Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2002-08-16
2004-06-22
Sterrett, Jeffrey (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S037000, C363S071000
Reexamination Certificate
active
06754090
ABSTRACT:
This invention relates to a power supply apparatus for use in electroplating, for supplying current to a load including an object to be plated, an electrolytic solution and electrodes, to thereby plate the object. (In this specification, this type of power supply apparatus is referred to as electroplating power supply apparatus, and the load is referred to as plating load.)
BACKGROUND OF THE INVENTION
In electroplating, it is known to invert, at a high speed, the polarity of current supplied to a plating load. When current with the positive polarity is being supplied to the plating load, plating takes place, and when the current of the negative polarity is being supplied to the load, the plating is interrupted or part of the metal forming a plated layer is dissolved back into the electrolyte solution, whereby crystals forming the plated layer are made finer so that the object can be uniformly plated.
When a multi-layered printed circuit board
2
, like the one shown in
FIG. 1
, is plated, some problems have happened. The multi-layered printed circuit board
2
includes substrates
2
a
and
2
b
, for example, on which electronic components are integrated to a high density. The circuit board
2
are provided with a number of through-holes like a through-hole
4
, and a number of via-holes, like a via-hole
6
. As the number of layered substrates is larger, the difference in thickness between plated metal layers on an edge
4
E and an inner wall
4
IN of the through-hole
4
becomes larger, resulting in non-uniform plating. In other words, it is difficult to uniformly plate the through-holes
4
. Similarly, as the number of substrates increases, the difference in thickness between plated metal layers on an edge
6
E and an inner wall
6
IN of the via-hole
6
becomes larger, which results in non-uniform plating. It has been found that in order to form a plated metal layer uniform in thickness over the entire surfaces of the substrates
2
a
and
2
b
, it is necessary to make a negative-polarity plating current of sufficiently larger magnitude flow for a shorter time period than a positive-polarity plating current.
In Japanese Patent Application No. HEI 10-281954 on Sep. 17, 1998 (Japanese Patent Application Publication No. 2000-92841), inventors including one of the inventors of the present invention proposed an electroplating power supply apparatus which supplies current having a polarity inverted at intervals of, for example, from 5 to 20 milliseconds, to a plating load, to thereby form a layer of uniform thickness over a plating load including a plurality of substrates, such as a multi-layered printed circuit board. The apparatus of this Japanese patent application is shown in FIG.
2
.
The power supply apparatus shown in
FIG. 2
includes DC power supplies
10
a
and
10
b
, voltage-boosting converters
16
a
and
16
b
, and choppers
22
a
and
22
b
, for supplying a plating load
24
with current alternating between positive and negative polarities. The voltage-boosting converter
16
a
includes a reactor
12
a
and an IGBT
14
a
, and the voltage-boosting converter
16
b
includes a reactor
12
b
and an IGBT
14
b
. The chopper
22
a
includes a reverse current blocking diode
18
a
and an IGBT
20
a
, while the chopper
22
b
includes a reverse current blocking diode
18
b
and an IGBT
20
b
. The IGBTs
14
a
,
14
b
,
20
a
and
20
b
are controlled by a controller
26
.
For example, when the IGBTs
20
a
and
14
b
are nonconductive and the IGBTs
20
b
and
14
a
are conductive, current flows through the DC supply
10
a
, the reactor
12
a
and the IGBT
14
a
, resulting in storage of energy in the reactor
12
a
. At the same time, a negative current is supplied to the plating load
24
from the DC supply
10
b
, through the reactor
12
b
, the diode
18
b
and the IGBT
20
b.
Then, the IGBTs
20
a
and
14
b
are rendered conductive and the IGBTs
20
b
and
14
a
are rendered nonconductive, a positive current flows from the DC supply
10
a
through the reactor
12
a
, the diode
18
a
and the IGBT
20
a
to the plating load
24
to plate an object to be plated. In this case, because of the turning off of the IGBT
14
a
, the voltage based on the energy stored in the reactor
12
a
is superposed on the voltage supplied by the DC power supply
10
a
, resulting in rapid change of the negative current flowing to the plating load
24
to the positive current. At the same time, energy is stored in the reactor
12
b
because the IGBT
14
b
is conductive.
Then, the IGBTs
20
a
and
14
b
become nonconductive again, with the IGBTs
20
b
and
14
a
rendered conductive, a negative current is supplied to the plating load
24
from the DC power supply
10
b
through the reactor
12
b
, the diode
18
b
and the IGBT
20
b
. In this case, too, the voltage generated in the reactor
12
b
is superposed on the voltage supplied by the DC power supply
10
b
, so that the change from the positive current to the negative current is rapid.
In this way, current with alternating polarity is supplied to the plating load
24
, and a multi-layered printed circuit boards with through-holes and via-holes can be plated with a layer of a uniform thickness.
The power supply apparatus described above requires separate DC power supplies
10
a
and
10
b
for positive and negative currents. Also, it requires, in addition to the IGBTs
20
a
and
20
b
used to switch the main current, the auxiliary IGBTs
14
a
and
14
b
for inverting the load current at a high speed, which makes the circuit arrangement complicated, which, in turn, leads to increase of the cost of the electroplating power supply apparatuses.
In order to downsize the electroplating power supply apparatus, the DC power supplies
10
a
and
10
b
are downsized by arranging them to rectify a commercial AC signal, convert the resulting rectification output to a high-frequency signal in an inverter, and transform and rectify the high-frequency signal to a DC signal.
The value of commercial AC power supply voltage differ from country to country or from area to area. Therefore, in electroplating power supply apparatuses for use in countries or areas where AC commercial power supplies provide a “400 V group” voltage, i.e. a voltage of from 380 V to 460 V, the DC power supplies
10
a
and
10
b
require an inverter including IGBTs which can withstand a voltage resulting from rectifying the “400 V group” AC voltage. However, such IGBTs are not widely available, so they are expensive, leading to increase of the cost of the power supply apparatuses.
An object of the present invention is to provide an inexpensive power supply apparatus for use in electroplating, which can provide uniform electroplating.
SUMMARY OF THE INVENTION
An electroplating power supply apparatus according to the present invention includes an input-side rectifier for rectifying a commercial AC signal. The output signal of the input-side rectifier is converted to a high-frequency signal in a DC-to-high-frequency converter. A chopper or an inverter may be used as the DC-to-high-frequency converter. A plurality of DC-to-high-frequency converters may be used, being connected in series. When a plurality of DC-to-high-frequency converters are used, they are connected in series. The high-frequency signal outputted by the DC-to-high-frequency converter is transformed in a transformer. The number of transformers is equal to the number of the DC-to-high-frequency converters. When plural DC-to-high-frequency converters are used, the same number of transformers are used being connected in parallel.
A first output-side rectifier is connected between the transformer and a load to rectify a transformed high-frequency signal provided from the transformer in such a way that a positive polarity current can be supplied to the load when the transformed high-frequency signal is positive in polarity. A second output-side rectifier connected in parallel with the first output-side rectifier rectifies the transformed high-frequency signal of negative polarity so that a negative polarity curren
Arai Toru
Nishioka Yoshiyuki
Sakurada Makoto
Duane Morris LLP
Sansha Electric Manufacturing Company Limited
Sterrett Jeffrey
LandOfFree
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