JP2003179175A - Wiring board - Google Patents

Abstract

(57) Abstract: A breakage occurs in a low melting point brazing material for connecting a connection pad of a wiring board to an external electric circuit, and the reliability of connection of the semiconductor element to the external electric circuit is reduced. A square-shaped insulating base made of an electrically insulating material and having a semiconductor element mounting portion on a surface, and the insulating base 1
A wiring board 4 comprising: a large number of connection pads 6 formed on the lower surface of the substrate; and a plurality of wiring conductors 2 extending from the mounting portion of the insulating base 1 to the connection pads 6. An auxiliary pad 9 is formed at a corner portion of the lower surface, and the insulating base 1 of the auxiliary pad 9 is formed.
An arc-shaped notch is provided at the outer edge located on the diagonal line of.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring board used for a package for accommodating semiconductor elements, and more particularly, to stably and electrically connect each electrode of a mounted semiconductor element to a predetermined external electric circuit for a long period of time. The present invention relates to a wiring board that can be used.

[0002]

2. Description of the Related Art Conventionally, a wiring board on which a semiconductor element is mounted is made of an electrically insulating material such as a glass ceramic sintered body, and has an insulating base having a mounting portion on which the semiconductor element is mounted, and an insulating base. A plurality of wiring conductors made of, for example, a metal powder such as copper or silver, which is led out from the semiconductor element mounting portion or its periphery to the lower surface, and a plurality of wiring conductors formed on the lower surface of the insulating base and electrically connected to the wiring conductors. Each of the connection pads having a rectangular shape in a plane, and the semiconductor element is adhered and fixed to the mounting portion of the insulating substrate through an adhesive made of glass, resin, brazing material, and each electrode and wiring of the semiconductor element. The conductor is electrically connected via an electrical connecting means such as a bonding wire, and then the semiconductor element is hermetically sealed with a lid or a sealing resin if necessary. The body system.

In such a semiconductor device, on the external electric circuit board, the circuit wiring of the external electric circuit board and the connection pad on the lower surface of the insulating substrate face each other with a low melting point brazing material such as tin-lead solder interposed therebetween. Then, the low melting point brazing material is heated and melted at a temperature of about 200 ° C. to 300 ° C., and the circuit wiring of the external electric circuit board and the connection pad on the lower surface of the insulating substrate are joined to each other to form an external electric circuit. Each electrode of the semiconductor element mounted on the board and simultaneously mounted on the wiring board is electrically connected to the external electric circuit board through the wiring conductor and the low melting point brazing material.

[0004]

However, in the wiring board on which the conventional semiconductor element is mounted, the insulating substrate is made of a ceramic material such as a glass ceramic sintered body, and its thermal expansion coefficient is about 3 × 10. ^-6 / ℃ ~ 10 × 10
^The external electric circuit board is generally formed of a resin material such as glass epoxy resin, while its thermal expansion coefficient is 30 × 10 ^-6 / ° C to 50 × 10 ^-6 / ° C. Yes,
Because of the large difference, after connecting the connection pad of the wiring board and the circuit wiring of the external electric circuit board via the low melting point brazing material and mounting the semiconductor device on the external electric circuit board,
When the heat generated during the operation of the semiconductor element repeatedly acts on the insulating substrate of the wiring board and the external electric circuit board, a large thermal stress is repeatedly generated between them due to the difference in the thermal expansion coefficient between the two, and the thermal stress causes the connection pad There is a problem that the low melting point brazing material is ruptured near the interface between the low melting point brazing material and the low melting point brazing material, and the electrical connection between the semiconductor element and the external electric circuit is broken in a short period of time.

Therefore, in order to solve the above drawbacks, auxiliary pads are provided at the corners of the insulating substrate, and the auxiliary pads are connected to the dummy pads or the like provided on the external electric circuit board by bonding them with a low melting point brazing material. Means for removing the thermal stress acting between the pad and the low melting point brazing material, strengthening the bond between the connection pad and the low melting point brazing material, and improving the reliability of the electrical connection between the semiconductor element and the external electric circuit. Can be considered.

