JP2009215592A - Etching liquid for spray etching for copper and copper alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an etching liquid for spray etching for copper and a copper alloy which can obtain a high etching factor. <P>SOLUTION: The etching liquid for spray etching for copper and the copper alloy comprises iron chloride (III) of 1 to 16 mass% and phosphoric acid of 10 to 100 mass% to the iron chloride (III). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an etchant for spray etching of copper and copper alloys. More specifically, the present invention relates to an etching solution for spray etching of copper and copper alloy that can obtain a high etching factor.

  2. Description of the Related Art In recent years, miniaturization and high functionality of electronic devices have rapidly progressed, and printed circuit boards incorporated in these devices are strongly demanded to have a high circuit density.

As a method of forming a circuit pattern of a printed wiring board, a resist pattern is formed on the surface of a copper foil laminated on an insulating substrate by a method such as screen printing or photolithography, and then an aqueous solution of iron (III) chloride or the like. A so-called subtractive method of removing an unnecessary portion of copper foil using an etching solution is widely used. FIG. 1 is a schematic cross-sectional view of a line pattern of a copper foil 2 on a substrate 3 obtained by an etching method, where t is the thickness of the copper foil line, W ₁ is the top width of the copper foil line, and W ₂ is the copper foil line. The bottom width W ₃ is the line width of the resist pattern 1. When manufacturing a printed wiring board by a subtractive method, it is known that the shape of a copper foil line cross section will not become a rectangle. When the etching factor, that is, 2t / (W ₂ −W ₁ ) in FIG. 1 is small, there is a problem that the electrical characteristics of the formed circuit deteriorate and the area required for mounting the components cannot be secured. Therefore, it has been difficult to manufacture a printed wiring board having a high circuit density by the subtractive method.

  From the above problems, in order to manufacture a printed circuit board having a high circuit density, a so-called additive method in which a circuit is formed using a plating technique is used. However, the additive method has an essential problem that the process is complicated and a plating process that takes a long time and is difficult to adjust is performed, so that the cost is very high and the yield is low. As long as a high etching factor can be obtained, a printed circuit board having a high circuit density can be manufactured even by the subtractive method, and thus an etching technique that can obtain a high etching factor is strongly demanded.

  As a technique for obtaining a high etching factor, it has been proposed to use an etching solution containing iron (III) chloride as a main component and thiourea added (see, for example, Patent Document 1). However, this technology uses thiourea that is suspected of causing carcinogenicity, as well as the etching factor obtained by this technique is not sufficient for use in the production of a substrate having a very high wiring density that has been required in recent years. There is a serious problem in terms of occupational health and pollution prevention that hydrogen sulfide gas, which is toxic and offensive odor, is generated during the storage and use of the etching solution.

  Furthermore, an etching solution is proposed in which an azole compound such as benzotriazole is added to an etching solution containing an oxidizing metal salt such as iron (III) chloride and an inorganic acid or an organic acid as components (see, for example, Patent Document 2). . However, this technology has a serious problem in terms of environmental conservation in that not only the etching factor obtained by this is insufficient, but also an azole compound that has low biodegradability and is difficult to remove from the etching solution after use. is doing.

It has also been proposed to perform etching using a first etching solution that does not include a compound that forms a coordination bond with copper ions and a second etching solution that includes a compound that forms a coordination bond with copper ions. However, the etching factor obtained by this method is not sufficiently high, and two etchings using different etching solutions are essential, and the process becomes complicated. Have a problem.
U.S. Pat. No. 3,144,368 JP-A-2005-330572 JP 2007-180172 A

  An object of the present invention is to provide an etching solution for spray etching of copper and copper alloy, which has been difficult in the past and can provide a high etching factor.

  An etching solution containing 10 to 100% by mass of phosphoric acid with respect to 1 to 16% by mass of iron (III) chloride and iron (III) chloride.

  Among them, an etching solution containing 20 to 100% by mass of phosphoric acid with respect to 1 to 8% by mass of iron (III) chloride and iron (III) chloride is preferable.

