JP2002016185A - Wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that a part of a nickel layer moves and disperses on a gold layer surface to form a nickel oxide there, resulting in a decreased joint strength of solder to a connection pad. SOLUTION: There are provided an insulating base body 1, a wiring layer 2 formed inside and/or on the surface of the insulating base body 1, a connection pad 3 which electrically connects to the wiring layer 2 while jointed to an external electric circuit through a lead-less solder 9. On the surface of the connection pad 3, a nickel layer 10 of thickness 3.0 μm or more, a copper layer 11 of thickness 2-5 μm, and a gold layer 12 of thickness 0.05-0.3 μm are sequentially coated.

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 for accommodating a semiconductor element.

[0002]

2. Description of the Related Art Conventionally, a wiring board, for example, a wiring board used for a semiconductor element housing package for housing a semiconductor element is generally made of an aluminum oxide sintered body, and a mounting portion for mounting the semiconductor element on an upper surface thereof. A wiring layer made of a refractory metal powder such as tungsten, molybdenum, or manganese derived from the mounting portion to the lower surface of the insulating base; and a tin-lead electrically connected to the wiring layer and connected to an external electric circuit. And a connection pad joined via solder such as solder.The semiconductor element is mounted on the mounting portion of the insulating base and each electrode of the semiconductor element is connected to the wiring layer via a conductive bonding material such as a gold bump. By connecting them mechanically and electrically, a metal cover is then joined to the upper surface of the insulating base, and the semiconductor element is hermetically sealed inside a container consisting of the insulating base and the cover. A semiconductor device as a product.

Such a semiconductor device is mounted on an external electric circuit board by connecting a connection pad formed on the lower surface of an insulating base and electrically connected to a wiring layer to a wiring conductor of the external electric circuit board via solder. At the same time, each electrode of the semiconductor element housed in the container is connected to a predetermined external electric circuit.

The wiring board used in the above-mentioned package for accommodating a semiconductor element or the like has a solder wettability and a joint property in order to effectively prevent oxidative corrosion of a wiring layer made of a high melting point metal powder such as tungsten. In order to improve the quality, a gold layer which is generally excellent in corrosion resistance and excellent in solder wettability and bonding property is applied to the exposed surface of the wiring layer by plating or the like.

[0005] However, the wiring layer made of a refractory metal powder such as tungsten has a low adhesion strength to the gold layer.
After the gold layer is directly applied to the wiring layer, even if a small external force is applied to the gold layer, the gold layer easily peels off from the wiring layer, thereby preventing the wiring layer from being oxidized and corroded for a long time. And the connection between the wiring layer and the conductive bonding material such as a gold bump and the connection between the wiring layer and the wiring conductor of the external electric circuit board are broken, and the reliability of the electrical connection of the semiconductor element to the external electric circuit board is broken. Has a drawback that it becomes low.

In order to solve the above-mentioned drawbacks, conventionally, a metal layer made of nickel, which is firmly adhered and bonded to both, is interposed between a wiring layer made of a high melting point metal powder such as tungsten and a gold layer. That is being done.

In a wiring board in which such a metal layer made of nickel is interposed between a wiring layer made of a high melting point metal powder such as tungsten and a gold layer, the gold layer is firmly formed on the wiring layer by the metal layer made of nickel. As a result, even if an external force is applied to the gold layer, the gold layer does not peel off from the wiring layer, which can prevent oxidative corrosion of the wiring layer for a long period of time, and can prevent the wiring layer from being exposed to the external electric circuit. The connection with the wiring conductor of the substrate can be made highly reliable.

In this case, if the thickness of the gold layer is large, a large amount of brittle intermetallic compound is generated between the gold layer and a component such as tin in the solder for joining the wiring layer to the wiring conductor of the external electric circuit board. Since the connection reliability of the external electric circuit board with respect to the wiring conductor becomes low, it is usually about 0.5 μm.
m or less.

[0009]

However, recently,
Lead-free solder (lead-free solder) such as tin-silver or tin-gold based, which does not contain lead harmful to the human body, is being widely used as a low melting point brazing material. (About 260 ° C. to 300 ° C.) is higher than the tin-lead solder (brazing temperature about 200 ° C.), so that part of the nickel layer moves and diffuses to the surface of the gold layer due to the heat at the time of brazing,
This is oxidized to form a large amount of nickel oxide on the surface of the gold layer, which has poor bonding property to lead-free solder. The reliability of the electrical connection with the wiring conductors of the board is reduced, and the electrical signals are reliably transmitted to the semiconductor element.
In addition, there has been a problem that it is not possible to take in and out correctly.