However, when the auxiliary pad is provided at the corner portion of the insulating substrate of the wiring board, immediately after the wiring board is mounted on the external electric circuit board, the auxiliary pad and the dummy pad provided on the external electric circuit board are provided. Can remove the thermal stress acting between the connection pad and the low melting point brazing material and effectively prevent the low melting point brazing material from breaking near the interface between the connection pad and the low melting point brazing material. Although it is possible, when thermal stress is repeatedly generated between the insulating substrate of the wiring board and the external electric circuit board, the auxiliary pad and the low melting point solder are located near the interface between the auxiliary pad and the low melting point brazing material, especially in the diagonal direction of the insulating substrate. It is impossible to remove the thermal stress acting between the connection pad and the low melting point brazing material due to breakage of the low melting point brazing material near the interface with the material. External The thermal stress generated between the air circuit board and the low melting point brazing material breaks near the interface between the connection pad and the low melting point brazing material, increasing the reliability of the electrical connection between the semiconductor element and the external electric circuit. It has the drawback that it cannot be maintained for a period of time.

Particularly, in recent years, the miniaturization of wiring boards has become remarkable,
In addition, the number of connection pads has increased in response to the increase in the number of electrodes of semiconductor elements and the like, and the density of the connection pads has been increasing to be formed on the lower surface of the edge substrate. Therefore, it is becoming more difficult to improve the connection reliability between the wiring board and the external electric circuit board.

[0008]

A wiring board of the present invention is made of an electrically insulating material and has a rectangular insulating base having a semiconductor element mounting portion on its surface, and a large number of connection pads formed on the lower surface of the insulating base. And a plurality of wiring conductors led out from the mounting portion of the insulating base to the connection pad, wherein an auxiliary pad is formed at a corner portion of the lower surface of the insulating base, and It is characterized in that an arcuate cutout portion is provided at an outer edge portion located on a diagonal line of the insulating base.

According to the wiring board of the present invention, the auxiliary pad is formed at the corner portion of the lower surface of the insulating base, and the outer edge portion of the auxiliary pad located on the diagonal of the lower surface of the insulating base is provided with an arcuate notch. Since the auxiliary pad is bonded to the dummy pad or the like provided on the external electric circuit board via the low melting point brazing material, the thermal stress acting between the connection pad and the low melting point brazing material can be removed. You can
At the same time, at the interface between the auxiliary pad and the low melting point brazing material, the thermal stress caused by the difference in thermal expansion coefficient between the insulating base of the wiring board and the external electric circuit board acting in the diagonal direction of the insulating base is the arc-shaped cutout portion of the auxiliary pad. It is not possible to break the low melting point brazing material dispersed near the interface between the auxiliary pad and the low melting point brazing material, especially near the interface between the auxiliary pad and the low melting point brazing material in the diagonal direction of the insulating substrate, and thereby the connection is made. The bond between the pad and the low melting point brazing material can be maintained for a long period of time, and the reliability of the electrical connection between the semiconductor element and the external electric circuit can be made extremely excellent.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described in detail with reference to the accompanying drawings. 1 is a cross-sectional view showing an embodiment of a package for housing a semiconductor device using a wiring board of the present invention, FIG. 2 is a bottom view thereof, and FIG. 3 is an enlarged plan view of a main part,
Reference numeral 1 is an insulating substrate, and 2 is a wiring conductor. The insulating substrate 1 and the wiring conductor 2 constitute a wiring board 4 on which the semiconductor element 3 is mounted.

The insulating substrate 1 is made of an electrically insulating material such as a glass ceramic sintered body, an aluminum oxide sintered body, an aluminum nitride sintered body, a mullite sintered body or a silicon carbide sintered body. The upper surface thereof has a concave portion 1a in which the semiconductor element 3 is mounted and accommodated, and the semiconductor element 3 is bonded and fixed to the bottom surface of the concave portion 1a via an adhesive material such as glass, resin, or brazing material.

