Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1999-11-30
2001-05-01
Bell, Bruce F. (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S230500, C204S230800
Reexamination Certificate
active
06224721
ABSTRACT:
TECHNICAL FIELD
The invention relates to an electroplating apparatus and, in particular, to an electroplating apparatus having a particular configuration of its anode and cathode.
BACKGROUND OF THE INVENTION
One important step in the manufacture of printed circuit boards is the plating of conductive material (typically, e.g., copper) onto a substrate to provide the desired circuit paths for the board. Usually the circuit board substrate will include holes extending through the thickness of the board. When plated, the holes connect the traces on one side of the board to traces on the other side of the board.
As electronic components get smaller, and the circuit traces on circuit boards get thinner (so as to provide more circuit density on a board), it becomes desirable to make the diameter of holes also proportionately smaller. As the size of the holes decrease, however, difficulties arise in obtaining the desired thickness of the copper plating within the hole. That is, the thickness of the copper deposited inside the holes tends to decrease (in comparison to the thickness deposited on adjacent circuit traces on the surface of the circuit board) as the hole diameter decreases.
This problem is fairly well-known, and one solution that is commonly employed to improve plating results is employing reverse pulsed DC power. In this technique, a DC current of, e.g., a few volts and about 300 amps is applied in the forward direction for, e.g., a few milliseconds, and then is reversed, typically at a higher amperage (e.g., about 900 amps) for a shorter time (e.g., a few microseconds). This pulsing has the effect of increasing the amount of material plated within the holes. With such rapid pulsing, however, inductance in the system prevents the actual waveform from being as square as would be desirable. That is, once current reversal is initiated, it takes some time to build the reverse current—this time is effectively wasted, and becomes a limiting factor on the frequency at which polarity reversal can be accomplished (higher frequencies being more effective and, therefore, desired). Thus, it is desirable to reduce the inductance in the overall system.
There are practical physical limitations on the configuration of plating systems, however. For example, in many plating line installations, the power supplies are mounted at one end of the plating tanks. Manufacturers prefer to have both ends of the anodes and cathodes supplied with current in an attempt to ensure even electrical distribution. This creates a problem in that one end of the anode may be, e.g., five feet from the power supply while the other end may be twenty feet away. The runs of cable to each end must be of the same length, however; if one were shorter than the other, it would have less resistance (a significant issue when working voltage is only a few volts), producing an uneven distribution of voltage on the anode and cathode and potentially overheating the shorter cable. The typical solution to this problem is to make both cables of the same length and simply coil the excess length of the cable that connects to the near end of the tank. Such lengths of cable, however, increase the inductance of the system, and therefore reduce the effectiveness of the reverse pulse technique.
SUMMARY OF THE INVENTION
The invention provides an electroplating apparatus that eliminates the excess lengths of cables and reduces the overall impedance of the plating system, substantially improving the plating performance of the system. The apparatus includes an elongated, hollow conductive anode tube having first and second ends, an inner conductive surface, and an outer conductive surface from which sacrificial plating metal may be suspended. An elongated cathode conductor is disposed within the hollow conductive anode tube, the cathode conductor having first and second ends, corresponding to the first and second ends of the anode tube, and an outer conductive surface. An insulation layer is placed between the outer surface of the cathode conductor and the inner surface of the anode tube. Positive and negative cables respectively connect the power supply to the first end of the anode tube and the first end of the cathode conductor, and a conductive jumper connects the second end of the cathode conductor to an elongated cathode bar, from which articles to be plated may be suspended.
By placing the cathode conductor within the anode tube, the far end of the cathode can be connected to the power supply without the need to string cables for the length of the plating tank, and the co-axial relationship of the cathode conductor within the anode tube reduces inductance within the system over this portion of the electrical distribution system.
REFERENCES:
patent: 488708 (1892-12-01), Craney
patent: 3065153 (1962-11-01), Hough et al.
patent: 3470082 (1969-09-01), Raymond et al.
patent: 3880725 (1975-04-01), Van Raalte et al.
patent: 4294670 (1981-10-01), Raymond
patent: 4461690 (1984-07-01), Rolff et al.
patent: 4490230 (1984-12-01), Fletcher
patent: 4828654 (1989-05-01), Reed
patent: 4871435 (1989-10-01), Denofrio
patent: 4933061 (1990-06-01), Kulkarni et al.
patent: 4964964 (1990-10-01), Murphy
patent: 5024732 (1991-06-01), Hübel
patent: 5049246 (1991-09-01), Hull et al.
patent: 5156730 (1992-10-01), Bhatt et al.
patent: 5281325 (1994-01-01), Berg
patent: 5439567 (1995-08-01), Cook
patent: 5441619 (1995-08-01), Kawachi et al.
patent: 5558757 (1996-09-01), Hübel
patent: 5788829 (1998-08-01), Joshi et al.
Maslach Tadeusz
Nelson Glenn M.
Bell Bruce F.
Fredrikson & Byron , P.A.
Nelson Solid Temp, Inc.
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