KR820000570B1 - Method of dissolution of metals - Google Patents

Abstract

In the etching of Cu in the prepn. of printed-circuit boards, improved metal dissoln. rates are obtained when using an aq. soln. contg. H2SO4, H2O2, and certain primary diols[I, R1 = cyclic paraffin or -(CR2R3)n-; R2,R3 = H, C1-4 alkyl; n >=2 . These additives have a dramatic effect in improving the etch rates both in the absence of added chloride ions or the presence of considerable quantities of chloride, i.e. 45 ppm. In 1 example, without chloride ion, the time required to completely remove the Cu from the bottom side of a laminate was reduced from 270 sec. to 75 sec. by adding 1,4-cyclohexanediol.

Description

How to dissolve metal

The present invention relates to dissolving metals in an aqueous bath containing sulfuric acid and hydrogen peroxide, and more particularly to a new bath material which can make the solvent consist of high hydrogen. According to one aspect, the present invention relates to copper etching in the production of printed circuit tubes.

In the manufacture of printed electrical circuits, as is well known in the art, copper laminates and etch resistant materials, generally plastic, are used. A common way of obtaining a circuit is to coat the desired surface on the copper surface of a laminate with a protective resistant material that does not act against the action of the etching solution. In the next etching step, the copper unprotected area is etched while the uncoated area remains intact to provide the desired circuit supported by plastic. The resistant material may be a plastic material or ink or solder.

In the past few years, plants that etch electrical circuit boards have been converted to hydrogen peroxide-sulfuric acid systems because of the low cost of the etching solution and the relative ease of recovering copper value from the waste etching solution. However, there are many problems associated with using hydrogen peroxide as an etchant component. The hydrogen peroxide stability in the sulfuric acid-hydrogen peroxide solution is adversely affected by the presence of heavy metal ions such as copper ions.

That is, as the etching proceeds, the copper ion content of the etchant increases, and the etching rate is severely dropped by decomposition of hydrogen peroxide in the etching bath, and the etchant immediately loses its effect. Various stabilizers have been proposed and used to improve the ability of the etchant, and have been somewhat successful in reducing hydrogen peroxide decomposition in the presence of copper ions.

For example, low gold saturated aliphatic alcohols such as methanol, ethanol, furopanol and butanol are known as useful stabilizing additives for acidified hydrogen peroxide-dietary solutions. The disadvantage of these stabilized solutions is that they are sensitive to the presence of their chlorine or cancel ions and therefore must be removed from the etch system prior to use by deionization reactions or, for example, precipitation of contaminated ions with warm salts. to be. Alcohols are also very volatile at the high temperatures typically required for etching processes and therefore significant loss of stabilizer during operation.

Ethylene glycol, whether mono- or poly-form, is known from US Pat. Nos. 3537895 and 3773577 to stabilize acidified hydrogen peroxide used in metal melting operations such as copper pickling and etching. In addition to the stabilizing effect, ethylene glycol also has other advantages associated with that indicated in the patent in that it has a relatively low volatility at normal tissue temperatures and somewhat improves the etching and pickling rates. However, these rates are not sufficient for many metal melting processes and problems of chlorine and cancellation sensitivity still exist for these stabilized metal treatment solutions. Hydrolysis can be significantly delayed even with the presence of metal ions by the addition of a suitable stabilizer, but the etch rate of stabilized hydrogen peroxide-sulfuric acid etchants is generally very low, requiring improvements, especially at high copper ion concentrations. Therefore, in the conventional method, it is proposed to use a catalyst or an enhancer to improve the etching rate. Special examples of such catalysts are metal ions such as silver, mercury, palladium, gold and platinum ions, all of which have lower oxidation values than copper. Other examples include various combinations of any of the above three components with dibasic oxidation, such as phenacetin, sulfatiazole and silver ions, or combinations of phenylurea or benzoic acid, or combinations of urea and thiourea compounds One thing is included.

Although the silver ions appear to provide an absolute solution to the problems of the low etch rate described above and the problems caused by the presence of free chlorine and canceling ions, the use of silver ions in the preparation of hydrogen peroxide-sulfuric acid etch solutions There are some drawbacks. One of these is that silver is very expensive. Another difference is that silver ions do not increase the etching rate as required.

It is therefore an object of the present invention to provide new effective water soluble compositions which dissolve the metal.

Another object is to provide an improved method of dissolving metals such as highway copper or copper alloys.

