RU2644486C1 - Method for cleaning of solder made as foil or tape before soldering - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: in the first bath of the ultrasound complex degreasing is carried out at a temperature of 180-200°C for 5-7 minutes with a detergent containing, wt %: KOH or NaOH alkali 15-25, glycerine 50-60, water - the rest. In the second bath, purification is carried out at a temperature of 50-60°C for 3-5 min with deionized water. In the third bath - at a temperature of 60-70°C for 20-30 minutes with detergent containing, wt %: KOH or NaOH alkali 3-4, sodium soda Na₂CO₃ 3-3.5, surfactant-syntanol 0.25-0.35, water - the rest, at a temperature of 60-70°C for 20-30 minutes. In the fourth bath, purification is carried out with deionized water at a temperature of 60-70°C for 2-3 min. In the fifth bath, purification is carried out in acetone at a room temperature for 2-3 minutes with ultrasound applied followed by drying with hot air.

EFFECT: invention provides complete removal of lubricated liquid residues rolled after hot rolling from the surface of gold-containing low-temperature eutectic solders.

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Description

The invention relates to the cleaning of solder before soldering from technological contaminants in aqueous alkaline solutions with the application of ultrasound, in particular to preparing the surface of foils, tapes of eutectic gold-containing solders after rolling before low-temperature (NT) flux-free soldering and can be used in the assembly of REA and microwave technology, more specifically - soldering crystals of semiconductor components.

The technological process of NT brazing consists of a number of operations, one of which is cleaning the surface of both the soldered parts and the solders used. To ensure physical contact of soldered parts with liquid solder, it is necessary to first remove organic and nonmetallic contaminants (oil, fats, scale) that are formed during chemical-thermal treatment (in our case, formed after rolling ribbons, foils to a given assortment), and which are not removed during flux-free NT soldering.

A simple degreasing of foils, strips of eutectic solders after rolling in organic solvents does not give the desired results - in the process of soldering, a poor-quality soldered joint is formed.

Known methods of chemical degreasing of the surface of soldered parts before soldering and the composition of the solutions [Khryapin V.E., Lakedemonsky A.V. Handbook soldering iron. Ed. 4th, rev. and add. M., "Mechanical Engineering", 1974, p. 159-160], in which to increase the wetting ability of water, surfactants, for example, OP-7, are added to it, and alkali (NaOH, KOH), trisodium phosphate, etc. General disadvantages of these methods of chemical degreasing of the surface are:

firstly, they are intended for degreasing steel, copper, aluminum, magnesium alloys;

secondly, the complex composition of baths for chemical degreasing leads to difficulties in their correction in the process of evaporation and etching of the surface.

There is a method of ultrasonic cleaning of metal parts [RF Patent No. 2275257 IPC V08B 3/12] by washing them in 5 baths of an ultrasonic complex (UZK): in the first bath in a degreasing aqueous solution containing detergent MS-15 or MS-37 with a concentration of 20- 25 g / l, solution temperature 60-70 ° C; in the second bath with the application of ultrasound with technical detergent (TMS) "Gremlos B" with a concentration of 20-30 g / l, a temperature of 45-55 ° C; in the third bath with the application of ultrasound with hot running tap water at a temperature of 45-55 ° C; in the fourth bath - cold running tap water and in the fifth bath - cold running distilled water, followed by drying with hot air.

As a result of ultrasonic chemical degreasing in five ultrasonic testing baths, the residues of the lubricant rolled up during hot rolling only begin to loosen, remain on the surface, and after cleaning, they must be cleaned from the surface of the tapes and foils with a technical blade. In this case, the upper layer of solder containing gold is partially scraped off (scraped off).

Trial cleaning of the surface of the AuSi solder foil in the ultrasonic cleaning bath with detergent MS-15 or MS-37 showed that the temperature of the solution in the first and second baths is clearly insufficient and the alkaline environment, which is formed as a result of hydrolysis of salts of sodium tripolyphosphate, sodium metasilicate, sodium carbonate ( MS-15) or sodium metasilicate and soda ash (MS-37) at this concentration does not dissolve the surface layer of organic contaminants. Subsequent cleaning of the surface of the AuSi solder foil in the second bath with the Gremlos B technical detergent, which includes a mixture of amino alcohols, anionic and nonionic surfactants such as syntanol ALM-10, neonol AF 9-12, also showed its inefficiency.

The technical result of the invention is the complete removal of rolled up after hot rolling residues of lubricating fluids from the surface of gold-containing NT eutectic solders, and, as a result, improving the quality of flux-free soldering of crystals of semiconductor components.

The technical result is achieved in that the cleaning before soldering the solder, made in the form of a foil or tape, includes degreasing in the first bath of the ultrasonic complex in an aqueous solution containing detergent, cleaning with the application of ultrasound in the second and third bath, cleaning with water in the fourth bath and cleaning in the fifth bath with the application of ultrasound followed by drying with hot air, while in the first bath the degreasing is carried out at a temperature of 180-200 ° C for 5-7 minutes; detergent containing, mass. %: alkali KOH or NaOH 15-25; glycerin 50-60; water - the rest; in the second bath, cleaning is carried out at a temperature of 50-60 ° C for 3-5 minutes with deionized water, in the third bath - at a temperature of 60-70 ° C for 20-30 minutes with a detergent containing, by weight. %: alkali KOH or NaOH 3-4, soda Na ₂ CO ₃ 3-3.5, surfactant syntanol 0.25-0.35, water - the rest, at a temperature of 60-70 ° C for 20-30 minutes, in the fourth bath, cleaning is carried out with deionized water at a temperature of 60-70 ° C for 2-3 minutes; and in the fifth bath, cleaning is carried out in acetone at room temperature for 2-3 minutes with the application of ultrasound.

