DE2815175A1 - AGENT FOR ELECTRIC TIN PLATING OF METALS - Google Patents

Description

PATENT LAWYERS

A. GRÜNECKER

DIPL-! Well

H. KINKELDEY

DR-ING

W. STOCKMAIR

DR-IMQ-AeE (CALTECH

K. SCHUMANN

DR RER NAT. ■ OPL-PHYS

P. H. JAKOB

G. BEZOLD

CR RERNAX-DPL-CHEM.

8 MUNICH 22

MAXIMILIANSTRASSE Λ3

P 12 530

April 7, 1978

ALFACHIMICI S.p.A. Corso Principe Oddone 18 I-Turin

Means for electroless tinning
of metals

The invention relates to a means for the production of baths for electroless .Niederschlag von
Tin on metals like copper, copper alloys like
Brass or bronze, alloys of tin and lead, lead, gold and others for the manufacture of in particular
coatings that protect against oxidation, improve solderability and serve other purposes. Electroless tinning is used in particular in

309843/0695

TELEPHONE (O8O) 22 08 62

TELEX OS-SS 3BO

telbqrammb monapat

TELECOPER

Manufacture of printed circuits for the treatment of tin-lead alloys to maintain their solderability and for other purposes.

There are already known means for electroless tinning of metals. Such agents usually contain a source of tin ions, for example tin (II) chloride, thiourea or a similar compound and an acid, for example hydrochloric acid, tartaric acid, citric acid, sulfamic acid or the like. The known agents, however, have various deficiencies. The tin deposit that can be achieved with them is not as pure, smooth, compact and resistant as modern technologies require. The thickness of the precipitate that can be achieved is extremely limited, as it becomes powdery with prolonged treatment and does not adhere well. The presence of relatively strong acids entails certain dangers when using these agents and makes them difficult to use in spraying processes. In addition, these agents tend to disintegrate quickly, so they have a very short shelf life, which prevents the production of concentrates to be diluted at the time of use. At normal ambient temperature, precipitates or flocculations form, which at most go back into solution at elevated temperatures. As can be seen in this connection from US Pat. No. 3,303,029, the agent described there has a ^{critical temperature between 30 and 40 °} C., below which flocculation occurs. With such means, electroless tinning cannot be carried out at normal ambient temperature, but only at an artificially elevated temperature. This results in increased costs for setting up and maintaining additional devices, increased energy consumption and increased release of harmful fumes.

8098 /> 3 / 069S

An object of the invention is to eliminate or at least alleviate the above-mentioned deficiencies known means for the electroless tinning of metals and the creation of such a means, which also is durable in concentrated form, which does not precipitate at normal ambient temperature or flocculation tends and with which relatively thick precipitates of improved quality with increased Precipitation speed are achievable "

The invention is based on the systematic investigations for the improvement of the known iiittel for electroless Tinning of metals from the knowledge that certain organic compounds have the property to form stable complexes with tin, which are capable of facilitating the transition of the tin from the divalent to the Prevent tetravalent form without the aid of special reducing agents. Is of particular interest the fact that the formation of the complexes mentioned by the simple addition of such compounds without excessive Care can be achieved, and that the concentration of the organic compounds in the solution is very has great leeway, being the organic compounds

not only do not hinder the chemical reactions necessary for precipitation, but rather an improvement the properties of the precipitate and the wettability of objects brought into the bath and thus contribute to the uniformity of the achievable precipitation.

In accordance with the invention, an agent for electroless tinning of metals which includes a source of tin ions is thiourea or contains a similar compound and an acid, characterized in that it additionally contains at least one compound from the group of dihydric alcohols with at least two and at most four carbons

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atoms of matter through. Dehydration from the above Compounds which can be prepared from dihydric alcohols by sulfuration from the dihydric alcohols mentioned compounds that can be prepared, the organic oxyacids with at least two and at most three carbon atoms, the compounds which can be prepared from the oxyacids mentioned by esterification and the compounds produced by salt formation contains the aforementioned oxyacids preparable compounds.

In the context of the invention, one or more of the abovementioned compounds can optionally be used those belonging to one category or also several belonging to different categories within those outlined above Connections belonging to the group can be used.

