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AssigneeMatsushita Electric Industrial Co., Ltd.
InventorsTakeshi Suzuki, Toshihiro Nishii, Satoru Tomekawa, Fumio Echigo
Estimating the term…
A circuit board includes an electrical insulator layer formed of a reinforcer sheet with density distribution in its in-plane direction, an electrical conductor filled in a plurality of inner via holes provided in the electrical insulator layer in its thickness direction, and a wiring layer connected to the electrical conductor. The inner via holes provided in a high-density portion of the reinforcer sheet are formed to have a smaller cross-section than the inner via holes provided in a low-density portion of the reinforcer sheet. In this manner, it is possible to provide a circuit board that can achieve a high-density wiring and an inner via connection resistance with less variation, when a base material including a reinforcer sheet with density distribution in its in-plane direction such as a glass-epoxy base material is used for an insulator layer.
A circuit board comprising:
Dependencies are inferred from the claim text.
From the US filing history. Foreign family members aren’t listed.
Drawings are temporarily unavailable. Open the PDF at USPTO
By thick-film techniques: for via connections in organic insulating substrates
Consisting of two or more materials, e.g. two or more polymers, polymer + filler, + reinforcement: reinforced, e.g. by fibres, fabrics
Printed elements for providing electric connections to or between printed circuits: via connections; Lands around holes or via connections
By laser ablation: of organic insulating material
Term ended 25 Oct 2021 (estimated)
1. Field of the Invention
The present invention relates to a circuit board and a method for manufacturing the same. In particular, the present invention relates to a circuit board using a reinforcer sheet with density variations in its in-plane direction and a method for manufacturing the same.
2. Description of Related Art
FIG. 1 is a schematic plan view showing a circuit board according to a first embodiment of the present invention.
FIGS. 2A to 2D are drawings for explaining processes in a method for manufacturing a circuit board (having through holes) according to the first embodiment of the present invention.
FIGS. 3A to 3B are drawings for explaining processes in the method for manufacturing the circuit board (having through holes) according to the first embodiment of the present invention.
In the case of making a connection by pressure using an electrically conductive paste, the connection resistance of inner via holes suddenly becomes unstable so as to have increased variation when the ratio of (insulator layer thickness/via hole diameter) exceeds 1. Thus, in order to achieve a via hole with a small diameter (for example, a diameter of 50 μm) in a circuit board, it is preferable that the insulator layer has a thickness of 50 μm or smaller. However, when a glass-epoxy base material or an aramid-epoxy base material is used, a circuit board as a core substrate usually has a thickness of 50 μm or larger. In addition, an excessively thin core substrate is not preferable because the mechanical strength is reduced. Therefore, it is preferable that a thin insulator layer has a thickness of 50 μm or smaller and the ratio of the insulator layer thickness/the via hole diameter is 1 or smaller.
In the present invention, it is preferable that the reinforcer sheet with density distribution in its in-plane direction is a woven fabric or a non-woven fabric formed of at least one fiber selected from the group consisting of a synthetic fiber and an inorganic fiber. Of course, the reinforcer sheet with density distribution in its in-plane direction may be a film formed of a synthetic resin.
Also, it is preferable that the reinforcer sheet with density distribution in its in-plane direction is a woven fabric formed of a glass fiber.