JP2001127418A - Wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem such that a disconnection takes place with a low melting-point solder which connects the connection pad of a wiring board to an external electrical circuit and a connection reliability of a semiconductor device with an external electrical circuit drops. SOLUTION: An insulating base body 1, which made from an electrically insulating material, comprises an semiconductor device mounting part 1a on its surface, multiple connection pads 6 formed on the lower surface of the insulating substrate 1, and a plurality of wiring conductors 2 led from the mounting part 1a of the insulating substrate 1 to the connection pad 6, are provided. Here, the connection pad 6 comprises a first region 6a which is almost circular, and a second region 6c, which is almost annular, formed outside the first region 6a, with an gap part 6b of a constant width and is lower than the first region 6a.

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 a semiconductor element, and more particularly, to stably electrically connect each electrode of a mounted semiconductor element to a predetermined external electric circuit for a long 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, for example, an electrically insulating material such as alumina ceramics. A plurality of wiring conductors formed of a high melting point metal powder such as tungsten or molybdenum, which are led out from the 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 conductor. And connection pads, and the semiconductor element is mounted on the mounting portion of the insulating base by glass, resin, or the like.
The electrodes of the semiconductor element and the wiring conductors are electrically connected via an electrical connection means such as a bonding wire, and then are fixed by an adhesive made of a brazing material or the like. A semiconductor device is obtained by hermetically sealing the element with a lid or a sealing resin.

In such a semiconductor device, on an external electric circuit board, circuit wiring of the external electric circuit board and connection pads on the lower surface of the insulating base face each other with a low melting point brazing material such as tin-lead solder interposed therebetween. After that, 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 pads on the lower surface of the insulating base are joined 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 via the wiring conductor and the low melting point brazing material.

[0004]

However, in the wiring board on which the above-mentioned conventional semiconductor element is mounted, the insulating substrate is formed of a ceramic material such as an aluminum oxide sintered body and has a thermal expansion coefficient of about 4 ×. 10 ^-6 / ° C to 10 x 1
In contrast to 0 ^-6 / ° C, the external electric circuit board is generally formed of a resin material such as a glass epoxy resin, and has a coefficient of thermal expansion of 30 × 10 ^-6 / ° C to 50 × 10 ^-6 / ° C. Since the semiconductor device is mounted on the external electric circuit board and the heat generated during the operation of the semiconductor element repeatedly acts on the insulating base of the wiring board and the external electric circuit board after mounting the semiconductor device on the external electric circuit board, there is a large difference between the two. A large thermal stress is repeatedly generated due to the difference in thermal expansion coefficient, and a crack is generated from an end near an interface between the connection pad and the connection pad of the low melting point brazing material joining the external electric circuit board due to the repeated thermal stress. As a result, there is a problem that the low melting point brazing material eventually breaks and the electrical connection between the semiconductor element and the external electric circuit is broken in a short period of time.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in a conventional wiring board, and an object thereof is to provide a low melting point brazing material for joining a connection pad of an insulating base to a circuit wiring of an external electric circuit board. Effectively preventing breakage, ensuring that each electrode of the semiconductor element is connected to an external electric circuit for a long time,
It is an object of the present invention to provide a wiring board which can be firmly connected with electric and has excellent long-term reliability.

[0006]

A wiring board according to the present invention is made of an electrically insulating material, and has an insulating substrate having a semiconductor element mounting portion on a surface thereof, a plurality of connection pads formed on a lower surface of the insulating substrate, and A wiring board comprising a plurality of wiring conductors led from the mounting portion of the insulating base to the connection pads, wherein each of the connection pads is substantially circular in a first region and is fixed outside the first region. And a substantially annular second region formed with a gap having a width of.

Further, in the wiring board according to the present invention, a difference in height between the first region and the second region is 10 μm or more.

In the wiring board according to the present invention, the radius of the first region is 60% to 82% of the radius of the connection pad.

Further, in the wiring board according to the present invention, the width of the gap is 5% to 35% of the radius of the connection pad.

