DE2256025C2 - Aqueous acid bath for the galvanic deposition of tin / lead alloy deposits - Google Patents

Description

O- (CH ₂ CH ₂ O) ₁₁₁ H

wherein R is an alkyl group having 5 to 15 carbon atoms and m is an integer from 5 to 20.

3. Bath according to claim 1, characterized in that the polyether surface agent is the general formula

R ₂ -C-NH- (CH ₂ CH ₂ O) _n -SO ₃ H

wherein Ri, R ₂ and R3 each represent a straight or branched alkyl group having 3 to 10 carbon atoms, π is 5 to 10 and M is a cation selected from hydrogen, sodium, potassium and ammonium.

4. Bath according to claim 2, characterized in that the polyether surface agent consists of one Nonylphenol / ethylene oxide condensate, which has about 15 ethylene oxide groups per molecule.

5. Bath according to one of the preceding claims, characterized in that the aryl hydroxy compound is selected from naphthols and substituted phenols.

6. Bath according to claim 5, characterized in that the aryl hydroxy compound of ^ -naphthol, 2,4,6-trichlorophenol, ρ, ρ'-dihydroxydiphenyl sulfone, 2,7-naphthalenediol, 1,1'-bi-2-naphthol or «-naphthol.

7. Bath according to one of the preceding claims, characterized in that it is 4 to 53 g / l Tin (II) ions, 1 to 85 g / L lead ions, 100 to 200 g / L fluoborate ions, 4 to 10 g / L of the polyether surfactant and contains 0.5 to 1.0 g / l of the aryl hydroxy compound.

The invention relates to an aqueous acidic bath for the galvanic deposition of white, continuous, fine-grained tin / lead alloy precipitates that provide excellent coverage in the lower area Have current density, the bath tin (II) ions, lead ions, fluoborate ions, a polyether surface agent and optionally contains boric acid.

An aqueous bath of the above type is known from US-PS 27 34 025. This bath provides tin / lead alloy deposits, which have good solderability. The precipitates are considered homogeneous, described as dense and non-porous. The surface of the precipitates is said to be smooth and clean

But it has been shown that shiny precipitates have better solderability, which is particularly advantageous for printed circuits

The invention was therefore based on the object of creating an aqueous acidic bath of the type described at the beginning to modify that the tin / lead alloy precipitates obtainable therewith have a bright, shiny appearance own.

The object is achieved according to the invention in that the bath of the type specified further an aryl hydroxy compound is added.

Those obtainable from the baths according to the invention

Precipitation is characterized by the following features :

1. They are much lighter in color than precipitates produced with known baths;

2. They are very uniform and of an exceptionally fine grain size;

^2j 3. they are glossy, if not mirror-glossy;

4. The coverage in the area of low current density is excellent.

The precipitates produced with the baths according to the invention are used in the electronics industry and other fields of application in order to give the electroplated articles an improved appearance to improve solderability and to increase the resistance to discoloration when. use to increase.

Polyether surfactants which can be used according to the invention are e.g. B. aromatic Polyethers and aliphatic polyethers. Preferably the surfactant is a polyalkoxylated alkyl phenol. Typical polyalkoxylated alkylphenols are polyethylated alkylphenols of the formula

_R _ / \ - O - <CH ₂ CH ₂ O) ^ H

where R is an alkyl group having 5 to 15 carbon atoms (preferably 9 carbon atoms), and m is an integer of at least 5 and preferably not more than 20. A polyether surfactant composed of a nonylphenol / ethylene oxide condensate containing approximately 15 ethylene oxide groups per molecule is particularly preferred.

Other useful polyether surfactants are nitrogen-containing aliphatic polyethers which contain the following general formula can be represented

JO

60 R ₂ -C -NH- (CH ₂ CH ₂ O) _n -SO ₃ H

wherein Ri, R ₂ and R3 each represent a straight or branched alkyl group having 3 to 10 carbon atoms

stand, η stands for an integer of at least 5 and not more than 10 and M stands for a cation which is selected from hydrogen, sodium, potassium and ammonium

Examples of aryl hydroxy compounds according to of the invention are naphthols and substituted phenols.

The naphthol compounds contain one or more hydroxyl groups.

The phenolic compounds have one or more hydroxyl groups. The phenolic compounds can be a or more but less than 4 inert substituents each Have benzene ring, and they can inert linking groups, such as. B. Sulphone groups (- SO2 -) contain, but should not have a negatively charged group.

Typical examples of naphthols and phenols that have been found to be effective are:

/ -Naphthol

-OH

α-naphthol

^u '- ^Bi - ² - ^naphtho1

2,7-naphthalenediol

2,4,6-trichlorophenol

ρ, ρ'-dihydroxydiphenyl sulfone

HO

The preferred contents of the bath components are listed below:

a) 4 to 53 g / l tin (II) ions;

b) 1 to 85 g / l lead ions;

c) 100 to 200 g / l fluoborate ions;

d) 4 to 10 g / l polyether surface agent;

e) 0.5 to 1.0 g / l aryl hydroxy compound.