In particular, the hydroxy acids mentioned can replace or familiarization I nl in such agents acid components used in whole or in part, be present in addition to these.

In the ready-to-use state, the agent according to the invention preferably has a pH value between 0 and 2, in particular a pH of approximately 1. The Solution may also contain a wetting agent, the presence of which is not essential.

Examples of dihydric alcohols and their compounds which can be used according to the invention are u.d. Ethylene glycol, Diethylene glycol, propylene glycol, trimethylene glycol, 1,4-butanediol, diethylene dioxide, dimethyl sulfoxide etc. Examples of organic oxyacids which can be used according to the invention include i.a. Glycolic acid, lactic acid, Glyceric acid and the like. In addition, according to the invention Esters and salts of such oxyacids can be used.

With regard to the concentration in which the said

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organic compounds according to the invention are added to the means for electroless tinning, consists, as already noticed a wide margin. To achieve The said organic compounds according to the invention can give satisfactory results in one concentration between about 0.03 and 3, preferably between 0.06 and i mol / l are present in the ready-to-use solution, and in a correspondingly higher concentration in one concentrated agent, which to dilute for use or to freshen up exhausted baths.

The treatment solutions prepared with the agent according to the invention have significantly improved properties compared to known solutions with regard to their durability, even in the concentrated state, their usability at normal ambient temperature, the rate of precipitation and the properties of the achievable precipitates, e.g. B. purity, gloss, compactness, resilience, adhesiveness as well as the absence of powder formation and achievable thickness of the precipitate. The precipitates achieved in this way therefore have an increased resistance to corrosive influences, in particular to oxidation, and can be melted and soldered particularly effortlessly.

Although an essential feature of the invention Means means that it can be used at normal ambient temperature, but the means can also be used in warmed state, which sometimes leads to Increasing the rate of precipitation is advantageous can be.

The agents according to the invention remain even after a long period of time Use clear and free of decay products and can therefore be used when exhausted by means of a corresponding

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Reinforcement solutions exhibiting settlement will.

To determine the behavior of the agents according to the invention were comparative tests with nine different agents, the composition of which is given below carried out. These are conventional means designated with 1 to 4, while those with 5 to 9 designated agents according to the invention are.

1. Tin (II) chloride hydrochloric acid
Thiourea

2. Tin (II) chloride citric acid thiourea

3. Tin (II) chloride, tartaric acid
Thiourea

4. Tin (II) chloride sulfamic acid thiourea

5. Tin (II) chloride citric acid ethylene glycol oil Thiourea

6. stannous chloride citric acid dimethyl sulfoxide Thiourea

0.012 until 0.04 mol / 1 0.4 until 1.3 mol / 1 0.4 until 0.8 mol / 1 0.012 until 0.04 mol / 1 0.07 until 0.24 mol / 1 0.4 until 0.8 mol / 1 0.012 until 0.04 mol / 1 0.1 until 0.53 mol / 1 0.4 until 0.8 mol / 1 0.012 until 0.04 mol / 1 0.15 until 0.5 mol / 1 0.4 until 0.8 mol / 1 0.012 until 0.04 mol / 1 0.07 until 0.24 mol / 1 0.08 until 0.65 mol / 1 0.4 until 0.8 mol / 1 0.012 until 0.04 mol / 1 0.07 until 0.24 mol / 1 0.06 until 0.4 mol / 1 0.4 until 0.8 mol / 1

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7-stannous chloride 0.012 to 0.04 mol / l

Glycolic acid 0.2 to 0.7 mol / l

ethylene glycol 0.08 to 0.65 mol / l

. "Lactic acid 0.1 to -0.55 mol / l

Thiourea 0.4 to 0.8 mol / l

8. Tin (II) chloride 0.012 to 0.04 mol / l lactic acid 0.3 to 1 raol / l Ethylene glycol 0.08 to 0.65 mol / 1 thiourea 0.4 to 0.8 mol / 1

9. Tin (II) chloride 0.012 to 0.04 mol / l lactic acid 0.1 to 0.55 mol / l Glycolic acid 0.2 to 0.7 mol / l thiourea 0.4 to 0.8 mol / l.

