JP2001308498A - Circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem of forming a fleck-like stain due to an exudation of a plating solution to a surface of a gold plated layer by retaining the solution in a pinhole or a void formed in a nickel plating layer of a substrate. SOLUTION: A circuit board 4 comprises a wiring layer 2 connected to an electrode of an electronic component 3 via a solder ball 5. In this case, a nickel- boron plating layer 6, a high purity nickel plating layer 7 containing a nickel of a content of 99.9 wt.% or more, and a gold plating layer 8 sequentially coat a surface of the layer 2 of an area to be connected to the electrode of the component 3 via the ball 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring board on which electronic components such as a semiconductor element, a capacitor, and a resistor are mounted.

[0002]

2. Description of the Related Art Conventionally, a wiring board on which electronic components such as a semiconductor element, a capacitor element, and a resistor are mounted is generally formed of an insulating base made of an aluminum oxide sintered body and an upper surface to a lower surface of the insulating base. And a plurality of wiring layers made of a refractory metal material such as tungsten, molybdenum, etc., and electronic components such as semiconductor elements, capacitance elements, and resistors are mounted on the upper surface of the insulating base and Each electrode is electrically connected to a wiring layer via solder.

[0003] Such a wiring board is mounted on the external electric circuit board by connecting a portion of the wiring layer extending to the lower surface of the insulating base to a wiring conductor of the external electric circuit board via solder or the like, and at the same time, is mounted on the wiring board. Each electrode of the mounted electronic component is electrically connected to a predetermined external electric circuit.

In the above-described wiring board, a nickel plating layer and a gold plating layer are sequentially deposited on at least a region of the wiring layer to which electronic components are connected via solder, and the nickel plating layer forms a high plating layer of tungsten or the like. The bonding of the solder to the wiring layer made of the melting point metal material is improved, and the gold plating layer prevents the formation of a nickel oxide on the surface of the nickel plating layer to prevent the deterioration of the solder bonding property and the like.

The method of applying the nickel plating layer and the gold plating layer is based on the fact that it is difficult to form lead wires for supplying power for plating due to the densification of the wiring layer accompanying the miniaturization of the wiring board. The electroless method is being used frequently.

Further, when the nickel plating layer is applied by the electroless method, a nickel compound such as nickel sulfate, a boron-based reducing agent such as dimethylamine borane, or sodium hypophosphite is generally used as the electroless nickel plating solution. An electroless nickel plating solution obtained by adding a complexing agent, a pH buffering agent, a stabilizer, etc. to an aqueous solution mainly containing a phosphorus-based reducing agent such as is used, and the formed nickel plating layer is reduced. It is a nickel-boron alloy or a nickel-phosphorus alloy containing several weight% of boron or phosphorus which is a decomposition product of the agent.

[0007]

However, in this conventional wiring board, when a nickel plating layer made of a nickel-phosphorus alloy is applied to a region on the wiring layer where electronic components are connected via solder. Since the phosphorus component of the nickel-phosphorus alloy is inactive and the surface of the wiring layer made of a refractory metal material such as tungsten and molybdenum is rough, the entire surface of the wiring layer is made of nickel-phosphorus alloy. The nickel plating layer cannot be uniformly deposited, and has many pinholes (small holes) and voids (small voids). As a result, the plating solution remains in the pinholes and voids. If the plating solution remains in the pinholes and voids, it will seep out onto the gold plating layer due to the heat when connecting the electronic component to the wiring layer via solder, and spots It has significant disadvantage results in poor appearance and form stains.

When a nickel plating layer made of a nickel-boron alloy is applied on the wiring layer, the nickel plating layer made of the nickel-boron alloy is easily eluted into an electroless gold plating bath, and the nickel plating layer and the gold Since the voids tend to remain between the plating layer and the thermal expansion coefficient of the nickel-boron alloy differ greatly from the thermal expansion coefficient of gold, etc. When heat is applied to connect the electronic components to the wiring layer via solder on both, a difference in the thermal expansion coefficient between the nickel plating layer and the gold plating layer made of a nickel-boron alloy occurs due to the difference between the two. The generated stress causes peeling or blistering, and thus has a disadvantage that the electronic component cannot be firmly attached to the wiring layer via solder.

The present invention has been devised in view of the above-mentioned drawbacks, and has as its object to effectively prevent poor appearance due to occurrence of spot-like spots and occurrence of peeling or blistering between a gold plating layer and a nickel plating layer. Another object of the present invention is to provide a wiring board that can securely attach electronic components to a wiring layer via solder.

[0010]

According to the present invention, there is provided a wiring board having a wiring layer to which electrodes of an electronic component are connected via solder, wherein at least an electrode of the electronic component of the wiring layer has a solder layer. A nickel-boron plating layer, a high-purity nickel plating layer having a nickel content of 99.9% by weight or more, and a gold plating layer sequentially deposited on the surface of the region connected via It is.

