CS271560B1 - Chemical currentless copper plating bath - Google Patents

Abstract

Chemical electroless copper bath containing soluble copper salt, alkaline metal hydroxide, formaldehyde, complexing agents of 1, 1', 1'', 1''', types -(1.2-ethanediyledinitrilo) tetrakis (2-propanol) and N,N -1.2-ethanediylbis/N-(carboxymethyl glycine)/ aliphatic alpha-hydroxy-acid, poly(ethylene oxide), eventually, soluble quicksilver salt, cyanide of alkaline metal, superficially efficient active substance, soluble compound of precious metal, methanol, and 1.10<-6> to 5.10<-4> moles/l of some quicksilver selenocyanate complexes, palladium, platinum, rhodium in a combination with 1.10<-5> to 1.10<-3> moles/l of an accelerating agent of 2.2 -bipyridyl or 1.10- phenantroline type.

Description

The use of electroless chemical baths capable of depositing a metal coating on various metal surfaces, respectively, is widespread in technical practice. for non-metallic surfaces. activated appropriately. The function of such baths is essentially based on the reduction of metals from solutions of their salts, respectively. of complex compounds by treatment with a suitable reducing agent. The composition of such baths is adapted so that metal precipitation occurs only on metal surfaces and on surfaces containing particles catalytically active for this process, i.e., in the process. to prevent the metal or its oxide from precipitating in the bath volume or on the walls of the process vessels. Among these chemical electroless plating baths, chemical electroless copper baths occupy a particularly important position, particularly with regard to their use in electrical engineering in the production of printed circuit boards. The development of PCB technology is associated with increased requirements for the user parameters of these baths, especially with regard to the rate of copper deposition, the quality of the deposited copper layer, the longevity and operational reliability.

The chemical electroless copper bath essentially comprises the following basic components: a source of copper ions, most commonly copper sulfate; a complexing agent forming complexes with the copper ions reasonably stable even in an alkaline medium (eg tartaric acid, ethylenediaminetetraacetic acid, hydroxyalkylderivatives of ethylenediamine, polyethylene polyamines and the like); a source of hydroxide ions, most commonly sodium hydroxide; a reducing agent, most commonly formaldehyde or paraformaldehyde; various additives, mostly in very low to trace concentrations, which influence the individual phases of the reduction process, possibly prevent the course of side reactions or eliminate the side reaction products, while favorably affecting the quality of the excreted copper. The motives leading to the choice of complexing agent and additives are summarized, for example, in the articles of Saubestre Ε. B .: Plating (6), 583 (1972) or Gemmler et al., Metalloberflache 38, 487 (1984).

The formulation of these chemical copper baths has been the subject of a series of patents, such as Japan Kokai No. 75,101,233, GB Patent No. 1,500,435, US Patent No. 3,485,643 » No. 3,492,135, U.S. Patent No. 3,515,563, U.S. Patent No. 3,607,317, U.S. Patent No. 3,615,732, U.S. Patent No. 3,615,735, U.S. Patent No. 3,615,737, U.S. Pat.

No. 635,758, U.S. Patent 3,650,777, U.S. Patent 3,663,242, U.S. Patent No. 3,959,531, U.S. Patent No. 4,124,399. These patent documents in particular address the stability requirements of the bath. , preferably while maintaining a sufficiently high copper deposition rate and high deposit quality. In addition to the choice of a complexing agent for copper, the subject-matter of these patents is, in particular, various additives intended to favorably influence the physical properties of the deposited copper or the stability of the bath in terms of copper ballast deposition, or both. The most common additives are alkali metal cyanides or complex cyanides (ferri-, ferro-), organic acid nitriles, inorganic and organic thio compounds, metal compounds VIII. groups of the Periodic Table of the Elements, compounds of the elements that may exist in several oxidation states, organic polymers (eg poly (ethylene oxide), poly (vinyl alcohol), poles (vinylpyrrolidone)), 2,2'-bipyridyl or 1,10-phenanthroline; or related substances forming stable complexes with Cu ions and others.

