Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/18—Electroplating using modulated, pulsed or reversing current
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D7/00—Electroplating characterised by the article coated

Definitions

• the invention relates to a method for generating short, cyclically repeating current pulses with a large current intensity and with a steep slope. Furthermore, it relates to a circuit arrangement for electrolytic metal deposition, in particular for carrying out this method.
• the method is used in the electrolytic metal deposition, preferably in the vertical or horizontal electroplating of printed circuit boards. This type of electroplating is called pulse plating.
• the publication DE 27 39 427 A1 describes electroplating with a pulsating bath current.
• the unipolar pulses have a maximum duration of 0.1 millisecond.
• the pulse time, the pause time and the Pulse amplitude are used to generate these pulses.
• Semiconductor switches here in the form of transistors, are used to generate these pulses.
• the disadvantage here is that the maximum applicable pulsating bath current is limited technically and economically by the use of switching transistors.
• the upper limit is around a few hundred amperes.
• GTO Gate turn off thyristor
• GB-A 2 214 520 which also deals with pulse plating, one embodiment avoids a second bath current source by using mechanical, electromechanical or semiconductor switches to reverse the polarity of the supplied DC voltage.
• the high-current switches required are disadvantageous.
• this system is inflexible because the same current amplitude must be used in both polarities, because with short high current pulses, the amplitude cannot be readjusted quickly enough in the practically available bath current sources. For this reason, a further embodiment in this document also works with two bath current sources that can be set independently of one another.
• bath current sources are connected to the workpiece and the electrode located in the electrolytic cell via a changeover switch. Since it is necessary in the case of printed circuit board electroplating for reasons of the required precision (constant layer thickness) to use individually adjustable bath direct current sources for the front and back of the board, the effort required to implement the method according to this embodiment is thus doubled a total of four bath power sources.
• the electronic high current switches cause large energy losses. A voltage drop occurs at each electronic switch when the internal non-linear resistor is switched on when current flows. This applies equally to all types of semiconductor elements, but with a different voltage drop. This voltage drop, also called saturation voltage or forward voltage U F , increases with increasing current.
• the forward voltage U F is about 1 volt for diodes and transistors and about 2 volts for thyristors.
• a galvanizing system consists of several galvanizing cells. They are fed with large currents of bath.
• a galvanizing system consists of several galvanizing cells. They are fed with large currents of bath.
• a galvanizing system consists of several galvanizing cells. They are fed with large currents of bath.
• a galvanizing system consists of several galvanizing cells. They are fed with large currents of bath.
• a galvanizing system consists of several galvanizing cells. They are fed with large currents of bath.
• a current density is preferably selected which is greater than or equal to the current density which is used with this electrolyte in direct current electroplating.
• a demetallization process takes place with one higher current density than during the cathodic pulse phase.
• the factor 4 of the anodic to the cathodic pulse phase is advantageous.
• the circuit boards are galvanized on both sides, ie on their front and rear sides with separate bath power supplies.
• Five electrolytic baths of a horizontal electroplating system are considered as an example. For example, you have five bath power supply units on each side with a nominal current of 1,000 amperes, ie 10 bath power supply units with a total of 10,000 amperes.
• the bath voltage for electroplating is 1 to 3 volts and is dependent on the current density. Because of the high currents, the energy balance for the circuit proposal in DE 40 05 346 A1 is considered as an example (FIG. 7).
• the semiconductor elements 6, 9, 5 in the circuit arrangement shown in FIG. 7 thus carry the full electroplating current for a period of 10 milliseconds.
• the power loss of these switching elements is per bath power supply with the above-mentioned forward voltages U F of
• the high-current switch power loss of an 11 millisecond cycle is 6,000 watts. With 10 bath power supplies, this results in a power loss of 60 kW (kilo watts). To determine the efficiency, this performance must be compared with the performance that is implemented directly on the electrolytic bath for galvanizing and demetallizing.
• the bath voltages are assumed for acidic copper baths with 2 volts for electroplating and with 7 volts for demetallization.