In the wiring board according to the present invention, the high-purity nickel plating layer has a thickness of 0.5 μm to 5 μm.

According to the wiring board of the present invention, the nickel-boron plating layer and the nickel content of 99.9% by weight are formed on the surface of at least the region of the wiring layer where the electrodes of the electronic components are connected via solder. Above high purity nickel plating layer,
A gold-plated layer was sequentially deposited, and a nickel-boron-plated layer containing boron having strong catalytic activity was directly deposited on the surface of the wiring layer. The surface can be extremely smooth and uniform in thickness, and can be firmly adhered to the nickel-boron plating layer. It is difficult to dissolve in the plating bath and hardly generates voids at the interface with the gold plating layer. Furthermore, since a high-purity nickel plating layer whose thermal expansion coefficient is close to that of the gold plating layer is applied, an intermediate layer is formed on the nickel-boron plating layer. A gold metal that can firmly adhere a gold plating layer via a high-purity nickel plating layer, and has excellent corrosion resistance and excellent wettability with solder on the high-purity nickel plating layer The nickel layer can be effectively prevented from being oxidized and corroded by the nickel-boron plating layer and the high-purity nickel plating layer, and the solder can be firmly joined. It is possible to effectively prevent spot-like spots and blisters from being generated on the layer, and it is possible to connect the electrodes of the electronic component to the wiring layer very firmly via solder.

DETAILED DESCRIPTION OF THE INVENTION Next, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows an embodiment in which the wiring board of the present invention is applied to a semiconductor element housing package for housing a semiconductor element, wherein 1 is an insulating base, and 2 is a wiring layer. The insulating substrate 1 and the wiring layer 2 form a wiring board 4 on which the semiconductor element 3 is mounted.

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 or a glass ceramic sintered body, and has a mounting portion for mounting the semiconductor element 3 on the upper surface thereof. The electrodes are connected via solder balls 5 such as tin / lead solder.

When the insulating substrate 1 is made of, for example, an aluminum oxide sintered body, an appropriate organic binder and a solvent are added to and mixed with raw material powders of aluminum oxide, silicon oxide, calcium oxide, magnesium oxide and the like. A ceramic green sheet (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 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 substrate 1 has a large number of wiring layers 2 formed on the upper surface thereof from the mounting portion on which the semiconductor element 3 is mounted to the lower surface. The electrodes of the semiconductor element 3 are electrically connected via solder balls 5, and a wiring conductor of an external electric circuit board is electrically connected to a portion led out to the lower surface of the insulating base 1 via solder or the like. Is done.

The wiring layer 2 has a semiconductor element 3 mounted thereon.
A function of connecting each electrode to an external electric circuit, for example, made of a refractory metal powder such as tungsten, molybdenum, and manganese, and obtained by adding a suitable organic binder or solvent to the refractory metal powder such as tungsten and mixing. The metal paste is applied to a ceramic green sheet serving as the insulating substrate 1 in a predetermined pattern by a well-known screen printing method in advance, so that the semiconductor element 3 of the insulating substrate 1 is formed.
Is attached from the mounting portion on which the is mounted to the lower surface.

As shown in FIG. 2, the wiring layer 2 has a nickel-boron plating layer 6, a high-purity nickel plating layer 7, and a gold plating layer at least in regions where electrodes of the semiconductor element 3 are connected via solder balls 5. Layers 8 are applied sequentially.

The nickel-boron plating layer 6 functions as a base metal layer that adheres the high-purity nickel plating layer 7 and the gold plating layer 8 to the wiring layer 2 with good adhesion.

The nickel-boron plating layer 6 is formed by electroless plating using an electroless nickel plating bath containing a nickel compound such as nickel sulfate and a boron-based reducing agent such as sodium borohydride and dimethylamine borane. A predetermined thickness is applied to the surface of the layer 2. in this case,
Since the nickel-boron plating layer 6 contains boron having strong catalytic activity therein, pinholes and voids are formed in the nickel-boron plating layer 6 even if the surface of the wiring layer 2 is rough. However, at the same time, the surface can be made extremely smooth and a uniform thickness can be firmly applied.

The nickel-boron plating layer 6
When the content of boron is as low as less than 0.05% by weight, the corrosion resistance of the nickel-boron plating layer 6 tends to be deteriorated and oxidized easily, and when it exceeds 3% by weight, the electric resistance increases. However, the characteristics as a wiring board tend to deteriorate. Therefore, the nickel-boron plating layer 6 preferably has a boron content in the range of 0.05% by weight to 3% by weight.

