JP2006013272A - Manufacturing method of multilayer ceramic substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve quality of a substrate by eliminating bleeding and projection caused by a connecting pad for interlayer connection formed by screen printing method in the manufacture of a multilayer ceramic substrate. <P>SOLUTION: In the manufacture of the multilayer ceramic substrate, conductor paste is filled into via-holes 111 worked on the green sheet 112 of ceramics and, thereafter, at least one layer or more of screens 101 with a circuit pattern 110 formed thereon by screen printing method employing the screen 101 without connecting pad between upper and lower layers are used as an inner layer to laminate, then, pressurizing adhesion or pressurizing calcination is applied. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a multilayer ceramic substrate.

  As shown in FIG. 5, in a general construction method of a multilayer ceramic substrate, (a) a ceramic powder is uniformly mixed with a binder, and a slurry is processed into a sheet by a doctor blade method, followed by drying, cutting, and green sheet 112 is created. (B) Thereafter, the green sheet 112 is affixed to a handling member for handling (this step can be omitted), and a via hole 401 is formed in the green sheet 112 to ensure conduction between the upper and lower layers. Make corrections. Next, (c) the conductor paste 111 is filled into the via hole 401. In many cases, the conductor paste filling step is performed by placing the via hole conductor filling paste 405 on the via hole conductor filling screen 404 and pressurizing and dragging the via hole conductor filling squeegee 403 (this method is called a screen printing method). Then, the conductor paste 111 on the via hole 401 is flattened, and inspection / correction is performed. Next, (d) a circuit pattern 110 is formed on the green sheet 112. When the circuit pattern 110 is formed by the screen printing method, the circuit pattern printing conductor paste 406 is placed on the mesh 102 and the circuit pattern printing squeegee 407 is used. Perform inspections and corrections as necessary. From the drilling process to the pattern printing process, there are a plurality of patterns according to the circuit design pattern, and the required number is created. Then, the green sheets 112 filled with the conductor paste 111 and formed with the circuit pattern 110 are laminated, heated and bonded, and then subjected to a sintering process to obtain a sintered body, thereby obtaining a multilayer ceramic substrate. Note that inspection / correction and planarization of the conductive paste 111 on the via hole 401 are optional steps.

When the circuit pattern 110 is formed on the green sheet 112, a lower layer connection pad 113 (hereinafter simply referred to as a pad) is provided on the conductor paste 111 of the via hole 401 in order to ensure the connection between the upper and lower layers. . Since this pad is processed into the screen 102 on which the circuit pattern is formed in advance, when the wiring pattern is formed by the screen printing method, it is simultaneously formed on the via hole 401 on the green sheet 112.
Documents related to these include Patent Document 1 and Non-Patent Document 1.

Japanese Patent Laid-Open No. 5-283272 New edition screen printing handbook (Japan Screen Printing Technology Association, issued on January 31, 1988, P217)

A multilayer ceramic substrate has over 100,000 pads and hundreds of meters of wiring, all of which must be defect-free. Further, the circuit pattern forming screen has a floating island pattern. For this reason, omission of the pattern is prevented by pasting a floating island pattern on the mesh on the circuit pattern forming screen. However, there are the following problems.
(1) Appearance of mesh blockage and openings For example, the basic lattice pitch in the board design is 0.3 mm, the pad diameter is φ0.1 mm, the wire diameter of the mesh used for the screen is φ0.04 mm, mesh # 250 ( Consider the case of the number of meshes per inch. When the bonding angle between the mesh and the substrate circuit pattern is 45 degrees, the pitch of the mesh with respect to the substrate is Equation 1.