  According to the present invention, a high etching factor, which has been difficult in the past, can be obtained. As a result, a printed wiring board having a high circuit density can be manufactured by the subtractive method. Moreover, the etching solution of the present invention does not generate a toxic gas such as hydrogen sulfide, and since it consists only of components for which a processing method has been established, it can be easily and completely processed after use, and occupational health. In addition, it is preferable from the viewpoint of pollution prevention and environmental conservation.

  In the present invention, spray etching is an etching method in which fine droplets of an etching solution are jetted onto the surface of a material to be etched held in a gas. In order to form fine droplets of the etching solution, a spray nozzle, that is, a nozzle provided with an orifice at the tip is used. Spray nozzles include a one-fluid nozzle that supplies pressurized liquid and ejects fine droplets without the help of other fluids, and a two-fluid nozzle that ejects pressurized gas together with the liquid to be ejected. The etching solution of the present invention can be preferably used when any of them is used. In addition, even if it uses the etching liquid of this invention for etching methods other than spray etching, an etching rate is very slow and is not practical.

  The etching solution of the present invention is an etching solution for copper and copper alloys. The copper alloy in the present invention refers to an alloy containing 75% by mass or more of copper, and examples thereof include bronze, red copper, and white copper. Even when the etching solution or etching method of the present invention is used for an alloy containing less than 75% by mass of copper, a high etching factor cannot be obtained.

  When manufacturing a printed wiring board using the etching solution of the present invention, the thickness of the copper foil to be etched (including copper alloy foil; the same shall apply hereinafter) is preferably 4 μm or more and 40 μm or less, and 8 μm or more and 20 μm or less. More preferably. According to the technique of the present invention, even if the thickness of the copper foil is less than this range, it is no longer advantageous for making the wiring pitch finer, but there may be a problem that the impedance of the formed wiring is rather increased. . Further, if the thickness of the copper foil exceeds this range, a high etching factor may not be obtained.

  When manufacturing a printed wiring board using the etching liquid of this invention, copper foil is laminated | stacked on an insulating base material. Insulating base materials include epoxy resins, phenol resins, melamine resins, bismaleimide / triazine resins, polyester resins, polyimide resins, polyamide resins, fluororesins, and other synthetic resins. Fiber reinforced resins such as paper phenol, paper epoxy, glass epoxy, etc. impregnated into the fiber, and various glasses, ceramics and metals can be used. When manufacturing a printed wiring board using the etching solution of the present invention, a heat-resistant resin such as a fiber reinforced resin, polyimide, or fluororesin, or a ceramic is suitably used from the viewpoints of insulation, mechanical properties, heat resistance, and the like. . Furthermore, it is also possible to use a base material in which two or more kinds of materials are combined and laminated.

  In the present invention, the method of laminating the copper foil on the substrate is not particularly limited, and phenolic, melamine-based, epoxy-based, urethane-based, silicon-based, modified silicon-based, chloroprene, nitrile, acrylic and other rubber-based, acetic acid The base material and the copper foil can be bonded using a vinyl-based adhesive or the like, and the base material and the copper foil can be laminated using a so-called heat seal method. Further, a so-called casting method can be used in which a hot melt or solution of a material to be a base material is applied onto a copper foil and solidified by cooling or drying to form a laminate. Moreover, if a structure similar to that obtained by bonding a copper foil to a base material is obtained, copper or a copper alloy may be obtained by using a method such as a vacuum deposition method such as electrolytic plating, electroless plating, or sputtering on the surface of the base material. It is also possible to use a laminate produced by forming the above layer.

  The etching solution of the present invention contains iron (III) chloride as the first essential component. The concentration of iron (III) chloride in the etching solution of the present invention needs to be 1 to 16% by mass with respect to the total amount of the etching solution. When the concentration of iron (III) chloride is lower than this, the etching rate is remarkably slow, which is not practical. Further, when the concentration of iron (III) chloride is higher than this, a high etching factor cannot be obtained.

