Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
1998-05-06
2001-04-17
Lam, Cathy (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C257S668000, C257S700000, C257S702000, C257S758000, C257S774000, C257S778000, C361S768000, C361S751000, C361S774000, C361S783000
Reexamination Certificate
active
06217990
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 9-116929 filed on May 7, 1997, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ceramic multilayer circuit board manufactured by baking several laminated green sheets, which respectively have wiring patterns thereon, and particularly relates to a ceramic multilayer circuit board suitable for holding electronic parts on a surface thereof.
2. Related Arts
A ceramic multilayer circuit board is generally manufactured by a green sheet lamination method using laminated green sheets. Specifically, first, via-holes are formed in the respective green sheets in a punching process and are filled with a tungsten paste or a molybdenum paste. Then, conductive layers are formed on the respective green sheets to form wiring patterns (inside wiring patterns) in a printing process using a paste such as a tungsten paste or a molybdenum paste as well. After performing the above-mentioned processes, a specific number of the green sheets are laminated and are hot-pressed to be united to each other. The united green sheets are cut into a specific shape, and then are baked at a specific temperature. Accordingly, the ceramic multilayer circuit board with a basic structure is obtained.
To mount an electronic parts such as a flip chip on the multilayer circuit board, a solder paste is previously applied to a mounting surface of the circuit board by a screen printing method using a print mask. In this case, however, it is difficult to apply the solder paste to a specific portion of the mounting surface with a uniform thickness. There is a case that the specific portion of the mounting surface has a part to which the solder paste is not applied. This results in deterioration of mounting reliability of the electronic part.
One of reasons why the solder paste cannot, be uniformly applied to the specific portion of the mounting surface is a warp locally generated on the circuit board, especially to raise a part of the mounting surface. The warp of the circuit board locally raising the mounting surface increases a pressure applied thereto by a squeegee in the printing process. As a result, the non-applied portion of the solder paste is produced. The warp further adversely affects the print mask to reduce a duration of life of the print mask.
On the other hand, in recent years, a flip chip having a plurality of bump electrodes is mounted on the circuit board to realize a high mounting density, so that the number of the bump electrodes on the circuit board is increased. To comply with the increase in number of the bump electrodes, each diameter and a bump pitch of the bump electrodes are decreased. This results in a decrease in a gap between the flip chip and the mounting surface of the circuit board. If the circuit board has the warp locally raising the mounting surface where the flip chip is mounted, the gap between the flip chip and the mounting surface of the circuit board is further decreased.
The gap between the flip chip and the circuit board is generally filled with a resin material containing inorganic filler such that the bump electrodes is not affected by thermal stress caused by a difference in thermal coefficient between the flip chip and the circuit board. When the resin material is supplied into the gap between the flip chip and the circuit board having the above-mentioned local warp, the warp prevents the inorganic filler from being uniformly distributed in the gap. As a result, the mounting reliability of the flip chip deteriorates.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-mentioned problems and an object of the present invention is to provide a multilayer circuit board with a simple structure capable of preventing a local warp of a mounting surface thereof. Another object of the present invention is to provide a multilayer circuit board capable of providing mounting reliability of an element which is mounted on the circuit board.
According to the present invention, a multilayer circuit board includes first laminated substrates and second laminated substrates laminated with the first laminated substrates. A first conductive pattern is disposed on a first surface of one of the first laminated substrates, while a second conductive pattern is disposed on a second surface of one of the second laminated substrates. The first and second conductive patterns respectively have pattern densities which are locally high on first and second pattern integrated portions corresponding to each other. Preferably, the first and second surfaces are symmetrical with respect to a center in a laminated direction of the laminated substrates.
The multilayer circuit board is formed by baking laminated green sheets to which conductive paste for the first and second conductive patterns is applied. According to the present invention, when the laminated sheets are baked, shrinkage forces of the conductive paste and the green sheets lie on the first and second pattern integrated portions can be canceled. As a result, the multilayer circuit board is formed without having a local warp on a mounting surface thereof.
To achieve the above-mentioned object, a multilayer circuit board composed of laminated substrates can have lead wiring members disposed on a surface of one of the laminated substrates, which is the most adjacent to a center in a laminated direction of the laminated substrates. The multilayer circuit board holds thereon an electronic part having electrodes, and the lead wiring members are electrically connected with the electrodes of the electronic part. Otherwise, a multilayer circuit board composed of laminated substrates can have lead wiring members disposed on two surfaces of the laminated substrates. The lead wiring members are electrically connected with electrodes of an electronic part mounted on the multilayer circuit board. Preferably, the two surfaces on which the lead wiring members are disposed are symmetrical with respect to a center in a laminated direction of the laminated substrates. In either case, the multilayer circuit board can be formed without having a local warp on a mounting surface thereof.
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Asai Yasutomi
Nagasaka Takashi
Nakagawa Syoichi
Ota Shinji
Terao Shinya
Denso Corporation
Lam Cathy
Pillsbury & Winthrop LLP
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