Patent Application
20080073614
With the metal removing solution of the present invention and the metal removing method of the present invention using the foregoing metal removing solution, the following can be achieved: an excellent property of selectively removing palladium, tin, silver, palladium alloy, silver alloy, and tin alloy without attacking copper; and excellent handleability because of the foregoing solution not containing any toxic substance. When an acid is contained additionally, the solution can promote oxidative dissolution of palladium, tin, silver, palladium alloy, silver alloy, and tin alloy. Therefore, a further excellent removing property can be obtained. When a halogen ion is contained additionally, the solution can hold removed palladium, tin, silver, palladium alloy, silver alloy or tin alloy stably. Therefore, the removal of these metals can be accelerated.
The metal remover of the present invention is useful not only for removing plating catalyst residues but also for removing, for example, a thin film of tin plating provided on a surface of copper while minimizing any possible damage to an underlying copper layer.
The present invention is particularly useful in the following case: when electroless copper plating is performed with respect to an insulating material of an electronic substrate such as a printed wiring board by adhering palladium particles, silver particles, or palladium-tin particles to the insulation material so that the particles serve as catalyst nuclei, the present invention is useful in a subsequent step of removing the particles therefrom by etching.
The metal remover of the present invention has a property of selectively removing palladium, tin, silver, palladium alloy, silver alloy, tin alloy, and the like without attacking copper. Suitable conditions for using the metal remover are, for example, a solution temperature of 10 to 70° C., preferably 20 to 50° C., an application time of 10 to 300 seconds, preferably 15 to 120 seconds. Under such conditions, a more excellent property of selective etching can be exhibited.
As an application method, either spraying or immersion may be used. In the case of spraying, a spraying pressure is 0.01 to 0.4 MPa, preferably 0.05 to 0.2 MPa.
For forming the metal remover of the present invention, the following components as described below, for example, can be used, though the components are not limited particularly:
(1) chain thiocarbonyl compound
(2) acid
(3) halogen ion
Examples of thiocarbonyl compounds include a thiocarbonyl compound having a thiocarbonyl group (>C═S) in which carbon is bonded in a chain structure (chain thiocarbonyl compound), and a thiocarbonyl compound having a thiocarbonyl group in which carbon is bonded in a cyclic structure. The compound having a cyclic structure is described in the above “Description of Related Art” section, being referred to as “cyclic thiocarbonyl compound”.
The chain thiocarbonyl compound is used in the present invention. This compound is a chain-form compound having a >C═S bond, in which the thiocarbonyl group (>C═S) is not included in a cyclic structure. Examples of the compound include thiourea compound, thiuram compound, dithiocarbamic acid compound, xanthogenic acid compound, ethyl methyl thioketone, 2,4-pentanedithione, 2-thioxo-4-thiazolidinone (Rhodanine), 2-thiouracil, and thioacetamide.
(1) Examples of thiourea compound: 1-acetyl-2-thiourea, 1-allyl-3-(2-hydroxyethyl)-2-thiourea, 1-amidino-2-thiourea, 1,3-diethylthiourea, 1,3-diphenylthiourea, 1,3-dibutylthiourea, 1,3-dimethylthiourea, thiourea, tributylthiourea, trimethylthiourea, 1,3-bis(dimethylaminopropyl)-2-thiourea, tetramethylthiourea, and N-methylthiourea.
(2) Examples of thiuram compound: tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetrabutylthiuram disulfide.
(3) Examples of dithiocarbamic acid compound: 2-(N,N′-diethylthiocarbamoylthio)benzothiazole, zinc dimethyldithiocarbamate, nickel diethyldithiocarbamate, nickel dibutyldithiocarbamate, and sodium dibutyldithiocarbamate.
(4) Examples of xanthogenic acid compound: zinc butylxanthate, and isopropylxanthogenic acid.
Thiourea compounds such as thiourea, tetramethylthiourea, N-methylthiourea, 1,3-diethylthiourea, and 1,3-dimethylthiourea are preferred particularly, owing to their excellent properties of removing palladium, tin and silver.
The chain thiocarbonyl compound is mixed so that the content thereof is, preferably, not less than 0.05 wt % and not more than 80 wt %, and more preferably, not less than 0.1 wt % and not more than 40 wt %. The efficiency for removing palladium, tin and silver decreases slightly when the content of the compound is less than 0.1 wt %. When the content of the compound is less than 0.05 wt %, the remover tends to be incapable of removing palladium, tin and silver sufficiently.
