RU2041575C1 - Process of preparation of combined copper-polyimide surface to formation of coating by chemical conversion - Google Patents

Abstract

FIELD: radio engineering. SUBSTANCE: process of formation of coating by chemical conversion of combined metal-dielectric surface consists in operations of etching, sensitization and activation during which additional treatment of surface in solution containing g/l: NaOH 200-400, ethylenediamine 70-80; monoethanoamine 60-70; trietanoamine 40-50 is conducted after etching operation at temperature 50-60 C and curing time 5-7 min. Activation of surface is performed in solution containing, g/l: PdCl₂·2H₂O 0.1-0.01; HCl 0.4-0.6; glycine 1.5-2.0 with pH 3.2-3.5 at temperature 20-26 C and curing time 9-10 min. EFFECT: reduced cost of process, improved working conditions, increased stability of activation solution to decomposition, enhanced output of good products. 2 tbl

Description

 The invention relates to processes for the manufacture of printed circuit boards (PCBs) by semi-additive and subtractive methods, namely, to the process of preparing a combined metal-dielectric surface for the application of metal coatings by chemical means, and can be applied at radio-electronic enterprises.

 Possible combinations of combined surfaces are copper-fiberglass, copper polystyrene, copper, all types of polyimides. When applying coatings to such combined surfaces, difficulties arise due to the fact that the known surface preparation methods used separately for a dielectric or separately for a metal do not provide the adhesion strength of the metal chemically applied to the substrate. Therefore, one of the main directions in the development of technology for chemical metallization of combined surfaces is the development of new methods for surface preparation by searching for the compositions of etching, sensitization and activation solutions that ensure the adhesion strength of the metal coating with the combined base.

 In addition, the transition to a new generation of PP has led to the use of polyimide as the base material. This provides a higher level of heat resistance and compactness of the PP, but additionally complicates the process of applying a metal coating, since the polyimide itself gives poor adhesion. Therefore, in combination with polyimide and metal, special etchants are needed for combined etching.

 Known metallization methods involving surface preparation before applying a chemical coating, consisting of sequential etching in an alkaline hydrolysis solution with potassium permanganate and then in an acid hydrolysis solution with the addition of urea. After this, usually carried out operations of sensitization and activation in standard solutions. These operations are unsuitable in the case of preparing a combined metal-dielectric surface due to the lack of adhesion to the substrate.

 To eliminate the contact displacement of palladium on copper, combined sensory activation solutions are used, which is also unsuitable for the combined surface under consideration.

 The closest in technical essence and the achieved results is a method of metallization of a combined surface, in which, after conventional etching operations, the surface is treated in a solution of mercury nitrate. After this, sensitization takes place in a combined ammonia-trilonate solution. As a result of the interaction of the metal with mercury, good adhesion is achieved during subsequent chemical and electrochemical deposition of the metal.

 The method has significant disadvantages. One of them is the use of toxic mercury solutions, which is especially unacceptable with significant production volumes. In addition, the amalgam formed on the surface causes embrittlement; ulceration occurs during subsequent manufacture of PP. This leads to a decrease in the percentage of yield. The solution of the combined activator used in this case quickly fails as a result of decomposition, after which the contact recovery of palladium on a copper base begins. These solutions also contain large amounts of palladium> 4 g / l, which is economically disadvantageous.

 The aim of the invention is to eliminate the above disadvantages.

This goal is achieved in that before applying the metal coating chemically in the proposed method, after the etching operation, an additional surface treatment is carried out in a solution of the composition, g / l: NaOH 200-400; ethylenediamine 70-80; monoethanolamine 60-70; triethanolamine 40-50; at a temperature of 50-60 ^{° C} and the holding time of 5-7 min, and lead to surface activation composition solution, g / l: PdCl ^_2. 2H ₂ O 0.1-0.01; HCl 0.4-0.6; 1.5-2.0 glycine at pH 3.3-3.5 modes, a temperature of 20-25 ^{° C} and holding time 9-10 minutes.

 The use of ethylene diamine, monoethanolamine and triethanolamine additives in the etching solution leads to the formation of nitrogen-containing groups on the surface of the dielectric (especially important for polyimides) and evens out the chemical interaction at the metal-insulator interface. This ensures uniform surface preparation of the metal and dielectric.

 The activation step also makes a significant contribution to ensuring a high bond strength of the coating to the surface of the dielectric (especially polyimide). This sensitivity is mainly due to the small surface roughness of the polyimide films after etching and is expressed in a narrow range of concentrations of active centers on the surface, which causes high adhesive characteristics of the coating. The lack of catalyst, as well as its excess, lead to a weakening of the metal-insulator interaction, therefore, the concentration of the catalyst on the surface should be optimal so that there is no shortage or excess of active centers on the surface of the dielectric.

It should be noted that high adhesion characteristics are achieved only if chemical copper plating provides fine crystalline copper sludge at an optimal rate. Otherwise, even with the perfect combination of the previous operations, it is not possible to obtain good adhesion. The best results are obtained by chemical copper plating from Meyers-Wayne solutions, for example, of the following composition, g / l: CuSO ₄ ^. 5H ₂ O 12; potassium sodium tartaric acid 60; NiCl ₂ ^. 6H ₂ O 3; NaCl 8; Na ₂ CO ₃ 2; 37% formalin aqueous solution 10 ml / l at 22 ^{° C} and time of 20 minutes.

