Plating device for dielectric resonators

Abstract: The dielectric resonator consists of a pole-like body (40) having a through hole. An electrode having a strong bonding force is provided on the surface of the body and on the inner peripheral surface of the through hole. The surface of the body is mechanically coarsened and then the whole body is chemically etched. The body coarsened in two steps is then fitted to a support pin (110) of a rotary member (100) installed vertically or tilted in a plating solution (26) in order to plate the electrode.

Description: The present invention relates to a plating device according to the preamble of claim 1. In line with recent developments of information communication equipment such as space communication and automobile telephones, there is a strong demand for dielectric resonators for use in generating microwaves. In addition, there is a demand for compact, high efficient and inexpensive resonators, and therefore, there is a demand for plating devices to make such resonators, i.e. the electrodes of such resonators. From US-A-1,836,066 a plating device comprising the features listed in the preamble of claim 1 is known. This plating device is adapted to plate diamonds which are supported in holders. This known device cannot be used to conduct steps necessary for the production of coatings of hollow bodies and in particular is not able to generate the electrodes of resonators or dielectric resonators as, for example, micro-wave resonators. From US-A-4,421,627 an article holder is known which, however, is not for use in a plating device comparable with the above discussed prior art device. This known device is prepared to support articles to be partially plated, and in particular, valve seats of combustion engines and other faces of those valves. It is the object of the present invention to provide a plating device which does not show the shortcomings of the prior art and is in particular useful for the production of improved bodies, e.g. dielectric resonators or microwave resonators. This object is solved the plating device having the features listed in claim 1. Advantages embodiments of this plating device according to the present invention are defined in the subclaims. The reasons why the device according to the present invention is advantagous over the prior art is due to the following features: The rotor of the plating device is adapted to be submerged in an electrolyte; the supporting pins of the device are adapted to support bodies of resonators; the axis of the rotor can also be vertical with respect to a horizontal plane of the device; and hills and valleys are provided on a surface of the rotor, the supporting pins being disposed on the hills. In the following, the present invention is discussed in relation to a preferred embodiment with reference to the figures attached hereto. During the discussion of this preferred embodiment and its function, further advantages and features which are in accordance with the invention are disclosed. The figures are briefly to be described as follows: Figure 1(A) is a plan view showing a rotor of a plating device for a process of producing a resonator, and Figure 1(B) is a cross-section taken along the line Z-Z in Figure 5(A); Figure 2 is a cross-sectional side view showing a main portion of the plating device; Figures 3-5 each are cross-sectional views showing various aspect of the positional relationship between the rotor and a supporting pin; Figure 6 is a perspective view showing a modified version of the dielectric resonator according to the present invention; Figure 7 is a cross-sectional view showing the dielectric resonator; Figure 8 is a graph showing the relationship between the temperatures at which an electroless plating is conducted and the Q value; Figure 9 is a graph showing the relationship between the temperatures at which a vacuum heat treatment and the Q value in one embodiment. Referring to Figures 1 to 5, a plating device for making an electrode of a resonator, e.g. a microwave resonator, will be described: In Figure 1, there is provided a rotor 100, which is made of plastics such as heat-proof PVC, polyethylene, polypropylene, or alternatively, plasticcoated metal, such as SUS 304 and SUS 316, each coated with the above-mentioned plastics. The used material is preferably resistant to the etching reagent whose temperature rises as high as 50 to 70°C, and capable of allowing no metal to deposit. The rotor 100 is