E.g. U.S. Pat. No. 3,615,732 discloses a combination of small amounts of cyanide compounds of element VIII as an additive improving deposit quality and bath stability. groups of the periodic system, some polyvalent elements (V, Nb, Mo, W, As, Sb, Bi, rare earths) and compounds forming addition compounds with formaldehyde. In U.S. Pat. No. 3,615,635, in addition to the addition of various types of organic polymers, the addition of a combination of small amounts of organosilicon compounds, compounds of certain metals VIII is claimed. groups and substances forming addition compounds with formaldehyde (sulphite, phosphite). U.S. Pat. No. 3,663,242 claims the addition of small amounts of mercury salt in combination with an inorganic cyanide or organic nitrile or a low molecular weight alkyne. U.S. Pat. No. 3,492,135 discloses copper for stability

CS 271 560 31 the bath claimed the addition of some of several dozen selenium compounds, mostly organic, in which the selenium is in the formal oxidation state of -1 or -2 ”.

Despite undeniable technical progress, the above-mentioned baths are not ideal; many do not produce sufficiently thick layers, their copper speed is too slow, or they do not produce a copper coating suitable for further processing and, above all, are difficult to operate for a long time.

These drawbacks are addressed by a chemical electroless copper bath consisting of an aqueous solution containing 0.025 to 0.085 mol / l of soluble copper salt, such as sulfate, nitrate or acetate, 0.10 to 0.45 mol / l of formaldehyde or an equivalent amount of paraformaldehyde, 0.04 to 0.2 mol / L complexing agent type 1,1,1 * 1 '', 1 '- (1,2-ethanediidinitrilo) tetraethanol or 1,1', 1 '', 1, '''- (1,2 -etandiyldinitrilo) of tetrakis (2-propanol), followed by concentration 5.1O _"5, z 2.1О" ⁴ mol / 1 N Ν'1,2-ethanediylbis / N- (carboxymethyl) glycine / or trans-Ν, Ν (1,2-cyclohexanediylbis / N- (carboxymethyl) glycine), respectively. their disodium salts, and up to 1.10 ' ⁴ mol / l of water-soluble mercury salts, such as chloride, nitrate, sulphate, acetate,

1.10 ^J to 1.10 mol / l of an aliphatic alpha-hydroxy acid, eg glycolic, lactic, tartaric, malic acid, 0.2 to 5 g / l of polyethylene oxide with an average molecular weight of 2,000 to 6,000 and traces of up to 5 g / l surfactants selected from the group of alkylsulfonates or phosphates of oxyethylated aliphatic alcohols, traces up to 1.10 ⁴ mol / l alkali metal cyanide, traces up to 0.8 mol / l methanol or traces up to 1.10 & mol / l soluble compounds from the chloride group palladium, chloroplatinic acid, chloroplatinate, chloroplatinate, alkali metal chlorolatate, according to the invention, comprising the addition of 1.10-4 to 5 · 1Ο- ⁴ mol / l of compounds of the group selenocyanatortutate, selenocyanatopalladenate, selenocyanatoplatnate, selenocyanate in a selenocyanate with 1.10 to 1.10 m 1/1 of a substance selected from the group

2,2'-bipyridyl, 2,2'-bichinolyl, 1,10-phenanthroline, 4,7-diphenyl-1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline, 2,9-dimethyl- 4,7-Di-phenyl-1,10-phenanthroline.

This electroless copper-free chemical bath meets the technical requirements of modern copper coating technology and, above all, the requirements for good forging of openings of double-clad plates. This bath is characterized by a sufficient rate of copper deposition within the broad concentration limits of the constituent components, the deposit deposit complies in all respects with the standard requirements and the bath is stable over a wide temperature range even with prolonged use and repeated refilling of depleted bath components.

The advantage of the bath is that it consists of commercially available components and its composition allows the user parameters to be adjusted to meet the technological requirements for bath stability and copper deposition rate, while maintaining the required physical properties of the deposit. The operating parameters of the bath can also be influenced by the addition of some low molecular weight aliphatic alcohols. E.g. the addition of methanol significantly affects the degree of utilization of the reducing agent used to remove copper from the bath; addition of isopropanol improves the solubility of some components.

The following examples illustrate the composition of the bath according to the invention and its coppering ability without limiting or limiting the invention. In all cases, a 1.5 mm layered dielectric, clad on both sides with 35 yum copper foil in FR 4 quality (a designation that clearly defines the quality of the material used according to the National Electrotechnical Manufacturers Association) was used to prepare the plating samples. without internal conductive layers. The 1 mm hole frequency was approximately 335 / dm. Plates of approximately 37 x 45 mm were prepared from this material. Copper baths of different compositions were prepared as specified in the following examples. The area of the plating plates was chosen so that the bath load was in the range of 1.0 to 2.0 dm / l. Plates were pre-etched, degreased and activated by a conventional procedure.

