RU2079930C1 - Method of removal of scale, oxides, rust from metal surfaces of parts - Google Patents

Abstract

FIELD: chemical cleaning of metal surfaces, in particular, metal surfaces of parts in the process of fabrication of semiconductor devices, radio engineering articles, for instance metallized surfaces of printed-circuit boards for installation, service lines and power-generating plants of municipal utility. SUBSTANCE: the method consists in treatment of metal surfaces to be cleaned with an aqueous solution of sulfomaleic anhydride, whose concentration makes up 10 to 30 percent by mass, for 10 to 20 min at 50 to 80 C. EFFECT: facilitated procedure.

Description

 The invention relates to the chemical cleaning of the surface of metals, in particular the metal surfaces of parts in the manufacturing process of semiconductor devices, electronic products such as metallized surfaces of printed circuit boards for installation, communications and power equipment of urban economy.

 The invention can also find application in other fields of technology - mechanical engineering, aircraft building and other areas related to the operation of cleaning (decapitating) metal surfaces of parts from oxides before galvanic coating in the production process of various products.

 In the manufacture of semiconductor devices, various metals and their alloys are widely used: copper, nickel, aluminum, tungsten, molybdenum, kovar, bronze, brass, steel and others.

 One of the most important operations in the manufacturing process of devices, including semiconductor ones, is the cleaning of metal surfaces of parts, the quality of which depends on the electrical parameters and technical and economic indicators of the finished product.

Known methods for cleaning metal surfaces from contaminants, in particular from scale, oxides, which consist in processing the cleaned parts in multicomponent solutions based on inorganic acids [1-5]
Common disadvantages of these methods are: significant environmental pollution by reaction products; toxicity of the cleaning process; pronounced erosion of the metal surface; the need and complexity of the disposal of spent chemicals.

The closest in technical essence to the claimed proposal is a method of cleaning metal surfaces of parts, currently used in production before applying surface coatings to metal parts of metal [6]
This method consists in immersing metal parts in a solution containing inorganic acids (NHO ₃ , H ₂ SO ₄ , HF, etc.), followed by processing in it. This method is adopted as a prototype of the invention. The disadvantages inherent in this method are the same as for [1-5]. In addition, a common disadvantage of the methods using inorganic acids and solutions based on them is the large amount of their consumption and, in some cases, the inability to reuse them.

 The aim of the invention is to eliminate the disadvantages of the prototype, i.e. the development of such a method for cleaning metal surfaces of parts from pollution (scale, oxides, rust, etc.), which would ensure environmental protection, nontoxicity of the process, high quality of the surface to be cleaned, no erosion of the surface to be cleaned, resource saving (exclusion of expensive inorganic acids ), increasing the life of the solution by reducing the amount of sludge and, consequently, increasing the productivity of the process, the possibility of recycling (repeated application) of the same solution.

This is achieved by a method of cleaning metal surfaces of parts from pollution, in particular oxides, scale, rust, by processing in a solution, characterized in that an aqueous solution of sulfomaleic anhydride (SMA) is used as a solution, an effective amount of which is from 10 to 30 wt. and the treatment is carried out for 10-20 minutes at 50-80 ^o C.

 SMA, which is an organic compound, is produced by reacting maleic anhydride with sulfur trioxide.

 This compound (CMA) is non-toxic. The proposed method for cleaning metal surfaces of parts from oxides using SMA is significantly different from the prototype method (cleaning in an acid solution), as well as from analogue methods.

 The solution composition used in the method containing water and SMA has a high cleaning ability with respect to metal surfaces due to the fact that SMA forms water-soluble compounds with metal oxides that pollute the surface, which, according to their conformation, are not adsorbed on the metal surface.

 This cleaning mechanism is fundamentally different from the cleaning mechanism in the prototype method, as well as in analogous methods. In addition, in contrast to the prototype method, the proposed method due to the use of SMA allows you to form a buffer solution with a constant pH of pH (pH≈1); provides the ability to regenerate the solution by cleaning it from metal impurities.

 The selected range of SMA content in the solution, as well as the time and temperature ranges of processing metal parts in this solution, were determined experimentally on the basis of research results on cleaning the surface of parts of semiconductor devices before assembling printed circuit boards before installation, as well as communication elements of power equipment (pipes, valves, etc. .).

 The proposed method was carried out in the operation of cleaning parts of semiconductor devices before assembly into the KD-1 enclosure in the technological route standard for the production of silicon switching diodes of the KD 407 type.

 The crystal holder was cleaned before soldering a silicon crystal onto a PTB-1 platelite crystal holder.

 The starting material for the solution was tap water GOST 2874-82 and СМА ТУ 38507-63-0268-02. SMA is a transparent yellowish oily liquid, non-toxic (4th hazard class), odorless. The solution was prepared as follows: the ingredients were measured in the desired mass parts, then the MCA was combined with water at room temperature and thoroughly mixed by any known method. After that, the solution was ready for use. The shelf life of the solution is not limited. Investigated 5 variants of the solution with different contents of the ingredients in 100 wt. solution: 1 option 5 wt. SMA; 2 option 10 wt. SMA; 3 option 20 wt. SMA; 4 option 30 wt. SMA; 5 option 40 wt. SMA.

 The prepared solution was poured into the working bath, then it was heated in any way to the desired temperature.

The following heating modes were selected: 1 mode 40 ^o C; 2 mode 50 ^o C; 3 mode 60 ^o C; 4 mode 70 ^o C; 5 mode 80 ^o C; 6 mode 90 ^o C.

 Then, crystal holders fixed in any way were immersed in the heated solution, for example, in the standard TTP7811.00 cassette.

 The exposure time was selected in the following options: 5 min; 10 min; 20 minutes; 30 min.

After the selected time, the cassette with the crystal holder was removed from the solution and transferred to known technological operations: washing in deionized water and drying in a thermostat at 100 ^° C for 15-20 minutes. Then, the surface cleanliness of the crystal holders was assessed visually: by the absence of discoloration and the characteristic color of the metal being processed.

The experiments showed that the most effective purification was obtained by processing in a solution containing 20 wt. SMA, at a temperature of 70 ^o C for 10 minutes

 In addition, the cleaning of the crystal holders before soldering the crystals and assembling them into the casing in an aqueous MCA solution reduced the number of rejected assemblies by a factor of 2–3 compared with the cleaning provided in the prototype method.

 The advantages of the proposed method also include the fact that the solution for cleaning is used in amounts an order of magnitude smaller than in cases where known acid solutions are used.

 In addition, the same solution can be used repeatedly, regenerating it by filtration, and when it is evaporated by adding to the original volume of deionized water.

Claims (1)

A method of cleaning metal surfaces of parts from scale, oxides, rust by treating them with a solution, characterized in that an aqueous solution of sulfomaleic anhydride with a concentration of the latter from 10 to 30 wt. and processing in it is carried out for 10-20 minutes at 50-80 ^o C.