COMPOSITION AND METHOD FOR MICRO ETCHING OF COPPER AND COPPER ALLOYS

Abstract

The present invention is related to a composition for micro etching of a copper or a copper alloy surface, wherein the composition comprises i) at least a source of Fe.sup.3+ ions, ii) at least a source of Br.sup.− ions, iii) at least an inorganic acid, and iv) at least one etch refiner according to formula I

##STR00001## wherein R1 is selected from the group consisting of hydrogen, C.sub.1-C.sub.5-alkyl or a substituted aryl or alkaryl group; R2 is selected from the group consisting of hydrogen, C.sub.1-C.sub.5-alkyl or C.sub.1-C.sub.5-alkoxy; R3, R4 are selected from the group consisting of hydrogen and C.sub.1-C.sub.5-alkyl; and X.sup.− is a suitable anion. Further, the present invention is directed to a method for micro etching of copper or copper alloy surfaces using such a composition.

Claims

1. Composition for micro etching of a copper or a copper alloy surface characterized in that the composition comprises i) at least a source of Fe.sup.3+ ions, ii) at least a source of Br.sup.− ions, iii) at least an inorganic acid, and iv) at least one etch refiner according to formula I ##STR00003## wherein R1 is selected from the group consisting of hydrogen, C.sub.1-C.sub.5-alkyl or a substituted aryl or alkaryl group; R2 is selected from the group consisting of hydrogen, C.sub.1-C.sub.5-alkyl or C.sub.1-C.sub.5-alkoxy; R3, R4 are selected from the group consisting of hydrogen and C.sub.1-C.sub.5-alkyl; and X.sup.− is a suitable anion.

2. Composition according to claim 1 characterized in that R1 is selected from the group consisting of hydrogen, methyl, ethyl, n-propyl, iso-propyl, phenyl and benzyl; R2 is selected from the group consisting of hydrogen, methyl, ethyl, n-propyl and iso-propyl; R3 is selected from the group consisting of hydrogen, methyl, ethyl, n-propyl and iso-propyl; R4 is selected from the group consisting of hydrogen, methyl, ethyl, n-propyl and iso-propyl.

3. Composition according to claim 1 characterized in that the R2 group is in the 5 or 6 position.

4. Composition according to claim 1 characterized in that R3 and R4 are the same.

5. Composition according to claim 1 characterized in that the etch refiner according to formula I is selected from the group consisting of 4-(6-methyl-1,3-benzothiazol-3-ium-2-yl)-N,N-dimethylaniline chloride, 4-(3-benzyl-6-methyl-1,3-benzothiazol-3-ium-2-yl-N,N-dimethylaniline chloride, 4-(3,6-dimethyl-1,3-benzothiazol-3-ium-2-yl)-N,N-dimethylaniline chloride, 4-(3-benzyl-5-methyl-1,3-benzothiazol-3-ium-2-yl)-N,N-dimethylaniline chloride, 4-(3,5-dimethyl-1,3-benzothiazol-3-ium-2-yl)-N,N-dimethylaniline chloride, 4-(3-methyl-6-ethoxy-1,3-benzothiazol-3-ium-2-yl)-N,N-dimethylaniline chloride, 4-(3-benzyl-1,3-benzothiazol-3-ium-2-yl)-N,N-dimethylaniline chloride, 4-(3-methyl-5-ethoxy-1,3-benzothiazol-3-ium-2-yl)-N,N-dimethylaniline chloride, 4-(3-benzyl-5-ethoxy-1,3-benzothiazol-3-ium-2-yl)-N,N-diemthylaniline chloride, 4-(3-benzyl-5-ethoxy-1,3-benzothiazol-3-ium-2-yl)-N,N-dimethylaniline chloride, 4-(6-methyl-1,3-benzothiazol-3-ium-2-yl)-N,N-diethylaniline chloride, 4-(3-benzyl-6-methyl-1,3-benzothiazol-3-ium-2-yl-N,N-diethylaniline chloride, 4-(3,6-dimethyl-1,3-benzothiazol-3-ium-2-yl)-N,N-diethylaniline chloride, 4-(3-benzyl-5-methyl-1,3-benzothiazol-3-ium-2-yl)-N,N-diethylaniline chloride, 4-(3,5-dimethyl-1,3-benzothiazol-3-ium-2-yl)-N,N-diethylaniline chloride, 4-(3-methyl-6-ethoxy-1,3-benzothiazol-3-ium-2-yl)-N,N-diethylaniline chloride, 4-(3-benzyl-1,3-benzothiazol-3-ium-2-yl)-N,N-diethylaniline chloride, 4-(3-methyl-5-ethoxy-1,3-benzothiazol-3-ium-2-yl)-N,N-diethylaniline chloride, 4-(3-benzyl-5-ethoxy-1,3-benzothiazol-3-ium-2-yl)-N,N-diethylaniline chloride, 4-(3-benzyl-5-ethoxy-1,3-benzothiazol-3-ium-2-yl)-N,N-diethylaniline chloride and mixtures thereof.