provided with supporting pins 110 upright on its surface. The pins 110 are preferably made of a substance which allows the plating metal to deposit. The surface of the rotor 100 is provided with hills 120a and valleys 120b, and the supporting pins 110 are planted on the hills 120a and the valleys 120b. The supporting pins 110 are inserted into the bores 50 of the bodies 40, and are retained on the rotor 100 as shown in Figure 1(B). As is clearly shown in Figure 1(B), each body 40 keeps point-to-point contact with the rotor 100. The reference numeral 130 denotes apertures designed to allow the plating gent to pass through so that the bodies 40 retained on the supporting pins 110 are completely submerged in the electrolyte or plating agent. A rotary shaft 20a or 20b (Figure 2) is inserted into a rotary shaft bore 140 having its rotary axis inclined against that of the rotor 100. Referring to Figure 2, the plating device and the plating process will be described: There is provided a plating tank 25 holding a plating bath 26. In the plating tank 25 the rotary shafts 20a and 20b are rotatably supported on a frame 22 in parallel with each other. The rotary shafts 20a and 20b support a plurality of rotors 100 carrying the bodies 40. Because of the inclined rotary axis, the rotors 100 are inclined on the rotary shaft 20a and 20b. The plurality of rotors mounted on one rotary shaft 20a or 20b are closed by a bottom plate 21. The rotary shaft 20a is connected to a gear 24a, and the rotary shaft 20b is connected to a gear 24b. The gears 24a is engaged with the gear 24b, which is engaged with a third gear 24c driven by a motor 23. In Figure 2, suppose that the gear 24c rotates in the clockwise direction when viewed in the Y direction, the gear 24b will rotate in the anti-clockwise direction, and the gear 24a will rotate again in the clockwise direction. The two rotors units on the shafts 20a and 20b are rotated in different directions, thereby agitating the plating bath26 in the plating tank 25. While the rotors 100 are rotated in the plating bath 26, the bodies 40 are subjected to electroless plating, thereby forming metallic films on the bodies 40 at one time. Referring to Figures 3 to 5, the positional relationship between the rotor 100 and the rotary shafts 24a, 24b will be described in greater detail: In Figure 3 the rotary shaft bore 140 has an inclined axis to that of the rotary shaft 24a, 24b so that the rotors 100 are supported at a tilt on the rotary shaft 20a and 20b. The angle of inclination (c) is preferably in the range of 60 to 75°. When the rotary shafts 20a and 20b are driven in the direction of arrow 150 at 5 to 7 rpm, the rotors 100 are rotated, the bodies 40 are rotated about the respective supporting pins 110. Because of the fact that the bodies 40 are at a tilt, the supporting pins 110 keep contact with the inside surfaces 51a of the bores 50 at varying spots. As a result, the plating is evenly carried out through the outside surfaces of the bodies 40 and inside surfaces 51a of the bores 50. Any gas (e.g. hydrogen gas when electroless plating takes place) generated in the bores 50 through chemical reaction is removed by the supporting pins 110 and uneven plating due to the gas is prevented. The bodies 40 supported on the rotary shafts 20a, and 20b are prevented from colliding with each other. In addition, the apertures 130 allow the electrolyte to reach every part of the bodies 40, thereby effecting the complete coverage thereof. The supporting pins 110 are preferably made of metal which allows the deposit of the plating metal on themselves. In addition, it is preferred that the pins are mechanically tough, stable to an electrolyte such as acid and alkaline solutions used as the plating bath and the reagent used for removing the deposits on the supporting pins 110. In the illustrated embodiment a glass fiber stick of 0.8 mm in outside diameter coated with a plating catalyst or a SUS 304 stick of 0.8 mm in outside diameter. As soon as the plating operation starts, metal starts to deposit on the outside surfaces of the bodies 40 and the inside surfaces 51a of the bores 50. The inside surfaces 51a of the bores 50 have deposits of the plating metal accelerated by the supporting pins 110. In this way plating areas extend over both inside and outside surfaces of the individual bodies 40, and as the chemical reaction becomes active, a greater volume of gases is generated. Thus the inside surfaces 51a of the bores 50 are