When the thickness of the gold layer is increased in order to prevent the migration and diffusion of nickel to the surface of the gold layer, a large amount of brittle intermetallic compound is generated between the component such as tin of the low melting point brazing material and gold,
The reliability of the joint of the low melting point brazing material is degraded.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and an object of the present invention is to connect a connection pad to a wiring conductor of an external electric circuit board firmly via lead-free solder. It is an object of the present invention to provide a wiring board capable of reliably and accurately sending and receiving electric signals to and from a semiconductor element via a wiring layer.

[0012]

A wiring board according to the present invention comprises an insulating base, a wiring layer formed inside and / or on the surface of the insulating base, an electrical connection with the wiring layer, and an external electrical connection. A wiring board comprising a connection pad joined to a circuit via a lead-free solder, wherein the connection pad has a nickel layer having a thickness of 3.0 μm or more on its surface and a nickel layer having a thickness of 2 μm.
m to 5 μm copper layer and thickness of 0.05 μm to 0.3
A gold layer of μm is sequentially applied.

According to the wiring board of the present invention, a nickel layer having a thickness of 3.0 μm or more and a thickness of
μm to 5 μm copper layer, thickness 0.05 μm to 0.3
μm gold layer was sequentially deposited and a copper layer having a thickness of 2 μm to 5 μm was interposed between the nickel layer and the gold layer.
The gold layer can be firmly adhered to the nickel layer, and even if relatively high heat is applied when the wiring layer is bonded to the wiring conductor of the external electric circuit board via the lead-free solder, the nickel layer remains The part is effectively prevented from moving and diffusing to the surface of the gold layer, and as a result, the wiring layer and the wiring conductor of the external electric circuit board can be reliably and firmly electrically connected to each other via the lead-free solder. .

At the same time, according to the wiring board of the present invention, since the thickness of the gold layer is as thin as 0.05 μm to 0.3 μm, a brittle intermetallic compound is formed between tin and gold in the lead-free solder. Is not generated in large quantities, and the reliability of the joint can be improved.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional view showing an example of an embodiment in which the wiring board of the present invention is applied to a semiconductor element housing package for housing a semiconductor element.
2 is a wiring layer and 3 is a connection pad. The insulating substrate 1, the wiring layer 2, and the connection pads 3 constitute a wiring board 5 for mounting and housing the semiconductor element 4.

The insulating substrate 1 is made of an aluminum oxide sintered body, an aluminum nitride sintered body, a mullite sintered body,
It is made of an electrically insulating material such as a silicon carbide sintered body, and has a concave portion 1a for mounting and housing the semiconductor element 4 on its upper surface,
The semiconductor element 4 is accommodated in the recess 1a.

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 such as aluminum oxide, silicon oxide, calcium oxide, and magnesium oxide. A ceramic green sheet is obtained by forming a slurry-like ceramic slurry and forming the ceramic slurry into a sheet by employing a sheet forming technique such as a conventionally known doctor blade method or a calendar roll method. Into a suitable shape by cutting or punching and laminating a plurality of this,
Finally, the laminated ceramic green sheets are manufactured by firing at a temperature of about 1600 ° C. in a reducing atmosphere.

The insulating substrate 1 has a large number of wiring layers 2 formed thereon from the bottom surface to the lower surface of the concave portion 1a. Are electrically connected via a conductive bonding material 6 such as a gold bump, and a connection pad 3 for external connection is formed at a portion led out to the lower surface of the insulating base 1 so as to be electrically connected. I have.

The wiring layer 2 and the connection pads 3 serve to electrically connect the respective electrodes of the semiconductor element 4 to be accommodated to the wiring conductors 8 of the external electric circuit board 7. For example, tungsten, molybdenum, manganese, etc. A metal paste made of a high melting point metal powder, obtained by adding a suitable organic binder or solvent to a high melting point metal powder such as tungsten, is mixed in a predetermined pattern on a ceramic green sheet serving as an insulating substrate 1 by a conventionally well-known screen printing method. Is formed on the insulating substrate 1 from the bottom surface to the lower surface of the concave portion 1a. The electrical connection between the connection pad 3 and the wiring conductor 8 of the external electric circuit board 7 is performed by joining the connection pad 3 and the wiring conductor 8 via a lead-free solder 9.