• the mean value of the total bath power for pulse electroplating is approximately 4.5 kW (for 10 milliseconds 2 volts x 1,000 Amps and for 1 millisecond 7 volts x 4,000 amps). With the losses of 6 kW calculated above, the efficiency of the high-current switch alone, based on the total bath output, is clearly below 50%.
• a galvanizing system equipped in this way with electronic high-current switches works completely inefficiently.
• the technical effort for the electronic switches and their cooling is very large.
• the consequence of this is that such pulse current devices also have a large volume, which prevents them from being placed close to the electrolytic cell.
• the spatial proximity is necessary in order to achieve the required slope of the bath current in the cell at the electrodes. Long electrical conductors counteract a rapid current rise with their parasitic inductances.
• Electromechanical switches have a significantly lower voltage drop when switched compared to electronic switches. Switches or contactors are, however, completely unsuitable for the required high pulse frequency of 100 Hertz. For the technical reasons described, the known pulse electroplating is limited to special applications and preferably to low pulse currents in the galvanotechnical sense.
• the present invention is therefore based on the problem of finding a method and a circuit arrangement with which it is possible to generate short, cyclically repeating unipolar or bipolar pulsed high currents for electroplating without the disadvantages mentioned occurring, especially without being generated with considerable power loss.
• the electronic circuitry required for this should also be implemented at low cost.
• the problem is solved by the invention specified in patent claims 1 and 11.
• the invention consists in that a pulsed current is coupled in such a way that a pulsed current is coupled in a galvanic direct current circuit, or high current circuit for short, comprising a bath direct current source, electrical conductors and an electrolytic cell with the galvanized material and anode by means of a suitable component, for example a current transformer the bath direct current is compensated or overcompensated.
• the component is preferably connected in series with the electrolytic electroplating cell.
• the current transformer secondary winding with a low number of turns is connected in series in the bath DC circuit so that the bath DC current flows through it.
• the current transformer On the primary side, the current transformer has a high number of turns, so that the pulses that feed it can have a low current with a high voltage, depending on the transmission ratio.
• the induced pulsed low secondary voltage drives the high compensation current.
• a capacitor which is connected in parallel to the bath direct current source, serves to close the circuit for the pulsed compensation current.
• FIGS. 1a to 1e unipolar and bipolar electroplating current profiles, as are usually used in practice;
• Figure 2a applies during electroplating and Figure 2b during demetallization;
• FIG. 3 is a schematic representation of the current diagram for the bath current when using the circuit arrangement shown in Figure 2;
• FIG. 4b shows an electrical circuit diagram with entered potentials
• FIG. 5 shows a possible control circuit for the current transformer
• FIG. 6 shows an overall view of the circuit arrangement for use in the electroplating of printed circuit boards.
• FIG. 7 shows a conventional circuit arrangement described in DE 40 05 346 A1.
• a positive bath current should apply to electrolytic metallization, i. H. the material to be treated has a negative polarity with respect to the anode.
• a bath current drawn negatively should apply to electrolytic demetallization. In this case, the material to be treated has a positive polarity with respect to the anode.
• FIG. 1a applies to electroplating with direct current.
• the bath flow is briefly interrupted. However, it remains unipolar, that is, the current direction is not reversed.
• the pulse times are preferably on the order of 0.1 milliseconds to seconds. The break times are correspondingly shorter.
• Figure 1c shows a pulse-shaped unipolar current with different amplitudes.
• FIG. 1d shows a bipolar, that is to say a short-term polarity reversed polarity, with a long electroplating time and with a short demetallization time.
• the demetallization amplitude here is a multiple of the metallization amplitude. Overall, however, with a plating time of z. B.
• FIG. 1e shows a double pulse shape that can be achieved with the method according to the invention. Unipolar pulses alternate with bipolar pulses.
• the electroplating cell represents an ohmic load for the electroplating current.
• bath current and bath voltage are therefore in phase.
• the low parasitic inductances of the electrical conductors to the electrolytic cell and back to the current source are negligible.
• pulse currents contain alternating currents. With As the pulse steepness increases, the proportion of high frequencies of the alternating currents increases. Steep pulse edges have a short pulse rise and fall time.
• the line inductances represent inductive resistances for these alternating currents. They delay the pulse edges.
• the simplest measures consist in using very short electrical lines with very low ohmic and inductive resistances.