[0010] According to the wiring board of the present invention, the connection pad is formed in a substantially circular first region, and is formed outside the first region with a constant width gap therebetween. The connection pad is joined to the circuit wiring of the external electric circuit board via the low melting point brazing material, and the insulating base of the wiring board and the external electric circuit are joined to the low melting point brazing material. When the thermal stress caused by the difference in the thermal expansion coefficient of the substrate repeatedly acts, a crack is generated by the thermal stress near the outer peripheral end of the low melting point brazing material, that is, near the joining interface with the outer peripheral end of the second region of the connection pad. The crack is prevented from progressing at the gap between the first region and the second region and at the side wall of the first region, and as a result, the low melting point brazing material is hardly broken, so that the connection pad and the external electric wire are hardly broken. Secure and strong circuit wiring on the circuit board It is possible to form excellent in long-term reliability of the connection to an external electric circuit of the semiconductor device it is possible to electrically connect to.

Further, according to the wiring board of the present invention, since the height of the second region of the connection pad is made lower than the height of the first region, the crack generated at the outer peripheral end of the low melting point brazing material is propagated. Is effectively prevented by hitting the side wall of the first region, and as a result, the risk of breakage of the low melting point brazing material can be further reduced, and the connection of the semiconductor element to the external electric circuit can be maintained for a long time. It can be made to be extremely excellent in properties.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional view showing one embodiment of a package for housing a semiconductor element using a wiring board of the present invention, wherein 1 is an insulating base, 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 an aluminum oxide sintered body, an aluminum nitride sintered body, a mullite sintered body, a silicon carbide sintered body, a glass ceramic sintered body, etc. 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 such as glass, resin, or brazing material.

When the insulating substrate 1 is made of, for example, an aluminum oxide sintered body, a suitable organic binder and a solvent are added to a raw material powder of aluminum oxide, silicon oxide, calcium oxide, magnesium oxide or the like, and the mixture is mixed to form a slurry. The ceramic slurry is formed into a ceramic green sheet (green ceramic sheet) by using a sheet forming technique such as a doctor blade method or a calender roll method, which is well known in the art.
The ceramic green sheet is manufactured by cutting and punching into an appropriate shape, laminating a plurality of the sheets, and finally firing the laminated ceramic green sheet at a temperature of about 1600 ° C. in a reducing atmosphere. You.

The insulating base 1 has a large number of wiring conductors 2 attached to the periphery of the recess 1a from the periphery to the lower surface thereof.
Are electrically connected via bonding wires 5, and a plurality of connection pads 6 electrically connected to the wiring conductor 2 are formed at portions led out on the lower surface of the insulating base 1.

The wiring conductor 2 and the connection pad 6 serve to connect the electrodes of the semiconductor element 3 to an external electric circuit, and are made of a high melting point metal powder such as tungsten, molybdenum, manganese or the like. A metal paste obtained by adding and mixing an appropriate organic binder and a solvent to the powder is preliminarily printed and applied in a predetermined pattern on a ceramic green sheet serving as the insulating substrate 1 by a well-known screen printing method. It is formed from the periphery of the concave portion 1a to the lower surface.

The connection pad 6 functions as an external terminal for mounting the wiring board 4 on an external electric circuit board, and the circuit wiring 8a of the external electric circuit board 8 via the low melting point brazing material 7.
Thus, the electrode of the semiconductor element 3 is electrically connected to the circuit wiring 8 a of the external electric circuit board 8.

As shown in FIGS. 2 and 3, the connection pad 6 is formed with a substantially circular first region 6a and a gap 6b having a constant width outside the first region. The first region 6a is formed by a substantially annular second region 6c lower than the first region. The first region 6a is used to reliably electrically connect the wiring conductor 2 to the circuit wiring 8a of the external electric circuit board 8. And the second region functions to further improve the bonding strength.

