JPH11261226A - Ceramic multilayered wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic multilayered wiring board which can prevent the occurrence of defective connection between an inner wiring layer and a via hole caused by the worse printability, etc., of the end section of an unbaked inner wiring layer. SOLUTION: The end sections 8a of an inner wiring layer 8 which connects the end faces 7a of the via holes 7 of upper and lower ceramic layers 2 to each other are protruded from the via hole 7 by about 20 μm. Consequently, the reliability of the electrical connection between the inner wiring layer 8 and the via hole 7 can be improved, because the layer 8 can be connected to the via hole 7 before the via hole 7 is baked by not using the end sections 8a of the wiring layer 8 having worse printability against conductor paste, but the sections of the layer 8 on the inside of the end sections 8a at the time of manufacturing an unbaked wiring board.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic multilayer wiring board used for an IC package or the like, and more particularly, to a green wiring board formed by laminating and pressing a plurality of green sheets, and firing the green board. A ceramic multilayer wiring board.

[0002]

2. Description of the Related Art FIG. 5 shows one such ceramic multilayer wiring board (hereinafter also referred to as a wiring board or simply a board).
It is a partially broken side view and a partially enlarged sectional view showing an example. As shown in FIG. 1, this type of ceramic multilayer wiring board 1 has a structure in which a plurality of ceramic layers 2 are laminated, and a surface (upper surface) 3 of the ceramic multilayer wiring board 1 is connected to an electronic component chip such as a semiconductor element (not shown). A large number of connection terminals 4 are provided,
Are provided with a number of terminals 6 for connection to a motherboard (not shown). Further, inside the substrate 1, there are provided a large number of vias (conductors) 7 perpendicular to the substrate surface 3 and an internal wiring layer 8 for connecting the end faces of the vias 7 to each other.
A circuit network is formed so as to continue from the terminal 4 on the front surface 3 to the terminal 6 on the rear surface 5 via these.

[0003] By the way, the unsintered wiring board before firing, which constitutes this kind of wiring board 1, is formed in a green sheet (hereinafter, also simply referred to as a sheet) by punching or the like. Then, for example, W (tungsten), Mo
A metallized paste or metallized ink (hereinafter, also referred to as a conductor paste) mainly containing (molybdenum) or the like is filled, and a conductor paste for an internal wiring layer is screen-printed on a sheet surface (hereinafter, also simply referred to as print).
Then, the green sheets on which the unfired vias and the unfired wiring layers are formed are laminated and pressed to manufacture.

The unsintered wiring layer made of the conductive paste in such a green sheet has a predetermined range from the end surface of the unsintered via on the sheet surface, that is, the end surface of the unsintered via of the green sheet laminated on the sheet. Are printed and formed up to the position where is connected. The end (tip) of the unsintered internal wiring layer is the end face (outline) of the unsintered via to be connected.
It was formed in a substantially semi-circular shape having the same radius as that of the end face so as to overlap the same. By stacking and pressing such green sheets, the unsintered via becomes an unsintered wiring board (so-called large size) connected by an unsintered internal wiring layer. 5, the internal wiring layer 8 is set so as to connect the vias 7 to each other at the end 8a as shown in FIGS.

[0005]

However, conventionally, in the wiring board 1 thus formed, the connection between the end 8a of the internal wiring layer 8 formed along the ceramic layer and the end of the via 7 is formed. An unknown disconnection (poor connection) sometimes occurred. Then, the inventor of the present application made many samples and repeated various tests and analyzes to find out that the cause is as follows.

That is, as shown in FIG. 7, when the unsintered internal wiring layer (conductor paste) 28 is screen-printed on the green sheet 22, the conductive paste is applied near both ends 28a of the unsintered internal wiring layer 28. The printability (adhesion or applicability of the conductive paste) tends to be poor, for example, it tends to be thin or faint. This is probably because the opening of the printing mask of the unsintered internal wiring layer 28 is narrow and elongated, for example, about 0.1 mm, so that the dischargeability of the conductive paste is reduced near the opening end. Therefore, such unsintered internal wiring layer 28
Although the printed green sheet 22 is pressed after lamination, it is based on poor printability of both end portions 28a.
Actually, as shown in FIG. 5 (enlarged view), the bonding is not performed well, and as shown in FIG. 8, even after the sheet 22 is pressed, the end face of each unfired via 27 and the unfired internal wiring layer 28 The connection with the end 28a tends to be incomplete. Then
The wiring board obtained by firing the unsintered wiring board having imperfect connections as described above may cause connection failures or reduce the reliability of the connection.

[0007] Such a problem arises when the thickness is 80 μm.
m or less, for example, about 40 to 50 μm. This is because such a thin sheet usually has a thickness (100 to 5).
Unlike the sheet of (00 μm), it is considered to contain alcohol for laminating and bonding, but the printability of the conductor paste is basically poor. On top of that, due to its thinness, the thickness of the conductor paste for the internal wiring layer has to be about 8 to 15 μm, which must be printed as extremely thin as about half or less of that of a normal green sheet (20 μm or more). For this reason, in the unfired wiring board formed by laminating such thin green sheets, the connection with the via tends to be incomplete particularly at the end of the unfired internal wiring layer.