よって、メッシュ網目の交差部分（以下単にクロス部という）と開口部は、基板の格子ピッチとメッシュのピッチの比率によって周期的に出現する。この場合のクロス部の出現は、概ね２３から３０格子に1回ずつとなる。
（２）メッシュのクロス部と開口部で印刷性に著しく差が出る
φ０．１ｍｍのパッドでは、クロス部においてほとんど導体ペーストが吐出されない。しかし、メッシュ開口部では簡単に導体ペーストが抜けていく。よって、クロス部に導体ペーストを完全に充填させるために印刷条件を合わせると、開口部ではにじみが発生する。また、にじみを抑えると、クロス部においてパッドがカスレてしまう。よって、印刷条件の調整が困難である。
（３）メッシュの開口部において導体ペーストが立ち上がり、その後の接着過程で倒れる
メッシュ開口部では、印刷時の版離れ過程において、パッドの導体ペーストが立ち上がることがある。この立ち上がった導体ペーストが、その後のハンドリングやシート積層時に欠損し、接続されてはならない部分に橋渡しされ、基板不良（ショート）になる。

Therefore, the mesh mesh crossing portion (hereinafter simply referred to as “cross portion”) and the opening appear periodically depending on the ratio of the lattice pitch of the substrate to the pitch of the mesh. In this case, the appearance of the cross portion is approximately once every 23 to 30 lattices.
(2) Significant difference in printability between mesh cloth and opening. With a φ0.1 mm pad, almost no conductor paste is discharged at the cloth. However, the conductor paste is easily removed from the mesh opening. Therefore, if the printing conditions are adjusted in order to completely fill the cross portion with the conductor paste, the opening portion is blurred. In addition, if the bleeding is suppressed, the pad becomes distorted at the cross portion. Therefore, it is difficult to adjust printing conditions.
(3) The conductive paste rises at the mesh opening and falls during the subsequent bonding process. At the mesh opening, the pad conductive paste may rise during the plate separation process during printing. The rising conductor paste is lost during subsequent handling and sheet lamination, and is bridged to a portion that should not be connected, resulting in a substrate failure (short circuit).

On the other hand, the pad is conventionally present for the following reasons.
(4) The pad has a role of absorbing the deviation generated when the upper and lower layers are stacked. If the pad does not have a certain size, various deformation factors (hole position shift, Due to sheet deformation, stacking misalignment, etc., the upper and lower layers are not connected (open), resulting in a substrate failure.
(5) Pads are design information Designing information such as circuit pattern routing and placement positions is the circuit pattern design of a multilayer ceramic substrate, and cannot be eliminated in design.
(6) The pad has connection information and is necessary for pattern inspection. Since the pad has connection information between layers and between pads, it is necessary for pattern defect inspection. If there is no pad, normal inspection cannot be performed.
Accordingly, an object of the present invention is to provide a method of manufacturing a multilayer ceramic substrate that eliminates bleeding and protrusions of connection pads and improves the quality of the substrate.

  In order to achieve the above object, the present invention provides a circuit pattern formed by screen printing using a screen having no connection pads between upper and lower layers on a green sheet after a conductor paste is filled into a via hole processed into a ceramic green sheet. At least one layer or more is used for the inner layer and laminated, followed by pressure bonding or pressure firing.

  According to the present invention, there is no substrate defect due to pad scraping or conductive paste rising during circuit pattern formation. In addition, the degree of freedom in printing conditions during circuit pattern formation is increased. For this reason, the trouble which generate | occur | produces at the time of printing decreases, and the correction man-hour of a pattern can be reduced. Furthermore, since the pad has a via hole diameter, the circuit density can be increased. Further, since the pads are substituted with via holes, the inspection can be performed as usual.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In all the drawings used in the present embodiment, the same reference numerals are assigned to components having the same function, and repeated description thereof is omitted.
Referring to FIG. 1, FIG. 1 (a) is a plan view of a circuit pattern forming screen 101, and FIG. 1 (b) is a sectional view taken along line AA of FIG. 1 (a). 1 (a) and 1 (b), a circuit pattern forming screen 101 has a pattern 103 for making a padless circuit bonded to a mesh 102 by Ni plating or the like using a known technique to make a plate (fixed on a screen frame). It is formed by pasting with the tension of). When screen printing is performed on the circuit pattern forming screen 101, the conductive paste is removed from the exposed portion of the mesh 102 to which the pattern 103 is not attached, and the conductive paste is printed on the green sheet 112. Since the conductive paste does not come off at the pasted portion, the conductive paste is not printed on the green sheet 112.

