JP2001177220A - Manufacturing method of wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem, where nickel of a nickel-plated layer is moved the surface of a gold-plated layer for diffusion, and the electrode of a semiconductor element cannot be connected firmly and electrically to a wiring layer. SOLUTION: A wiring board 4, where a wiring layer 2 is formed in an insulating substrate 1, is dipped into a nickel-plated bath using nickel salt and hydrazine as the metal supply source and the reduction agent, respectively, a nickel- plated layer 6 consisting of nickel particles with an average grain size of 20 nm or more is deposited onto the exposure surface of the wiring layer 2 of the wiring board 4, the wiring board 4 where the nickel-plated layer 6 is deposited is dipped into a gold-plating bath, and a gold-plated layer 7 is deposited on the surface of the nickel-plated layer 6.

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 layer made of a material is formed, and electronic components such as a semiconductor element, a capacitor element, and a resistor are mounted on the surface of the insulating base.
The electrode of each electronic component is electrically connected to the exposed surface of the wiring layer via a bonding wire or a low melting point brazing material.

In order to prevent the oxidative corrosion of the wiring layer and to improve the wettability of the low melting point brazing material, a nickel plating layer having excellent adhesion to the wiring layer is formed on the surface of the wiring layer. A gold plating layer having excellent corrosion resistance, low melting point brazing material wettability, and bonding properties is usually applied to the wiring layer to a predetermined thickness by the following method.

That is, (1) First, a wiring board is prepared in which a wiring layer made of a refractory metal material such as tungsten or molybdenum is formed on the surface of an insulating substrate made of an aluminum oxide sintered body or the like. On the exposed surface of the wiring layer, a nickel salt as a nickel source and sodium hypophosphite or dimethylamine borane as a reducing agent as main components, and an organic acid such as succinic acid and acetic acid or a salt thereof. Using a so-called phosphorus-based or boron-based electroless nickel plating solution made by adding auxiliary components such as a pH adjuster such as a complexing agent, sodium hydroxide, and ammonia, a nickel plating layer is applied to a predetermined thickness. (3) Finally, a gold plating layer is deposited on the exposed surface of the nickel plating layer to a predetermined thickness using an electroless gold plating solution using gold potassium cyanide as a gold supply source. It was done by the.

However, in the above-mentioned conventional method of manufacturing a wiring board, the electroless nickel plating solution for depositing the nickel plating layer on the exposed surface of the wiring layer is formed of sodium hypophosphite or boron (P) containing phosphorus (P). Since dimethylamine borane containing B) is used as a reducing agent, the reducing agent causes reduction and precipitation of nickel, and at the same time, is itself decomposed to precipitate phosphorus or boron (eutectoid).
The nickel plating layer to be formed contains about 5% by weight of phosphorus or about 0.3 to 3% by weight of boron, and particles of individual nickel particles forming the plating layer by eutectoids such as phosphorus or boron. Since the growth is hindered, the obtained nickel plating layer has an average particle size of 20 n.
m and 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.

Therefore, the temperature of the nickel plating layer is set to 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 and suppress diffusion by heat.

[0008]

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 onto the wiring board, which causes a problem that electric insulation between wiring layers is deteriorated and appearance is deteriorated.

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

The present invention has been devised in view of the problems of the above-mentioned conventional method, and has as its object to sequentially deposit a nickel plating layer and a gold plating layer on a wiring layer exposed on the surface of an insulating substrate. Bonding semiconductor elements on the wiring board,
The nickel of the nickel plating layer adhered to the wiring layer does not move and diffuse to the surface of the gold plating layer to form a nickel oxide layer even by heat at the time of mounting or the like. It is an object of the present invention to provide a method for manufacturing a wiring board free from defects such as image sticking and foreign matter burning.

[0011]

According to the present invention, there is provided a method of manufacturing a wiring board, comprising the steps of (1) preparing a wiring board having a wiring layer formed on an insulating base; and (2) using the wiring board as a metal supply source. (3) immersing in a nickel plating bath using nickel salt and hydrazine as a reducing agent, and applying a nickel plating layer made of nickel particles having an average particle diameter of 20 nm or more to the exposed surface of the wiring layer of the wiring board; D) dipping a wiring board having the nickel plating layer applied to the wiring layer in a gold plating bath, and applying a gold plating layer to the surface of the nickel plating layer.

According to the method for manufacturing a wiring board of the present invention, a nickel plating solution for forming a nickel plating layer is provided by:
Hydrazine (NH ₂ · NH ₂ ) is used as a reducing agent, and the decomposition products of the hydrazine (nitrogen gas, hydrogen gas, water, etc.) are easily vaporized or dissolved in the plating bath, and are used as in conventional phosphorus and boron. Hardly precipitates (eutectoid) in the nickel plating layer, so that during nickel plating, the grain growth of the precipitated nickel particles is hindered by eutectoids such as phosphorus and boron contained in the nickel particles. Therefore, the nickel particles can be grown to a size of 20 nm or more by grain growth.