The connection pad 6 has a substantially circular first region 6.
a, and a substantially annular second region 6c lower than the first region, which is formed outside the first region 6a with a gap 6b having a constant width therebetween. After bonding to the circuit wiring 8a of the external electric circuit board 8 via the low melting point brazing material 7, the heat generated due to the difference in the thermal expansion coefficient between the insulating base 1 of the wiring board 4 and the external electric circuit board 8 is applied to the low melting point brazing material. When the stress is repeatedly applied, a crack is generated due to the thermal stress near the outer peripheral end of the low melting point brazing material 7, that is, near the joint interface with the outer peripheral end of the second region 6c of the connection pad 6, but the crack progresses in the first direction. Gap 6 between region 6a and second region 6c
b and the side walls 6d of the first region 6a are effectively prevented, and as a result, the low melting point brazing material 7 hardly breaks, so that the connection pads 6 and the circuit wirings 8a of the external electric circuit board 8 are reliably formed. In addition, it is possible to make a strong electrical connection and to connect the semiconductor element 3 to an external electric circuit with excellent long-term reliability.

The height of the second region 6c is equal to that of the first region 6c.
a, the progress of the cracks generated at the outer peripheral end of the low melting point brazing material 7 is effectively prevented by hitting the side wall of the first region 6a. The risk of breakage can be further reduced, and the connection of the semiconductor element to an external electric circuit can be made extremely excellent in long-term reliability.

When the difference in height between the first region 6a and the second region 6c is less than 10 μm, the propagation of cracks generated at the outer peripheral end of the low melting point brazing material 7 is effective on the side wall of the first region 6a. Therefore, there is a risk that the low melting point brazing material 7 may be broken. Therefore, it is preferable that the difference between the heights of the first region 6a and the second region 6c is 10 μm or more, more preferably, about 20 μm.

When the radius of the first region 6a is less than 60% of the radius of the entire connection pad 6, the second region 6a is formed.
c and the width of the gap portion 6b are widened and the crack is greatly advanced, and the bonding area with the low melting point brazing material 7 is narrow, so that the long-term bonding reliability of the low melting point brazing material 7 to the connection pad 6 And when it exceeds 82%, the widths of the second region 6c and the gap 6c of the connection pad 6 become extremely narrow, and the risk of preventing the progress of cracks from being effectively prevented. There is.

Therefore, it is preferable that the radius of the first region 6a is set in a range of 60% to 82% of the entire radius of the connection pad 6.

Further, if the width of the gap 6b is reduced to less than 5% of the entire radius of the connection pad 6, it tends to be difficult to effectively prevent the progress of cracks, and 35%.
And the bonding area between the low melting point brazing material 7 and the first region 6a and the second region 6c of the connection pad 6 is reduced, and the bonding strength of the low melting point brazing material 7 to the connection pad 6 is low. There is a danger of becoming. Accordingly, the gap 6b has a width of 5% to 5% of the entire radius of the connection pad 6.
It is preferable to set the range to 35%.

Furthermore, when the connection pad 6 has the first region 6a circular and the gap 6b and the second region 6c annular, and the concentric circles respectively, the thermal stress does not concentrate on a specific portion, and As a result, the occurrence of cracks due to the concentration of thermal stress is effectively prevented, and the reliability of bonding can be further improved. Therefore, it is preferable that the connection pad 6 is formed so that the first region 6a is circular and the gap 6b and the second region 6c are annular, and concentric.

Further, the side wall 6d of the first region 6a and the side wall 6e of the second region 6c opposing each other with the gap 6b interposed therebetween.
A crack which propagates in the low melting point brazing material 7 can be formed by forming an angle θ1, 60 ° ≦ θ1 ≦ 85 ° with respect to the lower surface of the insulating substrate at least at the corner on the front surface side as shown in FIG. Can easily be changed to the direction of the insulating base to effectively prevent the progress of the crack. Therefore, the side wall 6d of the first region 6a and the side wall 6e of the second region 6c opposed to each other with the gap 6b interposed therebetween, at least at the corners on the surface side, in a range of 60 ° to 85 ° with respect to the lower surface of the insulating base. It is preferable to incline in advance.