  FIG. 1C is a plan view of the green sheet 112 printed by the circuit pattern forming screen 101 of FIGS. 1A and 1B, and FIG. B line sectional drawing is shown. 1C and 1D, printing is performed on the green sheet 112 in which the via paste described in FIG. 4 is filled with the conductive paste 111 by using the circuit pattern forming screen 101 in FIGS. 1A and 1B. The conductive paste that becomes the circuit pattern 110 is printed on the exposed portion of the mesh 102, and the portion of the pattern 103 has a circular non-printed portion as in the pattern 103. In FIG. 1 (c), a conductive paste 111 filled in the above-described via hole serving as a through hole is located at the approximate center of the circular non-printed portion.

  As shown in FIGS. 1A and 1B, the pattern 103 corresponding to the portion where the through hole 111 is present in FIG. 1C is formed in a circular shape so that the conductive paste is not printed. When printing is performed using the circuit pattern forming screen 101, printing is not performed on the through hole 111, and thus the above-described pad is not printed / formed on the through hole 111.

  Here, the reason why the pad is necessary in the prior art will be described with reference to FIG. FIG. 6A is a cross-sectional view of a multilayer ceramic substrate on which a padless circuit pattern is formed, and FIG. 6B is a cross-sectional view on which a conventional pad is formed. In FIG. 6B, a pad 113 is formed on the through hole 111 of the green sheet 511 stacked under the uppermost green sheet 510. When these are laminated and bonded, pressure is uniformly applied to the surface of the circuit pattern, and as shown in the middle and lower stages of FIG.

  In FIG. 6A, the pad 113 is not formed on the through hole 111 of the green sheet 502 laminated below the uppermost green sheet 501. In the multilayer ceramic substrate 502 having no connection pad between the upper and lower layers, the bonding pressure is not transmitted between the upper and lower layers in a portion where there is no pad, and a space 503 remains between the upper and lower through holes 111. Therefore, since transmission of an electric signal is interrupted in the gap 503, the substrate becomes defective. In order to prevent this, the pad 113 is necessary. In addition, the pad itself has information about the circuit pattern routing and arrangement position, and it is essential to design the arrangement of the pad because it is the circuit pattern design of the multilayer ceramic substrate itself.

  Next, the reason why the pad becomes inconvenient in manufacturing the substrate will be described with reference to FIG. 2A is a plan view showing a part of a circuit pattern formed in a green sheet shape, and FIG. 2B is a cross-sectional view taken along line AA in FIG. The pattern 302 attached to the mesh 102 shown in FIG. 2A has a hole in the center and the conductive paste is removed, so that the pad is printed.

As shown in FIG. 2C, when a circuit pattern is formed on the green sheet 112 by the screen printing method, the circuit pattern is printed from a place where the circuit pattern 302 is absent (missed) via the mesh 102 by the squeegee 407. The conductive paste 406 is discharged and transferred. At this time, the circuit pattern printing conductor paste 406 becomes a circuit pattern through the following process. Referring to Non-Patent Document 1,
(1) The circuit pattern printing conductor paste 406 is filled in the openings of the mesh 102.
(2) Immediately below the circuit pattern printing squeegee 407, the circuit pattern printing conductor paste 406 receives a strong pressure and is transferred onto the green sheet 112.
(3) Next, the mesh 102 is raised by the plate separation operation.
(4) Then, the pattern printing conductor paste 406 is torn off.
(5) The torn pattern printing conductor paste 406 is restored from the stringing state by viscoelasticity.