more activated, thereby effecting the complete coverage of metal deposits. The dimensional and positional relationships between the bodies 40 and the supporting pins 110: The body 40, e.g. a resonator, is preferably cylindrical as described above, but the configuration is not limited to it. A rectangular body is possible. Figure 3 shows a cylindrical body as a typical configuration, having a outside diameter (E) of about 8 mm, an inside diameter (F) of about 2 mm, and a length (D) of about 8 mm. Each supporting pin 110 is cylindrical or polygonal, having an outside diameter of about 0.8 mm, and a length of about 20 mm projecting from the rotor 100. The dimensional and positional relationships are the same throughout the Examples 2 to 3. Referring to Figure 4, a modified version of the embodiment will be described: A rotor 100a is provided with a rotary shaft bore 140a so that the rotor 100a is perpendicular to a rotary shaft 20b, and the supporting pin 110 is planted at a tilt to the surface of the rotor 100a. The angle of inclination is arrarged so as to be the same as the (c) shown in Figure 3. The rotor 100a is also provided with apertures 130a which are inclined at the same angle as the supporting pins 110 are. Under this arrangement the supporting pins 110 are inserted into the bores 50 of the bodies 40, and the rotary shaft 20b is rotated at 5 to 7 rpm in an arrow 150 in the plating bath 26 as described above. In this way the smooth or even plating surfaces have been obtained as by the Example of Figure 3. Referring to Figure 5, a further modified version of the embodiment will be described: A rotor 100b is provided with a rotary shaft bore 140b so that the rotor 100b is vertical to the rotary shaft 20b, and the supporting pin 110 is vertically fixed to the rotor 100b. The rotor 100b is provided with apertures 130b that are vertical to the surface of the rotor 100b. Likewise, the bodies 40 are supported on the rotor 100b and the rotary shaft 20b is rotated at 50 to 70 rpm in a direction 150 in the electrolyte. In this way the smooth or even plating surfaces have been obtained as by the examples of Figures 3 and 4. The characteristics of bodies, e.g. resonators, produced by means of a device according to the present invention will be described by way of example so as to enable one to assess the superiority of the present invention over the comparative example: EXAMPLE 1 A ceramic body 40 of BaO-TiO₂ having an outside diameter of 6.0 mm, an inside diameter of 2.0 mm and a length of 8.0 mm was facially abraded to Rz=6.0 µ by a barrel abrading machine. Then the body 40 was treated in an etching reagent containing HF-HNO₃ for 20 minutes. The resulting powdery leftovers were removed in a barrel 200 by a supersonic wave cleaning method for 30 minutes. After cleansing with water, the body 40 was treated with a stannous chloride solution so as to improve the sensitivity and then with a palladium chloride solution so as to increase the activation. After drying, resist ink was coated on the end wall, and after the resist ink dried, the body 40 was subjected to electroless plating in a bath containing copper sulfate, EDTA, formaldehyde, and NaOH, and coated with a copper film of 3 µ thick. After cleansing, the body 40 was subjected to electroplating with silver and coated with a silver film of 15 µ thick. After cleansing and drying, the bodies treated in this way were assembled into 100 pieces of resonators. These are referred to as Sample No.1. Thirty pieces (n=30) were selected from the Sample No.1 at random, and the characteristics of them were assessed. The characteristics are shown in Table 1, wherein the thickness of the plated film, the Q characteristic of high frequency is represented in terms of Q value at non-load, and the strength of bond between the electrode 80 and the body 40 is represented as the means value of the thirty resonators. The strength of bond between the electrode 80 and the body 40 was measured by the following manner: a copper wire with a nail head having a diameter of 0.8 mm was vertically soldered to the electrode 80 (in the Sample No.1, it was copper film) of the resonator at its head. The soldered area was 4 mm². The copper wire was pulled at a speed of 40 mm/min, and the breaking strength was measured. The assessment of the characteristics and the method of measuring breaking strength were the same throughout the following examples. EXAMPLE 2 A ceramic body 40 of BaO-TiO₂ having an outside