6. Composition according to claim 1 characterized in that the composition further comprises at least one source of Cu.sup.2+ ions.

7. Composition according to claim 6 characterized in that the source of Cu.sup.2+ ions is selected from the group comprising of CuSO.sub.4, CuBr.sub.2, CuO, Cu(OH).sub.2 and mixtures thereof.

8. Composition according to claim 1 characterized in that the composition further comprises at least one source of Fe.sup.2+ ions.

9. Composition according to claim 8 characterized in that the source of Fe.sup.2+ ions is FeSO.sub.4 and the source of Fe.sup.3+ ions is Fe.sub.2(SO.sub.4).sub.3.

10. Composition according to claim 1 characterized in that the composition comprises less than 100 mg/l.

11. Composition according to claim 1 characterized in that the composition is substantially free of organic acids and organic acid salts.

12. Composition according to claim 1 characterized in that the etch refiner according to formula I concentration ranges from 1 to 1000 mg/l.

13. Composition according to claim 1 characterized in that the concentration of Br.sup.− ions ranges from 1 to 200 mg/l.

14. Method for micro etching of copper or copper alloy surfaces characterized by the following method steps: i) providing a substrate having a copper or copper alloy surface, ii) contacting said surface with a cleaner composition, iii) contacting said surface with a composition according to one of the preceding claims in a first tank, wherein during contacting copper is oxidized to Cu.sup.2+ ions and the Cu.sup.2+ ions are disclosed in said composition, while Fe.sup.3+ ions are reduced simultaneously to Fe.sup.2+ ions.

15. Method according to claim 14 characterized in that the method further comprises the method steps: iv) transferring a portion of said composition after contacting with the substrate to a second tank, wherein said second tank comprises an anode and a cathode and v) reducing said Cu.sup.2+ ions to copper while oxidizing Fe.sup.2+ ions to Fe.sup.3+ ions by applying a current between said anode and said cathode.

16. Composition according to claim 2 characterized in that the R2 group is in the 5 or 6 position.

17. Composition according to claim 2 characterized in that R3 and R4 are the same.

18. Composition according to claim 3 characterized in that R3 and R4 are the same.

19. Composition according to claim 16 characterized in that R3 and R4 are the same.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0018] The source of the bromide ions is selected from the group comprising NaBr, KBr, NH.sub.4Br, LiBr and mixtures thereof.

[0019] The at least one inorganic acid present in the inventive composition is selected from the group comprising sulfuric acid (H.sub.2SO.sub.4), phosphoric acid (H.sub.3PO.sub.4). Sulfuric acid is preferred. The total amount of acid present in the inventive composition ranges from 0.1 to 500 g/l, more preferred from 1 to 200 g/l.

[0020] X.sup.− as a suitable anion can be a halide, such as chloride or bromide, wherein chloride is preferred.