An acid is mixed in order to promote the oxidization of palladium, tin and silver, thereby improving the solubility. Examples of acids that can be used in the present invention include sulfonic acid compounds such as methanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and taurine; inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, fluoroboric acid, and phosphoric acid; and carboxylic acids such as formic acid, acetic acid, propionic acid, and butyric acid. Among these acids, a hydrochloric acid preferably is used because a halogen ion, which will be described below, can be added at the same time. The concentration of an acid is preferably in a range of 0.001 wt % to 0.7 wt %, both inclusive, in terms of H+ (hereafter concentrations are presented in the same manner), more preferably 0.1 wt % to 0.7 wt %, both inclusive, and particularly preferably 0.5 wt % to 0.7 wt %, both inclusive. There is no disadvantage in mixing an acid in a large amount. However, if, for example, hydrochloric acid is used as acid, the compound is not easily dissolved in water when the used amount of the same exceeds 0.7 wt %. On the other hand, when the content of an acid is less than 0.001 wt %, the property of removing palladium, tin and silver tends to degrade.
A halogen ion is mixed so as to keep the removed palladium, tin and silver stably in the solution. An ion source for the halogen ion is not limited particularly. Examples of the same include hydrochloric acid and salts such as sodium chloride, ammonium chloride, calcium chloride, potassium chloride, potassium bromide, sodium fluoride and potassium iodide.
The concentration of a halogen ion is in a range of, preferably not less than 0.03 wt % and not more than 30 wt %, more preferably not less than 1 wt % and not more than 30 wt %, and particularly preferably not less than 7 wt % and not more than 30 wt %. Stable dissolution of palladium, tin and silver in a solution is not likely to be achieved if the concentration of the halogen ion is less than 0.03 wt %.
Moreover, if hydrochloric acid is mixed as the above-mentioned acid, the addition of a halogen ion can be achieved simultaneously.
Other additives such as a surface-active agent and a stabilizer may be added appropriately to the metal remover of the present invention as required.
Hereinafter, the present invention will be described more specifically by way of Examples. It should be noted that the invention is not limited to the following examples. In the following, “%” means “percent by weight”.
A substrate made of a glass epoxy resin having a thickness of 0.2 mm, a length of 10 cm and a width of 10 cm was treated as follows, whereby a Pd applied plate was produced.
(1) The substrate was immersed in a preconditioner (PIW-1 produced by Okuno Chemical Industries Co., Ltd.) at 45° C. for 2 minutes, rinsed with water, and thereafter, immersed in an ATS CONDICLEAN (CIW-1 produced by Okuno Chemical Industries Co., Ltd.) at 65° C. for 5 minutes, whereby the resin substrate was roughened.
(3) The substrate was then immersed in a catalyst (OPC-SALH produced by Okuno Chemical Industries Co., Ltd. and OPC-80 produced by the same) at 25° C. for 15 minutes, rinsed with water, and thereafter, immersed in an accelerator (OPC-505A produced by Okuno Chemical Industries Co., Ltd. and OPC-505B produced by the same) at 35° C. for 5 minutes, then, rinsed with water and dried, whereby a Pd catalyst was adhered. An amount of Pd in the Pd applied plate thus obtained was 19.1 mg/m2.
A Pd applied plate formed with a copper substrate to which palladium was applied was produced in the same manner as that for Examples 1 to 7 and Comparative Examples 1 to 3 described above except that a copper substrate (product name: MCL-E-679 having a thickness of 0.2 mm, produced by Hitachi Chemical Co., Ltd.) was used in place of the glass epoxy resin substrate. Plates thus formed were used in Example 8 and Comparative Example 4.
The Pd applied plates thus produced were immersed in solutions having components formulated as shown in Tables 1 to 3 (the remainder is ion-exchanged water), under temperature and time conditions shown in Tables 1 to 3. Then, the remaining Pd was measured. The removal efficiencies thus determined are shown in Tables 1 to 3.
As can be seen from Tables 1 to 3, whether palladium was adhered to the resin plate or to the copper plate, higher removal efficiencies with respect to palladium were exhibited in Examples 1 to 8 as compared with those exhibited in Comparative Examples 1 to 4.
Moreover, in the case where an acid and/or halogen ion was present in addition to a chain thiocarbonyl compound, an even higher removal efficiency with respect to palladium was exhibited as compared to the case where a chain thiocarbonyl compound was used alone.