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.

Further, according to the method of manufacturing a wiring board of the present invention, since the nickel particles are as large as 20 nm or more and it is not necessary to perform a heat treatment on the nickel plating layer, blisters, peeling, foreign matters, etc. of the nickel plating layer due to the heat treatment are eliminated. There are no problems such as poor appearance due to image sticking or deterioration in insulation between wiring layers.

[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 embodiment in which a wiring board manufactured by the manufacturing method of the present invention is applied to a package for accommodating a semiconductor element, wherein 1 is an insulating base, and 2 is a wiring layer. The insulating substrate 1 and the wiring layer 2 constitute 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, 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 the upper surface thereof. The semiconductor element 3 is bonded and fixed via an adhesive such as glass, resin, or brazing material.

The insulating substrate 1 has a large number of wiring layers 2 made of a metal material such as tungsten, molybdenum, manganese, silver, copper or the like formed thereon from the mounting portion 1a to the lower surface thereof. Each electrode of the semiconductor element 3 is electrically connected to a portion exposed to the mounting portion 1a through a metal bump 5 made of a low melting point brazing material such as tin-lead solder, and is led out to the lower surface of the insulating base 1. The portion is electrically connected to a circuit conductor of the external electric circuit board via a low melting point brazing material or the like.

Further, as shown in FIG.
A nickel plating layer 6 and a gold plating layer 7 are formed on the exposed surface.
Are sequentially applied.

The nickel plating layer 6 acts as a base plating layer for firmly attaching the gold plating layer 7 to the surface of the wiring layer 2, and the gold plating layer 7 oxidizes the wiring layer 2 and the nickel plating layer 6. In addition to preventing corrosion, it has an effect of improving the wettability of the low melting point brazing material to the wiring layer 2.

A cover 8 is attached to the upper surface of the insulating substrate 1 so as to cover the mounting portion 1a, and the semiconductor element 3 mounted on the mounting portion 1a of the insulating substrate 1 by the lid 8 is hermetically sealed. It is designed to stop.

Next, a method of manufacturing the above-described wiring board will be described with reference to FIGS. In the drawings, the same parts as those in FIGS. 1 and 2 are denoted by the same reference numerals.

First, as shown in FIG. 3A, an insulating substrate 1 having a wiring layer 2 on its surface is prepared.

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 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. And a sheet-shaped ceramic green sheet (ceramic green sheet) is obtained by employing a sheet forming technique such as a doctor blade method or a calendar roll method, which is well known in the art.
Cutting and punching the ceramic green sheet into an appropriate shape and 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. Produced by

When the wiring layer 2 is made of, for example, a high melting point metal such as tungsten, molybdenum, or manganese, a metal paste obtained by adding a suitable organic binder or solvent to a high melting point metal powder such as tungsten and mixing. The ceramic green sheet serving as the insulating substrate 1 is printed and applied in a predetermined pattern by a conventionally well-known screen printing method so that the ceramic green sheet is adhered to a predetermined position of the insulating substrate 1.

If the exposed surface of the wiring layer 2 is subjected to palladium activity to impart catalytic activity, the surface of the wiring layer 2 may be covered with a nickel plating layer in a later step to prevent chipping and unevenness. It can be firmly adhered without generation. Therefore, it is preferable that the wiring layer 2 be subjected to palladium activity on an exposed surface thereof with a palladium chloride solution or the like.

Next, a nickel plating bath using a nickel salt as a metal supply source and hydrazine as a reducing agent is prepared, and the nickel plating bath is used to form an exposed surface of the wiring layer 2 as shown in FIG. Then, a nickel plating layer 6 is formed by an electroless method.

The nickel plating layer 6 covers the exposed surface of the wiring layer 2 so as to improve the wettability of the wiring layer 2 with respect to the low melting point brazing material and to form a gold plating layer to be formed in a later step. 7 serves as a base for firmly adhering to the wiring layer 2.

The nickel plating layer 6 is formed by using a nickel plating bath using hydrazine as a reducing agent. Nitrogen and hydrogen which are decomposition products of the hydrazine hardly precipitate in the nickel plating layer 6. Therefore, at the time of plating, the precipitated nickel particles are formed of high-purity nickel, and the grain growth is hardly hindered by the eutectoid contained in the nickel particles,
The individual nickel particles can grow large, so that the average particle size of the nickel particles can be as large as 20 nm or more.

The average particle size of the nickel particles is 20 nm.
As described above, since a large number of grain boundaries are present, 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 a semiconductor element or the like, nickel is applied to the gold plating layer. It is possible to effectively prevent the problem of being transferred and diffused 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.

