JP2005191041A - Wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wiring board in which an electrode pad can be electrically connected certainly to the terminal pad of an external electrical circuit substrate for a long period of time through a conductor bump, and the connection can be assured particularly even if the stress due to the difference of the thermal expansion coefficients of an insulating substrate and the external electrical circuit substrate become large and which has high electric connection reliability to the external electrical circuit substrate. <P>SOLUTION: The wiring board 9 includes a rectangular plate-like insulating substrate 1 made of ceramics in which a wiring conductor 2 is formed in the interior, a plurality of electrode pads 3 arranged laterally and longitudinally and formed so that the entirety becomes the rectangular shape arraying pattern on the main surface of the insulating substrate 1, and a through conductor 4 formed from each electrode pad to the interior of the insulating substrate 1. The electrode pads formed at the corners of the rectangular shape arraying pattern of the plurality of the electrode pads 3 are formed more in the number of the through conductors 4 than the others. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a wiring board in which an electrode pad is disposed on a main surface of an insulating base and the electrode pad is connected to an external electric circuit board via a conductor bump, and in particular, connection of the electrode pad to the external electric circuit board. The present invention relates to a wiring board with good reliability.

  A wiring board on which electronic components such as a semiconductor element, a capacitive element, and a piezoelectric vibrator are mounted is generally composed of an aluminum oxide sintered body and the like, and a rectangular plate-like insulating base in which a wiring conductor is formed. The structure has a plurality of electrode pads arranged vertically and horizontally so as to form a square array pattern on one main surface of the substrate, and through conductors formed from the electrode pads to the inside of the insulating substrate. The through conductor is electrically connected to the wiring conductor, and the electrode pad and the wiring conductor are electrically connected through the through conductor.

  And while mounting an electronic component on the main surface (the other main surface) opposite to the main surface on which the electrode pad of the insulating substrate is formed, the electrode of the electronic component is connected to the wiring conductor via solder or a bonding wire, The electronic device is completed by sealing the electronic component with a resin or a cap as necessary.

  Thereafter, the electronic device is mounted on the external electric circuit board by connecting a large number of electrode pads arranged on the main surface of the insulating base to the circuit wiring of the corresponding external electric circuit board via conductor bumps.

When bonding the electrode pads of the wiring board and the terminal pads of the external electric circuit board, an adhesion aid such as flux is usually used to improve the wettability of the conductor bumps to the electrode pads.
Japanese Patent Laid-Open No. 10-92965

  However, such a wiring board is caused by thermal stress caused by the difference in thermal expansion coefficient between the insulating base and the external electric circuit board, stress due to shrinkage of the sealing resin when electronic components are sealed with resin, and the like. The electrode pads are easily peeled off from the insulating substrate, and the connection reliability between the electrode pads and the external electric circuit board may be reduced when the electrode pads of the wiring board are connected to the circuit wiring of the external electric circuit board via conductor bumps. There was a problem that there was.

  Such stress usually acts largely in the diagonal direction of the main surface of the insulating base, and acts most greatly at each corner. For this reason, the peeling of the electrode pad is particularly noticeable in the electrode pads formed in the square array pattern, which are formed at the corners where the stress acts most.

  In particular, in recent years, it is necessary to reduce the electrode pad in accordance with the miniaturization of the wiring board and the increase in the number of electrode pads, and the area of the bonding of the electrode pad to the insulating base is reduced, so that the electrode pad is not peeled The occurrence tends to increase, and securing such connection reliability has become an important issue.

  The present invention has been completed in view of the above-mentioned problems of the prior art. The purpose of the present invention is to firmly bond an electrode pad to an insulating base, and attach a conductor bump to a circuit wiring of an external electric circuit board. It is possible to ensure electrical connection over a long period of time, and it is possible to ensure the connection even when the stress due to the difference in thermal expansion coefficient between the insulating base and the external electric circuit board increases. Another object of the present invention is to provide a wiring board having high electrical connection reliability with respect to an external electric circuit board.

