JP2006339563A - Circuit board and semiconductor package employing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit board relating to an electrode pad for connecting a semiconductor element mounting substrate, an electrode pad for mounting components of the circuit board or the like which can be designed in highly dense wiring without degrading characteristic impedance and has high speed transmission characteristics and high design accuracy. <P>SOLUTION: A conductor 8 is placed so that an area of the conductor 8 in the electrode pad 1 of the circuit board is at or smaller than a predetermined value. A dielectric substance is introduced into a region of the pad 1 where the conductor 8 is not provided, thereby reducing a ratio of the area occupied by the conductor 8 in the electrode pad 1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a circuit board for high-speed transmission. More specifically, the present invention relates to a connection electrode pad for a semiconductor element mounting board, a component mounting electrode pad for a circuit board, and the like.

  In electronic devices and the like, pad electrodes are provided on a substrate in order to connect a circuit board and components. For example, as a method of connecting a semiconductor device and a circuit board, a pad electrode connection method using wire bonding and a pad electrode connection method using solder balls are known. As a mounting method using solder balls, there is BGA mounting in which solder balls are regularly arranged on the bottom surface of a semiconductor device and the semiconductor device and a circuit board are electrically connected via the solder balls. Electrode pads can be used for connection between the semiconductor device and the solder balls and between the circuit board and the solder balls.

The circuit board is generally composed of a wiring layer constituting wiring for transmitting a signal, a ground plane made of a conductor, and a dielectric layer formed between the conductor layers. The circuit board has electrode pads on the surface layer to ensure electrical connection with components and semiconductor devices outside the circuit board, or when the circuit board is used as a semiconductor device mounting board, to ensure connection with the motherboard. Is provided. Since signal transmission by a circuit board affects signal transmission characteristics by circuit design, appropriate wiring design is required. One of the important elements for determining the wiring design is the position and size of the electrode pad.
If a ground plane, which is a conductor, is present above the electrode pads on the circuit board, the electrode pads and the ground plane are electromagnetically coupled to have an electric capacity. For this reason, the characteristic impedance of the electrode pad portion is significantly reduced as compared with the characteristic impedance of the transmission line of the circuit board. The electrode pad becomes an impedance discontinuity due to the decrease in the characteristic impedance. And in the impedance discontinuity part, the signal which propagated through the transmission line reflected or radiated | emitted, and the problem of having lost the energy of the signal had arisen.
Therefore, conventionally, in the ground plane on the upper layer of the electrode pad of the circuit board, the region corresponding to the electrode pad is provided with a region called “clear” where no conductor exists. If a circuit is provided in a region overlapping with the clear in the wiring layer of the circuit board, the characteristic impedance of the wiring portion corresponding to the clear region is significantly reduced. For this reason, conventionally, in order to prevent the characteristic impedance of the transmission line of the circuit board from being lowered, a wiring circuit cannot be installed in the clear region (FIG. 1). The size of the electrode pad is very large compared to the size of the transmission line of the semiconductor device or the circuit board in order to ensure the positional accuracy of the connection, and the area where the wiring circuit cannot be installed also occupies a large area. Patent Document 1 is given as a prior document relating to a circuit board having such a structure.

However, with the recent increase in the speed of IC chips, it has become necessary to increase the speed, reliability, and density of circuit boards. For this reason, there has been a demand for a circuit board capable of designing wiring on the entire circuit board without reducing the characteristic impedance. And, as a measure to expand the area where wiring design can be done without reducing the characteristic impedance, there is a method of reducing the size of the electrode pad itself, but if the size of the electrode pad is reduced, the design accuracy of the circuit board will be increased accordingly. There was a problem that decreased.
Japanese Patent Laid-Open No. 7-307578

  The present invention has been made to solve the above-mentioned problems, and provides a circuit board with high design accuracy and high-speed transmission characteristics, capable of high-density wiring design without reducing characteristic impedance. is there.

  By the way, according to the study of the present inventor, the conductor is arranged so that the area of the conductor is less than a certain value among the electrode pads of the circuit board, and the dielectric is introduced into a region of the electrode pad where no conductor is provided. When the area ratio of the conductor in the electrode pad is reduced, the electromagnetic coupling between the electrode pad and the ground plane above the electrode pad is attenuated, and the characteristic impedance can be prevented from lowering without providing a clear. I found out. For this reason, it has been found that the wiring design of the circuit board can be performed even in a region where the conventional wiring cannot be designed due to clearness.

  The present invention has been made based on such knowledge. The invention according to claim 1 is a circuit board including at least a wiring layer, a ground plane layer, a dielectric layer, and an electrode pad, wherein the electrode pad is at least conductive. The circuit board includes a body and a dielectric, and the proportion of the conductor in the connection area of the electrode pad is 10% to 95%.

  The invention according to claim 2 is the circuit board according to claim 1, wherein the electrode pad includes a conductor having at least a plurality of concentric ring shapes.

  The invention according to claim 3 is the circuit board according to claim 1, wherein the electrode pad includes a conductor having at least a coil shape.

  A fourth aspect of the present invention is the circuit board according to any one of the first to third aspects, wherein a dielectric is filled in a gap between the conductors of the electrode pad.

  A fifth aspect of the present invention is a semiconductor package using the circuit board according to any one of the first to fourth aspects.