Another object is to provide a copper etchant composition and method that is relatively unaffected by etch rate or cancellation or the presence of chlorine ions.

Other objects of the present invention will become more apparent from the following specification.

According to the present invention there is provided a composition consisting of an aqueous solution containing about 0.2-4.5 g mol / l sulfuric acid, about 0.25-8 g mol / l hydrogen peroxide and an effective amount of a primary diol enhancer having the general formula:

Wherein R ₁ is selected from (a) and (b).

(a) (CR ₂ R ₃ ) n,

Wherein R ₂ and R ₃ are each independently hydrogen or a 1-4 carbon alkyl group, and n is at least 2.

(b) cyclic paraffin group or an alkyl-substituted cyclic paraffin group having 5-7 carbon atoms in the ring structure and having 1-4 carbon atoms in the alkyl substituent.

The sulfuric acid concentration of the etching solution should be maintained at about 0.2-4.5 g mol / l, preferably about 0.3-4 g mol / l. The hydrogen peroxide concentration of the solution is broad, about 0.25-6 g mol / l, but is preferably limited to about 4 g mol / l.

Examples of suitable primary diol enhancers useful in the present invention include 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol and the like; 2-methyl-1,4-butanediol, 2-ethyl-1,5 pentanediol, 3-furophyll-1,5-pentanediol and the like; 1,4-cyclohexanedimethanol; 2-methyl-1,3-cyclopentanedimethanol and the like.

Enhancers are generally added in an effective amount of at least 0.01 g mol / l, preferably about 0.1-0.5 g mol / l.

The amount of enhancer to be used in the solution depends, to some extent, on the free chlorine or cancellation content. For example, when the concentration of these contaminants is low, that is, about 2-25 ppm, the low concentration of the enhancer concentration, such as 0.01-0.2 g mol / l, is suitable for performing the desired etching rate. In contrast, if the contaminants are present at relatively high concentrations, for example about 25-60 ppm, at least 0.2 g mol / l of enhancer should be added.

When n is 0 or 1 in the general formula (1), as in the case of ethylene glycol and furopropylene glycol, an appropriate food acceleration rate is obtained when chlorine or minimum ions are present even if these primary diols are added to a conventional etching solution. Not obtained. Such a phenomenon is the same also in the polyform of ethylene glycol and furopropylene glycol. Similarly, hydroxyl substituted paraffins containing one or more secondary or tertiary hydroxyl groups are also not useful due to chlorine and cancellation sensitivity.

Water is used to replenish the remainder of the etch solution. No special treatment is required to remove free chlorine or cancellation from solution. This is because the presence of cyclic alcohols and diols administers sufficient insensitivity to the contaminants that will greatly reduce the etch rate.

The solution may also contain many other components, such as known stabilizers used to counteract the decomposition of hydrogen peroxide into which heavy metals have been introduced. Of course, other various compounds having a stabilizing effect on the metallized solution of acidified hydrogen peroxide can be equally advantageously used.

Any additive known to prevent over-corrosion, ie end or fatal corrosion, may be added as desired. Examples of such compounds are nitrogen compounds, which are described herein by reference. However, the use of such additives is not necessary in the present invention. This is because the rapid etching speed is obtained by including the enhancer in the etching composition.

The solution is particularly soluble in chemical milling and etching of copper and copper alloys, but other metals and alloys such as iron, nickel, zinc and steel can also be dissolved in the solution of the invention.

When this solution is used for dissolving a metal, normal operating conditions for the special metal are used. Thus, for copper etching, a temperature of about 105-140 ° F should be maintained, and preferably the operating temperature should be maintained at about 120-130 ° F.

The solution is excellently suited as an etchant, either by dipping or spray etching. The etching rate obtained with the composition of the present invention is very fast. Due to this unusually high etching rate, the composition is particularly suitable as an etchant in the manufacture of printed circuit boards. This is because, in this case, a relatively large number of workpieces are required to be machined per unit time, both economically and as a reason to minimize the etching or dissolution of undesirable fatal ends under resistant materials. Another important advantage of the present invention is that clean etching is achieved. Another advantage is that the presence of free chlorine or cancellation in concentrations of up to 2 ppm to 50 ppm in the solution can be tolerated without sacrificing etch rate. Conventional tap water can thus be used for the preparation of this solution. It has also been found that the primary diol enhancers of the present invention have significant stability and effect on hydrogen peroxide, thereby reducing or eliminating the need for additional hydrogen peroxide stabilizers. Another advantage is that the etch rate of this solution is relatively unaffected by high dynamic loads. Other advantages include the low volatility and high solubility of the enhancer in the solution.