The nickel-boron plating layer 6 is
When the thickness is thinner than 1 μm, it becomes difficult to apply the nickel-boron plating layer 6 to the rough wiring layer 2 to make the surface extremely smooth and to apply a uniform thickness. If it exceeds, the internal stress increases, and it becomes difficult to firmly apply the nickel-boron plating layer 6 to the wiring layer 2. Therefore, it is preferable that the nickel-boron plating layer 6 has a thickness in the range of 1 μm to 8 μm.

Further, a high-purity nickel plating layer 7 having a nickel content of 99.9% by weight or more is coated on the nickel-boron plating layer 6 to a predetermined thickness. Is the nickel-boron plating layer 6
In this case, the gold plating layer 8 is firmly adhered and bonded.

The high-purity nickel plating layer 7 comprises, as main components, a nickel compound such as nickel acetate and nickel chloride, and a reducing agent such as hydrazine and formalin which does not contain a component which is eutectoid in the nickel plating layer. Uses an electroless high-purity nickel plating bath containing a complexing agent such as acetic acid, citric acid, ethylenediaminetetraacetic acid (EDTA) or their sodium and potassium salts, a pH buffer such as boric acid, and a stabilizer such as saccharin. It is deposited on the nickel-boron plating layer 6 by the used electroless plating method. In this case, the underlying nickel-boron plating layer 6 has an extremely smooth surface, and the high-purity nickel plating layer 7 has good adhesion to the nickel-boron plating layer 6. A uniform thickness and firm attachment can be achieved without forming pinholes or voids on the surface of the boron plating layer 6.

The high-purity nickel plating layer 7 has a thermal expansion coefficient of about 13 × 10 ⁻⁶ / ° C., which is close to that of the gold plating layer 8 (about 14 × 10 ⁻⁶ / ° C.). Even when heat is applied when the electronic component is connected to the wiring layer 2 via the solder balls 5, the high-purity nickel plating layer 7
No large thermal stress is generated between the metal layer 8 and the gold plating layer 8. As a result, peeling or blistering of the gold plating layer 8 can be effectively prevented, and the electronic component is placed on the wiring layer 2. It can be firmly attached via the solder balls 5.

The high-purity nickel plating layer 7 is
When the nickel content is less than 99.9% by weight, the particle size of the nickel crystal forming the nickel plating layer becomes very small, less than 20 nm, and the crystal grain boundaries increase rapidly due to the effect of the eutectoid component. As a result, nickel (atoms) move and diffuse easily along the grain boundaries. As a result, when the electrodes of the semiconductor element 3 are connected to the wiring layer 2 via the solder balls 5, the high purity nickel plating layer 7 is formed. When heat is applied to the substrate, nickel of the high-purity nickel plating layer 7 moves and diffuses to the surface of the gold plating layer 8 and is oxidized to form a nickel oxide layer. Cannot be firmly connected via the solder ball 5. Therefore, the nickel content of the high-purity nickel plating layer 7 is specified to be 99.9% by weight or more.

The high-purity nickel plating layer 7 is
When the thickness is less than 0.5 μm, the nickel-boron plating layer 6 cannot be completely covered, and the adhesion strength of the gold plating layer 8 described later tends to be weak, On the other hand, if it exceeds 5 μm, the internal stress tends to be large and the adhesion strength to the nickel-boron plating layer 6 tends to be low. Therefore, it is preferable that the high-purity nickel plating layer 7 has a thickness in the range of 0.5 μm to 5 μm.

The total thickness of the nickel-boron plating layer 6 and the high-purity nickel plating layer 7 is 1
When the thickness exceeds 0 μm, the adhesion strength between the nickel-boron plating layer 6 and the wiring layer 2 and the adhesion strength between the wiring layer 2 and the insulating base 1 decrease due to the resultant force of the internal stress. And the wiring layer 2 tends to cause defects such as peeling and blistering. Therefore, it is preferable that the total thickness of the nickel-boron plating layer 6 and the high-purity nickel plating layer 7 is 10 μm or less.

The high-purity nickel plating layer 7 has a gold plating layer 8 formed on the surface thereof to a predetermined thickness. The gold plating layer 8 is formed by oxidizing the nickel-boron plating layer 6 and the high-purity nickel plating layer 7. Corrosion can be effectively prevented, and has the effect of firmly joining the solder to the wiring layer 2.

For the gold plating layer 8, for example, a substitution-type electroless gold plating solution containing a conventionally known gold compound such as potassium potassium cyanide and a complexing agent such as ethylenediaminetetraacetic acid (sodium salt) is used. It is formed on the surface of the high-purity nickel plating layer 7 by an electroless plating method.

