Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Depositing predominantly single metal or alloy coating on...
Patent
1999-06-02
2000-10-10
Gorgos, Kathryn
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Depositing predominantly single metal or alloy coating on...
205125, C25D 518, C25D 502
Patent
active
061298301
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a process to electrolytically deposit copper layers within a short preparation time, especially in the manufacture of printed circuit boards.
There are various requirements for copper deposits on printed circuit boards: On the one hand, the copper layers must satisfy certain requirements regarding material properties. For example, they cannot form any cracks when subject to thermal shock (immersed at least once for 10 sec. in liquid tin/lead solder at 288.degree. C.). In addition, the copper layers must be bright, smooth, and as uniformly thick as possible at all locations of the coated surfaces. In addition, the deposition procedure must be easy to manage and economical.
Copper anodes that decompose during electrolytic deposition are normally used in electrolytic copper deposition. These anodes are in the form of plates, bars or spheres. The plates and bars are connected to the power supply with suitable fastening means. The spheres come in specially-made baskets that usually consist of titanium, and these are connected to the power supply with suitable fastening means.
Since these anodes decompose at approximately the same rate during deposition as the copper is deposited from the deposition bath, the amount of copper in the deposition solution remains approximately constant. It is therefore unnecessary to replenish the deposited copper.
The electrolytically deposited layers are given specific material properties by feeding slight amounts of additives to the deposition bath. These are primarily organic substances, small amounts of which are usually consumed under the deposition conditions set for manufacturing printed circuit boards. To maintain the specified qualities, the lost organic additives are correspondingly replenished. However, the additives only slightly improve the throwing power, i.e., the uniform thickness of the copper layer on all the coated surfaces.
Another type of anode is the insoluble anode whose exterior dimensions do not change during the deposition process. These anodes consist of inert metals such as titanium or lead that can be coated with catalytic metals such as platinum to prevent high anodic overvoltages.
When insoluble anodes are used, suitable measures must be taken to maintain the copper ion concentration in the deposition bath, such as adding suitable solutions that contain the copper ions in a concentrated form. A recently-suggested option is to replenish the copper ions by chemically dissolving copper components in a separate treatment container by adding iron(III) ions or other metal ions that oxidize copper (DD 215 589 B5, DD 261 613 A1, DE-P 43 44 387 A1). The iron(II) ions formed by dissolving the copper are reoxidized at the anodes into iron(III) ions, and the solution enriched with copper ions is fed to the substrate to deposit the copper. A stationary equilibrium of the copper ion concentration is set by continuously circulating the deposition solution between the deposition container and the treatment container that contains the copper components. The added iron ions also suppress the oxidative decomposition of the organic compounds that are added to control the material properties of the deposited copper layers. If the baths with insoluble anodes are used without these ions, the compounds decompose very quickly, and useful metal layers cannot be obtained at all.
The process that uses insoluble anodes is complicated and, to maintain the copper ion concentration, requires precise settings for the iron ion concentration, the deposition solution circulation speed, the surface of the copper components and their morphology and other parameters in relation to the selected copper deposition flow. In addition, the additives added to the deposition bath to influence the material properties of the copper layers can decompose at the insoluble anodes if conditions are wrong so that the material properties cannot be reliably attained. In addition, it has also been observed that adding the iron ions harms the uniformity of the copper layer thickness on
REFERENCES:
"Pulse Plating of Copper for Printed Circuit Board Technology", Metal Finishing Apr. 21-21, 1991. M.R. Kalantary and D.R. Gabe, Loughborough University of Technology, Leicestershire, England and M. Goodenough, Lea Ronal (UK) Ltd. Buxton, England. See p. 3, paragraph 2 of the specification.
Dahms Wolfgang
Senge Gerd
Atotech Deutschland GmbH
Gorgos Kathryn
Smith-Hicks Erica
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