[0021] In one embodiment, R1 is selected from the group consisting of hydrogen, methyl, ethyl, n-propyl, iso-propyl, phenyl and benzyl; R2 is selected from the group consisting of hydrogen, methyl, ethyl, n-propyl and iso-propyl; R3 is selected from the group consisting of hydrogen, methyl, ethyl, n-propyl and iso-propyl; R4 is selected from the group consisting of hydrogen, methyl, ethyl, n-propyl and iso-propyl.

[0022] In another embodiment, the R2 group is in the 5 or 6 position.

[0023] In one embodiment, R3 and R4 are the same.

[0024] In one embodiment, the etch refiner according to formula I is selected from the group consisting of 4-(6-methyl-1,3-benzothiazol-3-ium-2-yl)-N,N-dimethylaniline chloride, 4-(3-benzyl-6-methyl-1,3-benzothiazol-3-ium-2-yl-N,N-dimethylaniline chloride, 4-(3,6-dimethyl-1,3-benzothiazol-3-ium-2-yl)-N,N-dimethylaniline chloride, 4-(3-benzyl-5-methyl-1,3-benzothiazol-3-ium-2-yl)-N,N-dimethylaniline chloride, 4-(3,5-dimethyl-1,3-benzothiazol-3-ium-2-yl)-N,N-dimethylaniline chloride, 4-(3-methyl-6-ethoxy-1,3-benzothiazol-3-ium-2-yl)-N,N-dimethylaniline chloride, 4-(3-benzyl-1,3-benzothiazol-3-ium-2-yl)-N,N-dimethylaniline chloride, 4-(3-methyl-5-ethoxy-1,3-benzothiazol-3-ium-2-yl)-N,N-dimethylaniline chloride, 4-(3-benzyl-5-ethoxy-1,3-benzothiazol-3-ium-2-yl)-N,N-dimethylaniline chloride, 4-(3-benzyl-5-ethoxy-1,3-benzothiazol-3-ium-2-yl)-N,N-dimethylaniline chloride, 4-(6-methyl-1,3-benzothiazol-3-ium-2-yl)-N,N-diethylaniline chloride, 4-(3-benzyl-6-methyl-1,3-benzothiazol-3-ium-2-yl-N,N-diethylaniline chloride, 4-(3,6-dimethyl-1,3-benzothiazol-3-ium-2-yl)-N,N-diethylaniline chloride, 4-(3-benzyl-5-methyl-1,3-benzothiazol-3-ium-2-yl)-N,N-diethylaniline chloride, 4-(3,5-dimethyl-1,3-benzothiazol-3-ium-2-yl)-N,N-diethylaniline chloride, 4-(3-methyl-6-ethoxy-1,3-benzothiazol-3-ium-2-yl)-N,N-diethylaniline chloride, 4-(3-benzyl-1,3-benzothiazol-3-ium-2-yl)-N,N-diethylaniline chloride, 4-(3-methyl-5-ethoxy-1,3-benzothiazol-3-ium-2-yl)-N,N-diethylaniline chloride, 4-(3-benzyl-5-ethoxy-1,3-benzothiazol-3-ium-2-yl)-N,N-diethylaniline chloride, 4-(3-benzyl-5-ethoxy-1,3-benzothiazol-3-ium-2-yl)-N,N-diethylaniline chloride and mixtures thereof.

[0025] Especially preferred from the group of etch refiners according to formula I is 4-(3,6-dimethyl-1,3-benzothiazol-3-ium-2-yl)-N,N-dimethylaniline chloride, which is also known as Thioflavin T.

[0026] In a preferred embodiment, the composition further comprises at least one source of Cu.sup.2+ ions.

[0027] Suitable sources of Cu.sup.2+ ions are selected from the group comprising CuSO.sub.4, CuBr.sub.2, CuO, Cu(OH).sub.2 and mixtures thereof. The quantity of copper ions in the inventive composition ranges from 1 to 300 g/l, more preferred from 10 to 50 g/l and most preferred from 20 to 40 g/l.