Experiment A: the various agents were prepared at normal ambient temperature and stored in closed containers, resulting in the following: Agent 1: Immediately after preparation, a large amount of precipitate formed, which was soluble at an elevated temperature of 45 to 55 ° C and was formed again on cooling to approx. 30 to 35 ^{° C.} Mean 2. after 72 h the formation of the same precipitate as mean 1. was observed, albeit less abundantly.

Medium 3 · After 48 h, the formation of precipitates could be observed, of which a gray or brown colored part could not be removed by simple heating. Medium 4. After 72 hours an increasing yellow coloration appeared and precipitates of the same color formed. Means 5 to 9 according to the invention: excellent stability, the solutions remained clear and free from precipitates even after several months.

Experiment B: a dried one defatted in the known manner and then with 20% ammonium persulfate

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Pickled copper platelets were first placed in a bath prepared from means 1 to 9 for about Ί0 min. This was done in the known baths 1 to 4 · at a temperature of 35 C to cause precipitation of avoiding precipitates during baths of the invention were left for 5 to 9 on the ambient temperature of about 20 ⁰ C. Regardless of the difference in the conditions in favor of the known baths, the rate of precipitation was essentially the same in all cases, the precipitates obtained with baths 5 to 9 being of considerably better quality.

Experiment C: Experiment B was carried out under the same conditions extended over a period of 12 hours. The precipitation achieved with the known baths 1 to 4 were dark, uneven and showed traces of powder formation. In soldering tests a found relatively poor solderability. The precipitates obtained with the baths 5 to 9 according to the invention were uniform, light-colored, compact, powder-free and increased in thickness, and excellent Solderability.

Experiments B and C were carried out with the baths 5 heated repeated up to 9 at 35 ° G. Depending on the duration of the treatment, precipitation increased Thickness achieved with unchanged quality. After completion of the tests, the baths according to the invention were in In contrast to the well-known baths, clear and free of precipitates and decay products.

Thus, the invention eliminates the shortcomings mentioned known means and thus enables a more economical one and more ecologically beneficial tinning of metals.

809843/0695

Claims (2)

PATENT ADVOCATES A. GRÜNECKER DW - 4NG. H. KINKELDEY Dn-ING. 2815175 W. STOCKMÄIR DR-Wa - AeE (CALTCCHl K. SCHUMANN DR RER NAT. - DtPL-PHYS P. H. JAKOB DIPL-ING G. BEZOLD ER HER NAT · DtPL-CHBVl 8 MUNICH MAXIMILIANSTRASSE Λ3 P_a_t_e_] Q._t_a_n_s_p_r_ü_c_h_e Means for electroless tinning of metals » containing a source of tin ions, thiourea or the like compound and an acid, thereby characterized in that there is at least one organic compound from the group of divalent Alcohols with at least two and at most four carbon atoms, obtained by dehydration from the above Compounds which can be prepared from dihydric alcohols by sulfuration from the dihydric alcohols mentioned producible compounds, the organic oxyacids with at least two and at most three carbon atoms, the compounds which can be prepared from the oxyacids mentioned by esterification and the compounds produced by salt formation contains the aforementioned oxyacids preparable compounds. 809843/0695 TELEPHONE (O8S) 992869 TELEX OB-SBSeO TELEGRAMS MONAPAT TELECOPY 2. Means according to claim 1, characterized in that the organic contained therein Compound at least one compound from the ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, 1,4-butanediol, diethylene dioxide, dimethyl sulfoxide, Glycolic acid, lactic acid, glyceric acid and esters and salts of the acids mentioned is. 3- Agent according to claim 1 and / or 2, characterized in that its pH value is between 0 and 2, preferably close to 1. 4 ·. Agent according to at least one of claims 1 to 3, characterized in that the at least one organic compound is in a concentration between 0.03 and 3 mol / 1, based on the ready-to-use Solution, is in place. 5. Agent according to claim 4, characterized in that the at least one organic compound contains a concentration between 0.06 and 1 mol / 1, based on the ready-to-use solution, % st. 809843/0695