  A wiring board according to the present invention includes a rectangular plate-like insulating base made of ceramics having wiring conductors formed therein, and a plurality of elements arranged vertically and horizontally so as to form a square-shaped array pattern on the main surface of the insulating base. Electrode pads and through conductors formed from each electrode pad to the inside of the insulating base, and the plurality of electrode pads formed at each corner of the square array pattern are The number of the through conductors is larger than the other ones.

  In the wiring board of the present invention, preferably, the electrode pads at each corner of the square array pattern are formed with two through conductors arranged along the diagonal of the main surface of the insulating base. It is characterized by this.

  According to the wiring board of the present invention, the number of through conductors formed in each corner of the square array pattern among the plurality of electrode pads is larger than the others, so that the anchor effect by the through conductors Even if stress such as thermal stress generated due to the difference in thermal expansion coefficient between the insulating base of the wiring board and the external electric circuit board acts on the electrode pad, the electrode pad and the insulating base have a high bonding strength. Can be prevented from peeling off from the insulating substrate. Therefore, the electrode pads formed on the main surface of the insulating base can be reliably electrically connected to the circuit wiring of the external electric circuit board through the conductor bumps over a long period of time, and high electrical connection reliability can be achieved. It can be set as the wiring board which has.

  According to the wiring board of the present invention, it is preferable that the electrode pad at each corner of the rectangular array pattern is formed with two through conductors arranged along the diagonal line of the main surface of the insulating base. Therefore, since the two through conductors are arranged along the direction in which the stress acts, the anchor effect becomes stronger, the bonding strength between the electrode pad and the insulating base is further increased, and the electrode pad is more easily peeled off. A wiring board that is effectively prevented and has excellent connection reliability can be obtained.

  The wiring board of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1A is a plan view showing an example of the embodiment of the wiring board of the present invention, and FIG. 1B is a cross-sectional view showing an example of the embodiment of the wiring board of the present invention. In these drawings, 1 is an insulating substrate, 2 is a wiring conductor, 3 is an electrode pad, and 4 is a through conductor. A wiring substrate 9 is mainly constituted by the insulating base 1, the wiring conductor 2, the electrode pad 3, and the through conductor 4.

  The insulating substrate 1 is made of ceramics such as an aluminum oxide sintered body, an aluminum nitride sintered body, a mullite sintered body, a silicon nitride sintered body, a silicon carbide sintered body, and a glass ceramic sintered body. When the insulating substrate 1 is made of, for example, an aluminum oxide sintered body, an appropriate organic binder and solvent are added to and mixed with ceramic raw material powders such as aluminum oxide, silicon oxide, magnesium oxide, and calcium oxide to form a slurry. A plurality of ceramic green sheets are obtained by adopting a doctor blade method to form a sheet, and then the ceramic green sheets are formed into an appropriate shape by cutting or punching, and a plurality of them are laminated, Finally, the laminated ceramic green sheets are manufactured by firing at a temperature of about 1600 ° C. in a reducing atmosphere.

  The insulating base 1 functions as a base for mounting and supporting electronic components such as semiconductor elements, capacitive elements, and piezoelectric vibrators, and usually has one main surface on which electrode pads 3 are formed as will be described later (FIG. 1). In this example, an electronic component is mounted on the other main surface (upper surface in the example of FIG. 1) opposite to the lower surface.

  A wiring conductor 2 is formed inside the insulating base 1. The wiring conductor 2 is electrically connected to the electrode pad 3 formed on one main surface of the insulating base 1 through the through conductor 4.

  Then, the wiring conductor 2 is led out to the other main surface of the insulating base 1, and the electrode of the electronic component is electrically connected to the lead-out exposed portion so that the electrode of the electronic component mounted on the insulating base 1 is connected to the wiring conductor 2. In addition, the electrode pad 3 is electrically connected through the through conductor 4.

  Such a wiring conductor 2 is formed of a metallized conductor such as tungsten, molybdenum, copper, or silver. The wiring conductor 2 is formed, for example, by printing and applying a metal paste such as tungsten, molybdenum, copper, or silver on the surface of a ceramic green sheet that becomes the insulating substrate 1.