  The form of iron (III) chloride used in preparing the etching solution of the present invention is not particularly limited, and iron chloride (III) commercially available as an aqueous solution can be used by dissolving an anhydrous or hexahydrate solid. ) May be diluted as appropriate. Solid iron (III) chloride is usually supplied as hexahydrate (formula 270.30), but the calculation of iron (III) chloride concentration in the present invention is anhydrous (formula 162.21). As a reference. For example, when 1.0 kg of the etching solution of the present invention containing 10 mass% of iron (III) chloride is prepared, the iron (III) chloride hexahydrate is 1.0 kg × 10% × (270.30 / 162.21) = 167 g.

  The etching solution of the present invention contains phosphoric acid as a second essential component. The addition amount of phosphoric acid needs to be 10 to 100% by mass with respect to iron (III) chloride. When the addition amount of phosphoric acid is less than this, a high etching factor which is the effect of the present invention cannot be obtained. Further, when the amount of phosphoric acid added is larger than this, there arises a problem that the etching is remarkably slow or the fine space is not sufficiently etched.

The form of phosphoric acid used for preparing the etching solution of the present invention is not particularly limited. Anhydrous crystals and aqueous solutions of various concentrations can be used. It can be used after being disassembled. The concentration of phosphoric acid in the present invention is a concentration as phosphoric anhydride represented by H ₃ PO ₄ (formula weight 98.00). For example, in the case of preparing 1.0 kg of the etching solution of the present invention containing 1.0% by mass of phosphoric acid using 85% by mass of phosphoric acid which is generally distributed, 1.0 kg × 1.0% / 85 % = 12 g will be used. When 1 kg of the same etching solution is prepared using diphosphorus pentoxide, the formula amount of phosphorous pentoxide is 141.94, and two formula amounts of phosphoric acid are obtained by hydrolysis per formula amount. Therefore, 1.0 kg × 1.0% × {(141.94 / 2) /98.00} = 7.2 g may be used. Phosphoric anhydride and phosphoric anhydride are different compounds. The former is a compound represented by the composition formula P ₂ O ₅ , that is, diphosphorus pentoxide, and the latter is water among the compounds represented by the composition formula H ₃ PO _4. It is not included and the two are clearly distinguished.

  The etching solution of the present invention particularly preferably contains 1 to 8% by mass of iron (III) chloride and 20 to 100% by mass of phosphoric acid based on iron (III) chloride with respect to the total amount of the etching solution. By using such an etching solution, it is possible to perform extremely stable etching without reducing the line width even if the etching time is excessive.

  The etching solution of the present invention is most reasonable from the standpoint of ease of material acquisition and preparation work, although it is most reasonable to prepare it by dissolving and diluting iron (III) chloride and phosphoric acid in water. It may be prepared from other materials as long as it contains iron (III) ions, chloride ions, and phosphate ions. For example, iron (III) salts such as iron (III) hydroxide are used as the source of iron (III) ions, various chlorides such as hydrochloric acid and sodium chloride are used as the source of chloride ions, and phosphate ions Various phosphates such as sodium dihydrogen phosphate can also be used as a supply source.

  When spray etching is performed using the etching solution of the present invention, any part of the surface to be etched starts etching, that is, when the target portion of the material to be etched is wetted by the etching solution, the etching is finished, That is, the copper foil corresponding to the space portion of the resist pattern is completely removed, and the time during which the etching solution from the spray nozzle does not reach directly reaches the time when the same space width as the space width of the resist pattern is obtained. It is preferable to perform the etching in such a way as not to occur. In addition, for example, there is no problem that the time when the liquid does not reach directly reaches the state where the liquid reaches directly after 4 seconds continues, and the time when the liquid does not reach again again continues for 4 seconds.