Further, since the average particle size of the nickel particles is increased to 20 nm or more without heat treatment, problems such as blistering, peeling, and seizure of foreign matter of the nickel plating layer 6 due to the heat treatment do not occur. In addition, it is possible to obtain a wiring board free from poor appearance and reduced insulation between wiring layers.

The nickel plating bath using hydrazine as a reducing agent is, for example, about 0.1 mol / liter of a nickel salt such as nickel lactate or nickel chloride as a metal source, and about 1 mol / liter of hydrazine as a reducing agent. Liters as a main component, a complexing agent, a pH buffering agent and the like are added thereto and mixed.
About 11 can be used.

In this case, it is preferable that the composition of the nickel plating bath using hydrazine as a reducing agent and the working conditions at the time of plating are such that the plating rate is suppressed.

This is because nickel particles can easily grow by suppressing the plating rate and nickel particles having an average particle diameter of 20 nm or more can be easily formed. The plating rate of nickel can be suppressed by lowering the salt concentration or the reducing agent concentration, lowering the plating solution temperature for the working conditions during plating, lowering the pH of the plating solution, and the like.

The pH buffering agent contained in the nickel plating bath has an effect of preventing the pH of the plating bath from suddenly fluctuating due to decomposition products such as nickel salts and reducing agents, and boric acid is preferred. Used for Further, the complexing agent has a function of forming a complex with nickel (ion) in a plating bath to stabilize it, and an organic acid such as citric acid or a salt thereof is suitably used.

When 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. Therefore, the nickel plating layer 6 is deposited on the surface in a later step. The adhesion strength of the gold plating layer to the wiring layer 2 tends to be low, and if it exceeds 10 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. There is. Therefore, it is preferable that the thickness of the nickel plating layer 6 be in the range of 1 μm to 10 μm.

Finally, the wiring layer 2 having the nickel plating layer 6 adhered to the wiring layer 2 is immersed in a gold plating bath, and the surface of the nickel plating layer 6 is coated with gold as shown in FIG. The plating layer 7 is applied.

The gold plating layer 7 is, for example, a substitutional type comprising gold potassium cyanide as a gold compound and ethylenediaminetetraacetic acid as a complexing agent as main components and adding potassium cyanide, potassium dihydrogen phosphate and the like. A gold plating bath and a reduction-type gold plating bath containing gold potassium cyanide as a gold compound and sodium borohydride as a reducing agent as main components were prepared, and the nickel plating layer 6 was applied thereto. The exposed surface of the wiring layer 2 is immersed for a predetermined time in the order of the replacement-type gold plating solution and the reduction-type gold plating solution for a predetermined thickness on the nickel plating layer 6.

The gold plating layer 7 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 connected to the wiring conductor of the external electric circuit board via a tin-containing low-melting brazing material such as tin-lead solder, a brittle intermetallic compound is generated between tin and gold. Connection reliability may be reduced. Therefore, the gold plating layer 7 has a thickness of 0.05 μm.
It is preferable to set it in the range of m to 1 μm.

[0039]

According to the method of manufacturing a wiring board of the present invention,
A nickel plating solution for forming a nickel plating layer uses hydrazine (NH ₂ · NH ₂ ) as a reducing agent and decomposes the hydrazine (nitrogen gas, hydrogen gas, water, etc.).
Easily evaporates or dissolves in the plating bath and hardly precipitates (eutectoid) in the nickel plating layer unlike conventional phosphorus and boron. The growth is not hindered by eutectoids such as phosphorus and boron contained in the nickel particles, and the nickel particles can be made to grow to 20 nm or more by grain growth.

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.

Further, according to the method of manufacturing a wiring board of the present invention, since nickel particles are as large as 20 nm or more and it is not necessary to perform heat treatment on the nickel plating layer, blisters, peeling, foreign matters, etc. of the nickel plating layer due to the heat treatment are eliminated. There are no problems such as poor appearance due to image sticking or deterioration in insulation between wiring layers.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an embodiment in which a wiring board manufactured by a manufacturing method 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.

FIGS. 3A to 3C are enlarged cross-sectional views of main parts in each step for explaining a method of manufacturing a wiring board according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Insulating base 1a ... Semiconductor element mounting part 2 ... Wiring layer 3 ... Semiconductor element 4 ... Wiring board 5 ... Metal bump 6 ... Nickel plating Layer 7: Gold plating layer 8: Lid

Claims (1)

[Claims] (1) a step of preparing a wiring board having a wiring layer formed on an insulating base; and (2) a step of preparing the wiring board in a nickel plating bath using a nickel salt as a metal supply source and hydrazine as a reducing agent. A nickel plating layer made of nickel particles having an average particle diameter of 20 nm or more on the exposed surface of the wiring layer of the wiring board; and (3) a wiring having a nickel plating layer deposited on the wiring layer. Dipping the substrate in a gold plating bath and applying a gold plating layer to the surface of the nickel plating layer.