The wiring conductor 2 and the connection pad 6 are provided with a plating layer made of a metal having excellent wettability and bonding property with respect to the low melting point brazing material 7 such as nickel, copper, gold, etc. Or about 1 piece of copper
If the metal is sequentially applied in a thickness of 0.05 μm to 5 μm, the wiring conductor 2 and the connection pad 6
Can be effectively prevented from being oxidized, and the low melting point brazing material 7 and the bonding wire 5
Can be firmly joined and connected. Therefore, the wiring conductor 2 and the connection pad 6 have nickel,
It is preferable that a plating layer of copper, gold, or the like be applied in a thickness of about 1 μm to 15 μm.

Thus, according to the wiring substrate of the present invention, the semiconductor element 3 is formed on the bottom surface of the concave portion 1a of the insulating base 1 by glass or resin,
The electrodes of the semiconductor element 3 are bonded and fixed via an adhesive such as a brazing material, and are electrically connected to the wiring conductors 2 via the bonding wires 5. A semiconductor device as a product by joining the lid 9 made of glass, resin, brazing material or the like via a sealing material and sealingly housing the semiconductor element 3 in a container formed of the insulating base 1 and the lid 9. Is completed.

The wiring board of the present invention is not limited to the above-described embodiment, and various changes can be made without departing from the gist of the present invention.

[0030]

According to the wiring board of the present invention, the first region is formed by forming a connection pad with a substantially circular first region and a gap having a fixed width outside the first region. The connection pad is joined to the circuit wiring of the external electric circuit board via a low melting point brazing material, and then the insulating base of the wiring board and the outside are joined to the low melting point brazing material. When the thermal stress caused by the difference in the coefficient of thermal expansion of the electric circuit board repeatedly acts, a crack is generated by the thermal stress in the vicinity of the outer peripheral end of the low melting point brazing material, that is, near the joining interface with the outer peripheral end of the second region of the connection pad. However, the cracks are prevented from progressing at the gap between the first region and the second region and at the side wall of the first region, so that the low-melting-point brazing material hardly breaks, and thereby the connection pad and the connection pad are hardly broken. Secure the circuit wiring of the external electric circuit board, Solid it is possible to form excellent in long-term reliability of the connection to an external electric circuit of the semiconductor device it is possible to electrically connect to.

According to the wiring board of the present invention, since the height of the second region of the connection pad is made lower than the height of the first region, the crack generated at the outer peripheral end of the low melting point brazing material is propagated. Is effectively prevented by hitting the side wall of the first region, and as a result, the risk of breakage of the low melting point brazing material can be further reduced, and the connection of the semiconductor element to the external electric circuit can be maintained for a long time. It can be made to be extremely excellent in properties.

[Brief description of the drawings]

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

FIG. 2 is an enlarged sectional view of a main part of the wiring board shown in FIG.

FIG. 3 is an enlarged plan view of a main part of the wiring board shown in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Insulating base 1a ... Depression 2 ... Wiring conductor 3 ... Semiconductor element 4 ... Wiring board 5 ... Bonding wire 6 ... Connection pad 6a ... 1st area 6b gap 6c 2nd area 6d 1st area side wall 6e 2nd area side wall 7 low melting point brazing material 8 outside Electric circuit board 8a ... circuit wiring 9 ... lid

Claims (4)

[Claims] 1. An insulating base made of an electrically insulating material and having a semiconductor element mounting portion on a surface, a number of connection pads formed on a lower surface of the insulating base, and a portion extending from the mounting portion to the connection pad of the insulating base. A wiring board comprising a plurality of wiring conductors led out, wherein each of the connection pads is formed with a substantially circular first region and a gap having a fixed width outside the first region. And a substantially annular second region lower than the first region. 2. A height difference between said first region and said second region is one.
The wiring board according to claim 1, wherein the thickness is 0 µm or more. 3. The semiconductor device according to claim 1, wherein a radius of the first region is 60% to 82% of a radius of the connection pad.
The wiring board according to claim 1. 4. The wiring board according to claim 1, wherein the width of the gap is 5% to 35% of the radius of the connection pad.