diameter of 6.0 mm, an inside diameter of 2.0 mm and a length of 8.0 mm was facially abraded to Rz=9.5 by a blasting device. Then the body 40 was treated in an etching reagent containing HF-HNO₃ for 20 minutes. The resulting powdery leftovers were removed in a barrel 200 by a supersonic wave cleaning method for 30 minutes. After cleansing with water, the body 40 was treated with a stannous chloride solution so as to improve the sensitivity and then with a palladium chloride solution so as to increase the activation. After drying, resist ink was coated on the end wall. After the resist ink was allowed to dry so as to form a resist layer, the body 40 was subjected to electroless plating in a bath containing copper sulfate, EDTA, formaldehyde, and NaOH, and coated with a copper film of 13 µ thick. Following cleansing, the body 40 was subjected to another electroless plating with nickel, and coated with a nickel film of 3 µ. After cleansing and drying, the bodies treated in this way were assembled into 100 sets of resonators. These are referred to as Sample No.2. Thirty sets (n=30) were selected from the Sample No.2 at random, and the characteristics of them were assessed as shown in Table 1. EXAMPLE 3 A ceramic body 40 of BaO-TiO₂ having a diameter of 6.0 mm, an inside diameter of 2.0 mm and a length of 8.0 mm was facially abraded to Rz=4 µ by a barrel abrading device. Then the body 40 was treated in an etching reagent containing HF-HNO₃ for 20 minutes. The resulting powdery leftovers were removed in a barrel 200 by a supersonic wave cleaning method for 30 minutes. After cleansing with water, the body 40 was treated with a stannous chloride solution so as to improve the sensitivity and then with a palladium chloride solution so as to increase the activation. After drying, resist ink was coated on the end wall and after the resist ink dried, the body 40 was subjected to electroless plating in a bath containing copper sulfate, EDTA, formaldehyde, and NaOH, and coated with a copper film of 13 µ thick. After cleansing and drying, the bodies treated in this way were assembled into 100 sets of resonators. These are referred to as Sample No.3. Thirty sets (n=30) were selected from the Sample No.3 at random, and the characteristics of them were assessed as shown in Table 1. COMPARATIVE EXAMPLE 1 A ceramic body 40 of BaO-TiO₂ having a diameter of 6.0 mm, an inside diameter of 2.0 mm and a length of 8.0 mm was facially abraded to Rz=6.0 µ by a barrel abrading machine. After cleansing with water, the body 40 was treated with a stannous chloride solution so as to improve the sensitivity and then with a palladium chloride solution so as to increase the activation. After drying, resist ink was coated on the end wall and after the resist ink was allowed to dry so as to form a resist layer, the body 40 was subjected to electroless plating in a bath containing copper sulfate, EDTA, formaldehyde, and NaOH, and coated with a copper film of 3 µ thick. After cleansing, the body 40 was subjected to electroplating with silver and coated with a silver film of 15 µ thick. After cleansing and drying, the bodies treated in this way were assembled into 100 sets of resonators. These are referred to as Sample No.4. Thirty sets (n=30) were selected from the Sample No.4 at random, and the characteristics of them were assessed. COMPARATIVE EXAMPLE 2 A ceramic body 40 of BaO-TiO₂ having a diameter of 6.0 mm, an inside diameter of 2.0 mm and a length of 8.0 mm was treated in an etching reagent containing HF-HNO₃ for 20 minutes. The resulting powdery leftovers were removed in a barrel 200 by a supersonic wave cleaning method for 30 minutes. After cleansing with water, the body 40 was treated with a stannous chloride solution so as to improve the sensitivity and then with a palladium chloride solution so as to increase the activation. After drying, resist ink was coated on the end wall and after the resist ink was allowed to dry so as to form a resist layer, the body 40 was subjected to electroless plating in a bath containing copper sulfate, EDTA, formaldehyde, and NaOH, and coated with a copper film of 3 µ thick. After cleansing, the body 40 was subjected to electroplating with silver, and coated with a silver film of 15 µ. The bodies treated in this way were assembled into 100 sets of resonators These are referred to as Sample No.5. Thirty sets (n=30) were selected from the Sample No.5 at random, and the characteristics of them were assessed as shown in