JPH01108383A - Pretreatment of ceramics before electroless plating - Google Patents

Abstract

PURPOSE:To effectively roughen the surface of ceramics with high reproducibility by adding a buffer soln. to a hydrofluoric acid type etching soln. and etching the ceramics with the etching soln. set at a prescribed pH. CONSTITUTION:Ceramics is washed and degreased. A buffer soln. contg. KCl, HCl, etc., is added to a hydrofluoric acid type etching soln. contg. HBF4, etc., and the surface of the ceramics is etched with the etching soln. and at a prescribed pH. At this time, a change in the hydrogen ion concn. with the progress of etching is suppressed by the action of the buffer soln., the prescribed etching ability is maintained and the surface of the ceramics is efficiently roughened. A metal film having high adhesive strength can be formed on the roughened surface by subsequent electroless plating with high reproducibility.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a pretreatment method for electroless plating of ceramics.

(bl Conventional Technology) Generally, in electronic components using ceramics, such as ceramic capacitors using dielectric ceramics, it is necessary to metalize the surface of the ceramics.A metal film is formed by electroless plating. If you do,
The important point is how to increase the adhesion strength of the metal film to the ceramic surface without impairing the electrical properties.

Conventionally, before electroless plating is applied to a ceramic surface, the surface of the ceramic is roughened by chemically etching the area where a metal film is to be formed. At that time, a hydronic acid solution with excellent etching ability is used as the etching solution.
A diluted solution is used so as to obtain an appropriate etching rate depending on the composition of the ceramic.

(C) Problems to be Solved by the Invention However, when using a dilute solution of a strong acid such as a hydrofluoric acid solution, as etching progresses, the pH (hydrogen ion index) of the solution changes.
will vary greatly, resulting in poor reproducibility of etching performance.

For this reason, it has not been possible to efficiently and stably roughen the ceramic surface.

An object of the present invention is to provide a pretreatment method for electroless plating of ceramics, which allows the surface of ceramics to be etched efficiently and stably when roughening the surface by etching the ceramics with a hydrofluoric acid etching solution. There is a particular thing.

(d) Means for Solving the Problems The pretreatment method for electroless plating of ceramics according to the present invention includes adding a buffer solution to a hydrofluoric acid etching solution, setting the pH to a predetermined value, and then etching the ceramics. It is characterized by

(01 Effect) In the electroless plating pretreatment method for ceramics of this invention, the surface of the ceramic to be electrolessly plated is roughened by etching it with a hydrofluoric acid etching solution. A buffer solution is added to the etching solution and the pH is set at a predetermined value.By adding the buffer solution to the etching solution, the hydrogen ion concentration decreases as etching progresses due to the buffering action of this buffer solution. Therefore, the etching solution maintains a predetermined etching ability and can roughen the ceramic surface efficiently and with good reproducibility.

Therefore, when a metal film is subsequently plated on the ceramic surface by an electroless plating process, a metal film with high adhesion strength and desired electrical characteristics is deposited on the roughened ceramic surface.

(f) Processing step when applying electroless plating to example ceramics
As shown in the figure, ceramics are first washed with water and degreased with a surfactant or the like. Thereafter, the ceramic surface is etched using an etching solution set to a predetermined pH by adding a buffer to a hydrofluoric acid-based etching solution such as hydrofluoric acid (hydrofluoric acid) or fluoroboric acid (fluoroboric acid). After etching, the ceramics are washed and then soaked in a solution of Sn (stannic chloride) or Pd (palladium chloride).
The ceramic surface is sensitized by dipping the lamics, and then the ceramic surface is activated. Thereafter, the ceramic is immersed in an electroless plating solution to deposit a predetermined metal film such as Cu or Ni.