  According to the present invention, since it is not necessary to clear the circuit board having the electrode pads, the area where wiring design is possible increases, and the degree of freedom of wiring is greatly improved. For this reason, it has become possible to design a circuit board having high-density wiring as compared with the prior art. Further, since the size of the entire electrode pad is not reduced, the design accuracy of the circuit board is not lowered.

  Furthermore, in this invention, when the conductor which has a coil shape was used for the electrode pad, the conductor functioned as a coil. For this reason, it was possible to improve the reliability of the signal transmission characteristics of the wiring provided on the region corresponding to the electrode pad.

  Detailed embodiments of the present invention will be described below.

  FIG. 2 is a cross-sectional view of the electrode pad portion of the circuit board of the present invention. As shown in FIG. 2, the circuit board is formed by a known method by laminating a dielectric layer, a ground plane layer, and a wiring layer. However, in the present invention, it is not necessary to provide a clear on the ground plane. The electrode pad is formed of a dielectric and a conductor. The electrode pad includes a conductor and a dielectric, and the proportion of the conductor in the area of the electrode pad is 30% to 99%. If it is 99% or more, the electrode pad and the ground plane function as capacitance, which is not preferable. If it is 30% or less, the effect of the present invention cannot be obtained, which is not preferable. The shape of the conductor of the electrode pad will be described in more detail with reference to FIGS. The shape of the electrode pad conductor is not particularly limited as long as electrical connection is ensured. For example, in the case of a circular electrode pad, a concentric ring shape (FIGS. 3 and 4), a spiral shape ( Fig. 5). Also in electrode pads having other shapes such as a quadrangle, the same shape as that of the circular electrode pad can be obtained. The electrode pad maintains a diameter that allows electrical connection. For example, when a semiconductor device and a circuit board are connected using solder ball connection, as shown in FIG. 3, the electrode pad of the semiconductor device and the electrode pad of the circuit board on which the semiconductor device is mounted are solder balls. The conductor is arranged in a ring shape while maintaining a possible diameter.

  For example, when the semiconductor device and the circuit board are connected by using solder ball connection, the electrode pad of the circuit board of the present invention includes an electrode pad of the semiconductor device and an electrode of the circuit board on which the semiconductor device is mounted as shown in FIG. The pad is configured by arranging conductors in a ring shape while maintaining a diameter that allows the current mounting with solder balls. At this time, it is desirable that the ring-shaped center has a diameter equal to or larger than the via land diameter of the circuit board based on the manufacturing rule. In a region where no conductor is present (hereinafter referred to as clearance), the ratio of the line width of the ring-shaped conductor to the clearance width present in the outer diameter ring and the inner diameter ring is 1: 1 to 1: 5. It is preferable to become. If the clearance width is narrower than this range, the capacitance increases due to the coupling with the solid pattern of the solder ball pad, which causes a problem that the characteristic impedance is lowered. On the other hand, if the clearance width is larger than this range, a problem of poor contact or the like occurs. The clearance is preferably filled with a dielectric. If a solder ball is attached without filling the clearance, air may enter between the solder ball and the IC chip package, which may cause defects. As a material that can be used for the dielectric, a material having a relative dielectric constant of 5.0 or less is preferably used. Examples of a material that can be used as a dielectric include a resin used for a solder resist. If a dielectric having a relative dielectric constant higher than this value is filled, the capacitance increases.

  In addition, the shape of the conductor of the electrode pad is a ring shape composed of a plurality of concentric circles as described above, the electrode pad and the transmission line of the circuit board are in the same layer, and the conductive pair of the outer circle of the electrode pad When the transmission line is connected, it is preferable that the outer circle conductor and the inner circle conductor are directly electrically connected. If the outer circle conductor and the inner circle conductor are not directly electrically connected, if the solder ball connection accuracy is poor, only the inner circle conductor is connected to the solder ball. There is a possibility that the circuit board is not properly connected. Since the outer circle conductor and the inner circle conductor are directly electrically connected, for example, it is desirable to form a line for electrical connection between the outer circle and the inner circle of the electrode pad conductors. . Moreover, when the shape of the conductor of the electrode pad was coiled or spiral, the inductance could be increased while the capacitance was reduced.

: Cross-sectional view of a conventional circuit board : Cross-sectional view of the circuit board of the present invention : Plan view of the circuit board of the present invention : Plan view of the circuit board of the present invention : Plan view of the circuit board of the present invention

Explanation of symbols

1 Electrode Pad 2 Clear 3 Ground Plane 4 Wiring 5 Dielectric Layer 7 Dielectric 8 Conductor

Claims (5)

In a circuit board including at least a wiring layer, a ground plane layer, a dielectric layer, and an electrode pad,
The circuit board, wherein the electrode pad includes at least a conductor and a dielectric, and a proportion of the conductor in a connection area of the electrode pad is 30% to 99%.   The circuit board according to claim 1, wherein the electrode pad includes a conductor having at least a plurality of concentric ring shapes.   The circuit board according to claim 1, wherein the electrode pad includes a conductor having at least a coil shape.   The circuit board according to claim 1, wherein a dielectric is filled in a gap between conductors of the electrode pad.   A semiconductor package using the circuit board according to claim 1.

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