At this time, the pads are simultaneously formed on the green sheet 112, but depending on the size and shape of the pattern, the opening diameter of the mesh 102, the pitch, the printing conditions, and the printing position, the normal part (upper and lower layer connecting conductor pads 113a), It is classified into a scraped portion (upper and lower layer connecting conductor pads 113b) and a sword mountain portion (upper and lower layer connecting conductor pads 113c). The left diagram in FIG. 2D shows a printed state, and the right diagram in FIG. 2D shows a single sheet when stacked. A multilayer ceramic substrate having a plurality of large-scale integrated circuits and serving as a multichip module has 100,000 or more pads per green sheet, and it is difficult to print all the pads uniformly. In particular, the upper and lower layer connecting conductor pads 113c having a sword mountain shape are deformed when the green sheets stacked at the time of stacking contact with each other, and are electrically connected to conductor portions of electrically different signals. When this phenomenon occurs, it is extracted in a subsequent continuity inspection process and becomes defective. Since the multilayer ceramic substrate after firing is close to the finished product, the defects here are serious damages. As a means to prevent this defect,
(6) When the circuit pattern is formed on the green sheet, the three-dimensional shape is inspected and corrected.
(7) Pad printing and other circuit pattern printing are printed separately (the pad is made into a uniform shape using a screen without a mesh).
(8) After sintering the multilayer ceramic substrate, the defective pad is detected and the signal is switched to another pad (repair).
However, in the above (6), the inspection time is enormous and unrealistic, and even if an automatic inspection is performed by an inspection facility, it cannot be performed because there is no inspection device itself. (7) is unsuitable for practical use from the viewpoint of initial investment and production man-hour (per layer, creation of circuit pattern forming screen and pad printing screen requires work). Since (8) is a set of transistor circuits in the case of a large scale integrated circuit, there are many power supplies and grounds (grounds). Even in a multilayer ceramic substrate, there are an infinite number of power supply and ground power supply pads, and since they are common within the multilayer ceramic substrate so that there is no potential difference between the pads, they cannot be bypassed. Therefore, repair is extremely difficult.

  Therefore, in the present invention, it has been considered to eliminate the upper and lower interlayer connection pads from the circuit pattern forming screen. The following method was used to ensure the connection between the upper and lower layers. According to Patent Document 1 and the like, there is a method of pressure sintering a laminated glass ceramic substrate. With this method, the upper and lower through-holes are brought into close contact with each other by the pressure during sintering even if there is no connection pad between the upper and lower layers. As shown in FIG. 6A, the green sheet 502 to be laminated was removed from the upper and lower interlayer connection pads, and an experiment was conducted. When there is the conventional pad of FIG. 6B, the green sheet 112 printed with the circuit pattern is laminated and heat-bonded to form an adhesive (middle figure), and the gap 503 between the upper and lower layers is not seen. . What is concerned about the method of the present invention is that the gap 503 between the upper and lower layers remains inside the adhesive. However, as a result of observing the cross section of the multilayer ceramic substrate sintered body 503 by sintering the adhesive body, as shown in the lower diagram of FIG. There were no gaps.

  Next, the application method to an actual product was considered. As described above, the pad is always present at the design stage. For this reason, it was decided to eliminate the circuit forming pattern screen. FIG. 3 shows a flowchart of board design and production data creation according to the present invention. In FIG. 3, the items within the solid line frame are indispensable items, but the items enclosed by dotted lines are optional items. The difference from the conventional method shown in FIG. 4 is that once a circuit pattern printing screen is designed by the conventional method, inspection data is created based on the data and redesigned except for unnecessary pads (see 2 in FIG. 3). A circuit pattern printing screen is created based on the data (heavy solid frame). Of the excluded pad data, a pad necessary for the substrate design (such as a surplus length to be stopped inside the multilayer ceramic substrate) is applied to the hole filling screen (via hole conductor filling screen 404).

The figure which shows the plane of the screen for circuit pattern formation which concerns on this invention, and its cross section. The figure for demonstrating the subject of this invention. The flowchart which shows one Example of the design of the multilayer ceramic substrate based on this invention, and the production data creation flow. The flowchart which shows the design and production data creation flow of the conventional multilayer ceramic substrate. The figure explaining the process of manufacturing a general multilayer ceramic substrate. The figure explaining the multilayer ceramic substrate of this invention, and the conventional multilayer ceramic substrate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Screen for padless circuit pattern printing 102 ... Mesh 103 ... Part of padless circuit 110 ... Circuit pattern 111 ... Through hole 112 for upper and lower interlayer connection ... Green sheet

Claims (1)

After filling the via hole processed into a ceramic green sheet with a conductive paste, use a screen without a connection pad between the upper and lower layers on the green sheet, and use at least one more inner layer as a circuit pattern. A method for producing a multilayer ceramic substrate, comprising: laminating and then pressure bonding or pressure firing.

Images