When the insulating substrate 1 is made of, for example, an aluminum oxide sintered body, a powdery raw material such as aluminum oxide, silicon oxide, calcium oxide, magnesium oxide, etc. is mixed with an appropriate organic binder and a solvent, and mixed in a slurry form. A sheet-shaped ceramic green sheet (ceramic green sheet) is obtained by using a sheet forming technique such as a doctor blade method or a calendar roll method which is conventionally well-known as well as forming the ceramic slurry.
It is manufactured by forming the ceramic green sheets into an appropriate shape by cutting or punching, stacking a plurality of these, and finally firing the stacked ceramic green sheets at a temperature of about 1600 ° C. in a reducing atmosphere. It

A large number of wiring conductors 2 are formed on the insulating substrate 1 from the periphery of the concave portion 1a to the lower surface through the side surface. The electrodes of the semiconductor element 3 are formed in the peripheral portion of the concave portion 1a of the wiring conductor 2. Are electrically connected via bonding wires 5, and a plurality of connection pads 6 each having a rectangular shape in plan view are formed at a portion led out to the lower surface of the insulating substrate 1 so as to be electrically connected to the wiring conductor 2.

The wiring conductor 2 and the connection pad 6 have a function of connecting the electrode of the semiconductor element 3 to an external electric circuit, and are made of a refractory metal such as tungsten, molybdenum, or manganese, and a refractory metal powder such as tungsten. An organic solvent and a metal paste obtained by adding and mixing a solvent are applied to a ceramic green sheet to be the insulating substrate 1 in advance in a predetermined pattern by a screen printing method which is well known in the prior art. To the lower surface.

Further, the connection pads 6 act as external terminals for mounting the wiring board 4 on the external electric circuit board, and the circuit wiring 8a of the external electric circuit board 8 through the low melting point brazing material 7.
, So that the electrode of the semiconductor element 3 is electrically connected to the circuit wiring 8a of the external electric circuit board 8.

Further, as shown in FIGS. 2 and 3, the insulating base 1 is provided with auxiliary pads 9 each having a rectangular shape in a plan view at each corner of the lower surface thereof, and the insulating base 1 of the auxiliary pads 9 is formed. An arcuate cutout 9a is formed in the outer edge portion located on the diagonal line.

The auxiliary pad 9 serves as an external electric circuit board 8.
Is bonded to a dummy pad or the like provided on the substrate via the low melting point brazing filler metal 7, and thermal stress generated between the insulating substrate 1 and the external electric circuit board 8 acts on the interface between the connection pad 6 and the low melting point brazing filler metal 7. This prevents the connection pad 6 and the circuit wiring 8a of the external electric circuit board 8 from being bonded to each other via the low melting point brazing material 7.

The auxiliary pad 9 is, for example, tungsten,
A metal paste made of a high melting point metal such as molybdenum or manganese, obtained by the same method as that of the wiring conductor 2 or the connection pad 6 described above, specifically, a high melting point metal powder such as tungsten by adding and mixing an organic solvent or a solvent. Is preliminarily printed and applied in a predetermined pattern on the ceramic green sheet to be the insulating substrate 1 by a conventionally known screen printing method, whereby the insulating substrate 1 is adhered to each corner portion.

The auxiliary pad 9 has an arcuate notch 9a formed on the outer edge of the insulating base 1 located on a diagonal line. The notch 9a is an interface between the auxiliary pad 9 and the low melting point brazing material 7. The thermal stress resulting from the difference in thermal expansion coefficient between the insulating base 1 and the external electric circuit board 8 acting in the diagonal direction of the insulating base 1 is dispersed and effectively prevents the thermal stress from being concentrated at one point. No breakage occurs near the interface between the auxiliary pad 9 and the low melting point brazing material 7, and particularly near the interface between the auxiliary pad 9 and the low melting point brazing material 7 in the diagonal direction of the insulating substrate 1, and the connection pad 6 and the low melting point brazing material 7 are not broken. The bonding with the material 7 can be maintained for a long period of time, and the semiconductor element 3
It is possible to make the reliability of the electrical connection between the electric circuit and the external electric circuit extremely excellent.

If the radius of the arcuate notch 9a formed in the auxiliary pad 9 is less than 100 μm, it becomes difficult to effectively disperse the thermal stress, and 400 μm.
If it exceeds, the bonding area between the auxiliary pad 9 and the low melting point brazing material 7 becomes small, so that the bonding strength between the auxiliary pad 9 and the low melting point brazing material 7 tends to decrease. Therefore, it is preferable that the arc-shaped notch 9a formed in the auxiliary pad 9 has a radius of 100 μm to 400 μm.

