate, and the laminate is fired. A method of manufacturing a ceramic substrate.