CS 271 560 Bl

Example 1

Copper bath containing

CuSO ₄ .5H ₂ O

1,1 *, 1 * \ 1,1 '- (1,2-ethanediidinitrilo) -tetrakis (2-propanol)

NaOH formaldehyde tartaric acid poly (ethylene oxide) m.v. 2000

N, N '-1,2-ethanediylbis N- (carboxymethyl) glycine, disodium salt

KCN

HgCl ² mixture of acidic oxyethylated aliphatic phosphates

0.085 mol / l bath

0.20 mol / l

0.45 mol / l

0.15 mol / l

0.01 mol / l

5.0 gl / l

5.10 " ⁵ mol / l

1.10 ^-4 mol / l

1.10 ⁴ mol / l a

of alcohols C 1 to C 2

PdCl ₂

K ₂ (Pt / SeCH / ₃ )

1,10-phenanthroline i-propanol

2.5 g / l

1.10 ^{- 6} mol / l

5.10 ^{- 4} mol / l

1.10 ^{- 3} mol / l

1.6.10 ^{- 2} mol / l methanol 0.044 mol / l was tempered to 40 + 1 ° C. The movement of goods in the bath was ensured in the usual manner. After 20 minutes of exposure, the layer thickness of the deposit on the surface of the copper foil was 2.3 to 2.9 µm, in the holes 2.9 to 3.4 µm. The deposited coating was salmon pink, ductile and hard at the edges of the holes, as shown by subsequent grinding.

Example 2

Bath containing

CuSO ₄ -5 H ₂ O

1,1 ', 1,1 (1,2-ethanediaminitrilo) tetrakis (2-propanol)

NaOH formaldehyde lactic acid poly (ethylene oxide) mw 6 000

Ν, Ν'-1,2-ethanediylbis (N- (carboxymethyl) glycine), disodium salt

Hg _{(NO3) 2}

K ₂ Birds ₄

Na ₂ / Rh (SeCN) ₆

K ₂ / Hg (SeCH) ₃ /

2,2-bipyridyl

0.055 mol / l

0.087 mol / l

0.35 mol / l

0.14 mol / l

5.10 ^{- 3} mol / l

3.25 g / l

7.5.10 ^{- 5} mol / l

2.5.10 ^{- 6} mol / l 5.10 “ ⁷ mol / l

5.10 ^{- 4} mol / l

1.10 ^{- 6} mol / l 8.10 - ⁵ mol / l i-propanol

0.016 mol / l methanol 0.05 mol / l was tempered at 45 and 1 ° C · After 35 minutes of exposure, the layer thickness of the deposit on the surface of the copper foil was 1.5 to 1.8 µm, in the openings 2.2 to 2, 9 / Um. The coating properties were the same as in Example 1.

Example 3

Bath containing

CuSO ₄ .5H ₂ O

1,1 ', 1,1- (1,2-ethanediidinitrilo) tetraethanol

NaOH paraformaldehyde glycolic acid

0.025 mol / l bath

0.040 mol / l

0.1 mol / l

2.6 g / l

1.10 ^-3 mol / l

CS 271 560 B1 poles (ethylene oxide) MW 60,000

Sodium Ν, Ν-1,2-ethanediylbis (N- (carboxymethyl) glycine), sodium dodecylsulfonate disodium salt

H ₂ PtCl ₆ .2H ₂ O

K ₂ (Pd / SeCN / ₄ )

4,7-Diphenyl-1,10-phenanthroline

0.2 g / l.

4.10 ^{- 3} mol / l 7.10 ⁵ mol / l

1.4.10 ^{- 3} mol / l

5.10 ^{- 7} mol / l

1.10 ⁶ mol / l

1.10 ^{- 5} mol / 1-propanol, and 0.016 mol / 1 was placed at 38 ± 1 ° C. After 50 minutes of exposure, the thickness of the deposit layer on the surface of the copper foil was 0.6 to 1.1 µm, in the openings 0.9 to 1.3 µm. The coating properties were similar to those in Example 1 and suitable for further processing after galvanic crosslinking.