Table 1. Table 1 shows the comparative data between the Examples 1 to 3 and the comparative examples 1 to 2. The plating was conducted in an electroless plating agent, and the bodies 40 were made of barium-titanate base dielectric ceramic. In the comparative example 1 the bodies 40 were placed in a cage that was submerged in the plating agent, and in the comparative example 2 the bodies 40 were supported on pins fixed on a stationary pillar. In the comparative example 2 the plating was conducted with the bodies 40 being motionless. Table 2 shows that the yields obtained by the Examples 1 to 3 are on average greater by about 20% than those by the comparative examples 1 and 2. After the electroless plating is finished, electroplating can be carried out by energizing through the supporting pins 110. The electroless plating takes a long time. Therefore at first a thin film is formed by electroless plating in a relatively short period of time, and after cleaning, electro-plating is applied. This double plating is effective to shorten a plating period of time. The bodies 40 have uneven top surfaces by a roughening process but it is preferred that they have the same rough bottom surfaces. Owing to the rough top and bottom surfaces, the bodies 40 and the rotor 100 keep point contact with each other, thereby securing the formation of even plated films. When the rotor 100 is made of plastic alone, it is preferred that the rotor is provided with hills and valleys on the top surfaces and on the bottom surfaces that cross each other at right angle. This expedient protects the plastic rotor from being adversely affected by curving at a high temperature that is unavoidable in the plating operation because the tendencies of curving in opposite directions on each surface mutually negate each other into no substantial curving. The electrolyte or plating agent used in the device of Figure 2 will be described: Referring to Figure 6 and 7, the reference numeral 40 denotes a body obtained by sintering strong electromagnetic ceramic, having a bore 50 and an electrode 80 deposited by electroless plating. The body 40 is extruded into a cylindrical shape through a suitable mold, and sintered at an elevated temperature (1000°C or more). The material is selected from BaO-TiO₂, ZrO₂-SnO₂-TiO₂, BaO-Nd₂O₃-TiO₂, and CaO-TiO₂-SiO₂. In the illustrated embodiment BaO-TiO₂ was used. The body 40 was abraded by a barrel abrading device so as to make rounded corners, and was submerged in an etching reagent such as hydrofluoric acid and phosphoric acid, so that the outside surface of the body 40 and the inside surface of the bore 50 were finely roughened. Subsequently, the roughened body 40 was submerged first in a stannous chloride solution (0.05 g/L), and then in a palladium chloride (0.1 g/L) so as to increase the activation, thereby covering the body 40 including the inside surface of the bore 50 with a catalytic layer having a core of palladium particles. If necessary, one of the end faces of the body 40 can be covered with a resist layer so as to prevent an electrode from being formed thereon, wherein the resist layer is resistant to the electroplating. Then, the activated body 40 was submerged in an electroless plating agent so that copper was deposited on the body 40 covered with the catalytic layer, thereby forming the electrode 80 of 5 to 10 µ thick. The electroless plating agent had the following composition, and the plating was conducted at a temperature ranging from 60 to 80°C: Copper sulfate : 0.030 to 0.050 M/L EDTA : 0.035 to 0.100 M/L Formaldehyde : 5 to 10 ml/L Sodium hypophosphite : 0.05 to 0.100 M/L 2,2′bipyridyl : 10 mg/L PH : 12.0 to 13.0 It has been found that the dielectric resonator having the electrode 80 of BaO-TiO₂ has a higher Q value by about 30% than that of a conventional resonator that is subjected to copper electroless plating with the use of Rochelle salt at a low temperature (40°C). Under the treatment using Rochelle salt at a low temperature, copper is likely to deposit at a relatively high speed, and hydrogen gas and univalent copper oxide (Cu₂O) are contained in the copper deposit, thereby reducing the purity of the copper layer. In addition, the copper deposit is blackened and coarse crystal results. What is worse, the Q value is low because of insufficient bond between the deposited copper and the surfaces of the body 40. In contrast, according to the present invention, the electroless plating agent comprises a basic bath