JPS63256588A - Electroless plating process for ceramic substrate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] This invention relates to a method of electroless plating on a ceramic substrate for forming a metal conductor on the ceramic substrate.

[Conventional technology]

FIG. 8 is a process diagram illustrating a conventional general method for forming a metal conductor such as nickel or copper on a ceramic substrate by electroless plating.

In the conventional electroless plating method, the ceramic substrate after sintering is degreased with a solvent, washed with alkali and acid, and then immersed in a solution containing 2-reaction catalyst metal ions (e.g., pd2+) for 9 reactions 7! ! A medium metal ion is layered on the substrate surface and activated, followed by chemical plating.

It performs alcohol immersion and drying.

A cross-sectional view showing the state in which reaction catalyst metal ions are adsorbed onto the ceramic substrate surface by this method is shown in FIG. 3 (at). ) are ceramic particles. Also,
A cross-sectional view showing a state in which a plating film is formed on a ceramic substrate by a chemical plating process is shown in FIG.
(5I is a plating film.

However, with this electroless plating method, it is difficult to obtain a uniform plated film with strong adhesion. Therefore, as another conventional example of improving adhesion, the publication (Electronic Materials, 1
Like the electroless steel plating method for metal additive ceramic wiring boards in May 958 issue No. 60 to 66),
It involves adding a process of chemical etching to the ceramic substrate after sintering.

Sufficient activation is carried out using an improved activating solution as in the electroless plating method described in the publication (Public Surface Technology, '1986, Vol. 33, No. 2, p. 38), and further improved toughening is performed. There are methods such as chemical plating with liquid.

First, an example (referred to as conventional example B) in which a step of pre-processing a ceramic substrate by chemical etching is added will be described.

The ceramic substrate uses 96% alumina ceramic, which is widely used as an electronic component material.

Ceramic is a sintered body of particles, and as shown in the cross-sectional view of the ceramic substrate shown in FIG. 9(a), it has countless irregularities and many voids σO. Generally, the adhesion of a plating film formed by electroless plating is caused by the plating depositing in these irregularities and gaps ae to obtain an anchor effect. Therefore, as shown in the cross-sectional view of the ceramic substrate after chemical etching in FIG. 9 IbJ.

Many minute irregularities (
91 is obtained. Thereafter, the substrate is degreased and cleaned, and a sheep (reaction catalyst metal such as Pd) that becomes the core of plating is applied (activated) to precipitate nickel ions in the presence of a reducing agent. The state in which plating has been completed is shown in FIG. 9 (a sectional view of a ceramic substrate on which a plating film of cl has been formed). In the figure (51 is the plating film).

That is, by performing the pretreatment for chemical etching, a large number of fine irregularities (9) that can be caught can be obtained, so that a greater anchoring effect can be obtained.

Improves adhesion with ceramics.

Next, as shown in the electroless plating method for ceramic substrates in Japanese Patent Application No. 61-105554, an example (conventional example C) of obtaining a plating film with excellent adhesion strength without chemically etching the ceramic is provided. ) will be explained. As mentioned above, adhesion is determined by the unevenness and voids (IQ) on the ceramic surface.
This is caused by the anchoring effect caused by the button as shown in Figure 4 (al).

It is difficult to fully utilize these irregularities and voids αe,
Furthermore, as in conventional example B shown in FIG. 9(C), the plating may not penetrate into the fine irregularities (9) obtained by chemical etching and may remain as voids. However, as in the activation process shown in the process diagram of FIG.

First, the surface of the ceramic substrate is modified using CellarClean, and then a three-step activation process is performed using an activation liquid with low surface tension.Even the minute irregularities that were difficult to repair can be activated to some extent. can.

This activation process is performed by Cellar Senshi (manufactured by Kizai, product name).
to sensitize the ceramic surface (N absorption of Sn), activate the ceramic surface to a uniform sensitive state with 9-order Acti-Cera (manufactured by Kizai, trade name), and reactivate it with ceramics (manufactured by Kizai, trade name). oxidation treatment (PD suction N).

This activated substrate is chemically plated (Nycocera).
By applying the electroless plating film (5) with excellent permeability as shown on the ceramic substrate on which the plating film is formed in Figure 1),
) is obtained, and a ceramic wiring board with strong adhesion is obtained due to the strong anchor effect.