It is preferable that the amount of sprayed liquid per unit area in the portion of the material to be etched that reaches directly from the spray nozzle is 10 to 100 g / cm ² · min. If the amount of sprayed liquid is less than this, the etching rate may decrease rapidly or may not substantially progress, and if the amount of sprayed liquid is larger than this, the etching factor will decrease. There is.

  Moreover, when performing spray etching using the etching liquid of this invention, it is preferable that the supply pressure of the etching liquid to a spray nozzle shall be 50-500 kPa, and it is more preferable to set it as 100 kPa-250 kPa. If the supply pressure is lower than this, the etching rate may be remarkably reduced. If the supply pressure is higher than this, the resist pattern is likely to be broken and the selection of the resist material is limited. .

  When etching is performed using the etching solution of the present invention, the temperature of the etching solution is preferably 15 to 45 ° C, more preferably 15 to 35 ° C. This is because if the temperature is lower than this, the etching uniformity may be lowered, and if the temperature is higher than this, a high etching factor may not be obtained.

  The etching solution of the present invention may contain a surfactant, an antifoaming agent, a wetting accelerator such as alcohol and glycol, but is not essential. In addition, thio compounds such as thiourea and nitrogen-containing heterocyclic compounds such as benzimidazole have been proposed as agents for improving the etching factor. However, even if these are added to the etching solution of the present invention, the etching factor is reduced. It is not preferable because it not only has an effect of further improvement but also significantly delays the progress of etching.

  The resist used in the production of the printed circuit board using the etching solution of the present invention is not particularly limited. For example, only necessary portions are insolubilized by light irradiation, and unnecessary portions are developed and removed using an alkaline aqueous solution or the like to form a pattern. So-called negative photoresist, solubilizing only unnecessary parts by light irradiation, developing and removing with an aqueous alkali solution etc. to form a pattern, so-called positive photoresist, screen printing, electrophotography, inkjet method, etc. A formed resist pattern or the like can be used. Among these, since a highly reliable printed wiring board can be manufactured without using copper around the bottom of the line by using a resist pattern formed by a positive photoresist, it is used together with the etching solution of the present invention. It is preferably used as a resist pattern.

  The etching solution of the present invention can be suitably used not only for the production of printed wiring boards but also for various other industrial applications when highly controlled etching of copper and copper alloys is required.

  When the etching solution of the present invention is discarded after use, it is a harmful chemical species contained by one of the most basic heavy metal processing steps, that is, a step of adjusting the pH to a weak alkali by adding calcium hydroxide. Thio compounds and azoles because iron (II) ions, iron (III) ions, copper (I) ions, copper (II) ions and phosphate ions are all easily precipitated and removed to the extent that there are no environmental problems. There is no need for a special wastewater treatment process that requires a large facility such as ozone oxidation, which is necessary for an etching solution containing a compound or an amine compound.

  Examples of the present invention will be described below.

[Example 1]
[Preparation of etchant]
Water is added to 0.27 kg (0.10 kg as an anhydride) of an aqueous solution of iron (III) chloride (concentration: 37 wt%) of 40 ° Baume and 0.012 kg of 85 wt% phosphoric acid (0.010 kg as an anhydride). An etching solution containing 10 kg and containing 1.0% by mass of iron (III) chloride and 0.10% by mass of phosphoric acid was prepared.

[Formation of resist pattern]
A glass epoxy base material having a rolled copper foil having a thickness of 12 μm adhered to the surface is immersed in an aqueous solution of sodium peroxodisulfate having a concentration of 5% by mass for 30 seconds, washed with water and dried, and then the resist layer thickness after drying is 5 μm. A positive photoresist was applied to the film. Here lines (W ₃₎ / after the width of the space was exposed for evaluation pattern of 15 [mu] m / 15 [mu] m, respectively, to remove the exposed portion with a concentration of 3 wt% sodium carbonate aqueous solution to form a resist pattern.