  On one main surface (the lower surface in the example of FIG. 1B) of the insulating base 1, a plurality of electrode pads 3 are arranged vertically and horizontally so as to form a square array pattern. A through conductor 4 is formed from each electrode pad 3 to the inside of the insulating substrate 1. The through conductor 4 has a function of electrically connecting the electrode pad 3 and the wiring conductor 2, and is in contact with and electrically connected to the wiring conductor 2 at its upper end or the like.

  The electrode pad 3 functions as a pad for external connection of the wiring board 9, and this electrode pad 3 is bonded to, for example, circuit wiring (not shown) of the external electric circuit board via a conductor bump (not shown). Thus, the wiring board 9 is electrically and mechanically connected to the external electric circuit board, and the electronic component is electrically connected to the external electric circuit.

  The electrode pad 3 and the through conductor 4 are usually made of the same metallized metal as that of the wiring conductor 2. For example, a through hole is previously formed in a portion of the ceramic green sheet to be the insulating base 1 where the electrode pad is formed. In addition, a metal paste similar to that of the wiring conductor 2 is printed and applied in a predetermined pattern on the surface and through-holes of the ceramic green sheet by a well-known screen printing method and filled.

  The electrode pads 3 are arranged vertically and horizontally so as to form a rectangular array pattern over almost the entire main surface of the insulating base 1 in order to cope with the downsizing and high density of the wiring board 9. In addition, electrode pads 3 a are also formed at each corner of the square array pattern on the main surface of the insulating substrate 1.

  In the wiring board 9 of the present invention, the electrode pads 3 a formed at the corners of the square array pattern of the electrode pads 3 are formed with more through conductors 4 than the other electrode pads 3. Thereby, due to the anchor effect by the through conductor 4, the bonding strength between the electrode pad 3a and the insulating base 1 is increased, and the difference in thermal expansion coefficient between the insulating base 1 of the wiring board 9 and the external electric circuit board (not shown). Even if stress such as thermal stress generated by the above acts on the electrode pads 3, 3 a, it is possible to effectively prevent the electrode pads 3, 3 a from peeling off from the insulating substrate 1. Therefore, the electrode pads 3 and 3a formed on the main surface of the insulating base 1 are reliably electrically connected over a long period to the circuit wiring (not shown) of the external electric circuit board via the conductor bumps (not shown). Therefore, the wiring board 9 having high electrical connection reliability can be obtained.

  When the number of through conductors 4 in each corner electrode pad 3a is made larger than the number of through conductors 4 in other electrode pads 3, the electrical connection between the other electrode pads 3 and the wiring conductor 2 is reduced. When one through conductor 4 can be secured, the number of through conductors 4 connected to the other electrode pads 3 is one, and the number of through conductors 4 connected to the electrode pads 3a at each corner is two or more. It is preferable to use four.

  When five or more through conductors 4 are formed in the electrode pads 3a at each corner, the bonding area of the electrode pads 3a to the insulating substrate 1 itself becomes small, so that the bonding strength of the electrode pads 3a to the insulating substrate 1 is instead. And the connection reliability of the wiring board 9 to the external electric circuit board may be reduced.

  In addition, it is preferable that the electrode pads 3 and 3a and the penetration conductor 4 are shapes without a corner | angular part, such as circular shape or ellipse shape by planar view. If there is a corner, stress such as thermal stress due to the difference in thermal expansion coefficient between the through conductor 4 and the insulating base 1 is concentrated on the corner, and the through conductor 4, the insulating base 1, or the through passes from the corner. Mechanical damage such as cracks is likely to occur at the bonding interface between the conductor 4 and the insulating base 1, and long-term reliability such as external connection of the wiring board 9 may be deteriorated.

  When the electrode pads 3 and 3a and the through conductors 4 are circular or elliptical in plan view, the diameter, the major axis, and the length of the minor axis depend on the size of the wiring board 9 and the outside of the electrode pads 3 and 3a. In order to ensure the reliability of the connection to the electric circuit board, the reliability of the electrical connection through the through conductor 4 between the electrode pads 3 and 3a and the wiring conductor 2, etc., it is formed in the range of 200 to 1000 μm, for example. Is good.