First Example> Ceramic composition MgTKOs-CaTi()+ Etching liquid Etching agent HB F 4 (0,042 wt%
) Buffer solution KCZ-H1l! Etching treatment was carried out under the conditions of pi (i, 5 solution temperature 50°C time 10 minutes or more. Also, for comparison, multiple samples were each used in an example in which an etching solution containing HBF40.42 wt% was used without using a buffer solution. and form an electroless plating film of Cu on each sample,
The film strength was measured. Specifically, to measure the film strength, we first form an electroless plating film of Cu on the entire surface of the ceramic, leave only a 4mm" area of the plating film, and remove the other area by polishing. (4 mm”) electrode is formed, and a lead wire is vertically soldered to this electrode. Thereafter, a tensile load was applied to the lead wire, and the load at which the electrode peeled off was measured. In addition, the Q value was also measured.

The results are shown in FIG. As shown in the figure, Conventional Example 1 without adding a buffer has high etching performance at the beginning of etching with a new etching solution, but as the etching progresses, the hydrogen ion concentration decreases, so after several etching treatments. Etching ability is drastically reduced. As a result, the surface of the ceramic is not sufficiently roughened, and the adhesion strength of the metal film is low, resulting in large variations in the adhesion strength. On the other hand, in Example 1, 6 to 7 kg/
A high adhesion strength of 4 mm'' was obtained, and the variation in adhesion strength among the samples was reduced.Furthermore, the Q value of the electrical characteristics increased and the variation was also reduced.

In the above example, the pH of the etching solution was set to 1 as the optimum value.
．． 5, but good enching can be performed within the pH range of 1.0 to 2.2.

In addition, the liquid temperature and etching time are 30 to 50℃.
, can be set in the range of 1 to 60 minutes.

Incidentally, the relationship between the composition of the buffer solution and the pH showing the buffering effect in the above examples is as shown in FIG. By changing the ratio of acid and salt in this way, the pH value that exhibits a buffering effect can be set.

<Second Example> Ceramics composition aTiO=based etching liquid Etching agent HB F 4 (Q, 042 wt/
%) Buffer CHa COON a-HC1pH1
, 7 Etching was carried out under the conditions of a liquid temperature of 40° C. and a time of 10 minutes or more. Further, as in the first example, for comparison purposes, a plurality of samples were prepared using an etching solution whose pH was adjusted without adding a buffer solution.

The results are shown in FIG. 2. Here, tan δ and its variation were measured. As shown in the figure, high adhesion strength of the metal film can be obtained due to the action of the buffer solution, and variations in the adhesion strength can also be suppressed. Additionally, since the adhesion of the metal film to the ceramic surface is improved, tan δ and its variation are improved.

In addition, in the second example, the pH of the etching solution was set to 0.65.
Good etching can be achieved by setting the value within the range of ~2.72. FIG. 4 shows an example of the ratio of the mixed solution to obtain a predetermined pH showing the buffering effect of the buffer solution in this second embodiment.

(g) Effects of the Invention As described above, according to the present invention, since etching is performed using a hydrofluoric acid etching solution, the surface of even difficult-to-etch ceramics can be efficiently roughened. By adding a buffer to the etching solution, the pt+ of the etching solution increases as etching progresses.
This suppresses variations in the electroless plating process, making it possible to form a metal film with high adhesion strength with good reproducibility through the subsequent electroless plating process, and also providing good electrical characteristics with good reproducibility.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing characteristics such as adhesion strength of a metal film of a sample according to a first embodiment of the present invention in comparison with a conventional example;
FIG. 2 is a diagram illustrating the characteristics of a sample obtained according to a second embodiment of the present invention in comparison with a conventional example. FIG. 3 and FIG. 4 are diagrams showing the relationship between the component ratio of different types of buffer solutions and the pH showing the buffering action, respectively. FIG. 5 is a diagram showing a general electroless plating process for ceramics.

Claims (1)

[Claims] (1) A pretreatment method for electroless plating of ceramics, which comprises adding a buffer solution to a hydrofluoric acid etching solution, setting the pH to a predetermined value, and then etching the ceramics.