[etching]
The above-mentioned etching liquid adjusted to 30 ° C. was supplied to the nozzle from a full cone spray nozzle (model number: ISJJX020PP, manufactured by Ikeuchi Co., Ltd.) with a jet angle of 65 ° provided at the tip of the substrate surface at a position of 6.0 cm. Etching was performed by spraying toward the substrate at a supply pressure of 200 kPa and a spray amount of 2.0 kg / min. The substrate after the etching is immediately washed with a 5 mass% hydrochloric acid aqueous solution and deionized water, and then immersed in a 10 mass% sodium hydroxide aqueous solution to remove the photoresist, and then deionized water is used. The printed wiring board for evaluation was produced.

[Examples 2 to 11]
Except that the concentrations of iron (III) chloride and phosphoric acid were changed as shown in Table 1, spray etching was performed in the same manner as in Example 1 to produce a printed wiring board for evaluation.

[Comparative Examples 1 to 9]
A printed wiring board for evaluation was produced by performing spray etching in the same manner as in Example 1 except that the concentration of iron (III) chloride, the concentration of phosphoric acid, and the liquid injection amount were changed as shown in Table 1. . In Comparative Examples 4, 6, 8, and 9, the copper foil in the space was not yet removed when the etching solution was sprayed for 900 seconds, and production was stopped here.

[Evaluation]
For each of the examples and comparative examples, the etching solution injection time X at which the bottom width W ₂ of the copper foil line is 15 μm was examined. Further, etching is performed with the etching time being 1.2 times and 2.0 times X, and the bottom width W ₂ of the line and the top width W _{1 of the} line are measured for each case, and the etching factor is 2t / (W ₂ − W ₁₎ was calculated. Note that an etching factor of 10 or more is practically sufficient, and it is not meaningful to discuss the superiority or inferiority between values higher than this. Therefore, all etching factors of 10 or more are described as 10+. The line width was measured by observation with a microscope (model number: VK-8500, manufactured by Keyence Corporation).

  As is clear from each example, according to the present invention, an extremely high etching factor that has been difficult to use by using a conventionally known etching solution and etching method can be obtained. In particular, when etching is performed under particularly preferable conditions in the present invention as in Examples 4 to 5 and 7 to 9, a predetermined space is obtained even when etching is continued for a long time after a sufficient space width is obtained. Therefore, the desired circuit pattern could be formed very stably. As a result, it is possible to perform etching for a long time without causing disconnection of the line, and it is possible to surely avoid a short circuit between circuits due to remaining unetched portions, so that a printed wiring board with an extremely high yield. Can be manufactured.

  Etching solution that does not contain phosphoric acid, which is an essential component of the etching solution of the present invention as in Comparative Example 1, and Etching solution in which the amount of phosphoric acid added is smaller than the range of the present invention as in Comparative Examples 2 and 3 Then, the high etching factor which is the effect of this invention was not able to be obtained. Further, as in Comparative Examples 5 and 7, even with an etching solution in which the amount of iron (III) added is larger than the range of the present invention, a high etching factor that is the effect of the present invention cannot be obtained.

  Further, as in Comparative Examples 4 and 6, an etching solution in which the amount of iron (III) added is smaller than the range of the present invention, and as in Comparative Examples 8 and 9, the amount of phosphoric acid is within the range of the present invention. If the etching solution is larger than the etching solution, even if the etching does not proceed, or if it proceeds, it takes a very long time to complete, which is not practical.

Schematic cross-section of pattern obtained by etching method

Explanation of symbols

W ₁ line top width W ₂ line bottom width W ₃ resist pattern line width t copper foil thickness 1 resist pattern 2 copper foil 3 substrate

Claims (2)

  An etching solution for spray etching of copper and copper alloy, which contains 10 to 100% by mass of phosphoric acid with respect to 1 to 16% by mass of iron (III) chloride and iron (III) chloride.   The etching solution for spray etching of copper and copper alloy according to claim 1, comprising 20 to 100% by mass of phosphoric acid with respect to 1 to 8% by mass of iron (III) chloride and iron (III) chloride.

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