JP2001308499A - Circuit board and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem of weak adhesive properties between a nickel plating layer and a gold plating layer covering a surface o a wiring layer. SOLUTION: A circuit board comprises a nickel-boron plating layer 6 exposed on the surface of the wiring layer 2 formed on an insulating base 1 and a gold plating layer 7 to be sequentially covered. In this case, an opening diameter of each of air gaps A formed on a surface of the layer 6 covered with the layer 7 is 3 μm or less. The overall opening area of the gaps A is 5% or less to a surface area of the layer 6.

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 mounting electronic components such as semiconductor elements.

[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 such as tungsten, molybdenum or the like on the inside and the surface of an insulating substrate generally made of aluminum oxide sintered body. It has a structure in which a wiring layer made of a metal material is formed, and electronic components such as semiconductor elements, capacitance elements, and resistors are mounted on the surface of the insulating base, and electrodes of the electronic component are bonded to the exposed surface of the wiring layer. Electrical connection is made via a wire or a low melting point brazing material.

The wiring board has a nickel plating layer and a gold plating layer sequentially deposited on the exposed surface of the wiring layer, thereby effectively preventing oxidation corrosion of the wiring layer and bonding wires and low melting points to the wiring layer. The brazing material has good bondability.

[0004] The nickel plating layer and the gold plating layer are not deposited because it is difficult to form lead wires for supplying plating power due to the densification of the wiring layer accompanying the miniaturization of the wiring board. Electroplating is being used extensively.

[0005] Such a wiring board is generally manufactured by the following steps. That is, (1) a step of preparing an insulating base made of an electrically insulating material such as an aluminum oxide sintered body having a surface provided with a wiring layer made of a high melting point metal material or the like; and (2) an exposed surface of the wiring layer. Forming a nickel plating layer using an electroless nickel plating solution containing a nickel compound serving as a nickel supply source such as nickel sulfate and a reducing agent as main components; and (3) an exposed surface of the nickel plating layer. Then, using an electroless gold plating bath containing a gold compound as a gold supply source such as potassium potassium cyanide and a complexing agent as a main component, a displacement plating method, that is, nickel is oxidized and eluted and gold is reduced and deposited. And forming a gold plating layer by a method for causing the gold plating layer.

As a reducing agent for the electroless nickel plating solution, dimethylamine borane having excellent catalytic activity is generally used, and the formed nickel plating layer contains about 0.3 to 3% by weight of boron. Nickel-boron alloy.

Further, as a complexing agent for the electroless gold plating bath, citric acid, EDTA (ethylenediamine) is used because of its good effect of complexing a gold compound (actually, gold ion) such as potassium potassium cyanide. Tetraacetic acid) and the like are generally used. Usually, an electroless gold plating bath formed by adding an additive such as a pH buffer to an aqueous solution mainly containing the above-described potassium gold cyanide and citric acid, The liquid temperature is about 85 ° C or more, and the working conditions are adjusted to weakly acidic to near neutral working conditions.

However, when the above-mentioned electroless method is used to form a gold plating layer, the rate of oxidative elution of nickel from the nickel plating layer made of a nickel-boron alloy is high, and the nickel is contained in the electroless gold plating bath. EDTA
The stability constant of the complexing agent such as
Since the elution of nickel is extremely promoted as high as 0 or more,
As shown in FIG. 4, the gold plating layer 22 does not adhere to the trace of nickel elution B formed on the nickel plating layer 21 and a large number of large-area voids remain. As a result, the nickel plating layer 21 and the gold plating The bonding area of the gold plating layer 22 to the nickel plating layer 21 becomes very weak, and the gold plating layer 22
There was a problem that peeling was easier than in 1.

Therefore, after the gold plating layer 22 is deposited on the surface of the nickel plating layer 21, heat treatment is performed at a temperature or higher (usually about 350 to 450 ° C.) at which nickel / gold interdiffuses. A method is considered in which 22 is baked on the nickel plating layer 21 to improve the adhesion strength between the two.