The gold plating layer 8 has a thickness of 0.05
When the thickness is less than μm, it is difficult to prevent oxidation of the high-purity nickel plating layer 7 and the nickel-boron plating layer 6, and when the thickness exceeds 0.8 μm, the electrodes of the semiconductor element 3 are attached to the wiring layer 2. A brittle intermetallic compound such as gold-tin may be formed between the solder ball 5 and the solder ball 5 to be connected, and the long-term reliability of the connection may be reduced. Therefore, it is preferable that the thickness of the gold plating layer 8 be in the range of 0.05 μm to 0.8 μm.

When the nickel-boron plating layer 6, the high-purity nickel plating layer 7, and the gold plating layer 8 are all formed by an electroless method, conductive wires for supplying electric power for plating are formed in the wiring board 4. There is no need to provide the wiring layer, the wiring layer 2 can be formed at a high density, and the size of the wiring board 4 can be easily reduced.

On the other hand, the insulating substrate 1 on which the semiconductor element 3 is mounted has a lid 9 joined to the upper surface thereof via a sealing material made of resin, glass, brazing material, or the like. The semiconductor element 3 is hermetically sealed by the base 1.

The lid 9 is made of a ceramic material such as an aluminum oxide sintered body, a mullite sintered body, or an aluminum nitride sintered body, or a metal material such as an iron-nickel-cobalt alloy or an iron-nickel alloy. For example, in the case of a sintered body made of aluminum oxide, a raw material powder such as aluminum oxide, silicon oxide, magnesium oxide, and calcium oxide is formed into a bowl shape by employing a conventionally known press molding method, and then formed into a bowl shape. It is formed by firing at a temperature of about 1500 ° C.

Thus, according to the wiring board 4 of the present invention, the electrodes of the semiconductor element 3 are electrically and mechanically connected to the wiring layer 2 exposed on the surface of the mounting portion on the upper surface of the insulating base 1 via the solder balls 5. Thereafter, a lid 9 made of metal or ceramics is bonded to the upper surface of the insulating base 1 via a sealing material such as glass, resin, brazing material or the like, and a semiconductor element is placed inside the container formed of the insulating base 1 and the lid 9. The semiconductor device as a product is completed by housing 3 in an airtight manner.

It should be noted that 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 gist 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.

[0037]

According to the wiring board of the present invention, the nickel-boron plating layer and the nickel content of 99.9 are formed on the surface of at least the region of the wiring layer where the electrodes of the electronic components are connected via solder. A high-purity nickel plating layer and a gold plating layer of at least
The nickel-boron plating layer containing boron with a strong catalytic activity is applied, so that the nickel-boron plating layer has a very smooth and uniform thickness without any pinholes or voids on the wiring layer. It can be adhered, has good adhesion to the nickel-boron plating layer on the nickel-boron plating layer, and hardly dissolves in the electroless gold plating bath, and generates a void at the interface with the gold plating layer. Difficult, and because a high-purity nickel plating layer whose thermal expansion coefficient is close to that of the gold plating layer was deposited, the gold plating layer was firmly covered on the nickel-boron plating layer with a high-purity nickel plating layer interposed therebetween. And a gold plating layer with excellent corrosion resistance and excellent wettability with solder is deposited on the high-purity nickel plating layer. Layer and the high-purity nickel plating layer can be effectively prevented from being oxidized and corroded, and the solder can be firmly joined. This prevents spot-like spots and blisters on the wiring layer of the wiring board. It is possible to prevent it effectively and to connect the electrodes of the electronic component to the wiring layer very firmly via solder.

According to the wiring board of the present invention, the nickel content in the high-purity nickel plating layer is 99.9% by weight or more, the average grain size of nickel crystals is 20 nm or more, the crystal grain boundaries are small, Is difficult to move and diffuse, the thickness of the gold plating layer is set to, for example, 0.05 μm to 0 μm to prevent the formation of a large amount of a brittle intermetallic compound composed of gold and solder (such as tin). Even if the thickness is reduced to 0.8 μm, there is no problem that nickel migrates and diffuses to the surface of the gold plating layer to form a nickel oxide layer and deteriorates solder wettability. The connection can be made very easily and reliably via solder, and the long-term reliability of the solder connection can be improved.

[Brief description of the drawings]

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

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Insulating base 2 ... Wiring layer 3 ... Semiconductor element 4 ... Wiring board 5 ... Solder ball 6 ... Nickel-boron plating layer 7 ... High purity nickel plating layer 8 Gold plating layer 9 Lid

Claims (2)

[Claims] 1. A wiring board having a wiring layer to which electrodes of an electronic component are connected via solder, wherein at least a surface of a region of the wiring layer where electrodes of the electronic component are connected via solder, A wiring substrate comprising a nickel-boron plating layer, a high-purity nickel plating layer having a nickel content of 99.9% by weight or more, and a gold plating layer sequentially deposited thereon. 2. The high-purity nickel plating layer has a thickness of 0.
The wiring board according to claim 1, wherein the thickness is 5 μm to 5 μm.