The following examples illustrate the invention.

Example 1-5

In the next series of experiments, a dynamic lamellar plate (2 ″ × 2 ″) with one ounce of coating per square foot was immersed in a stirred solution maintained at 129 ° F. Each solution contained 15 vol% 66 ° Baume sulfuric acid (2.7 g mol / l), 15 vol% (50% w / w) hydrogen peroxide (2.6 g mol / l), and 70 vol% deionized or distilled water. . This solution was stabilized with 2.5 g / l sodium phenolsulfonate. The time required for complete removal of copper from the bottom of the laminate in the absence of any catalyst and added chlorine ions (Example 1) was 270 seconds (190-200 seconds in a solution made with distilled water).

The etching solution of Example 2-5 had the same composition as that of Example 1 except for containing a primary diol enhancer as shown in Table 1. The results of the etch test showed that all additives had a dramatic effect on increasing the etch rate in the absence of added chlorine ions or in significant amounts of 45 ppm added chlorine ions.

TABLE 1

It should be noted that for large scale operations such as by spray etching methods, good results can still be obtained with the solution of the present invention. In particular, the etching rate was increased compared to the comparative solution, and the etching time was substantially lower than 1 / 3-2 / 3 of the value obtained by the above-described small immersion method.

Example 6-15

In these examples, various diols of about 20 ml or 20 g / l which did not satisfy the requirements of the present invention were added to an etching solution having the same composition as that of Example 1. As can be seen from the measured values shown in Table II, the etching test results were poor in that the etching rate in the presence of 45 ppm free chlorine was inadequate.

TABLE II

[Example 16-21]

150 g of a comparative solution (Example 16) prepared with distilled water to have a stabilizing effect by the enhancer of the present invention, having a composition of Example 1 and having an ision of 38.2 g / l (about 5 ounces / gallon) / l in the form of copper sulfate pentahydrate. The solution was kept at 129 ° F. for 24 hours with continued stirring and periodically measured during the test period by first measuring the peroxide concentration and then titrating with a standard ammonium cerium sulfate solution with a ferroin indicator.

Example 17 was carried out in the same form, except that sodium phenol sulfonate and good hydrogen peroxide stabilizer were added in the usual stabilizing amount. The diols shown in Table III were added to the solution of Examples 18-21 in amounts known to enhance the optimum visual velocity. The test results indicate that primary diols are very effective as stabilizers against hydrogen peroxide decomposition.

TABLE III

[Examples 22-26]

To demonstrate the effect of promoter concentration on the etch rate, the following comparative experiments were performed in a DEA-30 literal etchant using a dynamic lamellar 2 ″ x2 ″ with a copper sheath of 10 ounces / ft ² at approximately 122 ° F. It was. The comparative solution (Example 22) contained 10 vol% of 50% w / w hydrogen peroxide (1.8 g mol / l), 20 vol% of 66 ° Baume sulfuric acid (3.6 g mol / l) and 70 vol% of distilled water. 1 g / l sodium phenol sulfonate stabilizer and 15 g / l copper sulfate pentahydrate were added thereto.

Examples 22-26 also included various amounts of 1,4-butanediol. The effect of diol concentration on etching time is shown in Table IV.

TABLE IV

It will be apparent to those skilled in the art that various modifications and variations can be made to the specific embodiments described above. All derivatives from the foregoing specification are also considered to be within the scope of the invention as defined in this specification and claims.

Claims (1)

Dissolving the metal, comprising contacting the metal with an aqueous solution containing about 0.2-45 g mol / l sulfuric acid and about 0.25-8 g mol / l hydrogen peroxide and an effective amount of a primary diol enhancer having the following general formula: Way.

Wherein R ₁ is selected from (a) and (b). (a)-(CR ₂ R ₃ ) n- Wherein R ₂ and R ₃ are each independently hydrogen or an alkyl group of 1-4 carbon atoms, and n is at least 2. (b) cyclic paraffinic groups, or alkyl-substituted cyclic paraffinic groups having 5-7 carbon atoms in the ring structure and 1-4 carbon atoms in all alkylsubstituents.