JP2001127390A - Wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem where the electrode of a semiconductor element cannot be strongly and electrically connected to a wiring conductor layer since the nickel of a nickel-plated layer is moved and diffused to the surface of a gold-plated layer. SOLUTION: In the wiring board where a nickel-plated layer 6 and a gold- plated layer 7 are successively deposited on the exposed surface of a wiring layer 2 on an insulation substrate 1, the content of boron in the nickel-plated layer 6 is 0.1 wt.% or less, and the average diameter of a nickel particle is 20 nm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device housing package for housing a semiconductor device and a wiring board used for a hybrid integrated circuit board.

[0002]

2. Description of the Related Art Conventionally, a wiring board on which electronic components such as a semiconductor element, a capacitance element and a resistor are mounted has a high melting point metal such as tungsten, molybdenum or the like on and inside an insulating substrate made of an aluminum oxide sintered body. It has a structure in which a wiring conductor made of a material is formed, and electronic components such as semiconductor elements, capacitance elements, and resistors are mounted on the surface of the insulating base, and the electrodes of each electronic component are placed on the exposed surface of the wiring conductor layer. Electrical connection is made via a bonding wire or a low melting point brazing material.

In order to prevent the wiring conductor layer from being oxidized and corroded, and to improve the wettability of the low melting point brazing material, the surface of the wiring conductor layer is coated with nickel plating having excellent adhesion to the wiring conductor layer. A layer and a gold plating layer having excellent corrosion resistance, low melting point brazing material wettability, and bonding properties are sequentially applied.

The nickel plating layer and the gold plating layer are formed by electroless plating because it is difficult to form a lead wire for supplying power for plating due to the high density of the wiring conductor layer accompanying the miniaturization of the wiring board. The law is being heavily used.

[0005] The electroless nickel plating solution generally comprises a nickel compound such as nickel sulfate and a reducing agent as main components.
Dimethylamine borane, which is capable of forming a nickel plating layer under mild conditions near neutrality of about 7 to 7, is often used. In order to stably form a plating layer at a practical plating rate, about 2 to 5 g is used. / Liter in the plating solution.

However, when the nickel plating layer is formed by the above-described electroless plating method, the reducing agent causes nickel to be reduced and precipitated, and at the same time, it is also decomposed to deposit boron. This boron is contained at a ratio of about 0.3 to 3% by weight, and the boron prevents the individual nickel particles forming the plating layer from growing. Therefore, the obtained nickel plating layer has an average particle size of less than 20 nm. It is formed by fine nickel particles.

Since the average particle size of nickel particles is small and there are many grain boundaries, nickel easily moves and diffuses along these many grain boundaries, and heat is generated when a semiconductor element is joined to a wiring board with a brazing material or the like. When applied, nickel easily migrates and diffuses along the grain boundaries to the surface of the gold plating layer and is oxidized, forming a nickel oxide layer to form a low melting point brazing material of the wiring conductor layer and the bonding property. Has been deteriorated, and it has been impossible to electrically connect the electrode of the semiconductor element to the wiring conductor layer.

[0008] Therefore, the nickel plating layer has a temperature of about 500 ° C.
A method is conceivable in which a heat treatment at 1200 ° C. is applied to grow the nickel particles by recrystallization, and the average grain size is increased to reduce the grain boundaries to suppress diffusion by heat.

[0009]

However, when the nickel plating layer is heat-treated, the heat may cause problems such as blistering and peeling on the nickel plating layer, and the heating of a tunnel furnace or the like used for the heat treatment. Foreign matter such as carbides in the device is burned on the surface of the wiring board, which causes a problem that electric insulation between wiring layers is deteriorated and appearance is deteriorated.

In the case where the nickel plating layer is subjected to a heat treatment, if the insulating substrate is formed of a material having low heat resistance, the heat treatment cannot be performed at a high temperature and the nickel particles cannot be sufficiently grown. appear.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to bond a semiconductor element to a wiring board formed by applying a nickel plating layer and a gold plating layer to a wiring layer exposed on the surface. The nickel of the nickel plating layer applied to the wiring conductor layer does not move and diffuse to the surface of the gold plating layer to form a nickel oxide layer even by heat during mounting, and the nickel plating layer has no blister. Another object of the present invention is to provide a wiring board free from defects such as peeling and burning of foreign matter.

[0012]

According to the present invention, there is provided a wiring board comprising a nickel plating layer and a gold plating layer sequentially deposited on an exposed surface of a wiring layer formed on an insulating substrate. The plating layer has a boron content of 0.1% by weight or less, and the nickel particles have an average particle size of 20 n.
m or more.

In the wiring board according to the present invention, the thickness of the nickel plating layer is 1 μm to 10 μm.

In the wiring board according to the present invention, the gold plating layer has a thickness of 0.05 μm to 1 μm.