In addition, after chemically plating conductive metals such as nickel,
There is also a conventional example in which a ceramic substrate is heat treated at 250 to 300 tons to improve adhesion. for example.

Publications (Practical Surface Technology, Volume 33, No. 2, 198
6, p. 41), the adhesion strength after plating is 2.1k.
g/, 2, but if it is heat treated at 250 r/h.

There is an example where the weight is 4.1kg71)m+2. This is P.I.
F. This is due to the effect that by performing the treatment, nickel crystallization begins around 200t and hardness increases.

The crystallization temperature varies depending on the content of P and H contained in the plating solution, and the lower the content, the lower the temperature and the maximum hardness is reached.

Finally, as shown in the electroless plating method for ceramic substrates in the specification of 2% Application No. 103606/1983, as a conventional example, as shown in Figure 12 of the process diagram, there is a difference between activation and chemical plating of conventional was subjected to heat treatment in hydrogen.

There is also a method in which the reaction catalyst metal is distributed widely and deeply.

[Problem that the invention seeks to solve]

Conventional electroless plating methods are as described above, and in order to improve the adhesion of the plated film, a chemical etching process using acid or alkali (Conventional Example B), a complicated activation process (Conventional Example C), etc. was being administered.

However, although these steps are complicated and require a lot of time and effort, the adhesion strength of the resulting plating film is about 1.5 to 2.5 kg/ff1)12.

As wiring becomes thinner, even greater adhesion strength is required.

In addition, in the conventional method, the amount of reaction catalyst metal ions adsorbed onto the ceramic substrate is small, so when heat treatment is performed, the amount of reaction catalyst metal per unit area on the ceramic substrate surface decreases, and the plating deposition rate decreases. becomes late or
There is also the problem of uneven precipitation.

Furthermore, as a reference, in the ceramic circuit board disclosed in Japanese Patent Publication No. 5S-1IZSSS, a circuit is formed on a green sheet using a paste containing a reaction catalyst metal for electroless plating, and then sintered in a reducing atmosphere. There is also a method of plating, but since the sintering temperature is high, the two-reaction catalyst metal is covered with glass, making it difficult to perform plating in the subsequent process.

This invention was made to solve the above-mentioned problems, and aims to improve the conventionally low adhesion strength and to obtain a plating method that solves the problem of ceramic substrates that can form a uniform and even plating film. With the goal.

[Means for solving problems]

The electroless plating method for ceramic substrates of this invention is as follows.

The method includes the steps of providing a paste layer containing two-reaction catalyst metal ions on a ceramic substrate, heat-treating the ceramic substrate provided with the paste layer in a reducing atmosphere, and electroless plating the heat-treated ceramic substrate. .

[Effect]

In this invention, the step of providing a paste layer containing reactive PBA-mediated metal ions on a ceramic substrate and the step of heat-treating the substrate in a reducing atmosphere spread the reaction catalytic metal ions contained in the paste over the ceramic surface. And deep X
In addition to diffusing and distributing, active nuclei for chemical plating (
reaction catalyst (metal ions).

FIG. 3 is a cross-sectional view showing a state in which reaction catalyst metal ions are adsorbed on a ceramic substrate, where (3) is a reaction catalyst metal ion and (4) is a ceramic particle. FIG. 3 (al is by conventional method (process in FIG. 8).

FIG. 3 is a cross-sectional view of a case where a reaction catalyst metal is adsorbed onto a ceramic surface. Figures 3 and 3) are cross-sectional views when the reaction catalyst metal according to the present invention is distributed on the ceramic surface. In this invention, since the two-reaction catalyst metal is distributed by thermal diffusion, it can be distributed deep into voids and open pores. In addition, since the catalytic metal for two reactions is retained in a large amount (several 100 to several 1000 ppm in terms of X amount ratio) in the paste carrier, it is less than the conventional in-liquid adsorption (wet method) (several ppm to several 100 ppm).
Compared to conventional methods (where ppm adsorption is considered), the inventive diffusion (dry method) can distribute a sufficient amount of reaction catalytic metal on the ceramic surface. Furthermore, since the thermal diffusion treatment is performed in a reducing atmosphere, the two-reaction catalyst metal is reduced and becomes more active, which also has the effect of promoting the chemical plating reaction.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a process diagram illustrating an electroless plating method according to an embodiment of the present invention. As is clear from the figure.

