RU1720467C - Process of metal spraying of holes of printed circuit boards - Google Patents

Abstract

FIELD: chemical copper plating. SUBSTANCE: for performance of process printed circuit board is activated in matched solution containing palladium chloride and tin chloride. After rinsing printed circuit board is treated in solution of accelerator containing nonorganic acids or their salts or caustic soda and is rinsed again. Then printed circuit board is treated in solution of reductant in which capacity hydrazine (or its derivatives) or hydroxylamine (or its derivatives) is used under following conditions: concentration of reductant should be 10-30 g/l; temperature of solution 20-27 C, treatment duration 0.5-1.5 min. After rinsing for 1 min chemical plating of holes of holes in printed circuit board is conducted. EFFECT: improved quality of chemical copper plating. 2 cl, 1 tbl

Description

 The invention relates to chemical copper plating and can be used in the manufacture of printed circuit boards (PP).

 The purpose of the invention is improving the quality of chemical metallization of printed circuit boards by eliminating the separation layer of palladium on the foil surface of the circuit boards and at the ends of the inner layers in the holes.

According to the invention, a method for metallizing PP holes involves activating in a combined solution containing palladium chloride and tin chloride, washing, processing in an accelerator solution containing inorganic acids or their salts, or caustic soda, washing, processing in a solution of a reducing agent and chemical copper plating. As a reducing agent, hydroxylamine or hydrazine, or their derivatives, are used. All of these compounds in aqueous solutions are powerful reducing agents. In addition, they have the ability to enter into the composition of complex compounds with platinum group metals (with palladium, tin ^2+, tin ⁴⁺ ) as an add-on.

 The physical nature of the processes that occur during the processing of printed circuit boards in a recovery solution and excluding the formation of a layer of palladium on the foil is as follows.

If the process of formation of catalytic particles during the operations of activation, washing, processing in an accelerator solution, washing has passed to the end, i.e. Pd ^{2+ is} completely reduced to Pd ⁰ , and the tin (II) and tin (IV) compounds are completely removed from the surface of the foil and dielectric, then when palladium metal is deposited on the foil elements in the solution of the reducing agent, it forms a complex compound with the reducing agent and goes into solution. In this case, the Pd ⁰ located on the dielectric also partially transforms into the complex and is washed off, but to a much lesser extent, since it is located on the extremely developed surface of the dielectric in microdepans, in microchannels, and is less accessible for interaction with the solution. A positive role for the conservation of Pd ⁰ on the dielectric is also played by the low concentration of the reducing agent in the solution, the low (room) temperature, and the short processing time.

A much more important role is played by the reducing agent solution in the case when the normal chemistry of the formation of catalytic particles is impaired, for example, due to the aging of the activator or with insufficient leaching, or in violation of the technological conditions during activation. In these cases, residues of tin (II), tin (IV) compounds, as well as unreduced Pd ²⁺ particles, may be present on the foil elements and on the dielectric of the printed circuit boards entering the chemical metallization operation. Residues of Pd ²⁺ compounds on foil elements can be reduced due to the exchange reaction with copper foil according to the equation
Pd ²⁺ + Cu ^o __ → Pd ^o + Cu ²⁺ or are reduced directly in a solution of chemical copper plating. In both cases, a separation layer of palladium will inevitably form on the foil surfaces.

Processing in a solution of a reducing agent in accordance with the proposed method eliminates this disadvantage due to the following reactions:
reduction of Pd ²⁺ to Pd ⁰ and binding of Pd ⁰ to the complex compound which is readily soluble and easily removed from the surface of the foil (1);
reduction of Sn ²⁺ to Sn ⁴⁺ , their binding to a readily soluble complex compound, which contributes to the complete release of catalytic palladium particles from gels and insoluble tin compounds and facilitates their removal from the foil surface due to the reaction according to claim 1 (2).

 Thus, due to processing in a reducing agent solution, the formation of a palladium separation layer is eliminated both on the foil surface and on the ends of the inner layers of multilayer printed circuit boards, and this in turn improves the quality of the chemical copper coating (increases the adhesion to the foil) and increases the reliability of the printed circuit boards .

It should be noted another positive role of the reducing agent solution. Removal of tin (II) and tin (IV) compounds and additional reduction of Pd ²⁺ to Pd ⁰ contributes to the completion of the formation of Pd ⁰ catalytic centers on the dielectric and better activation of the dielectric, which subsequently increases the continuity of the chemical copper coating.

Conditions of the reducing agent in the solution processing: reductant concentration of 10-30 g / l, solution temperature is 20-27 ^{° C,} the residence time of 0.5-1.5 min. Subsequent flushing for 0.5-1 minutes is desirable.

 To extend the life of the reducing agent and obtain reproducible results, it is desirable to introduce buffer mixtures in the composition of the solution to maintain a certain constant pH value of the solution in the range of 5-10.

In the proposed technical solution, known solutions, the content of sulfuric or hydrochloric, or hydrofluoric acid, or sodium hydroxide can be used as an accelerator, but it is preferable to use ammonium bifluoride (NH ₄ HF ₂ ), which gives more stable results on the activation of the dielectric and guarantees the formation of a dense, continuous layer of chemical copper in the holes of the printed circuit boards.

 The metallization results of the holes of the printed circuit boards were evaluated using a microscope by the continuity of the coating of the walls of the holes. The presence of a layer of palladium was evaluated using metallographic sections.

 PRI me R 1. The preparation of MPP from foil-coated fiberglass type FCS after drilling holes and cleaning them is processed in solutions, the compositions of which are given below (g / l).

1) degreasing Trisodium phosphate 30 Sodium carbonate 30 Preparation OS May 20 Water to 1 liter Temperature 50 ^{° C,} 3 min duration;
2) etching Ammonium persulfate 200 Sulfuric acid 10 Water, l to 1
temperature 20 ^{° C,} duration 1 min;
3) decapitation Sulfuric acid 100 Water, l to 1
temperature ²⁰ ° C, duration 0.5 min;
4) processing in a solution of surfactants Antistatic 2 Sulfuric acid 10 Water, l to 1
temperature 40 ^{° C,} 2 min;
5) processing in a solution of a mixture of salts Sodium sulfate 70 Sodium chloride 200 Water, l to 1
temperature 20 ^{° C,} duration 1 min;
6) treatment in an activation solution Palladium chloride 0.5 Tin chloride 15 Hydrochloric acid 20
Sodium sulfate 70 Sodium chloride 200 Water, l to 1
temperature 30 ^{° C,} 7 minutes duration.

The time elapsed from the moment of preparation of the activator is 14 months;
7) washing with running water for 2 minutes or jet for 0.5-1 minutes;
8) processing in an accelerator solution: Sulfuric acid 30 Water, l to 1
temperature 20 ^о С, duration 3 min;
9) rinsing with running water for 2 min or jet washing for 0.5-1 min;
10) processing in a solution of a reducing agent Hydroxylamine sulfate 10 Phosphoric acid 10 Water, l to 1
temperature 20 ^{° C,} duration 1 min;
11) jet washing for 1 min;
12) chemical copper plating Copper sulfate 10
Potassium tartrate 50 Trilon B 10 Nickel chloride 4 Sodium hydroxide 10 Alkaline stabilizer 0,0005 Water, l to 1
temperature ²⁰ ° C, duration 30 minutes, the coating thickness of 1.5 microns;
13) rinse with running tap water for 3 minutes;
14) decapitation Sulfuric acid 300 Water, l to 1
temperature ²⁰ ° C, duration 1.5 min;
15) preliminary electrochemical copper plating Copper sulfate 110 Sulfuric acid 110
Brightening additive LTI 0.1 Preparation OS-20 0.5 Water, l up to 1
temperature ²⁰ ° C, duration 20 minutes, a current density of 2 A / dm ² is applied continuously filtering the solution. The applied coating thickness is not less than 5 microns (usually 5-10 microns).

 In the process of chemical copper plating in the openings of the MPP, a solid, dense chemical copper coating is obtained. After preliminary electrochemical copper plating, a metallographic thin section of the longitudinal section of the hole was made, the study of which under a microscope showed the absence of a dividing layer of palladium at the ends of the inner layers, as well as on the upper and lower contact pads.

 PRI me R 2 (prototype). The MPP billet from foil fiberglass type FCS after drilling holes and cleaning them is processed in solutions in accordance with technological operations N 1-9 and 11-15 of example 1.

 A continuous coating was obtained in the holes of the MPP with a layer of chemical copper, but when examining the wall of the hole using a metallographic thin section, a layer of palladium was found.

 The results of the proposed method, the boundary conditions, as well as the compositions of the used accelerator solutions are shown in the table.

Claims (2)

 1. METHOD FOR METALIZING HOUSES OF PRINTED BOARDS, including activating a dielectric substrate in a combined solution containing palladium chloride and tin chloride, washing, processing in an accelerator solution containing inorganic acids or their salts, or caustic soda, washing and chemical copper plating, characterized in that , in order to improve the metallization quality of printed circuit boards, before the operation of chemical copper plating, the boards are treated in an aqueous solution of a reducing agent - hydrazine or its derivatives, or hydroxylamine, or derivatives. 2. The method according to claim 1, characterized in that, in order to increase the efficiency of the method, the treatment is carried out for 0.5 - 1.5 minutes at a concentration of reducing agent in the solution of 10 - 30 g / l, the temperature of the solution is 20 - 27 ^o C .

Images