This application claims the priority benefit of Taiwan application serial no. 97125137, filed Jul. 3, 2008. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.
1. Field of the Invention
The present invention generally relates to a circuit substrate and a method of fabricating the same, in particular, to a circuit substrate in which a solder mask covering a surface thereof has at least one opening, with an upper diameter larger than a lower diameter, for exposing a bonding pad, and a method of fabricating the same.
2. Description of Related Art
Recently, with the increasingly high demand of the market on electronic products and the advanced processing technique, more and more 3C products emphasize portable convenience and popularization of the demand of the market, the conventional signal chip packaging technique cannot meet the increasingly new demand of the market, it has become a well-known product trend to design and manufacture products with characteristics of being light, thin, short, and small, an increased packaging density, and a low cost. Therefore, under the precondition of being light, thin, short, and small, various integrated circuits (ICs) with different functions are integrated by using various stacking packaging manners, so as to reduce the package volume and package thickness, which is a main stream for the research on the market of various packaging products. As for the current various packaging products under mass production, package on package (POP) and package in package (PIP) products are new products as the main stream of the research in response to the development trend.
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Accordingly, the present invention is directed to a circuit substrate and a method of fabricating the same, in which through changing a thickness of a solder mask and a shape of an opening in the solder mask, a pre-solder disposed in the opening is prevented from being spilled out off the opening during a reflow soldering process, so as to enhance the reliability for bonding the circuit substrate with another package.
The present invention provides a circuit substrate, suitable for being connected to at least one solder ball. The circuit substrate includes a substrate, at least one bonding pad, and a solder mask. The substrate has a surface. The bonding pad is disposed on the surface of the substrate for being connected to the solder ball. The solder mask covers the surface of the substrate and has an opening for exposing a portion of the bonding pad. The opening has a first end and a second end. As compared with the second end, the first end is much farther from the bonding pad, and a diameter of the first end is larger than that of the second end.
In an embodiment of the present invention, a thickness of the solder mask is larger than 30 μm.
In an embodiment of the present invention, a thickness of the solder mask falls between 50 μm and 150 μm.
In an embodiment of the present invention, a proportion of the diameter of the second end to that of the first end falls between 0.8 and 0.9.
In an embodiment of the present invention, the opening is a tapered opening.
In an embodiment of the present invention, the circuit substrate further includes: a pre-solder, disposed on the exposed bonding pad, in which the bonding pad is connected to the solder ball through the pre-solder.
In an embodiment of the present invention, the pre-solder is filled in the opening.
In an embodiment of the present invention, the substrate further comprises a first surface opposite to the surface and the circuit substrate further comprises a first solder mask which covers the first surface of the substrate wherein the thickness of the solder mask is different from the thickness of the first solder mask.
In an embodiment of the present invention, the thickness of the solder mask is larger than the thickness of the first solder mask.
In an embodiment of the present invention, the circuit substrate further comprises a plurality of first bonding pads disposed on a center portion of the surface of the substrate wherein the solder mask comprises a center opening which exposes the first bonding pads and a diameter of the center opening is larger than a diameter of the opening.
In an embodiment of the present invention, the circuit substrate further comprises a metal layer covering the first bonding pads.
In an embodiment of the present invention, the metal layer comprises a gold layer or a solder layer.
In an embodiment of the present invention, the solder mask is formed by stacking a plurality of solder masks together.
The present invention further provides a method of fabricating a circuit substrate, which includes the following steps. Firstly, a core layer, a first patterned circuit layer, and a second patterned circuit layer are provided. The first patterned circuit layer and the second patterned circuit layer are respectively disposed on a first surface and a second surface of the core layer, so as to be electrically connected to each other through a plurality of conductive through-holes penetrating the core layer, and the first patterned circuit layer has at least one bonding pad. Next, a solder mask is formed on the first patterned circuit layer. Finally, an opening is formed in the solder mask, for exposing a portion of the bonding pad, in which the opening includes a first end and a second end, the first end is much farther from the bonding pad as compared with the second end, and a diameter of the first end is larger than that of the second end.
In an embodiment of the present invention, a thickness of the solder mask is larger than 30 μm.
In an embodiment of the present invention, a thickness of the solder mask falls between 50 μm and 150 μm.
In an embodiment of the present invention, a proportion of the diameter of the second end to that of the first end falls between 0.8 and 0.9.
In an embodiment of the present invention, the opening is a tapered opening.
In an embodiment of the present invention, the solder mask is formed by stacking a plurality of solder masks together. Each solder mask has an opening, and a diameter of a second end of each opening is larger than that of a first end of the opening located under the second end.
In an embodiment of the present invention, the method of fabricating the circuit substrate further includes forming a pre-solder on the bonding pad exposed by the opening.
The present invention provides a chip package structure. The chip package structure includes a substrate, at least one bonding pad, a plurality of first bonding pads, a solder mask, and a chip. The substrate has a surface. The bonding pad is disposed on the surface of the substrate for being connected to the solder ball. The first bonding pads are disposed on a center portion of the surface of the substrate. The solder mask covers the surface of the substrate and has an opening for exposing a portion of the bonding pad and a center opening which exposes the first bonding pads. The opening has a first end and a second end. As compared with the second end, the first end is much farther from the bonding pad, and a diameter of the first end is larger than that of the second end.
In an embodiment of the present invention, the chip package structure further comprises an underfill layer which is filled between the chip and the substrate.
In an embodiment of the present invention, the chip package structure further comprises a plurality of bumps which is disposed between the chip and the substrate and electrically connects the chip and the first bonding pads.
In an embodiment of the present invention, the chip package structure further comprises a pre-solder, disposed on the exposed portion of the bonding pad and filled in the opening.
In an embodiment of the present invention, the chip package structure further comprises a first chip package structure which is disposed on the substrate and electrically connected to the pre-solder.
In an embodiment of the present invention, the chip package structure further comprises a molding compound which is disposed on the substrate and covers the chip.
In an embodiment of the present invention, the solder mask and the molding compound have at least one recess exposing the pre-solder.
In an embodiment of the present invention, the chip package structure further comprises a first chip package structure which is disposed on the substrate and electrically connected to the pre-solder.
In the circuit substrate and the method of fabricating the same according to the present invention, the thickness of the solder mask is mainly increased, and the opening with an upper diameter larger than a lower diameter for exposing the bonding pad is formed in the solder mask. Therefore, the diameter of the upper end of the opening is larger than that of the lower end, so that the pre-solder disposed in the opening is not spilled from the opening during the reflow soldering process, so as to enhance the reliability of bonding the circuit substrate with another package.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.
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To sum up, in the circuit substrate and the method of fabricating the same according to the present invention, the thickness of the solder mask is mainly increased, and the opening with an upper diameter larger than a lower diameter for exposing the bonding pad is formed in the solder mask. In this manner, when the solder of the circuit substrate is bonded with the solder ball of another package during the reflow soldering process, the solder in the opening of the solder mask is prevented from being spilled out of the opening to result in a hollow phenomenon, thereby enhancing the reliability of bonding the circuit substrate with another package.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.
Number | Date | Country | Kind |
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97125137 | Jul 2008 | TW | national |