Example 4

Bath containing

CuSO..5H _about 0 ² 4 ZZ ZZZ

1,1,1,1- (1,2-ethanediyldinitrilo) tetrakine (2-propanol)

NaOH formaldehyde malic acid poly (tylene oxide) m.w. 20 000 trans-N, N 1,2-cyclohexanediylbis (N- (carboxymethyl) glycine), disodium salt

NaGN

KAuCl ₄

Na ₂ (Rh / SeCN / ₆ )

2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline i-propanol

0.057 mol / l bath

0.084 mol / l

0.35 mol / l

0.14 mol / l

З.Ю ^-3 mol / l

1.80 g / l

5.Ю ⁴ mol / l

1.10 ^{- 4} mol / l

1.10 ⁴ mol / l

2.10 ^{- 6} mol / 1

8.10 ^{- 5} mol / 1

0.016 mol / l methanol 0.8 mol / l was tempered to 35 and 1 ° C. After 25 minutes of exposure, the layer thickness of the deposit on the surface of the copper foil was 1.0 to 1.3 µm, in openings 2.1 to 2.5 µm. The coating properties were the same as in Examples 1 and 2.

Example 5

Copper acetate bath 0.045 mol / l 1,1 /, 1 ^, 1 ^- (1,2-ethanediindinitrilo) ethanol tris (2-propanol) 0,080 mol / l NaOH 0,30 mol / l paraformaldehyde lactic acid poly (ethylene oxide) mv 4 000 trans-N, N ^Z -1,2-cyclohexanediylbis (N-carboxymethyl) glycine), disodium salt

Hg (ciop ₂

K ₂ Pt (CN) g

Na ₂ / Rh (SeCN) ₆

Na ₂ / Hg (SeCN) ₄ /

2,2-quinolyl

KCN

3.20 g / l

8.10 ^{- 3} mol / l

2.50 g / l

7.5.10 ^{- 5} mol / l

2.5.10 ^{- 6} mol / l 5.10 ⁷ mol / l

5.10 ^{- 4} mol / l

1.10 ^{- 6} mol / l

5.10 ^{- 5} mol / 1 ^e

1.10- ⁵ mol / 1-propanol, and 0.035 mol / 1 methanol, 0.08 mol / 1 was placed at 39 ° C X 1. After 25 minutes exposure of the goods in the bath, the thickness of the deposit layer on the surface of the copper foil was 0.9 to 1.3 µm, in the openings 2.1 to 2.4 µm. The deposit properties were the same as in Examples 1, 2 and 4.

Claims (1)

SUBJECT OF THE INVENTION A current-free copper bath consisting of an aqueous solution containing 0,025 to 0,085 mol / l of soluble copper salt, eg sulphate, nitrate or acetate, 0,10 to 0,45 mol (1 formaldehyde or equivalent amount of paraformaldehyde, 0,04 to 0, 2 mol / l of a complete reagent of 1,1 ', 1,1 *' - (1,2-ethanediyldinitrilo) tetraethanol or 1,1 ', 1,1''- (ethanediyldinitrilo) tetrakis (2-propanol), 5-10'5 further concentration _to 2.10 "4 _Mo i / i N, ^from -l, 2-ethanediylbis / N- (carboxymethyl) glycine / or trans-N, N'-l, 2-cyklohexandiylbis / N (carboxymethyl) glycine / or. their disodium salts, and from traces up to 1.10 "^ mol / 1 soluble rtuínaté or mercuric salts (e.g. chloride, nitrate, sulphate, acetate), 1.10 ^'3 to 1.10" ² mol / 1 aliphatic .alpha. -hydroxy acids, e.g. glycolic, lactic, tartaric, malic acids, further 0.2 to 5 g / l of polyethylene oxide with an average molecular weight of 2,000 to 60,000, traces of up to 5 g / l of a surfactant selected from the group consisting of of alkylsulfonates or phosphates of oxyethylated aliphatic alcohols, traces up to 1.10 mol / l alkali metal cyanide, traces up to 0.8 mol / l methanol or traces up to 1.10 mol / l of soluble palladium chloride, chloroplatinic acid , chloroplatinate, chloroplatnatan, tetrachloroaurate alkali metal, characterized in that it comprises the addition of 5.10 g 1.10'6 _and "^ mol / 1 compounds from the group selenokyanátortutnatan, selenokyanátopalladnatan, selenokyanátoplatnatan, selenokyanátorhoditan alkali metal in combination with 1.10 to 1.10 ^" ³ mol / 1 substances selected from the group of 2,2'-bipyridyl, 2,2'-bichinolyl, 1,10-phenanthroline, 4,7-diphenyl-1, 10-phenanthroline, 2,9-dimethyl-1, 10-phenanthroline, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline.