JPH08325744A - Method for activating nickel-boron electroless plating film - Google Patents

Abstract

PURPOSE: To activate the surface of a heat-treated Ni-B electroless plating film. CONSTITUTION: An Ni-B electroless plating film is formed 2-5μm thicker than the specified film thickness, the film is heated in a nonoxidizing atmosphere, and then the surface layer of the film is removed by etching to obtain a specified thickness. For example, the Ni-B electroless plating film is formed 2-5μm thicker than specified, pin brazing is applied in a nonoxidizing atmosphere, then etching is conducted to obtain a specified thickness, substitution gold plating is performed, and a chip is soldered to produce an IC package. Consequently, the depositing rate of the substitution gold plating is increased, and the solder wettability is improved.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to electroless nickel-boron whose surface has become inactive due to heat or heat treatment.
(Ni-B) A method for activating a plating film. As a specific application field of the present invention, a brazing process (for example, pin brazing) is performed at a high temperature after electroless Ni-B plating,
Next, the production of a ceramic IC package in which displacement gold plating is performed may be mentioned, but the present invention is not limited to this application, and the electroless nickel-boron plating film is heated or heat-treated, and then plating or plating is further performed. The present invention can be applied to any manufacturing process for performing coating or adhesion treatment that requires wettability such as soldering.

[0002]

2. Description of the Related Art Pin-type ceramic IC packages with complicated wiring patterns [eg PGA (pin grid array), MCM (mult)
i chip module) etc.] is roughly as follows.

A conductive paste containing a large amount of powder of refractory metal such as W or Mo-Mn alloy as conductive powder is screen-printed on a ceramic substrate mainly made of sintered alumina,
It is fired in a reducing atmosphere to form a metallized layer to be a circuit. Alternatively, as is known as the green sheet method, the metallization layer is fired simultaneously with the sintering of the substrate ceramic (especially in the case of a multilayer ceramic substrate).

Since this metallized layer cannot be brazed, the metallized layer is coated with nickel by an electroless plating method to enable brazing. Then, after brazing the pins (leads for external connection), thin gold plating (0.2 μm or less) is applied by the displacement plating method to secure the bondability at the time of wire bonding, and then the electroless plating method is applied. (2 to 3 μm) gold plating is performed. BG
In the case of the ball bonding method used in A (ball grid array), etc., thinning (0.1 μ
m or less) is sufficient for gold plating. After that, the die is bonded by mounting (mounting) the IC chip at a predetermined position by soldering, then the connection between the chip and the external lead is secured by wire bonding or ball bonding, and finally a ceramic or metal lid is covered. When airtightly sealed by welding, soldering, or low melting point glass, and post-processing such as solder plating, ceramic IC
The package is complete.

The nickel plating film formed by the electroless nickel plating method is Ni-P depending on the type of reducing agent.
It is either an alloy (reducing agent is hypophosphite) or a Ni-B alloy (reducing agent is amine borane compound or sodium borohydride). Although the surface activity of each plating film is high, the Ni-B alloy plating film is superior in solderability and has good adhesion to the metallized layer. Therefore, in the above IC package manufacturing process, after the metallized layer is formed, an amine borane compound (especially dimethylamine borane) is used as a reducing agent to remove Ni-B.
It is common to perform electroless nickel plating so as to form an alloy plating film.

The plating film formed by the electroless nickel plating method using this amine borane reducing agent is a Ni-B alloy plating film containing boron derived from a reducing agent in addition to nickel, and its B content is% by weight. It ranges from less than 1% to several%. Therefore, this plating method is called electroless nickel-boron plating to distinguish it from other electroless nickel plating. The present invention is a plating film formed by this electroless nickel-boron plating method, that is,
Electroless nickel-boron plating film (hereinafter referred to as electroless Ni-
B plating film).

[0007]

In the above-mentioned IC package manufacturing process, the surface activity is lowered depending on the atmosphere of pin brazing performed after electroless Ni-B plating.
It has been experienced that the product is rejected due to defective deposition of gold during subsequent displacement gold plating and poor solder wettability during chip mounting. This phenomenon of decrease in surface activity occurs when the atmosphere during pin brazing (which is also called sintering since it is performed at high temperature) is not 100% hydrogen but a non-oxidizing atmosphere containing nitrogen. Remarkably recognized.

As a solution to this problem, the brazing of the pins has been carried out in a nitrogen-free atmosphere consisting of 100% hydrogen or an inert gas such as argon. But,
High costs are inevitable. Also, 100% hydrogen
Even when brazing was performed in the atmosphere, the solder wettability was sometimes poor.

In Japanese Patent Publication No. 59-33665, a conductive paste containing a glass frit is screen-printed on a substrate, an electroless Ni-B plating film is formed, and then in an unreactive atmosphere at 750 ° C. or higher. It is described that heating to a temperature to diffuse boron in the plating film into the glass prevents a decrease in the wettability of the plating film. But,
When the present inventors applied this method to an alumina substrate and conducted an experiment, it was found that after heating for brazing (sinter), boron did not diffuse to the alumina / conductive paste interface, and it was not possible to prevent deterioration of wettability. Admitted.

An object of the present invention is to obtain electroless Ni having high surface activity.
-When the B plating film is heated or heat-treated in an atmosphere containing nitrogen, the reduced surface activity can be activated and the deterioration of wettability can be prevented, and the surface activation of the electroless Ni-B plating film can be prevented. Is to provide a method.

Another object of the present invention is to apply this method to the manufacture of a ceramic IC package to prevent defective deposition of gold in a subsequent displacement gold plating process even if the brazing process is performed in an atmosphere containing nitrogen. An object of the present invention is to provide a method for manufacturing an IC package, which does not cause poor solder wettability when mounting a chip.

[0012]

According to one aspect of the present invention, an electroless nickel-boron plating film is formed on a substrate having a crystal grain structure so as to have a thickness of 2 to 5 μm from a predetermined film thickness. After being heated in a non-oxidizing atmosphere,
A method for activating an electroless nickel-boron plating film heated in a non-oxidizing atmosphere, characterized in that the surface layer of the plating film is removed by etching to a predetermined thickness.

From another aspect, the present invention is a method in which a conductive paste is applied and fired on a ceramic substrate, an electroless nickel-boron plating film is formed on the conductive paste, and then pins are brazed and then displacement gold plating is performed. In the production of the ceramic IC package, the electroless nickel-boron plating film is formed to a thickness of 2 to 5 μm thicker than a predetermined film thickness, the pins are brazed in a non-oxidizing atmosphere, and then the surface layer of the plating film is etched. After removing to a predetermined thickness,
Ceramic IC characterized by performing displacement gold plating
It is a method of manufacturing a package.

[0014]

The present inventor has found that the cause of the decrease in the surface activity of electroless Ni-B plating when it is heated or heat-treated (eg, brazing) particularly in a nitrogen-containing atmosphere is ESCA (X-ray photoelectron spectroscopy) or EPMA. As a result of investigation using (X-ray microanalyzer), the following points were clarified.

The electroless Ni-B plating film contains boron (B) in an amount of several wt% or less. This boron is Ni ₂ B.
In the form of, it is distributed almost uniformly over the entire plating film. That is, this plating film is composed of a mixture of Ni and Ni ₂ B. The presence of Ni ₂ B was confirmed by oblique-angle incident X-ray diffraction.

When this electroless Ni-B plating is heated in a nitrogen-containing atmosphere, Ni ₂ B reacts with nitrogen and changes into Ni metal and boron nitride (BN) as shown in the following formula. Ni ₂ B + 1/2 N ₂ → 2 Ni + BN (ΔG ₀ = −60 kcal / J · mol) Since ΔG ₀ is negative, if the above reaction is in an equilibrium state, it will be easily converted into a product system by heat treatment. Move to. When oxygen is present in the atmosphere, Ni ₂ B also reacts with oxygen to generate boron oxide (B ₂ O ₃ ). This reaction also occurs extremely easily, even if the atmospheric gas contains a trace amount of oxygen.

Therefore, when nitrogen or oxygen is present in the heating atmosphere, Ni ₂ B in the vicinity of the surface of the plating film first reacts with nitrogen or oxygen to change into a nitride (BN) or an oxide (B ₂ O ₃ ). To do.
When Ni ₂ B near the surface is consumed, Ni ₂ B diffuses from the inside of the plating and is replenished, and the above reaction continues on the surface of the plating film. In this way, when heating is continued, the boron in the electroless Ni-B plating film is finally concentrated as a nitride or an oxide on the plating surface layer and is deposited on the surface of the plating film, so that the inside of the plating film The B concentration of is very low.

As a result of confirmation by EPMA by the present inventor, in electroless Ni-B plating after heat treatment, B was concentrated in the surface layer portion up to about 1 μm from the surface, and the inside thereof was essentially pure Ni. . Although the reaction mechanism described above is not shown, MT Evans et al shows that when heat treatment is performed on electroless Ni-B plating, boron is completely diffused on the surface of the plating film and the boron disappears from the film body. ., J. Elec
trochem. Soc., Vol. 141, No. 1 (1994), pp. 78-82.

BN and B ₂ O ₃ concentrated on the surface layer of this plating film
Is inactive and has poor wettability, which hinders gold deposition and solder wettability in displacement plating. Therefore, as a means for preventing the deposition failure of the gold plating and the solder wettability, it is conceivable to prevent the above-mentioned nitriding and oxidation reaction of boron. However, this requires heating in an atmosphere consisting of hydrogen or an inert gas (eg, argon) of a high purity gas of 100%, which is costly.

From the above, when an inexpensive atmosphere gas containing nitrogen or oxygen is used, it is avoided that BN or B ₂ O ₃ is generated on the surface layer of the electroless Ni-B plating film to lower the surface activity. Based on the conclusion that it is not possible, the present inventor examined means for activating the thus-deactivated plating film surface. As a result, they have found that BN and B ₂ O ₃ on the surface layer can be removed by etching.

Boron nitride (BN) is chemically stable, and it is difficult to remove it by dissolving it in an acid or alkali aqueous solution. Also, it was found that diboron trioxide (B ₂ O ₃ ) formed on the surface layer of the electroless Ni-B plating film was insoluble in an acid or alkali aqueous solution, which was unexpectedly expected (this is pure pure).
In B ₂ O _3, not considered because it is chemically shifted B-rich or O rich). Therefore, it is not conceivable to remove them by etching using an aqueous solution of acid or alkali from common sense. However, it has been found that BN and B ₂ O ₃ existing on the surface layer of the electroless Ni-B plating film formed on the substrate having a crystal grain structure can be easily removed by etching for the reason described below.

For example, in a ceramic IC package,
As described above, the conductive paste is applied to the alumina substrate formed by the powder metallurgy method, and electroless Ni-B plating is performed on the fired conductor layer. In this case, the alumina of the substrate is not a metal-like surface but an aggregate of crystal grains, and grain boundaries exist. A conductor layer formed by applying and firing a conductive paste containing a refractory metal powder such as W or Mo-Mn alloy also has a surface having a crystal grain structure.

Therefore, the electroless Ni-B plating film formed thereon (that is, the surface of the substrate having the crystal grain structure) was formed by the aggregation of crystal grains as schematically shown in FIG. It has a fine structure and has grain boundaries similar to the alumina of the substrate. In addition, the BN and B ₂ O ₃ deposited on the surface of the plating film by heat treatment do not form a continuous phase that completely covers the surface of the plating film, but as shown in FIG. Is deposited on the surface as.

Due to this film structure, heat-treated electroless Ni
Metal Ni is partially exposed on the surface of the -B plating film. Then, when the plating film of this structure is treated with an etching solution capable of dissolving and removing Ni, the etching solution penetrates into the plating film from the exposed portion of Ni, and particularly penetrates into the plating film along the grain boundaries, and near the grain boundaries. Ni is dissolved and removed. As a result, the Ni crystal grains in the surface layer part are removed from the plating film together with the BN and B ₂ O ₃ adhered thereon, and are removed. That is, BN and B ₂ O ₃ are not dissolved and removed by etching, but Ni underneath is dissolved to remove BN and B ₂ O ₃ together with Ni in the lower layer. This removes BN and B ₂ O ₃ and provides an active plating surface consisting essentially of Ni.

The present invention utilizes this knowledge.
As shown in FIG. 2, a substrate having a crystal grain structure (in this case, a conductive layer formed by screen-printing a conductive paste)
Electroless Ni-B plating film on top of
It is formed to a thickness of 5 μm. For example, the desired plating thickness is 4μ
If the thickness is m, an extra plating film of 2 to 5 μm is formed thereon to make a total of 6 to 9 μm.

This plating film is heated or heat-treated in a non-oxidizing atmosphere, especially in a non-oxidizing atmosphere containing nitrogen.
(Eg brazing). As a result, as described above, B in the plating film diffuses to the surface and is concentrated in the surface layer in the form of BN or B ₂ O ₃ , resulting in the structure shown in FIG. 2 (A). After that, the plating film is treated with an etching solution, and the excess thickness of the surface layer of the plating film is removed together with the boron compound (BN, B ₂ O ₃ ) concentrated on the surface layer. As shown, essentially free of boron compounds, essentially
A plating film consisting of Ni only and having an active surface and easily wetted remains. Therefore, this plating film can be used in the subsequent processes and thereafter without any trouble in the treatments requiring wettability such as displacement plating and soldering.

Here, the thickness of the extra plating film is 2 μm.
If it is less than the range, there is a possibility that B concentrated in the surface layer cannot be surely completely removed by etching. Further, if the extra plating thickness exceeds 5 μm, the Ni-B plating film becomes too thick, which may cause problems such as bleeding (short circuit of fine wiring pattern) and the like. There is a large amount, which is economically disadvantageous.

The electroless Ni-B plating may be formed in the same manner as the conventional one except that the plating film thickness is increased as described above. As the reducing agent for the electroless plating solution, an amine borane compound (eg, dimethylamine borane, diethylamine borane, etc.) and sodium borohydride can be used, but dimethylamine borane is preferable. In addition to reducing agents, electroless plating solutions include nickel salts (eg, nickel sulfate)
, A complexing agent (eg, hydroxycarboxylic acid such as citric acid or lactic acid or a salt thereof), and a pH adjuster.

The atmosphere for the heating or heat treatment of this thickly formed electroless Ni-B plating is a non-oxidizing atmosphere. This non-oxidizing atmosphere may contain a small amount of oxygen as long as it is not oxidizing as a whole. The non-oxidizing atmosphere includes a reducing gas atmosphere, an inert gas atmosphere and a vacuum. When heat treatment is performed in an oxidizing atmosphere such as air, even Ni is oxidized. Atmospheres that are particularly advantageous for use in the present invention are non-oxidizing atmospheres containing nitrogen, such as 70-90.
% N ₂ and 30 to 10% H ₂ mixed gas.

The atmosphere for the heat treatment may be 100% hydrogen gas, and even in this case, the plating surface is activated by the present invention to a small extent. Even if 100% hydrogen gas is used, in an open heating furnace such as a belt furnace that is generally used for brazing, the atmosphere gas contains a trace amount of oxygen and nitrogen because it is exposed to air at the inlet and outlet. It is thought that this is because the plating surface becomes somewhat inactive.

Any etching solution may be used as long as it can dissolve Ni metal, and a commercially available product may be used. A preferable etching liquid is a mixed liquid in which acetic acid / nitric acid / hydrofluoric acid are mixed at a weight ratio of 1/3/1. Since the etching rate at room temperature when this mixed solution is used is about 1 μm / min, the etching time can be easily adjusted. The etching may be performed under heating.

Next, a method of manufacturing the ceramic IC package according to the present invention will be briefly described in the order of steps. Circuit formation Conductive paste on unfired or fired ceramic substrate
(For example, a paste containing W and / or Mo-Mn alloy powder and a binder) is screen-printed and then fired to obtain a ceramic substrate having a conductor layer serving as a circuit formed on the surface.

Electroless Ni-B Plating The substrate on which the conductor layer is formed is immersed in an electroless Ni-B plating solution to deposit an electroless Ni-B plating film on the conductor layer. At this time, the plating film is formed to be 2 to 5 μm thicker than the desired film thickness. The thickness of the plating film can be easily adjusted by the plating time and the like.

Pin brazing The substrate is heated to a high brazing temperature to braze the pins serving as external leads to predetermined positions of the conductor layer covered with the electroless Ni-B plating film. The heating atmosphere at this time may be any gas atmosphere as long as it is non-oxidizing. That is, air cannot be used because it is an oxidizing gas, but a nitrogen-containing gas such as an inexpensive N ₂ / H ₂ mixed gas can be used. Of course, hydrogen gas, inert gas, and vacuum are also possible.

Etching When the atmosphere contains oxygen and nitrogen due to being heated to a high temperature in the above brazing process (there is a small amount of oxygen and nitrogen even in vacuum), the electroless Ni-B plating film Surface activity and wettability are reduced. Therefore, the excess plating layer of 2 to 5 μm is removed from the surface layer by etching as described above, and B concentrated in the surface layer is removed. As a result, the plating surface is activated. Since B is removed from the plating film activated by this etching,
Ni plating film.

Substitution Gold Plating When a substrate is dipped in a gold substitution plating solution (which usually contains an additive for improving adhesion in addition to a gold compound), a local cell action (ionization substitution reaction between metals) occurs. , The more base Ni is ionized, and the more precious gold from the plating solution
Gold is plated on the Ni plating film.

At this time, if the above etching is not performed,
The Ni-B plating film has reduced surface activity due to the heating in the brazing process described above, causing defective deposition of gold. In the present invention, however, the plated surface is activated, and this defective deposition is avoided. As a result, a good gold plating film is formed. It should be noted that this displacement gold plating is preferably performed after the etching step, when the surface just washed with water is sufficiently wet with water and in an undried state. If necessary, electroless gold plating is further performed to form a thick gold plating film.

Mount (Die Bonding) The IC chip is fixed and mounted at a predetermined position using solder. Also at this time, since the electroless Ni-B plating film is activated, the solder wettability is good, the chip can be securely fixed at a predetermined position, and the generation of defective products due to protrusion of bumps or the like is prevented.

After that, wire bonding or ball bonding, sealing is performed, and post-treatment such as solder plating is performed to complete the ceramic IC package. These can be as usual.

The method of activating the electroless Ni-B plating film of the present invention is useful for manufacturing the above-mentioned ceramic IC package, particularly the solder ball bonding type PGA, BGA, MCM, etc. Is also available. For example, even in a plastic IC package, electroless Ni
-B plating may be performed, and the method of the present invention can be applied to activation of the plating film. Further, for example, it can be applied to activation of a plating film when electroless Ni-B plating is applied to the surface of an insulating substrate for the purpose of imparting conductivity.

[0041]

[Example] The electroless Ni of the present invention was applied to a sintered alumina substrate on the surface of which a conductor layer containing W powder as a conductive powder is formed.
-The B plating film activation method was applied. The substrate used is of a type that is bonded to a chip by a solder ball, which is produced by screen-printing a W-containing conductive paste on an alumina green sheet and then firing it simultaneously.
This is a substrate for BGA (ball grid array).

A commercially available electroless Ni-B plating solution is applied to the above substrate.
(Contains dimethylamine borane as a reducing agent, pH 6.
5) Immerse in 70 ℃, and place on the conductor layer containing W for 7
An electroless Ni-B plating film having a thickness of μm was formed. Since the desired plating thickness is 4 μm, an extra thick plating film of 3 μm was used. The B content in this plating film is 1.02 wt.
%Met. In this example, the plating film thickness was measured by a fluorescent X-ray film thickness meter.

The substrate on which the electroless Ni-B plating film having a thickness of 3 μm was formed was then passed through a belt-type heating furnace divided into a temperature rising zone, a temperature holding zone, and a temperature lowering zone for heat treatment. The atmosphere of this heating furnace is 20% H ₂ −80% N at 900 ℃, which simulates the sintering conditions of pin brazing.
_Two kinds of atmospheres were used: a mixed gas atmosphere, and a heat spreader (called a heat sink or a heat radiation fin) 790 ° C. 100% H ₂ atmosphere imitating the brazing sinter conditions. The heating time in the temperature holding zone was about 10 minutes.

The heat-treated substrate is dipped in a commercially available nickel etching solution at 45 ° C. for about 3 minutes to remove the plating film having a thickness of about 3 μm, and the Ni-B alloy plating film having a predetermined thickness of about 4 μm. Then, the plating film was activated. The surface activity of the plating film (product of the present invention) after this etching is
It was evaluated by the following (1) deposition property of displacement gold plating and (2) solder wettability after displacement gold plating.

For comparison, an electroless Ni-B plating film having a predetermined thickness of 4 μm was formed on the substrate by the same method as above, and then heat-treated under the same conditions as or under the conditions of etching. The surface activity of an electroless Ni-B plating film (conventional product) which has not been evaluated was similarly evaluated.