In this Example, a test to evaluate the etching rate with respect to copper was conducted. A solution according to the formulation of Example 6, and a solution according to the formulation of Comparative Example 4, i.e., a solution obtained by blending 8 wt % of 35 wt % HCl, 20 wt % of 65 wt % HNO3, and the ion-exchanged water as the remainder, were prepared, and the etching rates with respect to copper exhibited by these solutions were compared.
A copper plate (product name: MCL-E-679 having a thickness of 0.2 mm, a length of 4 mm, and a width of 4 mm, produced by Hitachi Chemical Co., Ltd.) was immersed in each of 100 ml solutions for one minute, and the etching rate was measured based on a change in the weight of the copper plate. The etching rate was measured at predetermined levels of the copper concentration, and the results thereof are shown in
In the case of the solution of Comparative Example 4, the etching rate with respect to copper increased as the concentration of copper increased, in other words, in a state in which palladium was removed continuously. On the other hand, in the case of the solution of Example 6, the etching rate remained low, which means that the attack against copper was suppressed.
In these Examples, a test to evaluate the property of removing tin was carried out. A tin plate (having a thickness of 0.2 mm, a length of 4 mm, and a width of 4 mm, Japan Metal Service, Ltd. (distributor)) was immersed in each of 100 ml solutions of Examples 10 to 14 shown in Table 4, at 40° C. for one minute, and the etching rate was measured based on a change in the weight of the tin plate.
In these Comparative Examples also, a test to evaluate the property of removing tin was carried out. A copper plate (product name: MCL-E-679 having a thickness of 0.2 mm, a length of 4 mm and a width of 4 mm, produced by Hitachi Chemical Co., Ltd.) was immersed in each of 100 ml solutions of Comparative Examples 5 to 7 shown in Table 4, at 40° C. for one minute, and the etching rate was measured based on a change in the weight of the copper plate.
Table 4 shows conditions and results of the tests in Examples 10 to 14 and Comparative Examples 5 to 7 altogether.
(*1)TMU: trimethylthiourea
(*2) EUR: 1,3-diethylthiourea
As can be seen from Table 4, each solution of Examples 10 to 14 exhibited a high etching rate (0.20 to 0.79 μm/min) with respect to tin, but a low etching rate (0 to 0.02 μm/min) with respect to copper. This means that each solution of these Examples can etch tin selectively, without etching copper.
In these Examples, the removal efficiency with respect to silver was evaluated. A substrate made of a glass epoxy resin having a thickness of 0.2 mm, a length of 10 cm and a width of 10 cm was treated as follows, whereby a test plate was produced.
(1) The substrate was immersed in a preconditioner (PIW-1 produced by Okuno Chemical Industries Co., Ltd.) at 45° C. for 2 minutes, rinsed with water, and thereafter, immersed in an ATS CONDICLEAN (CIW-1 produced by Okuno Chemical Industries Co., Ltd.) at 65° C. for 5 minutes, whereby the resin substrate was roughened.
(3) The substrate thus treated was immersed in a catalyst (OPC-SALH produced by Okuno Chemical Industries Co., Ltd. and OPC-80 produced by the same) at 25° C. for 15 minutes, rinsed with water, and thereafter, immersed in an accelerator (OPC-505A produced by Okuno Chemical Industries Co., Ltd. and OPC-505B produced by the same) at 35° C. for 5 minutes, rinsed with water and dried, whereby a Pd catalyst was adhered to the substrate.
(4) The substrate thus treated was immersed in an electroless silver plating solution (containing silver nitrate, Rochelle salt, ammonia, and sodium hydroxide) at 25° C. for 10 minutes, rinsed with water and dried, whereby silver was deposited on a surface of the resin base material.
The test plates thus produced were immersed in solutions having components that were formulated as shown in Tables 5 and 6 (the remainder is ion-exchanged water), under temperature and time conditions shown in Tables 5 and 6. Then, remaining silver was measured. The removal efficiencies thus determined are shown in Tables 5 and 6.
As can be seen from Tables 5 and 6, high removal efficiencies with respect to silver were exhibited the above-described Examples as compared to those exhibited in Comparative Examples.
The present invention is useful in the manufacture of an electronic substrate such as a printed wiring board, as well as in the patterning of a transparent conductive film and the wiring for use in a thin-type flat-panel display (e.g. liquid crystal display, plasma display)
The invention may be embodied in other forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed in this application are to be considered in all respects as illustrative and not limiting. The scope of the invention is indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-259126 | Sep 2006 | JP | national |