The advantage of the proposed method is the cheaper process as a result of a significant reduction in the amount of expensive palladium chloride in activation solutions from 3-4 to 0.1-0.01 g / l, and elimination of the amalgamation operation; improvement of working conditions due to the elimination of the stage of amalgamation using toxic material mercury salt; an increase in the stability of activation solutions to decomposition, which is facilitated by a reduced content of palladium chloride and a well-chosen ratio of palladium to glycine concentrations and the pH of the solution, under these conditions there is no immersion release of palladium on the copper surface, which leads to an increase in the percentage of yield of suitable PP from 50-60 to 80% additional surface treatment in the proposed etching solution improves the adhesive properties of the combined surfaces. This leads to an increase in the percentage of yield of suitable PP from 30-35 to 80%
PRI me R 1. The base was a plate measuring 5x10 cm ² of copper and polyimide grade PPK-6. Processing was carried out according to the technological scheme:
1. Etching in a solution of the composition, g / l: KMnO ₄ 55; KOH 55; temperature 60 ^{° C,} processing time is 6 min.

2. Etching in a solution of the composition, g / l: H ₃ PO ₄ 100; H ₂ SO ₄ 100, urea 20, temperature 40 ^{° C,} treatment time 3 minutes.

3. Processing in a solution of the composition, g / l: NaOH 300; ethylene diamine (EDA) 75; monoethanolamine (MEA) 65; triethanolamine (TEA) 45, temperature 55 ^{° C,} processing time is 6 min.

4. Sensitization in a solution of the composition, g / l: SnCl ₂ ^. 2H ₂ O 8; HCl 8, room temperature, processing time 3.5 min.

5. Activation in solution of the composition g / l: PdCl ₂ ^. 2H ₂ O 0.2; HCl 0.5 ml / l (conc.); glycine 1.5; pH 3.3; room temperature, processing time 10 min.

6. Chemical copper plating in a solution of the composition, g / l: CuSO ₄ ^. 5H ₂ O 12; potassium sodium tartaric acid 60; NiCl ₂ ^. 6H ₂ O 3; NaOH 8; Na ₂ CO ₃ 2; formalin 37% 12 ml / l, room temperature, processing time 20 min.

 After each operation, a thorough washing of the sample was carried out with running and distilled water. According to this scheme, the adhesion force of the coating to samples of 100 g / mm of the surface of the polyimide film and 300 g / mm of the surface of copper was obtained. The yield of samples is 80% (see tables 1 and 2). As can be seen from tables 1 and 2, the maximum yield of suitable PP is provided only at the optimal operating conditions of the proposed solutions of etching and activation.

PRI me R 24 (prototype). The sample is similar to example 1. The processing of the sample was carried out as follows. 1 and 2 (see example 1), further:
3. Amalgamation in a solution of the composition: Hg (NO ₃ ) ₂ 5 g / l, room temperature, exposure time 15 s.

4. Sensitization in an ammonian-trilonate solution of the composition, g / l: SnCl ₂ 20; HCl 50; NH ₄ F 100 II PdCl ₂ 10; Trilon B 100; pH 9; 1 min each

 5. Chemical copper plating (see paragraph 6 of example 1).

According to this scheme, an adhesion force of 50 g / mm of the surface of the polyimide film and 200 g / mm of the surface of copper was obtained. Yield 31%
Note. In table 1, example 1 represents the optimal conditions for the operation of the etching (p. 3).

 Examples 2 through 13 show the excess of the boundary conditions of the solutions, which leads to a decrease in the percentage of yield of printed circuit boards. In all examples, the optimal conditions for the activation solution are taken (item 5).

 Tab. 2 shows an exit beyond the boundary conditions during operation 5 of Example 1.

Comparison with the conditions used in the prototype (example 24) shows a significant gain in the proposed method in the yield of products from 31 to 80%
The life of the solutions of sensory activation (example 24) is 6 days. The life of the activation solutions (example 1 13) is 30 days.

Claims (1)

METHOD FOR PREPARING A COMBINED SURFACE COPPER-POLYIMIDE FOR CHEMICAL METALLIZATION, including surface etching, sensitization and its activation in a solution containing hydrochloric acid, palladium chloride and water, characterized in that after the etching operation, the surface is additionally treated in a solution containing sodium hydroxide , monoethanolamine and triethanolamine in the following ratio of components, g / l:
Caustic soda 200 400
Ethylene diamine 70 80
Monoethanolamine 60 70
Triethanolamine 40 50
Water Else
moreover, the processing is carried out at 50 to 60 ^o C for 5 7 min, and glycine is additionally introduced into the activation solution in the following ratio of components, g / l:
Palladium chloride 0.1 0.01
Hydrochloric acid 0.0004 0.0006
Glycine 1.5 2.0
Water Else
at a pH of 3.2 to 3.5, and the treatment in the activation solution is carried out at 20 25 ^o C for 9 to 10 minutes

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