The connection pad 3 is provided on its surface as shown in FIG.
As shown in the figure, the nickel layer 1 having a thickness of 3.0 μm or more
0, a copper layer 11 having a thickness of 2 μm to 5 μm, and a thickness of 0.0
A gold layer 12 of 5 μm to 0.3 μm is sequentially applied.

Since the nickel layer 10 has excellent adhesion to both the wiring layer 2 and the copper layer 11, the nickel layer 10 functions as an underlayer for firmly bonding the copper layer 11 to the surface of the wiring layer 2.

The nickel layer 10 is formed by electroless plating or electrolytic plating. For example, if the nickel layer 10 is formed by electroless plating, nickel sulfate 2
0-40 g / l, sodium succinate 40-
60 g / l, boric acid 25-35 g / l, ammonium chloride 25-35 g / l,
Prepare an electroless nickel plating solution consisting of dimethylamine borane 2.5 to 4.5 g / liter, etc., degrease and acid-treat the exposed surface of the connection pad 3, and then immerse it in a solution containing a catalyst agent. Activate and then
By immersing the exposed surface of the connection pad 3 in the electroless nickel plating solution set at 60 to 65 ° C. for about 30 minutes or more, the exposed surface of the connection pad 3 is adhered to a predetermined thickness of 3 μm or more.

The nickel layer 10 has a thickness of 3 μm
If it is less than the above, the wiring layer 2 cannot be completely covered, and the copper layer 11 cannot be firmly adhered to the surface of the wiring layer 2. Therefore, the nickel layer 10
Is specified to have a thickness of 3 μm or more.

On the surface of the nickel layer 10, a copper layer 11 having a thickness of 2 μm to 5 μm is adhered. The copper layer 11 allows the gold layer 12 to be firmly adhered to the nickel layer 10 and the nickel layer 10 to be adhered. Does not effectively move and diffuse to the surface of the gold layer 12, thereby preventing nickel oxide having poor bondability to the lead-free solder from being formed on the surface of the gold layer 12. In addition, it is possible to reliably electrically connect the connection pad 3 to the wiring conductor 8 of the external electric circuit board 7 via the lead-free solder 9.

The copper layer 11 is formed by an electrolytic plating method or an electroless plating method. For example, copper sulfate 10 g / l, EDTA-2Na 30 g / l, formaldehyde (37% solution) 3 cc / l, and some bipyridyl and After preparing an electroless copper plating solution composed of polyethylene glycol or the like, degrease and acid-treat the exposed surface of the nickel layer 10, the exposed surface of the nickel layer 10 is immersed in the electroless copper plating solution for about 10 to 30 minutes. 2 to 5 μm on the exposed surface of the nickel layer 10 by immersion.
To a predetermined thickness.

The copper layer 11 has a thickness of 2 μm.
If the thickness is too small, it is not possible to effectively prevent a part of the nickel layer 10 from moving and diffusing into the gold layer 12,
When the thickness is more than m, a large stress is present inside the copper layer 11 when formed by the plating method, and this stress reduces the reliability of adhesion of the connection pad 3 to the insulating base 1 and the wiring layer 2. Would. Therefore, the thickness of the copper layer 11 is specified in the range of 2 μm to 5 μm. Further, when the copper layer 11 is formed by an electroless plating method, if the copper layer 11 is deposited thicker than 3 μm at a time, the internal stress of the plating layer increases, and the copper layer 11 and the connection pad 3
Of the connection pad 3 and the reliability of the connection between the connection pad 3 and the insulating base 1 and the wiring layer 2 may be reduced. Depositing a layer and then heat treating the primary copper layer at a temperature of about 700 ° C. to 900 ° C. to relieve the intrinsic stress of the copper layer, and then deposit a secondary copper layer on the primary copper layer It is preferable to form it so as to adhere to the thickness.

Further, the copper layer 11 is provided with a gold layer 12 having a thickness of 0.05 μm to 0.3 μm on its surface.