[0010]

However, when a gold plating layer is applied to the surface of the nickel plating layer and then heat-treated, the inside of the void formed between the nickel plating layer and the gold plating layer is reduced. The existing gas or liquid undergoes a large thermal expansion, which leads to a drawback in that the gold plating layer causes defects such as blistering and peeling.

At the same time, when a heating device such as a tunnel furnace is used for the heat treatment, foreign substances such as carbides present in the heating device adhere to the surface of the wiring substrate and are burned, resulting in poor appearance of the wiring substrate. In addition, a drawback that the electrical insulation between adjacent wiring layers is greatly reduced is also induced.

The present invention has been devised in view of the above-mentioned drawbacks, and has as its object to provide a method in which a nickel plating layer and a gold plating layer are firmly adhered to the exposed surface of a wiring layer without causing blisters or peeling. Another object of the present invention is to provide a wiring board having extremely high reliability.

[0013]

A wiring board according to the present invention is a wiring board comprising a nickel-boron plating layer and a gold plating layer sequentially deposited on an exposed surface of a wiring layer formed on an insulating substrate. The opening diameter of the void formed on the surface of the nickel-boron plating layer to which the gold plating layer is applied is 3 μm or less, and the total opening area of the void is the surface of the nickel-boron plating layer. It is not more than 5% of the area.

Further, the method of manufacturing a wiring board according to the present invention
(1) a step of preparing an insulating substrate provided with a wiring layer on the surface; (2) a step of forming a nickel-boron plating layer on the exposed surface of the wiring layer; and (3) exposure of the nickel-boron plating layer. Forming a gold plating layer on the surface using an electroless gold plating bath containing a gold compound serving as a gold supply source and a complexing agent having a stability constant of a complex with nickel of 5 or less as a main component. The opening diameter of the void formed on the surface of the nickel-boron plating layer by applying the gold plating layer is 3 μm or less, and the total opening area of the void is 5% or less with respect to the surface area of the nickel-boron plating layer. It is characterized by the following.

According to the wiring substrate of the present invention, for example, the rate of oxidation and elution of nickel is suppressed by using an electroless gold plating bath containing, as a main component, a gold compound and a complexing agent having a stability constant for nickel of 5 or less. About 1 volumetrically to elute nickel.
Preventing the trace of nickel elution from remaining due to the reduction precipitation of gold corresponding to the ratio of 1, the opening diameter of the void portion generated on the exposed surface of the nickel-boron plating layer is 3 μm or less, and the total opening area of the void portion Is 5% or less with respect to the surface area of the nickel-boron plating layer, the joining area between the nickel-boron plating layer and the gold plating layer becomes extremely large. As a result, the gold plating on the nickel-boron plating layer By making the adhesion strength of the layer very strong, the reliability as a wiring board can be made high.

Further, according to the wiring board of the present invention, the bath composition of the electroless gold plating bath is such that the elution of nickel is suppressed, and gold is reduced and precipitated in response to the oxidation and elution of nickel. The nickel-boron plating layer hardly forms voids on the surface, and the adhesion strength of the gold plating layer to the nickel-boron plating layer is increased. Since no heat treatment is required, the nickel plating layer and the gold plating layer Gases and liquids present inside the voids formed between them undergo large thermal expansion, which does not cause problems such as blisters or peeling on the gold plating layer, and provides good appearance and shape. Can also.

[0017]

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 formed.

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 its upper surface, and a large number of mounting portions from the mounting portion on which the semiconductor element 3 is mounted to the lower surface. The wiring layer 2 is formed by adhesion.

The insulating substrate 1 has a semiconductor element 3
Is mounted, and each electrode of the semiconductor element 3 is electrically connected to the wiring layer 2 exposed at the mounting portion via the solder ball 5 and is led out to the lower surface of the insulating base 1 of the wiring layer 2. Is electrically connected to the wiring conductor of the external electric circuit board via solder or the like.