• the plating current is always shown or assumed in phase with the voltage in order to simplify the drawing.
• FIGS. 2a and 2b show the feeding of the pulse-shaped compensation current according to the invention by means of the current transformer 1.
• the bath direct current source 2 is connected by electrical conductors 3 to the electrolytic bath, which is shown here as bath resistance R B with the reference number 4.
• the secondary winding 6 of the current transformer 1 is connected in series with the electrolytic bath.
• the primary side 7 of the transformer is fed by a power pulse electronics 8.
• the power Frelektronik 8 is connected via the mains voltage connection 9
• the current and voltage profiles for the pulses according to FIG. 1d also correspond in principle to the pulse shapes of the other diagrams in FIG. 1. They differ only in the instantaneous size of the compensation current. Therefore, the voltages or currents belonging to FIG. 1d are drawn in and considered in the following figures.
• FIG. 2a shows the operating state during the electroplating. Potentials are shown in parentheses as an example.
• the capacitor C is charged to the voltage U c ⁇ U GR .
• the voltage U ⁇ s at the current transformer 1 is 0 volts.
• the rectifier voltage U GR is thus present at the bath resistor R B and causes the galvanizing current I G.
• This temporary state corresponds to the electroplating Direct current. According to the invention, no switches are required in the high-current circuit 5.
• Figure 2b shows the operating state during the demetallization.
• the potentials can no longer be viewed statically. For this reason, the potentials for the temporal end of the demetallization pulse are entered in brackets in FIG. 2b.
• the starting point is the potential of FIG. 2a.
• the power electronics 8 feeds the primary winding 7 of the current transformer 1 with a current that changes in amplitude over time.
• the current flow time corresponds to the duration of the compensation current flow in the main circuit 5.
• the primary voltage U ⁇ p at the transformer is so great that a transformer pulse voltage U ⁇ s , which is able to drive the required compensation current l ⁇ , is secondary to the number of transformer turns .
• the charging current is the compensation current I ⁇ and at the same time the demetallization current I E. If the capacitor C has a large capacitance, the voltage increase can be kept low in the short time of the charging current flow. In principle, an accumulator can also be used instead of the capacitor C.
• the bath direct current source 2 consisting of a rectifier bridge circuit, switches off automatically for the duration of the demetallization time, because the voltage U c > U GR due to the charging. Without additional switching elements being used, the DC source 2 therefore does not automatically feed any during the period in which the bath current I GR is fed into the circuit by the induced voltage U Ts
• the power loss to be used for pulse generation is very low compared to known methods.
• 8 watts are required for the reverse flow of transformer current to saturate the transformer. With 10 bath power supplies, this results in a total power loss of around 160 watts.
• the current transformer losses must be included in the circuit according to the invention. If a very good coupling of the transformer z. B.
• the technical outlay for carrying out the method according to the invention is likewise substantially less than when using conventional circuit arrangements. Only passive components are loaded with the high electroplating currents and with the even higher deplating currents. This significantly increases the reliability of the pulse power supply devices. Electroplating systems equipped in this way therefore have a significantly higher availability. This is also achieved with significantly less investment. At the same time, the ongoing energy consumption is lower. Because of the lower technical expenditure, the volume of such pulse devices is small, so that their implementation in the vicinity of the bath is facilitated. The line inductances of the main circuit are therefore reduced to a minimum.
• the pulse-shaped current profile at the bath resistor R B (electroplating cell 20) is shown schematically in FIG. Because of the ohmic resistance R B , bath current and bath voltage are in phase here.
• the compensation current flow begins. The size and direction is determined by the instantaneous voltages U c and U ⁇ s .
• the compensation current flow ends at time t 2 .
• the subsequent electroplating current I G is determined by the rectifier voltage U GR , in each case in connection with the bath resistance R B.
• the time course of the voltages is shown in more detail in the diagrams in FIGS. 4a and 4b.
• the electroplating current I G is practically in phase with the electroplating voltage U G. I G is therefore not shown because of the same course.
• the rectifier voltage U GR the capacitor voltage U c and also the electroplating voltage U G are approximately the same.