[0028] In one embodiment, the composition further comprises at least one source of Fe.sup.2+ ions.

[0029] In a preferred embodiment, the concentration of Fe.sup.2+ ions and Fe.sup.3+ ions in the inventive composition are the same.

[0030] In one embodiment, the source of Fe.sup.2+ ions is FeSO.sub.4 and the source of Fe.sup.3+ ions is Fe.sub.2(SO.sub.4).sub.3.

[0031] The quantity of Fe.sup.2+ ions and Fe.sup.3+ ions in the inventive composition ranges from 1 to 100 g/l, preferably from 1 to 50 g/l, and more preferably from 1 to 30 g/l.

[0032] The pH value of the inventive composition is less than 3, preferably less than 2, and more preferably less than 1.5.

[0033] In another embodiment, the composition comprises less than 100 mg/l, preferably less than 50 mg/l, and more preferably less than 25 mg/l of Cl.sup.1− ions.

[0034] In one embodiment, the composition is substantially free of organic acids and organic acid salts.

[0035] In one embodiment, the etch refiner according to formula I concentration ranges from 1 to 1000 mg/l, preferably from 1 to 300 mg/l, and more preferably from 1 to 100 mg/l.

[0036] In one embodiment, the concentration of Br.sup.− ions ranges from 1 to 200 mg/l, preferably from 1 to 100 mg/l, and more preferably from 1 to 25 mg/l.

[0037] Imaging resists are photosensitive polymeric systems applied either as liquids or dry films. Solder masks are polymeric material deposits that provide a permanent protective coating for the copper or copper alloy surface of a PCB.

[0038] Further, the object of the present invention is also solved by a method for micro etching of copper or copper alloy surfaces using the above described composition in order to enhance the adhesion of an image resist or a solder mask to be attached to said surface. The method is characterized by the following method steps: [0039] i) providing a substrate having a copper or copper alloy surface, [0040] ii) contacting said surface with a cleaner composition, [0041] iii) contacting said surface with a composition according to one of the preceding claims in a first tank, [0042] wherein during contacting copper is oxidized to Cu.sup.2+ ions and the Cu.sup.2+ ions are disclosed in said composition, while Fe.sup.3+ ions are reduced simultaneously to Fe.sup.2+ ions.

[0043] The method according to this invention is carried out by contacting the copper or copper alloy surfaces with aforementioned compositions. The substrate can be immersed into the solution or the solution can be sprayed onto the copper or copper alloy surface of the substrate. For this purpose common horizontal or vertical equipment can be utilized.

[0044] Using a spray, the solution is sprayed onto the substrate having a copper or copper alloy surface at a pressure of 1-10 bar.

[0045] For both methods (spray or solution) the process is preferably carried out at a temperature ranging from 10 to 60° C., more preferably from 20 to 50° C. and most preferably from 30 to 45° C. The treatment time ranges from 10 to 360 s, more preferably from 20 to 200 s and most preferably from 30 to 90 s.

[0046] After the copper or copper alloy surface has been treated as such, the copper or copper alloy surfaces are rinsed with water, e.g., deionized water and then dried, e.g., with hot air.

[0047] Optionally, the etched copper or copper alloy surfaces can also be treated for 5-300 s with diluted acid after being rinsed, preferably with 10 vol.-% hydrochloric acid or diluted sulphuric acid. After being treated with acid, the copper surfaces are again rinsed, preferably with deionized water.

[0048] The samples are preferably treated by spraying the etching compositions according to the invention onto the samples. The compositions can be sprayed in a vertical mode or horizontal mode, depending on the equipment desired. Alternatively, the samples can be immersed into the etching compositions. To achieve the same roughness values compared to spraying, the compositions need to be penetrated by oxygen, e.g., by bubbling air through them.