According to the wiring board of the present invention, since the boron content of the nickel plating layer applied to the exposed surface of the wiring layer is reduced to 0.1% by weight or less, the boron is formed during nickel plating. The grain growth of the nickel particles is not hindered by the boron contained in the nickel particles, and the nickel particles can be easily grown to a grain size of 20 nm or more.

The average particle size of the nickel particles is 20 n.
m, the grain boundaries of the nickel particles are small, and even if heat is applied to the wiring board, a large amount of nickel does not easily move and diffuse, but the nickel moves and diffuses to the surface of the gold plating layer and is oxidized. It is possible to effectively prevent the problem that the nickel layer is formed to deteriorate the wettability of the low melting point brazing material to the wiring layer and the bonding property.

According to the wiring board of the present invention, the nickel particles are as large as 20 nm or more, and it is not necessary to perform heat treatment on the nickel plating layer. There are no problems such as poor appearance and reduced insulation between wiring layers.

[0018]

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 one 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 element 1 and the wiring layer 2 form a semiconductor element 3
Is mounted on the wiring board 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, a glass ceramic sintered body, an epoxy resin, a polyimide resin, and a glass epoxy resin, and has a mounting portion 1a for mounting the semiconductor element 3 on an upper surface thereof. The semiconductor element 3 is bonded and fixed to the upper surface of 1a via an adhesive such as glass, resin or brazing material.

When the insulating substrate 1 is made of, for example, a sintered body of aluminum oxide, an appropriate binder and a solvent are added to a raw material powder of aluminum oxide, silicon oxide, calcium oxide, magnesium oxide, etc. and mixed to form a slurry. And a ceramic green sheet is obtained by forming the ceramic slurry into a sheet by employing a sheet forming technique such as a doctor blade method or a calendar roll method, which is well known in the art, and then cutting the ceramic green sheet. It is manufactured by forming an appropriate shape by processing or punching, 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.

The insulating substrate 1 has a large number of wiring layers 2 formed thereon from the periphery of the mounting portion 1a to the lower surface, and each electrode of the semiconductor element 3 is formed on the wiring layer 2 around the mounting portion 1a. The part connected to the lower surface of the insulating base 1 is electrically connected to the wiring conductor of the external electric circuit board via a low melting point brazing material such as tin-lead solder. .

The wiring layer 2 is made of a high melting point metal powder such as tungsten, molybdenum, manganese or the like. A metal paste obtained by adding a suitable organic binder or a solvent to the high melting point metal powder such as tungsten is mixed with an insulating substrate. By printing and applying a predetermined pattern on the ceramic green sheet to be used in advance by a conventionally known screen printing method, the ceramic green sheet is applied from the periphery of the mounting portion 1a of the insulating base 1 to the lower surface.

On the exposed surface of the wiring layer 2, as shown in FIG.
Gold plating layers 7 are sequentially applied.

The nickel plating layer 6 has excellent adhesion to the wiring layer 2 and thus acts as a base plating layer for firmly bonding the gold plating layer 7 to the surface of the wiring layer 2.

Since the nickel content of the nickel plating layer 6 is as low as 0.1% by weight or less, the grain growth of the nickel particles deposited and formed during plating is not hindered by the boron contained in the nickel particles. Hardly any
The individual nickel particles can grow large, so that the average particle size of the nickel particles is as large as 20 nm or more.

The average particle size of the nickel particles is 20 nm.
Since the above is large and the number of grain boundaries is small, a large amount of nickel does not diffuse along the grain boundaries, and when heat is applied to the wiring board at the time of bonding of a semiconductor element or the like, nickel is deposited on the gold plating layer 7. Can be effectively prevented from being caused to move and diffuse to the surface and oxidized to form a nickel oxide layer, thereby deteriorating the wettability and bonding property of the low melting point brazing material.

Also, since the average particle size of the nickel particles is increased to 20 nm or more without heat treatment,
There is no problem such as blistering, peeling, or sticking of foreign matter of the nickel plating layer 6 due to the heat treatment, and it is possible to obtain a wiring board having no poor appearance and no decrease in insulation between wiring layers.

The nickel plating layer 6 having a boron content of 0.1% by weight or less and an average particle size of the nickel particles of 20 nm or less contains, for example, nickel sulfate and dimethylamine borane as a reducing agent as main components. , Complexing agents, stabilizers,
Use of an electroless nickel plating solution to which an auxiliary component such as a pH buffer is added, while keeping the temperature of the plating solution low at 50 ° C. or lower, and slightly increasing the pH to a neutral to weakly alkaline region. Decomposition of hydrazine or the like by adjusting the working conditions, or by using an organic acid (or a salt thereof) having a low stability constant when nickel such as acetic acid or oxalic acid is complexed as a complexing agent. The compound can be formed by using, as a reducing agent, a compound in which a product is less likely to be mixed into the nickel plating layer and a high-purity nickel plating layer is easily obtained. In this case, when the boron content exceeds 0.1% by weight, the grain growth of the nickel particles is hindered by the boron, so that the individual nickel particles forming the nickel plating layer 6 cannot grow large. When the average particle size is smaller than 20 nm, and when the average particle size of the nickel particles is smaller than 20 nm, the grain boundaries of the nickel particles increase and nickel is easily diffused. The nickel oxide layer is diffused to deteriorate the wettability and bonding property of the low melting point brazing material. Therefore, the nickel plating layer 6 needs to have a boron content of 0.1% by weight or less and an average particle diameter of nickel particles of 20 nm or more.