The use of an increased concentration of alkali and glycerin in an aqueous alkaline solution allows to increase the temperature of the solution to 180-200 ° C. At a temperature of 180-200 ° C due to the active boiling of the solution, a cavitation effect is formed, which contributes to loosening of the surface layer during cleaning, which is formed during heat treatment during rolling.

Soda and surfactant contribute to the transfer of the remaining particles into the solution - the hydrophobic part of the surfactant molecule captures the remaining particles of oil, the process of emulsification occurs, the surface becomes clean and acquires a golden color.

After cleaning the surface in acetone and drying in air, the solder foil becomes shiny without smudges and discoloration.

Example

The Au-Si solder foil was cleaned in 5 baths of an ultrasonic complex. The foil is made in the form of squares measuring 50 × 50 mm and a thickness of 30 microns.

The compositions of the solutions and the chemical degreasing regimes of the Au-Si solder foil are shown in Table 1.

The squares of the Au-Si foil were placed in the first bath with a mass composition solution heated to 190 ° C. %: KOH 20, glycerin 55, water 25. The squares of the Au-Si foil were cleaned for 6 min.

The squares of the foil were removed from the first bath and placed in the second, where they were purified with the application of ultrasound (frequency 40 kHz) in deionized water at a temperature of 55 ° C for 4 min.

The squares of the foil were placed in a third bath with a solution of the composition in mass heated to a temperature of 65 ° C. %: KOH 3.5, soda Na ₂ CO ₃ 3.25, syntanol DS-10 0.3, water - the rest. Cleaning was carried out with the application of ultrasound (frequency 40 kHz) for 25 minutes

The squares of the foil were removed from the third bath and placed in the fourth, where they were purified in deionized water at a temperature of 65 ° C for 2.5 min.

The squares of the foil were placed in the fifth acetone bath with the application of ultrasound (frequency 40 kHz) and the final cleaning was performed at room temperature for 2.5 min. Then the foil was dried with hot (100 ° C) air.

The solder foil became shiny, without smudges and discoloration.

For bath 1 and bath 3 were prepared 3 solutions in accordance with table 1. The first composition with a lower limit, the second with an average limit and the third with an upper limit of the concentration of components in accordance with the claims.

The concentration of the components of the solutions outside the limits stated in the formula leads to the following results:

in bath 1-a) a composition with a concentration lower than in the first: loosening of the surface layer is just beginning, the surface of the foil becomes dull;

b) composition with a concentration higher than in the third:

loosening of the surface layer is complete, but due to the strong boiling of the solution, increased foaming is observed that goes beyond the bath.

In bath 3-a) a composition with a concentration lower than in the first: incomplete degreasing, the surface of the foil is light gray, semi-shiny;

b) composition with a concentration higher than in the third:

with an increase in the concentration of DS-10 (>> 0.35 wt.%), increased micelle formation (turbidity of the solution) is observed, which reduces the effect of surfactants [A.P. Bobrov, S.V. Tsaplin, P.P. Purygin. Development and research of the process of cleaning metal parts from lubricants with surfactant solutions. Bulletin Sam SU - Natural Science Series, 2007. No. 2 (52)].

Solutions were prepared as follows.

For bath I.

ChDA glycerin (GOST6259 - 75) was poured into a stainless steel bath, KOH solid alkali was poured (GOST 24363 - 80), deionized water was added, observing the proportions indicated in the table. The mixture was heated to 180-200 ° C and kept until a homogeneous composition. The bath was placed in the first bath.

For bath III.

Deionized water was poured into a stainless steel bath (see Table 1), then KOH alkali and soda ash Na ₂ CO ₃ were dissolved, then the solution was heated to a temperature of 50 ° C and white paste syntanol DS-10 was added (TU 6- 14-577-88), stirring with a glass rod until it is completely dissolved.

Thus, the cleaning of solder in ultrasonic cleaning baths with an increased concentration of alkaline medium and an increased temperature of solutions ensures the complete removal of organic contaminants from the surface of tapes and foils after rolling eutectic NT solders and, as a result, improves the quality of flux-free soldering of crystals of semiconductor components.

The crystals of silicon transistors were soldered with a purified Au-Si solder foil; a 100% solder was obtained around the entire perimeter of the soldered seam.

In addition, the advantages of the proposed cleaning method are the simplicity of the preparation of solutions, the availability and low cost of components of domestic production, the absence of toxic substances in their composition, as well as increased fire safety (flash point of syntanol ALM-10 and DS-10 brand 220 ° C and 247 ° C) and environmental friendliness of the cleaning process (biodegradability of syntanol DS-10 about 80%).

Claims (1)

The method of cleaning before soldering solder made in the form of a foil or tape, including its degreasing in the first bath of the ultrasonic complex in an aqueous solution containing detergent, cleaning with the application of ultrasound in the second and third bath, cleaning with water in the fourth bath and cleaning in the fifth bath with applying ultrasound followed by drying with hot air, while in the first bath, degreasing is carried out at a temperature of 180-200 ° C for 5-7 minutes with a detergent containing, wt.%: alkali KOH or NaOH 15-25, glycerol 50-60, water - the rest , in the second bath, cleaning is carried out at a temperature of 50-60 ° C for 3-5 min with deionized water, in the third bath - at a temperature of 60-70 ° C for 20-30 min with a detergent containing, wt.%: alkali KOH or NaOH 3-4, soda Na ₂ CO ₃ 3-3.5, surfactant syntanol 0.25-0.35, water - the rest, at a temperature of 60-70 ° C for 20-30 minutes, in the fourth bath carried out with deionized water at a temperature of 60-70 ° C for 2-3 minutes, and in the fifth bath, the cleaning is carried out in acetone at room temperature for 2-3 minutes with the application of ultrasound.