Bell Telephone Laboratories

At&t Bell Laboratories

At+t Corp.

American Telephone & Telegraph Co., At&t Bell Laboratories

Craig G Smith

Yutaka Okinaka

Sudarshan Lal

Lawrence Edwin Smith

Harvey S Trop

Mary J Mitchell

Alfred J Grady, Jr

Chwan-Tsann Wang

Disclosed is a method of monitoring electroless plating solutions. The solutions are used to plate a light-transmitting medium. Measurements are made to determine the time it takes for light transmission through the medium to be reduced to a certain level. This measurement can be used to determine whether articles will be sufficiently plated by the solutions.

Monitoring electroless plating baths

This invention is a process for etching copper sheets on insulating boards for use in fabricating multilayer printed circuit boards. The improvement resides in adding to a standard copper etching solution certain alkyltrimethyl ammonium chlorides with alkyl chain lengths ranging from 6 to 20 carbon atoms in amounts sufficient to yield intermediate kinetics behavior. Of special interest are dodecyltrimethyl ammonium chloride, hexadecyltrimethyl ammonium chloride and octadecyltrimethyl ammonium chloride present in an amount of from 0.01 to 1.0 wt %. A silicon-based antiforming agent may be added in amounts of from 0.05 to 2.0 wt. % to prevent an unacceptably large amount of foam from occurring during etching. With this formulation, the rate is mass transport controlled at low rates and almost independent of mass transport at high rates due to the inhibition of the surface reaction rate. As a result, non-uniformities in etch rates due to variations in mass transport conditions in processing equipment may be eliminated. This unique formulation could significantly improve the yields presently obtained in manufacturing as well as allow the processing of fine-line multilayer circuit boards.

Uniformity of copper etching in the fabrication of multilayer printed

Processes are described in which solution composition is monitored by extremely accurate measurements of index of refraction involving measurement of reflectivity from a glass-solution interface. A particularly useful application is the swelling operation in metallizing polymer surfaces where dimethylformamate-water solution is contacted with the polymer surface to produce the swelling. Accurate, continuous control of the solution composition is necessary to insure optimum amount of swelling.

Solution monitoring procedure

The invention comprises improvements in inert anode electroplating processes that make possible the utilization of typically inexpensive and otherwise advantageous cation-yielding compounds for replenishing the plating bath, compounds that typically are not well suited for such use in prior art systems due to their relatively low dissolution rate which typically requires their use in powder form, and the tendency of the powder particles to aggregate. Exemplary applications for the improved plating process are in Cu-, Ni-, and Pd-plating, and exemplary cation-yielding compounds or CuO, NiO, PdO, Cu(OH).sub.2,Ni(OH).sub.2, and Pd(OH).sub.2. The improvements according to the invention comprise agitating the powder/electrolyte mixture or slurry in a reactor vessel separate from the plating tank, and maintaining the cation concentration in the plating tank within predetermined limits. Agitation typically requires power input to the slurry of at least about 2.5 watt/liter of slurry, with a preferred range of power for CuO of about 10 .mu.m average particle size and concentration between about 5 and about 200 gram/liter being between about 5 and about 200 watt/liter of slurry. Schemes for maintaining the cation concentration in the plating bath within predetermined limits are described, and include controlling the rate of addition of cation-yielding compound to the slurry, and/or controlling the flow rate of electrolyte between reactor and plating tank.

Electroplating process with inert anodes

A copper electroplating process is described in which the anode is surrounded by a cation-permeable membrane so as to prevent decomposition of additives in the electrochemical bath. Such a feature adds to bath lifetime and permits better control of bath chemistry and plating quality during the electroplating process. The feature is especially advantageous for copper electroplating processes using nonconsumable electrodes because of the high consumption of additives and that the copper can be added to the cathode side of the membrane so that acid copper ions need not pass through the membrane.

Copper electroplating process

In traditional copper electroplating processes, soluble copper anodes are used as the source of copper. There are certain potential advantages to using nonconsumable anodes and adding a source of copper such as copper oxide to replenish the electroplating bath. Periodic reverse current plating is used by some manufacturers to obtain smoother deposits without the use of additives. This periodic reversal of current drastically reduces the service life of the nonconsumable anodes because of dissolution of the metal oxide on the insoluble anode. The invention is a copper electroplating process with a dual-element anode assembly. This assembly consists of electrically isolated copper and metal-oxide electrodes. The metal-oxide electrode is active only during the anodic part of the cycle while the copper electrode is active only during the cathodic part of the cycle. Electrical isolation is achieved by the use of diodes or relays.

Copper electroplating procedure

A process is described for the electrodepositon of copper on various surfaces. The process involves use of a nonconsumable counterelectrode. Of particular significance is the composition of the surface of the counterelectrode. The surface of the counterelectrode comprises iridium oxide and tantalum oxide. Such processes can be carried out at high speeds, with smaller and more efficient equipment and can use various copper compounds as a source of copper.

Copper plating procedure

A particular type of electrode structure is described which is useful as a counter electrode in gold plating processes. The electrode surface comprises oxides of certain group eight elements and oxides of certain valve metals. A process for preparing the electrodes is also described. Such electrodes or anodes exhibit long life and reduced undesirable side reactions in the gold plating process. For example, consumption of buffer material is greatly reduced and formation of trivalent gold is reduced.

Electrolytic gold plating

An electrochemical process is described in which a particular kind of electrode is used. The electrode surface is made up of certain types of oxides. A process for preparing the electrodes is also described. Such electrodes exhibit long life and are highly efficient in that reduced electropotential is observed. This property is particularly advantageous in that it reduces power consumption for the electrochemical process and reduces undesirable side reactions in the electrochemical process. Particular processes where this electrode is useful are electrodeposition of metals such as gold, copper, nickel, and palladium, the production of chlorine and oxygen by electrolysis, electrolytic loading of electrodes for batteries, and production of electricity in fuel cells.

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North Plainfield, NJ, United States of America

Craig G Smith