Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Depositing predominantly single metal coating
Reexamination Certificate
2000-07-28
2002-07-30
Mayekar, Kishor (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Depositing predominantly single metal coating
C205S296000, C205S291000
Reexamination Certificate
active
06425996
ABSTRACT:
DESCRIPTION
The invention relates to an aqueous bath and a method for the electrolytic deposition of copper coatings. The bath can be used both for reinforcing conducting paths on printed circuits and for producing decorative coatings, for example on sanitary appliance and automobile parts.
The addition of organic additives to acid, especially sulphuric, electrolytic copper baths has been known for a long time. By this means, the decorative and functional properties of the copper coatings can be controlled. Above all, brightening agents are added to the baths in order to obtain bright layers. Numerous compounds and mixtures of compounds used for this purpose, for example thiourea, gelatine, molasses, coffee extract, “basic” dyes and thiophosphoric acid ester, do not have any practical significance any more since the quality of the copper coatings obtained with these compounds do not meet today's requirements. For example, with these additives no uniformly bright layers can be obtained and no layers with sufficiently high breaking elongation.
The best copper-plating baths known at this time contain as additives generally a mixture of polyethers and organic, especially aromatic thio compounds. Such a mixture is known from DE-OS 15 21 062. According to this document, the copper-plating bath can also contain phenazine dyes.
Furthermore, in DE-AS 12 46 347, the use of polyalkylenimines together with organic thio compounds was proposed for electrolytic copper-plating.
The baths mentioned do not however lead to copper layers with satisfactory properties: the layers are not uniformly thick on the frequently complexly shaped workpieces. Moreover these baths also level irregularities on the surface of the substrates to be coated to a varying extent. For this reason, copper coatings deposited from these baths do not have any uniform appearance. The functional properties are also not easily controllable.
To improve the deposition baths, in DE-OS 20 39 831 a sulphuric copper bath is described which in addition to a polymer compound containing oxygen and a thio compound with functional groups to increase water a s solubility, contains at least one dye from the group of polymeric phenazonium compounds. These baths can furthermore contain non-ionic wetting agents and organic sulphur compounds.
In EP 0 071 512 A1 is described a copper-plating bath which contains the dye crystal violet in addition to the potassium salt of N,N-diethyldithiocarbamate-S-&ohgr;-propylsulphonate.
In DE 34 20 999 A1 is described a bath with organic thio compounds and polyether compounds together with phthalocyanine derivatives and aposafranine compounds.
However it has been shown that, with these baths, especially in the upper current density region high levelling of the copper coating occurs whilst the levelling in the low current density region is relatively small. When the bath is used for the production of printed circuit boards this leads to the so called phenomenon of hole edge flattening in which a reduction in the copper layer thickness in the immediate proximity of bores in the printed circuit boards is observed, such that breaks occur in the copper coating at the hole entrances during soldering. In decorative copper deposition, this disadvantage leads to a non-uniform appearance of the layer at different locations of the workpiece, such that the bath can only be used up to a point for this application.
Instead of dyes, transformation products of polyalkanolamines with an alkylation or quarternisation agent, for example benzyl chloride (U.S. Pat. No. 4,110,176) and of polyalkylenimines with epichlorohydrine and an alkalisation agent (EP 0 068 807 A2) have also been proposed as additives in copper baths. Furthermore, in EP 0 107 109 A2 transformation products of thio compounds with acrylamide are also described.
In U.S. Pat. No. 664,278 is disclosed a copper-plating bath which contains, in addition to the usual bath constituents, transformation products of epichlorohydrine with aromatic compounds containing nitrogen.
Through the addition of these compounds, the levelling of the copper coating can be improved in a lasting manner. However the metal distribution is worsened, that is the uniformity of the layer thickness at different locations of a workpiece, at which also different current densities occur. By this means only layers of non-uniform appearance can be obtained. It has emerged that this disadvantage appears in particular if thio compounds containing nitrogen are used as the additives. Moreover, these compounds only act in the desired manner within a very narrow concentration range, such that during the practical operation of a bath with these compounds, the optimal concentration range can frequently not be maintained. For example, on increasing the concentration by several milligrams per liter above the upper concentration limit, already hole wall flattenings occur on printed circuit boards, such that the printed circuits get cracks during subsequent soldering and become unusable.
In DE 27 46 938 A1 is described a bath which contains as additives inter alia acid amides together with a high-molecular compound containing oxygen and an organic thio compound with functional groups to increase the water solubility. With this bath only an improvement of the distribution of the brightness could be achieved, but not an improvement of the metal distribution.
The high-molecular compounds containing oxygen usually used as additives in electrolytic copper baths only have low stability. They decompose when used on the electrodes to polymers which are insoluble in the bath and which accumulate in the bath. These undesired reaction products cream out as a gelatinous mass on the container walls and are even deposited on the surfaces of the items to be treated, such that defects are formed on the item to be treated and it therefore becomes unusable. Particularly at increased bath temperatures the decomposition is accelerated, such that very quick decomposition is observed at temperatures above 28° C.
It has also become apparent that the additives mentioned frequently lead to a worsening of the mechanical properties, in particular the hardness and the breaking elongation of the copper coatings, compared with deposition methods in which these additives are not used. Equally the layers deposited with these substances have signs of passivity, which require subsequent activation for further treatment by electroplating means. Moreover many of these types of substances, which act as inhibitors for the copper deposition, worsen the metal dispersion, such that on account of low metal layer thickness in places, cracks occurs in bores and hole edges on printed circuit boards, especially if the copper layer is thermally stressed by soldering processes.
Moreover, from U.S. Pat. No. 3,502,551 is known an aqueous acid copper bath which contains at least one copper salt, at least one inorganic acid and possibly a chloride and, as additives, an aliphatic hydrocarbon compound having a plurality of amino groups, a high-molecular organic compound containing oxygen and, to increase the water solubility, an organic thio compound with functional groups. Through the combination of these additives, the brightening and levelling of the deposited copper layer is intended to be improved.
Furthermore, from DE 27 06 521 A1 copper electrolytes are known which contain transformation products of epihalohydrins with substituted pyridines, organic thio compounds and wetting agents as bath additives. With this bath, an improvement of the distribution of brightness could be achieved but not any improvement in the metal distribution however.
The two last-mentioned types of baths have the disadvantage of poor metal dispersion. Uniform distribution of metal is however necessary, particularly in the metallisation of printed circuits which have a large number of small bore holes. If a layer of too small a thickness is deposited in these bores, it tears under thermal stress, for example during soldering, such that the passage of current is interrupted.
Dahms Wolfgang
Jonat Michael
Nitsche Detley
Senge Gerd
Atotech Deutschland GmbH
Mayekar Kishor
Paul & Paul
Tran Thao
LandOfFree
Water bath and method for electrolytic deposition of copper... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Water bath and method for electrolytic deposition of copper..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Water bath and method for electrolytic deposition of copper... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2832325