Further, in the production of such green sheets, a printing shift (error) occurs at a printing position of the conductive paste for the unfired internal wiring layer or the like regardless of the thickness. Although such printing deviation is basically slight, it is more likely to occur as the sheet becomes thinner. This tendency is particularly strong in a very thin green sheet having a thickness of about 50 μm. This is because such an ultra-thin green sheet is extremely thin, so it is difficult to handle it by attaching it to a frame (frame), and because of its thinness, it is easy to expand and contract, and it is easy for wrinkles to enter. It is. Further, when such green sheets are laminated and pressure-bonded, misregistration occurs for the same reason. As described above, poor printability of the unfired internal wiring layer, particularly at the ends, in combination with such errors, has had a great effect on the reliability of electrical connection of the fired wiring board.

The present invention has been made in order to solve such problems and the like, and an object of the present invention is to reduce the printability at the end of the unsintered internal wiring layer in the manufacture of the unsintered wiring board. An object of the present invention is to provide a ceramic multilayer wiring board that can prevent poor connection between an internal wiring layer and a via due to the above.

[0010]

In order to achieve the above object, a ceramic multilayer wiring board according to the present invention is characterized in that an end of an internal wiring layer connecting end faces of vias formed in upper and lower ceramic layers has the same structure. It is characterized in that it protrudes in a direction to extend the internal wiring layer beyond the via.

According to the present invention, the via is connected to the via before the end of the internal wiring layer, that is, on the base side (inner side) of the end by the means. The connection is not made to the end of the bad internal wiring layer, but to a portion having relatively good printability. Therefore, the connection reliability is higher than the connection with the end portion, and the connection reliability of the wiring board can be improved.

In the wiring board according to the present invention, the thickness of the upper and lower ceramic layers is 80 μm or less, and the thickness of the internal wiring layer connecting the end faces of the vias of the upper and lower ceramic layers is 15 μm.
It is effective when applied to a ceramic multilayer wiring board of μm or less. In such a wiring board, as described above, poor printability of the conductor paste for the unsintered internal wiring layer tends to be a problem, and printing misalignment is easily generated. Cheap. Therefore,
When applying the present invention to this, a particularly large effect is expected.

It is preferable that the amount of protrusion of the end portion of the internal wiring layer from the via is in the range of 10 to 30 μm. With this amount of protrusion, poor printability can be substantially avoided,
This is because a gap for preventing short circuit with a nearby via (circuit) can be secured.

[0014]

Next, an embodiment of the present invention will be described in detail with reference to FIGS. In the drawing, reference numeral 1 denotes a multilayer wiring board composed of a plurality of alumina ceramic layers 2 and 2, which is of a flip-chip connection type in this example, and has an electronic component such as a semiconductor element (not shown) on a front surface (upper surface) 3 thereof. A large number of connection terminals 4 of
The back surface 5 has a large number of terminals 6 for connection to a motherboard (not shown). Although not shown in detail, a large number of vias 7 and internal wiring layers 8 are formed inside the substrate 1 to form a circuit network connecting the terminals 4 on the front surface 3 to the terminals 6 on the rear surface 5, respectively. In addition, the ceramic layer 2 can be formed from various ceramic materials, such as a ceramic simple substance, such as mullite and aluminum nitride, and a glass ceramic besides alumina.

As shown in FIG. 1 (partially enlarged view) and FIG. 2, the internal wiring layer 8 formed along the ceramic layer 2 and connecting the end faces 7a of the vias 7 has both ends 8a. They are semicircular in plan view, and are formed to project from the vias 7 by a predetermined amount L (about 20 μm in this example).
However, in this example, the thickness 2t of the ceramic layer 2 is 50 μm, the thickness 8t of the internal wiring layer 8 is 10 μm, the width 8w of the internal wiring layer 8 and the diameter of the via 7 are 100 μm. The via 7 and the internal wiring layer 8 are formed by simultaneously firing a conductive paste mainly containing tungsten, molybdenum, or the like.

Thus, such a wiring board 1 is formed by laminating and compressing predetermined green sheets to form an unfired wiring board, and then firing and dividing. That is, a via hole having a predetermined diameter is formed at a predetermined position of a green sheet forming each ceramic layer 2 by punching or the like, and the via hole is filled with a conductive paste to form an unfired via. A conductive paste is printed in a predetermined range (the formation area of the internal wiring layer) to form an unfired internal wiring layer.

At this time, as shown in FIG. 3, the unsintered internal wiring layer 28 is laminated on the unsintered via 27 provided on the sheet 22 on which it is formed and the green sheet 22. Green sheet 2 indicated by a two-dot chain line in the figure
Printing is performed such that each end 28a protrudes by a predetermined amount L (20 μm) from the unfired via 27 formed in No. 2.
Strictly, when the green sheet or the unsintered wiring board is manufactured, that is, before firing, it is formed to have a size larger by the firing shrinkage, including the protrusion amount L.

In the unsintered wiring board formed by laminating and pressing the green sheets in this manner, the end of the unsintered internal wiring layer exists beyond the unsintered via. Therefore, the end face of the unsintered via does not have a portion having poor printability at the end of the unsintered internal wiring layer, that is, a portion where the thickness of the conductive paste is thin or a faint portion is not located. In the wiring substrate 1 to be formed, the connection failure between the via 7 and the internal wiring layer 8 is prevented. That is, the end 8 a of the internal wiring layer 8 is
The via 7 is connected not at its end 8a but at its base, as much as it protrudes from the wiring board, so that a wiring board with high electrical connection reliability can be formed.

In the above embodiment, the end 8 of the internal wiring layer 8 is formed.
Although a is a semicircle in a plan view, the present invention does not use a semicircle in this way, and as in the case of the internal wiring layer 8 shown in FIG.
It may be formed in a slender rectangular shape or a band shape, and protrude from the via 7 by a predetermined amount L at the end 8a. in this case,
To print the conductor paste for the internal wiring layer 8, a print mask having a constant width may be used up to the end of the printed surface. In this case, even if the protrusion amount L is the same, the discharge area of the conductive paste is improved because the opening area of the print mask at the end is increased as compared with the case where the protrusion amount is a semicircle. . However, even when such a print mask is used, the end (planar shape) of the pattern to be actually printed may be slightly rounded with its corners removed.

The size of the end 8a of the internal wiring layer 8 protruding from the via 7 (protruding amount L) is preferably large, but if it is too large, it may hinder the insulation from neighboring vias. You. In consideration of the printing shift of the conductive paste and the positional shift (error) at the time of lamination, it is appropriate that the protrusion amount is about 10 to 30 μm as described above.

The width of the internal wiring layer is usually equal to the diameter of the via, but may be larger. Further, in the above-described embodiment, the description has been made on the case where the planar shape (transverse cross-sectional shape) of the via is an elongated linear internal wiring layer, but the planar shape is not limited to these in the present invention. .

Furthermore, in the above embodiment, the wiring board for flip chip connection is used, and the thickness of one ceramic layer is 50
In the present invention, the thickness of the green sheet and the thickness of the internal wiring layer are not limited to those of the above-described embodiment. Absent. The wiring board to which the present invention can be applied is not limited to such a wiring board for flip chip connection, but can be widely applied to a ceramic multilayer wiring board.

[0023]

As is apparent from the above description, the ceramic multilayer wiring board according to the present invention is effective in preventing a poor connection between an internal wiring layer and a via, and therefore has an effect of preventing electrical connection. A highly reliable wiring board is obtained. In particular, the effect is expected for a wiring board in which one ceramic layer is thin and the thickness of the internal wiring layer is thin, and not only the reliability of the wiring board but also the improvement of the manufacturing yield is expected.

[Brief description of the drawings]

FIG. 1 is a partially cutaway side view and a partially enlarged cross-sectional view showing an embodiment of a ceramic multilayer wiring board according to the present invention.

FIG. 2 is an explanatory plan view of an internal wiring layer taken along line AA of FIG. 1;

FIG. 3 is an explanatory diagram of a process of forming a green internal wiring layer.

FIG. 4 is a plan view for explaining another example of the internal wiring layer.

FIG. 5 is a partially cutaway side view and a partially enlarged cross-sectional view of a conventional ceramic multilayer wiring board.

FIG. 6 is an explanatory plan view of an internal wiring layer taken along line AA of FIG. 5;

FIG. 7 is an explanatory cross-sectional view showing a state where an unfired internal wiring layer is printed on a green sheet.

FIG. 8 is a diagram illustrating incomplete connection between the end surface of the unfired via and the end of the unfired internal wiring layer after the green sheet is pressed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic multilayer wiring board 2 Ceramic layer 2t Ceramic layer thickness 7 Via 7a Via end face 8 Internal wiring layer 8a Internal wiring layer end 8t Internal wiring layer thickness L Projection amount

Claims (3)

[Claims] An end of an internal wiring layer connecting end faces of vias formed in upper and lower ceramic layers projects in a direction to extend the internal wiring layer beyond the via. Ceramic multilayer wiring board. 2. A ceramic multilayer wiring board wherein the thickness of upper and lower ceramic layers is 80 μm or less, and the thickness of an internal wiring layer connecting end faces of vias formed in the upper and lower ceramic layers is 15 μm or less, A ceramic multilayer wiring board, wherein an end of an internal wiring layer protrudes in a direction to extend the internal wiring layer beyond the via. 3. The ceramic multilayer wiring board according to claim 1, wherein an amount of protrusion of the end of the internal wiring layer from the via is 10 to 30 μm.