As shown in FIG. 4, in the auxiliary pad 9, if both ends of the arcuate notch 9a are further rounded, the both ends of the arcuate notch 9a are formed. , The auxiliary pad 9 and the low melting point brazing material 7 are prevented from being concentrated and acting on the auxiliary pad 9, and the auxiliary melting point brazing material 7 and the low melting point brazing material 7 are more firmly joined to each other to form an external electric circuit board of the wiring board 4. It is possible to further improve the reliability of the connection to the device 8. Therefore, it is preferable that both ends of the arc-shaped notch 9a of the auxiliary pad 9 be formed in a shape that is further rounded.

Thus, according to the wiring board of the present invention, the semiconductor element 3 is provided on the bottom surface of the concave portion 1a of the insulating substrate 1 with glass or resin,
The electrodes of the semiconductor element 3 are electrically connected to the wiring conductors 2 via the bonding wires 5 while being fixedly adhered via an adhesive such as a brazing material, and then the upper surface of the insulating substrate 1 is made of metal or ceramics. The lid 10 made of glass is bonded through a sealing material such as a resin or a brazing material, and the semiconductor element 3 is hermetically sealed inside the container made of the insulating base 1 and the lid 10. The device is completed.

The wiring board of the present invention is not limited to the above-mentioned embodiment, and various modifications can be made without departing from the gist of the present invention. For example, the wiring conductor 2, If nickel or copper is sequentially deposited on the exposed regions of the connection pad 6 and the auxiliary pad 9 in a thickness of 1 μm to 10 μm and gold is 0.05 μm to 5 μm, the wiring conductor 2, the connection pad 6, and the auxiliary pad are formed. The oxidative corrosion of 9 can be effectively prevented, and the low melting point brazing material 7 can be firmly joined to the connection pad 6 and the auxiliary pad 9 and the bonding wire 5 can be firmly connected to the wiring conductor 2.

[0024]

According to the wiring board of the present invention, the auxiliary pads are formed on the corners of the lower surface of the insulating base, and the outer edges of the auxiliary pads located on the diagonal of the lower surface of the insulating base are arcuately cut. Since the notch is provided, the auxiliary pad is joined to the dummy pad or the like provided on the external electric circuit board through the low melting point brazing material to remove the thermal stress acting between the connection pad and the low melting point brazing material. At the same time, at the interface between the auxiliary pad and the low melting point brazing material, the thermal stress caused by the difference in thermal expansion coefficient between the insulating base of the wiring board and the external electric circuit board acting in the diagonal direction of the insulating base is the arc shape of the auxiliary pad. No fracture occurs in the low melting point brazing material dispersed near the interface between the auxiliary pad and the low melting point brazing material, especially near the interface between the auxiliary pad and the low melting point brazing material in the diagonal direction of the insulating substrate. Ku, whereby it is possible to maintain the bonding between the connection pad and the low melting brazing material over a long period of time, it is out forming a very good thing the reliability of the electrical connection between the semiconductor element and the external electric circuit.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a wiring board of the present invention.

FIG. 2 is a bottom view of the wiring board shown in FIG.

3 is an enlarged plan view of an essential part of the wiring board shown in FIGS. 1 and 2. FIG.

FIG. 4 is an enlarged plan view of an essential part of another embodiment of the wiring board according to the present invention.

[Explanation of symbols]

1 ... Insulating substrate 1a ... recess 2 ... Wiring conductor 3 ... Semiconductor element 4 ... Wiring board 5 ... Bonding wire 6 ... Connection pad 7 ... Low melting point brazing material 8 ... External electric circuit board 8a ... Circuit wiring 9 ... Auxiliary pad 9a ... notch 10 ... Lid

Claims (2)

[Claims] 1. A rectangular insulating base made of an electrically insulating material and having a semiconductor element mounting portion on its surface, a large number of connection pads formed on the lower surface of the insulating base, and the mounting portion of the insulating base to the insulating pad. A wiring board comprising a plurality of wiring conductors led out to a connection pad, wherein an auxiliary pad is formed at a corner portion of the lower surface of the insulating base, and an outer edge portion of the auxiliary pad located on a diagonal line of the insulating base. A wiring board, characterized in that an arcuate notch is provided in the. 2. The notch has a radius of 100 μm to 4
The wiring board according to claim 1, wherein the wiring board has an arc shape of 00 μm.