[0049] In a preferred embodiment of the method, the method is characterized in that the method further comprises the method steps: [0050] iv) transferring a portion of said composition after contacting with the substrate to a second tank, [0051] wherein said second tank comprises an anode and a cathode and [0052] v) reducing said Cu.sup.2+ ions to copper while oxidizing Fe.sup.2+ ions to Fe.sup.3+ ions by applying a current between said anode and said cathode.

[0053] During use the composition is enriched in Cu.sup.2+ ions (they are disposed in the composition according to the present invention). At the same time Fe.sup.3+ ions are reduced to Fe.sup.2+ ions. Cu.sup.2+ ions have a negative impact on the performance of the composition. Cu.sup.2+ ions increase the density and viscosity of the micro etching solution and thereby negatively effect the micro etching behaviour. The etch rate and side wall etching performance may decrease. Furthermore, precipitation of Cu.sup.2+ ion complexes can occur. Such precipitates pose a mechanical danger to the equipment and the surfaces coming into contact with the etching composition.

[0054] In processes according to prior art some or all of the added Cu.sup.2+ ions are removed by bleeding (removing) an adequate amount of etching solution and adding (feeding) fresh etching solution to the remaining solution.

[0055] One particular method to remove Cu.sup.2+ ions from a solution is to electrolytically reduce Cu.sup.2+ ions to metallic copper.

[0056] In principle, a second tank equipped with an anode and a cathode and a rectifier is required for electrolysis.

[0057] Portions of the composition according to the present invention are transferred from a first tank where or from which the micro etching of copper or a copper alloy layer is performed to a second tank equipped for electrolysis. During electrolysis Cu.sup.2+ ions are cathodically reduced to metallic copper and at the same time Fe.sup.2+ ions are oxidized anodically to Fe.sup.3+ ions.

[0058] The metallic copper can be collected and recycled. Without an electrolytic regeneration cell the oxidizing agent (Fe.sup.3+ ions) would need to be continuously added to the micro etching solution. By application of the above described regeneration the spent Fe.sup.3+ ions are regenerated at the anodes (Fe.sup.2+ is oxidized to Fe.sup.3+) and thereby no adding (feeding) of the oxidizing agent during use of the etching solution is required.

[0059] For such a regeneration cycle, it is mandatory that certain conditions are fulfilled. The pH value has to be low in order to ensure a high dissociation of the inorganic acid of the inventive composition. Therefore, the composition has to be free of any organic acids or organic acid salts, if such a regeneration cycle of such a preferred method is intended to be executed.

[0060] Furthermore, it is helpful if the second tank is equipped with a measurement device, which is able to measure, ideally in situ, the concentration of Fe.sup.3+ ions and Cu.sup.2+ ions. If the concentration of Fe.sup.3+ ions becomes too low, the measurement device detect it and initiates subsequent application of current in the second tank in order to start the regeneration of the bath composition being in the second tank. If the concentration of Fe.sup.3+ ions is still above a predetermined benchmark value, the bath composition does not need yet regeneration. Then, the portion of the bath composition is transferred back to the first tank without any executed electrolysis. A user can set up the predetermined benchmark value in dependence of his system.

[0061] The same applies in principle for the concentration of Cu.sup.2+ ions, which can be measured by such a measurement device. But, in this case the concentration of Cu.sup.2+ ions is observed to determine if the concentration is too high. If the concentration of Cu.sup.2+ ions exceeds a predetermined benchmark value, the bath composition needs regeneration in order to plate out Cu.sup.2+ ions as copper as described above.

[0062] In a preferred embodiment of the method, the micro etching composition further comprises right from the beginning a source of Cu.sup.2+ ions and a source of Fe.sup.2+ ions, wherein the concentration of the Fe.sup.2+ ions and the Fe.sup.3+ ions already comprised by the composition is the same. This generates right from the beginning of the method an equilibrium in the composition for the redox pairs of Fe.sup.2+/Fe.sup.3+ and Cu.sup.0/Cu.sup.2+, which allows direct initiating of the regeneration cycle.