The gold layer 12 effectively prevents oxidative corrosion of the connection pads 3 (actually, the connection pads 3 and the nickel layer 10 and the copper layer 11 deposited on the surface of the connection pads 3), and the connection pads 3 3 is formed by an electrolytic plating method or an electroless plating method, for example, potassium hydroxide 20-4.
0 g / liter, ethylenediaminetetraacetic acid 30-5
0 g / liter, potassium dihydrogen phosphate 15-45
Grams / liter, potassium cyanide 0.01-0.1
G / l, 1-4 g of potassium gold cyanide /
Liter gold plating solution (liquid temperature: 85-95 ° C)
After the exposed surface of the copper layer 11 is degreased and acid-treated, the exposed surface of the copper layer 11 is immersed in the electroless gold plating solution for about 5.5 to 15 minutes to expose the copper layer 11. It is applied to the surface to a thickness of 0.05 to 0.3 μm.

Since the thickness of the gold layer 12 is as thin as 0.05 μm to 0.3 μm, when the connection pad 3 is joined to the wiring conductor 8 of the external electric circuit board 7 via the lead-free solder 9, A large amount of brittle intermetallic compound is not generated between the component such as tin in the non-containing solder 9 and gold, and the reliability of the electrical connection between the connection pad 3 and the wiring conductor 8 is improved. be able to.

The gold layer 12 has a thickness of 0.05.
When the thickness is less than μm, the oxidation corrosion of the connection pads 3 (actually, the connection layers 3 and the nickel layer 10 and the copper layer 11 deposited on the surface of the connection pads 3) cannot be effectively prevented, and When the thickness exceeds 0.3 μm, the amount of brittle intermetallic compounds generated with components such as tin in the lead-free solder 9 increases, and the reliability of the electrical connection of the connection pad 3 to the wiring conductor 8 increases. Will drop. Therefore, the thickness of the gold layer 12 is specified in the range of 0.05 μm to 0.3 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 layer 2 via a conductive bonding material 6. The lid 13 made of ceramics is joined via a sealing material such as glass, resin, brazing material or the like, and the insulating base 1 and the lid 13 are joined together.
A semiconductor device as a product is completed by housing the semiconductor element 3 in an airtight manner inside the container consisting of

The wiring board of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention. Although the wiring board of the present invention is applied to a semiconductor element housing package for housing a semiconductor element, it may be applied to other uses such as a hybrid integrated circuit board.

[0033]

According to the wiring board of the present invention, a nickel layer having a thickness of 3.0 μm or more, a copper layer having a thickness of 2 μm to 5 μm, and a thickness of 0.05 μm to 0.
Since a 3 μm gold layer was sequentially deposited and a copper layer having a thickness of 2 μm to 5 μm was interposed between the nickel layer and the gold layer,
The gold layer can be firmly adhered to the nickel layer, and even if relatively high heat is applied when the wiring layer is bonded to the wiring conductor of the external electric circuit board via the lead-free solder, the nickel layer remains The part is effectively prevented from moving and diffusing to the surface of the gold layer, and as a result, the wiring layer and the wiring conductor of the external electric circuit board can be reliably and firmly electrically connected to each other via the lead-free solder. .

At the same time, according to the wiring board of the present invention, since the thickness of the gold layer is as thin as 0.05 μm to 0.3 μm, a brittle intermetallic compound is formed between tin and gold in the lead-free solder. Is not generated in large quantities, and the reliability of the joint can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment in which a wiring board of the present invention is applied to a package for housing a semiconductor element.

FIG. 2 is an enlarged sectional view of a main part of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Insulating base 1a ... Depression 2 ... Wiring layer 3 ... Connection pad 4 ... Semiconductor element 5 ... Wiring board 6 ... Conductive bonding material 7 ···································································································································································································································································· lid · lid ·

Claims (1)

[Claims] An insulating substrate, a wiring layer formed inside and / or on the surface of the insulating substrate, electrically connected to the wiring layer, and joined to an external electric circuit via a lead-free solder. A connection pad comprising: a nickel layer having a thickness of 3.0 μm or more; a copper layer having a thickness of 2 to 5 μm;
A wiring substrate, comprising a gold layer having a thickness of from 0.3 μm to 0.3 μm.