(1) Precipitation of displacement gold plating The above-mentioned substrate of the present invention product and the substrate having a plating film of the conventional product were mixed with a commercially available replacement gold plating solution [KAu (CN) ₂ , containing aminopolycarboxylic acid, pH 3.5] to 90%. 10 minutes, 20 minutes or 60 ° C
After dipping for a minute, gold plating was applied on the plating film. The film thickness of the deposited gold plating film was determined by measuring 50 points of 10 arbitrary pads of 5 samples arbitrarily extracted and calculating an average value thereof. The results are shown in Table 1 below.

[0047]

[Table 1]

As can be seen from the comparison between the conventional products (a) and (c) in Table 1, when the electroless Ni-B plating is heat-treated in a nitrogen-containing atmosphere, compared with the heat-treatment in a 100% hydrogen atmosphere, The deposition rate of displacement gold plating is significantly reduced. The deposition thickness of gold plating is, for example, 0.067 μm to 0.037 after 10 minutes.
In 60 minutes, the deposition rate becomes about half from 0.112 μm to 0.060 μm. That is, it is shown that the depositability of the displacement gold plating is lowered and the surface activity is lowered.

On the other hand, comparing (b) and (d) of the product of the present invention in which the thick electroless Ni-B plating film was first formed and the excess plating film was removed by etching after the heat treatment was compared. The deposition rates of substitutional gold plating are the same between the case of heat treatment and the case of heat treatment in a 100% hydrogen atmosphere, and even if heat treatment is performed in a nitrogen-containing atmosphere, the same plating deposition rate as in a case of treatment in a 100% hydrogen atmosphere is obtained. Has been obtained.

In addition, the plating deposition rates of these products (b) and (d) of the present invention are the same as those of the conventional products not etched.
Heat treatment of Ni-B plating film in 100% hydrogen atmosphere (C)
In comparison with (c), the deposition rate of the displacement gold plating is further increased in comparison with (c). That is, compared with the case of heat treatment in a 100% hydrogen atmosphere where it was considered that the surface activity did not decrease in the past, the plating surface was more activated and the displacement plating film could be deposited more quickly and uniformly. Therefore, even when the heat treatment atmosphere is 100% hydrogen, the surface activation method of the present invention is effective.

In any of (a) to (d), the thickness of the deposited plating film tends to increase with time.
Not proportional to time. This is because the displacement plating is a substitution reaction with gold due to the ionization of the underlying Ni, and when the entire surface layer is covered with gold, the precipitation reaction stops there.

From the above results, it is understood that the method of the present invention is effective for the surface activation of the electroless Ni-B plating film which has been subjected to the heat treatment regardless of whether or not the heat treatment atmosphere contains nitrogen. . However, if the heat treatment atmosphere contains nitrogen, the surface activity of the electroless Ni-B plating is greatly reduced, and thus the surface activation effect of the present invention is increased. According to the present invention, even if the heat treatment atmosphere is an inexpensive gas containing nitrogen, the electroless electrolysis is performed to the same extent as when an expensive gas consisting of 100% hydrogen is used.
The surface of Ni-B plating can be activated.

(2) Solder wettability after displacement gold plating The solder wettability after formation of the displacement gold plating film was evaluated by two types of tests: the wet state after immersion in molten solder and the wet spread diameter of solder balls. did. The test method is as follows.

Wetting state after immersion in molten solder In the production of a ceramic package that is actually produced, an electroless Ni-B plating film corresponding to (a) to (d) in Table 1 is formed in the same manner as above. After performing pin brazing and etching (only the product of the present invention) in a predetermined atmosphere,
The displacement gold plating was applied to a thickness of 0.05 μm ± 0.03 μm, and this was immersed in a molten solder bath at 240 ° C. to evaluate the wet state of the molten solder. The molten solder bath used was a low temperature solder (Sn / 38.1% Pb) manufactured by Senju Metal Industry Co., Ltd. and a flux (Alfbond ANF-10). The good wet condition of the molten solder means that the fine pad (diameter 140
(μm) all wet with solder, and wide area pad (diameter 3m)
It means that m) is evenly spread and has no roughness. When this condition was not satisfied, the wettability was evaluated as poor.