According to this method, the ceramic substrate after bonding is degreased with a solvent, washed with alkali and acid, an active paste layer containing two reaction catalyst metal ions is provided on the ceramic substrate, and then heat treated in a reducing atmosphere and cooled. Afterwards, chemical plating is applied, followed by alcohol immersion and drying.

Hereinafter, this invention will be explained in more detail based on specific examples.

Example 1゜ 9696 alumina ceramic substrate (manufactured by Kyocera).

The ceramic surface is pretreated (degreasing, cleaning, etc.) according to the conventional electroless plating process (see FIG. 8). Then an active paste containing two reactive catalytic metal ions (e.g.
Several thousand p of palladium ions are placed on a tungsten carrier.
pm) is printed on a ceramic substrate as shown in FIG. 2, which is a cross-sectional view of a ceramic substrate provided with a paste layer according to the present invention. Thereafter, the paste was dried in an electric oven at 120° C. for 30 minutes, and then set in a precision atmosphere furnace, and the air in the furnace was replaced with nitrogen gas. After the replacement is complete, hydrogen gas is introduced into the furnace.

This time, nitrogen gas is replaced with hydrogen gas to create an atmosphere of 100% H2. The flow rate of hydrogen gas is as follows for 91 core tubes.
The speed was approximately 31/min. The temperature increase rate is 10/min
Then, raise the temperature to 5oot, hold that temperature for 10 minutes,
The temperature was lowered at a rate of 15 min/min. This heat treatment in a reducing atmosphere causes the reaction catalyst gold pA (palladium) contained in the paste K on the ceramic substrate to be distributed by thermal diffusion through the open pores and voids on and near the ceramic surface. Furthermore, by carrying out the reaction in a reducing atmosphere, the 9 reaction catalyst metal is reduced and becomes more active. Due to the above two effects.

If a ceramic substrate is printed with a paste containing reaction catalyst metal ions and heat-treated in a reducing atmosphere, and then chemically plated with nickel, for example, the ceramic substrate with a plating film shown in Fig. Plating precipitates to a depth of microns or more.

A larger anchor effect can be obtained compared to FIG. 4 (al).

Example λ A 96% alumina ceramic substrate without pretreatment was used, except that the heat treatment temperature was 400″C.

Plating was carried out in the same manner as in Example 1. FIG. 5 is a characteristic diagram showing the relationship between treatment temperature and average tensile strength. In the figure, (Xi (2) (2)) is the characteristic of the ceramic substrate according to the embodiment of this invention, (Pi is the characteristic of the ceramic substrate according to the conventional method, (2) is 400°C, (Yl is 60
0″C2■) is a characteristic at a heat treatment temperature of 800 t.

In the tensile test, a circular pad of electroless nickel of 2w*φ was formed on a ceramic substrate, and a pad with a length of 101
゜Solder a copper lead bin with a thickness of 06u and make a 5fi
The test was performed by vertically pulling at a speed of /min. The number of samples is
Thirty pieces were used for each condition. The heat-treated product (this invention) had nearly twice the adhesion of the conventional method.

Example The heat treatment temperature in hydrogen was 600° C. in Example 2, and the other conditions were the same. The average tensile strength is shown in (a) in Figure 5.
As shown in the figure, there was not much difference between the heat treatment at [,400t] and the heat treatment. Furthermore, even when the heat treatment temperature in hydrogen is 800°C, as shown in (2) in Figure 5,
There was not much difference from that heat treated at 400t.

Example 4゜ The heat treatment temperature in hydrogen in Example 2 was set to I5ol)C.

Other conditions were the same. However, no plating was deposited after heat treatment. This is thought to be because the glass component contained in the ceramic substrate becomes fluid due to the high heat treatment temperature, and palladium on the ceramic surface is incorporated into the glass. From the above, when palladium is used as the 2-reaction catalyst metal ion, the heat treatment temperature is preferably 200 to 1200 t.

Example 5: A 96% alumina ceramic substrate with through holes,
When electroless nickel plating was performed under the same conditions as in Example 2, the thickness of the plating film inside the through hole was uniform and the adhesion strength was high.

This is thought to be because palladium was distributed more uniformly by thermal diffusion than in the conventional method and penetrated into the ceramic to a depth of several microns.

The electroless plating method of the embodiment of this invention is conventional.