The divalent tin in the bath provides the tin that is present in the deposited tin / lead alloy. In a freshly prepared bath containing 10 g / l tin and 90 g / l lead, about 85% of the tin is in a bivalent state, the remainder being tetravalent tin % Tin contains When the amount of tetravalent tin increases and the amount of divalent tin decreases , the percentage of tin in the precipitate falls below 10%. However, at higher concentrations, for example 50 g / l tin and 35 g / l lead, there is less tendency for tetravalent tin to form in the bath

During normal operation of the bath, the content remains on

ίο bivalent tin largely constant, creating a Precipitation with a uniform content of tin is obtained if, however, the solution for some time is out of order, then it is advisable to filter the bath and protect it as far as possible from the ingress of air,

ι> to keep the formation of tetravalent tin to a minimum. The lead bath supplies the lead; which is contained in the deposited tin / lead alloy. The fluoboric acid is therefore contained in the bath that the necessary activity arises, that the conductivity

2 (i speed is increased that a fine-grained precipitate is obtained and that dendritic formation is prevented.

Boric acid can be added to the bath to maintain bath stability. Nearly 25 g / l roric acid has been found to be useful, but this concentration is not critical.

The preferred operating conditions, such as B. pH, temperature and current density, depending on the the respective bath composition and the nature of the object on which the Tin / lead alloy to be deposited will vary. Generally good galvanic Tin / lead alloy precipitates obtained within a specific range of working conditions.

The galvanic deposition of the tin / lead alloy using the bath according to the invention can be carried out at temperatures of approximately 10 to 60 ^° C. (preferably 15 to 20 ^° C.) either with or without stirring. The temperature of the electroplating bath is usually room temperature. At lower temperatures, such as Ί5 to 20 ⁰ C, optimal results are obtained. In some modes of operation in which a substantial cell flow is used, which results in a temperature increase, cooling must be carried out in a suitable manner, for example by cooling water flowing through a submerged cooling coil or by cooling machines. When using average current densities of 0.5 to 5.0 A / dm ² , tin / lead alloy deposits with an average thickness of 0.25 to 25 μm are obtained in deposition times of 0.1 to 10 minutes on average.

If necessary, uniform movement of the electroplating bath can be provided, namely either by mechanical movement of the object to be coated or by bath stirring during electrodeposition. Such agitation may involve the use of high deposition current densities enable on the object to be electroplated.

During the galvanic deposition of tin / lead alloys, the parts can be coated on rails be, d. H. on holders that hold one or more parts, which in general can be the same, but which can also have a different size, different geometric shape, etc. The parts can also be coated as a mass in rotating drums. With this type of coating,

which is usually used to coat smaller parts, is the loading of the drum usually from the same parts, although mixed charges can also be used. Because of the number, size and shape of the parts, it is important that the applied electroplating bath is one the largest possible current density range in which a gloss is obtained. It is also important that the Limiting current density, d. H. the current density at which the precipitation has no healthy structure and no Have a healthy appearance as high as possible to accommodate the wide variations in the cathode current density to take into account, due to the size and the complicated shape of the to be coated Parts can be encountered.

The invention is illustrated in more detail by the following example.

example
A. Prior art bathroom

An electroplating bath for the deposition of an alloy containing 60% tin and 40% lead of the following Composition was made:

Tin (II) fluorate concentrate 16.2% by volume (49.6% by weight) Lead fluorate concentrate 6.3% by volume (50% by weight) 15.0 vol.- V-, Fluoboric acid (49% by weight) 15.6 g / l Boric acid 62.5% by volume water 52 g / l ir gives
divalent tin 30 g / l lead 100 g / l free fluoboric acid 25 g / l free boric acid

The deposition conditions in a Hull cell were as follows:

Solution volume 267 ml

Temperature 20 ⁰ C

Stirring magnetic stirring

Cell current 1A

Time 5 min

Anode plate made of an alloy
with 60% tin and 40% lead

Polished brass cathode

8 g / l of a nonylphenol / ethylene oxide condensate were added to the above bath, which was approximately Contained 15 ethylene oxide groups per molecule

The precipitates from this system were white, continuous and fine-grained.

B. bath according to the invention

A base solution of ^ -naphthol was prepared by adding 144.2 g (1 mole) of powdered ^ -naphthol U.S.P. grade was added to water with mechanical stirring. Then 50 g became chemical pure NaOH pellets previously in 200 ml of water had been dissolved, admitted. Stirring was continued until the jS-naphthol was dissolved. then 3 g of commercially available activated charcoal were added and stirring was continued for 1 hour, followed by filtration became. The filtrate was diluted to 1440 ml with water, so that the solution with 100 g / l ^ -naphthol was obtained. 1 part by volume of purified 100 g / l - /? - naphthol base solution was with 1 part by volume 100 g / l basic solution of the above-mentioned nonylphenol / ethylene oxide condensate mixed.

10 ml / l of the base solution became the bath composition of Example 1 was added, with 0.5 g / l of jS-Naphtho! were obtained. The ^ -naphthol was completely resolved. The resulting precipitate was white, semi-glossy, microcrystalline, solid and fine-grained and showed no defects and much better coverage at lower current density than without 0-naphthol.

Similar results are obtained with other polyether surfactants and other aryl hydroxy compounds.

Claims (2)

Patent claims: 1. Aqueous acid bath for the galvanic deposition of white, continuous, fine-grained Tin / lead alloy deposits that provide excellent coverage in the low current density range have, the bath tin (II) ions, lead ions, fluoborate ions, a polyether surfactant and optionally contains boric acid, characterized in that it also contains an arylhydroxy compound 2. Bath according to claim 1, characterized in that the polyether surface agent has the formula