Wetting and Spreading Diameter of Solder Balls On a solid substrate of sintered alumina, a conductive paste containing W powder was printed in a square of 50 × 50 mm and placed in a reducing atmosphere.
It was fired at 00 ° C. for 1 hour to form a conductor layer having a thickness of about 20 μm. On top of this conductor layer, in the same manner as above, from (a) to
After forming an electroless Ni-B plating film corresponding to (d), heat treatment and etching in a predetermined atmosphere (this invention only), displacement gold plating was applied to a thickness of 0.05 μm ± 0.03 μm. .

Five solder balls were placed on this displacement gold plating film, and after passing through a furnace in a 15% H ₂ / N ₂ atmosphere maintained at 270 ° C. (passing time about 20 minutes), soldering was performed. The wetting and spreading diameter of was measured with a caliper and the average value was calculated. The solder ball used was a 0.9 mm diameter solder ball (Sn / 38.1% Pb) manufactured by Sumitomo Metal Mining Co., Ltd. The results of these tests are shown in Table 2.

[0057]

[Table 2]

As can be seen from Table 2, according to the present invention,
When substitution gold plating is applied after surface activation by etching the electroless Ni-B plating film, the solder wettability of this gold plating film is good, and all the fine pad parts are wetted by the solder. In the area, the solder was uniformly wet and spread and covered the gold plating film. On the other hand, in the conventional product, even if the heat treatment atmosphere was a hydrogen atmosphere, there was a portion that did not wet the fine pad portion, and the wide-area pad portion had poor wettability and spreadability, and all had poor wettability.

In addition, the wetting and spreading diameter of the solder ball
The product of the present invention that was etched after the heat treatment had a larger wetting and spreading diameter than the conventional product that was not etched, regardless of the heat treatment atmosphere. The rate of increase in the wetting and spreading diameter was larger when the heat treatment atmosphere was a nitrogen-containing gas, but the wetting and spreading diameter was significantly increased even when the heat treatment was performed in a hydrogen atmosphere. That is, also with respect to solder wettability, the method of the present invention, not only the heat treatment in a nitrogen-containing atmosphere, 100
It was also shown to be effective for heat treatment in% hydrogen.

[0060]

According to the method of the present invention, it is possible to recover the decrease in surface activity that occurs when an electroless Ni-B plating film is heat-treated, and to activate the surface of this plating film regardless of the heat treatment atmosphere. . As a result, this heat treatment can be performed in an inexpensive nitrogen-containing gas atmosphere. In addition, the electroless Ni-B plating surface-treated by the method of the present invention has the same plating film as the conventional one.
The surface activity was higher than that in the case of heat treatment in 0% hydrogen, and the depositability of gold plating and the subsequent solder wettability were extremely good. Therefore, when this method is applied to the manufacture of a ceramic IC package, the pin brazing step can be performed in an inexpensive nitrogen-containing gas, and the product quality and yield are greatly improved.

[Brief description of drawings]

FIG. 1 is a schematic view showing the vicinity of a plating film surface layer after heat treatment of an electroless Ni-B plating film in an atmosphere containing nitrogen and oxygen.

FIG. 2 is an explanatory view schematically showing the method of the present invention.

Claims (4)

[Claims] 1. An electroless nickel-boron plating film is formed on a substrate having a crystal grain structure so as to have a thickness of 2 to 5 μm above a predetermined film thickness, and the formed plating film is heated in a non-oxidizing atmosphere, and then the plating film is formed. The method for activating an electroless nickel-boron plating film heated in a non-oxidizing atmosphere, characterized in that the surface layer is removed by etching to a predetermined thickness. 2. The method of claim 1, wherein the non-oxidizing atmosphere is a nitrogen-containing atmosphere. 3. In the manufacture of a ceramic IC package in which a conductive paste is applied and fired on a ceramic substrate, an electroless nickel-boron plating film is formed thereon, and then pins are brazed and then displacement gold plating is performed. ,
After forming the electroless nickel-boron plating film to a thickness of 2 to 5 μm from a predetermined thickness and brazing the pins in a non-oxidizing atmosphere, the surface layer of the plating film is removed by etching to a predetermined thickness, A method of manufacturing a ceramic IC package, which comprises performing displacement gold plating. 4. The non-oxidizing atmosphere is a nitrogen-containing atmosphere, and after removing the surface layer of the plating film by etching,
The displacement gold plating is performed without drying the plating surface.
The described method.