  In the present invention, it is preferable that the electrode pads 3a at each corner of the square array pattern are formed with two through conductors 4 arranged along the diagonal of the main surface of the insulating substrate 1. With this configuration, since the two through conductors 4 are arranged along the direction in which the stress such as thermal stress acts, the influence of the anchor effect becomes stronger, and the bonding strength between the electrode pad 3a and the insulating substrate 1 becomes higher. It is possible to more effectively prevent peeling, breakage, deterioration of connectivity, and the like due to stress such as thermal stress generated by the difference in thermal expansion coefficient between the insulating base 1 of the wiring board 9 and the external electric circuit board.

  Therefore, the electrode pad 3 formed on the main surface of the insulating base 1 can be reliably electrically connected to the terminal pad of the external electric circuit board through the conductor bump for a long period of time, and high electrical connection reliability. A wiring board 9 having

  When the two through conductors 4 are arranged along the diagonal line of the main surface of the insulating base 1 with respect to the electrode pad 3a at each corner, the long axis of the cross-sectional shape of the through conductor 4 is positioned in the direction along the diagonal line. In this case, since the area of the junction between the through conductor 4 and the electrode pad 3a in the direction in which the stress acts increases, the anchor effect can be obtained more effectively, and the reliability of the external connection Can be further improved.

  However, when two cross-sectional shapes of the through conductors 4 formed on the electrode pads 3a at each corner are formed in an elliptical shape, two elliptical ones are connected in the longitudinal direction, and the electrode pad 3a has a diameter. If the electrode pad 3a is crossed in the direction or the like, the electrode pad 3a appears to be divided by the through conductor 4, so that the bonding strength of the electrode pad 3a to the insulating substrate 1 may be reduced. Therefore, when the two through conductors 4 are formed on the electrode pads 3a at the corners along the diagonal line of the main surface of the insulating base 1, the distance between the through conductors 4 and the through conductors 4 and the electrode pads 3a. It is preferable that the space | interval between the outer periphery of this is 20 micrometers or more.

  Further, when the two through conductors 4 are arranged along the diagonal lines in the electrode pads 3a at the respective corners, the through conductors 4 positioned on the outer side where a larger thermal stress acts on each electrode pad 3a, It is preferable to have a larger shape (cross-sectional shape) in plan view than the through conductor 4 located inside.

  The electrode pads 3 and 3a and the wiring conductor 2 are preferably coated with a plating layer such as nickel or gold on the exposed surfaces. For example, if a nickel plating layer having a thickness of about 1 to 10 μm and a gold plating layer having a thickness of about 0.05 to 2 μm are sequentially deposited, the oxidative corrosion of the electrode pads 3 and 3a and the wiring conductor 2 is caused. Can be effectively prevented, and the wettability of the conductor bumps with respect to the electrode pads 3 and 3a can be improved.

  In this case, the plating layer to be applied to the electrode pads 3 and 3a and the plating layer to be applied to the wiring conductor 2 do not have to have the same layer configuration and the same thickness, depending on the purpose of use of each part, The layer configuration and thickness may be changed. For example, a thin gold plating layer is applied to the electrode pads 3 and 3a to prevent the formation of a large amount of brittle intermetallic compounds between the conductive bump component and the gold component, and the reliability of external connection May be made even more excellent.

  Note that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

(A), (b) is the top view and sectional drawing which show an example of embodiment of the wiring board of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Insulation base | substrate 2 ... Wiring conductor 3 ... Electrode pad 3a ... Electrode pad formed in each corner of arrangement pattern 4 ... Penetration conductor 9 ... Wiring board

Claims (2)

A rectangular plate-like insulating base made of ceramics with wiring conductors formed therein, a plurality of electrode pads arranged vertically and horizontally so as to form a square-shaped array pattern on the main surface of the insulating base; A through conductor formed from each electrode pad to the inside of the insulating substrate, and the plurality of electrode pads formed at each corner of the square array pattern than the others A wiring board having a large number of through conductors. The electrode pad at each corner of the square array pattern is formed with two through conductors arranged along a diagonal of the main surface of the insulating base. Wiring board.

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