[0063] If the starting composition does not comprise Fe.sup.2+ ions and Cu.sup.2+ ions, the micro etching method can be conducted, but not the regeneration cycle due to the absence of these ions. Then, a user has to wait until enough (waiting time period is depending on the predetermined benchmark value) Fe.sup.3+ ions become reduced to Fe.sup.2+ ions and/or until enough Cu.sup.2+ ions become generated by oxidizing copper from the copper surface of the substrate, which is treated by the micro etching composition in method step iii).

[0064] A measurement device is selected from the group comprising spectroscopic devices, preferably UV spectroscopic devices, and titration, preferably online UV titration, devices.

[0065] The present invention thus addresses the problem of improving the adhesion of either imaging resists or solder masks on copper and copper alloy surfaces, in particular in the production of printed circuit boards.

[0066] The following non-limiting examples are provided to illustrate an embodiment of the present invention and to facilitate understanding of the invention.

EXAMPLES

[0067] The performance roughness values of copper surfaces micro etched with different compositions, which are within or without the scope of the appended claims, were determined using an atomic force microscope. A copper clad laminate substrate (CCI) was used throughout experiments 1 to 4, respectively. The measurement window was 10 μm×10 μm.

[0068] The process sequence used throughout experiments 1 to 4 was [0069] 1. cleaning of the copper surface (Softclean UC 168, a product of Atotech Deutschland GmbH, t=20 s, T=35° C.) [0070] 2. micro etching of the copper surface by spraying the micro etching compositions onto the copper substrates [0071] 3. drying of the micro etched copper surface [0072] 4. determining the copper surface roughness with an atomic force microscope (AFM)

[0073] The copper surface micro etch depth was adjusted to 1 μm in examples 1 to 4. The resulting performance roughness values obtained from experiments 1 to 4 are summarized in table 1 (see below).

[0074] Different micro etching compositions are contacted with a CCI type substrate for 40 s at a temperature of 35° C. The micro etching compositions consists of

TABLE-US-00001 CuSO.sub.4 30 g/l (related to Cu.sup.2+ ions) FeSO.sub.4 15 g/l (related to Fe.sup.2+ ions) Fe.sub.2(SO.sub.4).sub.3 15 g/l (related to Fe.sup.3+ ions) Sulfuric acid (50%) 160 ml/l NaCl 10 mg/l (related to Cl.sup.− ions) NaBr 0 or 8 mg/l (related to Br.sup.− ions) Thioflavin T 0 or 5 or 200 mg/l

TABLE-US-00002 TABLE 1 performance roughness values obtained from examples 1 to 4. Experiment no. [Cl.sup.−] [Br.sup.−] [Thioflavin T] RSAI* (%) 1 10 0 5 8.1 2 10 8 0 8.5 3 (invention) 10 8 200 23.1 4 (invention) 10 8 5 33.0 *RSAI = relative surface area increase

[0075] The copper surface roughness representing parameter RSAI obtained by atomic force microscopy show the highest values for the inventive composition according to examples 3 and 4 compared to compositions being outside the scope of the appended claims (examples 1 and 2). Especially, it is clearly demonstrated that the presence of a certain etch refiner according to formula I and the presence of a source of bromide ions is required to obtain amended surface roughness values. At the same time, it is notable that the constant concentration of chloride ions has obviously, at least at this concentration of 10 mg/l, no remarkable influence on the achieved copper surface roughness.

[0076] Different micro etching compositions, which are within or without the scope of the appended claims, have been used for adhesion performance tests wherein a solder mask (Elpemer SG 2467, a product of Peters) is attached to the micro etched copper surfaces in form of crosses. Such a cross consists of geometry of 10 lines×10 lines, which all have the same diameter. Experiments have been conducted with 5 crosses, wherein the respective diameters of the cross lines of the different crosses are 10 μm, 20 μm, 30 μm, 40 μm and 50 μm. Again, CCI type copper substrates are used. The copper surface micro etch depth is adjusted to 1 μm throughout all experiments.