As shown in FIG. 2, the wiring layer 2 has a nickel-boron plating layer 6 and a gold plating layer 7 on its exposed surface.
And are sequentially attached.

Since the nickel-boron plating layer 6 has excellent adhesion to the wiring layer 2, the nickel-boron plating layer 6 acts as a base plating layer for firmly joining the gold plating layer 7 to the surface of the wiring layer 2; Is formed on the exposed surface of the wiring layer 2 by an electroless plating method using a reducing agent.

The gold plating layer 7 functions to effectively prevent oxidative corrosion of the wiring layer 2 and to improve the wettability of the solder balls 5 and the like to the wiring layer 2. It is formed on the exposed surface of the nickel-boron plating layer 6 by electroless plating using a plating solution.

When the gold plating layer 7 is formed on the surface of the nickel-boron plating layer 6 by a nickel-gold substitution reaction, a void is formed due to a difference between a nickel elution rate and a gold deposition rate. A is formed, but in the wiring board of the present invention, the opening diameter of the gap A is 3 μm or less, and the total opening area of the gap A is 5% or less with respect to the surface area of the nickel-boron plating layer 6. It is important that

This is because the gold plating layer 7 is firmly adhered to the nickel-boron plating layer 6 without performing a heat treatment at a temperature higher than a temperature at which nickel and gold mutually diffuse (for example, 350 ° C. to 450 ° C.). It is important to reduce the opening diameter of the gap A to 3 μm or less and to make the total opening area of the gap A 5% or less with respect to the surface area of the nickel-boron plating layer 6. 6
And the gold plating layer 7 have an extremely large bonding area, and have a very high adhesion strength of the gold plating layer 7 to the nickel-boron plating layer 6 without heat treatment, thereby increasing the reliability as a wiring board. Can be made.

The gap A formed on the surface of the nickel-boron plating layer 6 on which the gold plating layer 7 is to be adhered becomes large when the opening diameter exceeds 3 μm. The bonding area with the gold plating layer 7 becomes narrow, and the adhesion strength of the gold plating layer 7 to the nickel-boron plating layer 6 becomes weak, and as a result, the reliability as a wiring board is greatly reduced.
Therefore, the nickel plating on which the gold plating layer 7 is deposited
The void A formed on the surface of the boron plating layer 6 has an opening diameter specified to be 3 μm or less.

When the total opening area of the gap A exceeds 5% of the surface area of the nickel-boron plating layer 6, the bonding area between the nickel-boron plating layer 6 and the gold plating layer 7 is also small. As a result, the adhesion strength of the gold plating layer 7 to the nickel-boron plating layer 6 becomes weak, and as a result, the reliability as a wiring board is greatly reduced. Therefore, the total opening area of the gap A is specified to be 5% or less of the surface area of the nickel-boron plating layer 6.

Further, when the total opening area of the void A is less than 1% of the surface area of the nickel-boron plating layer 6, the nickel-boron plating layer 6 having a different crystal lattice constant and the gold plating layer 7 Since there is almost no region for alleviating the strain caused by the bonding, the stress caused by the strain acts on the gold plating layer 7 and the gold plating layer 7 may have problems such as peeling and blistering. Therefore, it is preferable that the total opening area of the gap A is in the range of 1% to 5% with respect to the surface area of the nickel-boron plating layer 6.

Thus, according to the wiring board of the present invention, the semiconductor element 3 is mounted on the mounting portion of the insulating base 1, and each electrode of the semiconductor element 3 is electrically connected to the wiring layer 2 via the solder ball 5, Thereafter, a bowl-shaped lid 9 made of metal or ceramics is joined to the upper surface of the insulating base 1 via a sealing material such as glass, resin, brazing material, or the like. The semiconductor device as a product is completed by housing the semiconductor element 3 in an airtight manner.

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, an insulating substrate 1 provided with a wiring layer 2 on the surface and inside shown in FIG. 3A is prepared.

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, a glass epoxy resin, and has a mounting portion for mounting a semiconductor element on an upper surface thereof. A semiconductor element is mounted on the semiconductor device.

When the insulating substrate 1 is made of, for example, an aluminum oxide sintered body, an appropriate binder and a solvent are added to a raw material powder such as aluminum oxide, silicon oxide, calcium oxide, magnesium oxide, etc. 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 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 previously printing and applying a predetermined pattern on the ceramic green sheet to be 1 by a well-known screen printing method, the insulating substrate 1 is attached from the mounting portion where the semiconductor element is mounted to the lower surface.

Next, as shown in FIG. 3B, a nickel-boron plating layer 6 is formed on the exposed surface of the wiring layer 2.

The nickel-boron plating layer 6 is formed using an electroless nickel plating solution containing a nickel compound such as nickel sulfate and nickel chloride and a boron-based reducing agent such as dimethylamine borane and diethylamine borane as main components. For example, in an aqueous solution containing nickel sulfate and dimethylamine borane as main components, a complexing agent, a stabilizer, pH
After the exposed surface of the wiring layer 2 is degreased and acid-treated using an electroless nickel plating solution to which an auxiliary component such as a buffer is added, the wiring layer is immersed in the electroless nickel plating solution for a predetermined time to form a wiring layer. 2 to a predetermined thickness on the exposed surface.

Next, as shown in FIG. 3C, a gold plating layer 7 is formed on the exposed surface of the nickel-boron plating layer 6.

The gold plating layer 7 comprises a gold compound serving as a gold source such as potassium gold cyanide and a complexing agent having a stability constant of a complex with nickel of 5 or less, for example, acetic acid, lactic acid, malic acid and the like. After the exposed surface of the nickel-boron plating layer 6 is degreased and acid-treated by using a substitution type electroless gold plating bath containing It is applied to the surface of the nickel-boron plating layer 6 to a predetermined thickness.

In this case, as schematically shown in the following reaction formula (1), nickel (ion, N
i ²⁺ ) and the complexing agent (A) in the gold plating bath cause an equilibrium reaction to form a complex (NiA) as schematically shown in the following reaction formula (2), and the complex is stabilized. If the degree constant is as high as, for example, 10 or more, the reaction formula (2) preferentially proceeds in the right-hand direction to promote the consumption of nickel ions, and a reaction for supplying the consumed nickel ions, that is, elution of nickel However, in the production method of the present invention, the complexing agent used in the gold plating bath has a low stability constant for nickel of 5 or less, so that the formation of a nickel complex is not promoted. Since the equilibrium reaction of the reaction formula (2) does not easily proceed to the right side, the progress of the reaction of oxidizing and eluting nickel can be suppressed, and the oxidizing and eluting of nickel from the nickel-boron plating layer 6 is effectively suppressed. be able to.

Ni → Ni ²⁺ + 2e ⁻ (where e ^{− is an} electron) ··· Reaction formula (1) Ni ²⁺ + A? (NiA) ²⁺ ··· Reaction formula (2) (where A: complex (The charge of the complexing agent is omitted.) The stability constant (k) is k = log _{10 、} [(NiA)] / ([Ni] ×
[A])｝ (where [] represents the concentration of the component in []).

Thus, the nickel-boron plating layer 6
Gold can be reduced and precipitated from the gold plating bath in response to oxidation and elution of nickel from the nickel, and nickel elution traces can be effectively prevented from remaining on the surface of the nickel-boron plating layer 6 over a wide area. The opening diameter of the portion A can be 3 μm or less, and the total opening area of the void portion A can be 5% or less with respect to the surface area of the nickel-boron plating layer 6.

When the stability constant of the complex of the complexing agent with respect to nickel exceeds 5, the formation of the nickel complex is promoted and the oxidative elution of nickel from the nickel-boron plating layer 6 is promoted. The opening diameter of the gap A generated on the surface of the nickel-boron plating layer 6 on which the nickel-boron plating layer 6 is formed becomes larger than 3 μm, and the total opening area of the gap A is reduced.
Over 5% of the surface area. Therefore, the complexing agent which is a main component of the gold plating bath is specified to have a stability constant of the complex with respect to nickel of 5 or less, and considering the stability of the gold plating bath itself, 0.1.
It is even more preferred to be in the range of 5-5.

The opening diameter of the void A formed on the surface of the nickel-boron plating layer 6 is 3 μm or less.
In order to make the total opening area of 5% or less with respect to the surface area of the nickel-boron plating layer 6, the gold plating bath is subjected to conditions under which reduction and precipitation of gold are suppressed or conditions under which nickel is hardly eluted. For example, adjusting the working conditions of the gold plating bath, such as lowering the bath temperature, increasing the pH, or lowering the gold concentration, or using nickel such as a weak acid salt as a pH buffer For example, a method of using a substance having a low corrosive property to the substance, adding an agent for suppressing the corrosion of nickel, or the like can be used.

It should be noted that 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. For example, before forming the nickel-boron plating layer 6, A conventionally well-known palladium activity is applied to the surface of the wiring layer 2 and the nickel-boron plating layer 6 is formed.
May be more evenly and firmly adhered to the wiring layer 2.

[0044]

According to the wiring board of the present invention, for example, the rate of oxidation and elution of nickel is determined by using an electroless gold plating bath containing a gold compound and a complexing agent having a stability constant for nickel of 5 or less as main components. To prevent nickel from leaving traces of elution due to the reductive deposition of gold in a volumetric one-to-one correspondence with the elution of nickel, and to prevent voids generated on the exposed surface of the nickel-boron plating layer. The opening diameter is 3 μm or less,
Since the total opening area of the voids is set to 5% or less with respect to the surface area of the nickel-boron plating layer, the joining area between the nickel-boron plating layer and the gold plating layer becomes extremely large. -The adhesion strength of the gold plating layer to the boron plating layer can be made very strong, so that the reliability as a wiring board can be made high.

According to the wiring board of the present invention, the bath composition of the electroless gold plating bath is such that the elution of nickel is suppressed, and gold is reduced and deposited in response to the oxidation and elution of nickel. The nickel-boron plating layer hardly forms voids on the surface, and the adhesion strength of the gold plating layer to the nickel-boron plating layer is increased. Since no heat treatment is required, the nickel plating layer and the gold plating layer Gases and liquids present inside the voids formed between them undergo large thermal expansion, which does not cause problems such as blisters or peeling on the gold plating layer, and provides good appearance and shape. Can also.

[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.

3 (a) to 3 (c) are enlarged cross-sectional views of essential parts in each step for explaining a method of manufacturing the wiring board shown in FIG.

FIG. 4 is an enlarged sectional view of a main part of a conventional wiring board.

[Description of Signs] 1 ... Insulating substrate 2 ... Wiring layer 3 ... Semiconductor element 4 ... Wiring board 5 ... Solder ball 6 ... Nickel-boron plating layer 7: Gold plating layer A: Void

Claims (2)

[Claims] 1. A wiring board comprising a nickel-boron 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 is deposited on the nickel-boron plating layer. -The opening diameter of the void formed on the surface of the boron plating layer is 3 µm or less, and the total opening area of the void is 5% or less with respect to the surface area of the nickel-boron plating layer. Wiring board. And (2) forming a nickel-boron plating layer on an exposed surface of the wiring layer, and (3) forming a nickel-boron plating layer on an exposed surface of the wiring layer. Forming a gold plating layer on the exposed surface of the boron plating layer using an electroless gold plating bath containing a gold compound serving as a gold supply source and a complexing agent having a stability constant of a complex with nickel of 5 or less as a main component. The opening diameter of the void formed on the surface of the nickel-boron plating layer by applying the gold plating layer is 3 μm or less, and the total opening area of the void is reduced to the surface area of the nickel-boron plating layer. A method for manufacturing a wiring board, wherein the content is 5% or less.