It can be performed independently of various electroless plating methods (conventional examples B, C, etc.) that are used to increase adhesion. 2For example, it can be applied to ceramics that have been subjected to etching treatment to have many fine irregularities on the surface. It is also possible to apply it to a substrate or to a substrate that adopts a three-step activation process.

Naturally, a plating film with the strongest adhesion can be obtained by electroless plating, which is a combination of these methods.

Figure 6 is a characteristic diagram showing the relationship between treatment temperature and average tensile strength when this invention is applied to a ceramic substrate etched with am7nium fluoride.
, (8) are the characteristics of the ceramic substrate according to the embodiment of the present invention, αG is the characteristic according to the conventional method, and (Q) is 500'
c, (R1 is the characteristic of heat treatment temperature of 70 () C. That is, paste printing and heat treatment in hydrogen gas (heat treatment is 5
00C and 700°C) K plating and conventional plating method (excluding). Again, the example to which this invention is applied is better than the conventional example.

The average adhesion strength has increased by about 2 times. Inside.

Some exhibit strengths of up to 7-/IIJI2. A fractured cross-sectional view of the same is shown in FIG. (7) is a steel lead pin, (8
) is solder.As is clear from the figure, the plating has penetrated into the unevenness of the ceramic surface well, and has also precipitated in gaps of several microns from the surface, indicating that destruction has occurred within the ceramic.

In addition, in the process diagram for explaining the electroless plating method according to one embodiment of the present invention shown in FIG. 1, the order of the solvent degreasing process, alkali cleaning process, and acid cleaning process may be reversed, or
In some cases, it may be omitted. Further, the alcohol immersion step and the drying step may also be omitted in the same way.

Furthermore, in the above embodiments, the metal conductor is mainly nickel.

Although the case where the conductor is 1 is described, other metal conductors such as copper may be used, and the same effects as in the above embodiments can be obtained.

〔Effect of the invention〕

As explained above, this invention includes a step of providing a paste layer containing two-reaction catalyst metal ions on a ceramic substrate, a step of heat-treating the ceramic substrate provided with the paste layer in a reducing atmosphere, and an electroless plating process on the heat-treated ceramic substrate. By carrying out this step, it is possible to obtain an electroless plating method for ceramic substrates with excellent adhesion strength, uniformity, and less unevenness.

[Brief explanation of the drawing]

FIG. 1 is a process diagram of an electroless plating method according to an embodiment of the present invention, and FIG. g2 is a sectional view of a ceramic substrate provided with a paste layer according to an embodiment of the present invention. FIG. 3 is a sectional view showing the adsorption state of the reaction catalyst metal obtained by the conventional method (a) and the embodiment of the present invention (bl). FIG. 5 is a cross-sectional view of a ceramic substrate provided with a plating film obtained by the present invention, and FIG. is a characteristic diagram comparing the average tensile strength of the plated film obtained by another embodiment of the present invention and the conventional plated film. A cross-sectional view of the fracture surface after a tensile test, FIG. 8 is a process diagram explaining a conventional general electroless plating method, and FIG. 9 is a cross-sectional diagram explaining a conventional electroless plating method in the order of steps. Figure 10 is a process diagram explaining the conventional electroless plating method, Figure 1) is a cross-sectional view of a ceramic substrate provided with a plating film obtained by the conventional method, and Figure 12 is a process diagram explaining the conventional electroless plating method. This is a process diagram of the plating method. In the figure, (1) is a ceramic substrate, (2) is a paste containing reaction catalyst metal ions, (3) is a reaction catalyst metal, (4) is a ceramic particle, and (51 is a plated film). In addition, according to Tanizu's middle rule, the symbols indicate the same or equivalent parts.

Claims (3)

[Claims] (1) A process of providing a paste layer containing reaction catalyst metal ions on a ceramic substrate, a process of heat-treating the ceramic substrate provided with the paste layer in a reducing atmosphere, and a process of electroless plating the heat-treated ceramic substrate. Electroless plating method for ceramic substrates. (2) The electroless plating method for ceramic substrates according to claim 1, wherein the reducing atmosphere is a hydrogen gas atmosphere. (3) the reaction catalyst metal ion is a palladium ion,
The electroless plating method for ceramic substrates according to claim 1 or 2, wherein the heat treatment temperature is 200 to 1200°C.