containing EDTA for forming copper complex ions, and formaldehyde as a reducing agent, with the addition of a small amount of 2,2′bipyridyl and a large amount of sodium hypophosphite. When the plating is carried out in this electrolyte at such high temperatures as 60 to 80°C, the 2,2′bipyridyl prevents the deposit of univalent copper oxide and the intrusion of hydrogen gas, thereby maintaining the purity of the deposited copper and increasing the crystalline fineness. These merits enhance the strength of bond between the deposited copper layer and the surfaces of the body 40, thereby increasing the Q value. It has been found that the sodium hypophosphite facilitates the depositing of copper on the outside surface of the body 40 and the inside surface of the bore 50, thereby improving the Q characteristics. As shown in Figure 8, better Q characteristics were obtained when the plating was carried out under the thermal condition indicated by (A) in which the plating bath was heated at temperatures ranging from 60°C to 80°C, but when the temperature was lower than 60°C, an uneven deposit of copper results, and the bond of the copper layer was poor. When it was higher than 80°C, the plating bath was likely to decompose, thereby resulting in coarse crystals of copper. Figure 9 shows that excellent Q characteristics have been obtained by carrying out electroless plating at a vacuum. The vacuum condition increases the crystalline fineness, and also strengthens the bond between the copper layer and the surfaces of the body 40. As shown in Figure 9, the optimum range is the zone indicated by (B) where the temperature is in the range of 300 to 500°C. If the temperature is higher than 500°C, the body 40 is liable to alteration, thereby reducing the Q characteristics. If the temperature is lower than 300°C, the crystals remain coarse, thereby making no contribution to the improvement of the Q characteristics.

Claims: A plating device comprising: a rotor (100) mounted for rotation about an axis inclined to a horizontal plane with respect to the device; driving means (23, 24a, 24b, 24c) for rotating the rotor (100) about the axis; and supporting pins (110) provided on the rotor (100) for supporting objects to be plated; characterized by the following features: a) the rotor (100) is adapted to be submerged in an electrolyte; b) the supporting pins (110) are adapted to support bodies of resonators (40); c) the axis can also be vertical with respect to a horizontal plane of the device; d) and hills (120a) and valleys (120b) are provided on a surface of the rotor (100), the supporting pins (110) being disposed on the hills (120a). A plating device as claimed in claim 1, wherein the rotor (100) is provided with a plurality of apertures (130). A plating device as claimed in claim 2, wherein each of the apertures (130) is provided between a respective pair of adjacent supporting pins (110). A plating device as claimed in any of claims 1, 2 or 3, wherein the supporting pins (130) are made of metal. A plating device as claimed in any preceding claim, wherein the supporting pins (130) are coated with a plating metal. A plating device as claimed in any preceding claim, wherein the rotor (100) is provided with a bore (140) in which a rotary shaft (20a) can be received. A plating device as claimed in claim 6, wherein the bore (140) is perpendicular to or inclined with respect to the plane of the rotor (100). A plating device as claimed in any preceding claim, wherein hills (120a) and valleys (120b) are provided on another surface of the rotor (100). A plating device as claimed in any preceding claim, wherein the supporting pins (110) are parallel to the axis. A plating device as claimed in any of claims 1 to 8, wherein the supporting pins (110) are inclined with respect to the axis. A plating device as claimed in any preceding claim and comprising at least two rotors (100), wherein the driving means (23, 24a, 24b, 24c) is adapted to rotate at least one of the rotors (100) in one direction and at least another one of the rotors (100) in another direction. A plating device as claimed in any preceding claim, wherein the rotor (100) is made of plastics or a plasticcoated metal.

Inventors: HISADA NOBORU, MAKINO YOSHIYUKI, NAKAMURA TSUNESHI, UENISHI YOSHITSUGU, HISADA, NOBORU, MAKINO, YOSHIYUKI, NAKAMURA, TSUNESHI, UENISHI, YOSHITSUGU
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1989
Main classification: H01P7
IPC codes: H01P11, B65C3, H01P7