If the thickness of the nickel plating layer 6 is less than 1 μm, it is difficult to completely cover the exposed surface of the wiring layer 2, so that the adhesion strength of the gold plating layer 7 to the wiring layer 2 is low. Tend to be
When the thickness exceeds 0 μm, the stress inherent in the plating layer increases, and the adhesion strength of the nickel plating layer 6 to the wiring layer 2 tends to decrease. Therefore, it is preferable that the thickness of the nickel plating layer 6 be in the range of 1 μm to 10 μm.

The gold plating layer 7 effectively prevents oxidative corrosion of the wiring layer 2 (actually, the wiring layer 2 and the nickel plating layer 6 deposited on the surface of the wiring layer 2), Acting to improve the wettability and bonding properties of the low melting point brazing material, formed by electrolytic plating or electroless plating, for example, potassium gold cyanide,
Using a substitution type electroless gold plating solution containing a complexing agent such as ethylenediaminetetraacetic acid as a main component, the exposed surface of the nickel plating layer 6 is degreased and acid-treated. By being immersed for a certain time, it is adhered to the exposed surface of the nickel plating layer 6 to a predetermined thickness.

The gold plating layer has a thickness of 0.1 mm.
When the thickness is less than 05 μm, it is difficult to effectively prevent the oxidative corrosion of the wiring layer 2 (actually, the wiring layer 2 and the nickel plating layer 6 deposited on the surface of the wiring layer 2). When the wiring layer 2 is made thicker, a brittle intermetallic compound is generated between tin and gold when the wiring layer 2 is connected to the wiring conductor of the external electric circuit board via a tin-containing low-melting brazing material such as tin-lead solder. However, the connection reliability may be reduced. Therefore, the gold plating layer 7 has a thickness of 0.05
It is preferable to set it in the range of μm to 1 μm.

Thus, according to the wiring board of the present invention, the semiconductor element 3 is bonded and fixed to the surface of the mounting portion 1a of the insulating base 1 via an adhesive such as glass, resin, brazing material, etc. Is electrically connected to the wiring layer 2 via the bonding wire 5, and then a bowl-shaped lid 8 made of metal or ceramic is placed on the upper surface of the insulating base 1 with a sealing material such as glass, resin, or brazing material. Then, the semiconductor element 3 is hermetically accommodated in a container including the insulating base 1 and the lid 8 to complete a semiconductor device as a product.

It should be noted that 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 substrate is applied to a package for housing a semiconductor element, it may be applied to other uses such as a hybrid integrated circuit substrate.

[0034]

According to the wiring board of the present invention, a nickel plating layer and a gold plating layer are sequentially deposited on the surface of the wiring layer,
The nickel plating layer has a boron content of 0.1% by weight or less, an average particle size of nickel particles of 20 nm or less, and a small number of grain boundaries between nickel particles. It is possible to effectively prevent nickel from moving and diffusing on the surface of the gold plating layer to form a nickel oxide layer, and to improve the wettability and bonding property of the low melting point brazing material of the wiring layer.

According to the wiring board of the present invention, the boron content of the nickel plating layer is reduced to 0.1% by weight, and the average particle diameter of the nickel particles is increased to 20 nm or more. The layer does not need to be subjected to heat treatment, and the heat treatment may cause defects such as blistering and peeling of the nickel plating layer, poor appearance due to sticking of foreign matter to the wiring board surface, and reduced insulation between wiring layers. There is no.

[Brief description of the drawings]

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

FIG. 2 is an enlarged view of a main part of the wiring board shown in FIG. DESCRIPTION OF SYMBOLS 1 ... Insulating base 2 ... Wiring layer 3 ... Semiconductor element 4 ... Wiring board 5 ... Bonding wire 6 ... Nickel plating layer 7 ... Gold plating layer

Claims (3)

[Claims] 1. A wiring board comprising a nickel plating layer and a gold plating layer sequentially deposited on an exposed surface of a wiring layer formed on an insulating substrate, wherein the nickel plating layer has a boron content of 0.1. % By weight and the average particle size of the nickel particles is 20 nm or more. 2. The wiring board according to claim 1, wherein said nickel plating layer has a thickness of 1 μm to 10 μm. 3. The wiring board according to claim 1, wherein the gold plating layer has a thickness of 0.05 μm to 1 μm.