[0077] For the purpose of better detection, the areas between the cross lines have been treated by a selective finishing, in a first series of experiments by immersion tin and in a second series of experiments by ENIG (Electroless Nickel Gold).

[0078] An optical qualitative evaluation has been conducted to determine, if the solder mask on the cross lines have been partially or completely removed caused by low adhesion to the underlying copper surface, which has been before roughened by the applied micro etching compositions.

[0079] The resulting qualitative evaluation for both series of experiments has been found comparable overall and is summarized in table 2 (see below).

[0080] Different micro etching compositions are contacted with a CCI type substrate for 40 s at a temperature of 35° C. The micro etching compositions consists of

TABLE-US-00003 CuSO.sub.4 30 g/l (related to Cu.sup.2+ ions) FeSO.sub.4 15 g/l (related to Fe.sup.2+ ions) Fe.sub.2(SO.sub.4).sub.3 15 g/l (related to Fe.sup.3+ ions) Sulfuric acid (50%) 160 ml/l NaCl 10 mg/l (related to Cl.sup.− ions) NaBr 0 or 8 or 100 mg/l (related to Br.sup.− ions) Thioflavin T 0 or 5 or 200 mg/l

TABLE-US-00004 TABLE 2 Optical qualitative evaluation of solder mask adhesion on copper surfaces roughened before by different micro etching compositions. Experiment no. [Cl.sup.−] [Br.sup.−] [Thioflavin T] Evaluation 5 10 0 5 Very Low 6 10 8 0 Very Low 7 (invention) 10 8 200 Good 8 (invention) 10 8 5 Very Good 9 (invention) 10 100 5 Acceptable

[0081] As can be derived from the Evaluation listed in Table 2, the AFM results are confirmed that the presence of an etch refiner according to formula I and of bromide ions are mandatory in order to achieve a good adhesion of the solder mask on the copper surface, which has been before roughened by the inventive micro etching composition. Even a very high concentration of Thioflavin T of 200 mg/l still delivers good adhesion results.

[0082] The adhesion performance of the above-cited two series of experiments has been further analyzed for a selected number of individual experiments of Table 2 by applying a tape test according to IPC-TM-650 from 8/97, revision D.

[0083] An optical qualitative evaluation has been again conducted to determine, if the solder mask on the cross lines have been partially or completely removed caused by low adhesion to the underlying copper surface, which has been before roughened by the applied micro etching compositions.

[0084] The resulting qualitative evaluation for both series of experiments has been found comparable overall and is summarized in table 3 (see below).

TABLE-US-00005 TABLE 3 Optical qualitative evaluation of solder mask adhesion on roughened copper surfaces after applying tape test. Experiment no. [Cl.sup.−] [Br.sup.−] [Thioflavin T] Evaluation 10 10 0 5 Very Bad 11 10 8 0 Very Bad 12 (invention) 10 8 5 Very Good

[0085] The results from Table 3 clearly show the superior adhesion of solder mask on copper surfaces treated with a composition according to the present invention and application of a tape test. While nearly all solder mask lines of the respective crosses independently from their line diameter remain, at least after a qualitative optical evaluation, on the roughened copper surface after executing the tape test; the respective lines of solder mask are removed from the copper surfaces for the micro etching compositions lying outside of the scope of the appended claims.

[0086] The results obtained from adhesion tests of solder mask dots on micro etched copper surfaces show a superior performance of the inventive micro etch composition (examples 3, 4, 7, 8, 9, and 12) compared to those of compositions lying outside of the scope of the appended claims (examples 1, 2, 5, 6, 10 and 11). The superior solder mask adhesion performance of the inventive micro etch composition is obvious especially after applying a tape test.

[0087] It will be understood that the embodiments described herein are merely exemplary and that a person skilled in the art may make many variations and modifications without departing from the scope of the invention. All such variations and modifications, including those discussed above, are intended to be included within the scope of the invention as defined by the appended claims.