• the voltage U ⁇ s is 0 volts at this time.
• the rise of the voltage pulse U TS1 at the secondary winding 6 of the current transformer 1 begins.
• the voltage U TS1 is polarized so that the galvanizing voltage U G1 becomes negative so that demetallization can take place.
• U G is formed from the sum of the instantaneous voltages U c and U ⁇ s .
• the voltage U ⁇ s is polarized across the capacitor C in the direction of the existing charge.
• T R B x C.
• At the instant 1 2 begins the drop in the voltage pulse U TS1 .
• a voltage U TS2 with reverse polarity occurs due to voltage induction . This now adds up with the capacitor voltage U c .
• a brief voltage surge U G2 occurs at the bath resistor R B.
• T R B x C
• the voltage U ⁇ s is therefore 0 volts.
• the voltages U GR , U c and U G are then approximately the same size again.
• the brief voltage increase across the bath resistor R B is undesirable for electro-technical reasons. In practice, this tip and the other tips, unlike shown here, are clearly rounded.
• a freewheeling diode parallel to the secondary winding or parallel to another winding on the core of the current transformer bring about a further weakening of the voltage increase across the bath resistor R B. The lower overvoltage is then longer.
• These known circuits of inductors will not be discussed further here, nor will the construction of the current transformer, which is to be constructed as a pulse transformer. Pulses must be fed into the transformer on the primary side in such a way that magnetic saturation of the transformer iron is avoided. To desaturate, there is enough time in the pulse pauses after each current pulse to feed in a current with reverse polarity. For this purpose, an additional winding can be applied to the transformer core.
• An example of the primary-side control of the current transformer 1 is shown in FIG. 5.
• An auxiliary voltage source 12 is supported by a charging capacitor 13 with the capacitance C.
• An electronic switch 14, here an IGBT (isolated gate bipolar transistor), is driven by voltage pulses 15.
• IGBT isolated gate bipolar transistor
• a primary current flows into the partial winding I of the primary winding 7 of the current transformer, and a desaturation current flows into the partial winding II to simplify the circuit.
• only one desaturation current flows in the partial winding II
• the number of turns of the partial windings I and II as well as the series resistor 17, through which a current of small size flows permanently, are matched to one another in such a way that the transformer iron is not saturated.
• the primary current I TP is shown schematically in the current diagram 18 in FIG. 5.
• FIG. 6 shows the application of the pulse current units 19 in a galvanizing bath 20 with vertically arranged electroplating material, for which two bath direct current sources 2 for the front and the back of the flat electroplating material, for example a printed circuit board, are used.
• a galvanizing bath 20 with vertically arranged electroplating material, for which two bath direct current sources 2 for the front and the back of the flat electroplating material, for example a printed circuit board, are used.
• Printed circuit board 21 is supplied with galvanizing current separately from one of these current sources 2.
• An anode 22 is arranged opposite each circuit board side. During the short demetallization pulse, these anodes act as cathodes against the material to be treated, which is then anodically poled.
• Both pulse current units can work asynchronously or synchronously with each other.
• the pulse trains of the same frequency of both pulse current units are synchronized and if there is a phase shift of the pulses at the same time.
• the phase shift must be such that during the electroplating phase on one side of the circuit board the demetallization pulse occurs on the other side and vice versa.
• the metal scattering that is to say the hole plating, is improved.
• the pulse trains with the same frequency can, however, also run asynchronously to one another in the case of separate electrolytic treatment of the front and the back of the material to be treated.
• the invention is suitable for all pulse electroplating processes. It can be used in vertical or horizontal electroplating systems, immersion and continuous systems. In the latter, plate-shaped electroplating material is held in a horizontal or vertical position during treatment.
• the times and amplitudes mentioned in this description can be changed over a wide range in practical applications.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electroplating Methods And Accessories (AREA)
• Electrolytic Production Of Metals (AREA)
• Ac-Ac Conversion (AREA)
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• 1995
  • 1995-12-21 DE DE19547948A patent/DE19547948C1/de not_active Expired - Fee Related
• 1996
  • 1996-09-27 CZ CZ19981700A patent/CZ290052B6/cs not_active IP Right Cessation
  • 1996-09-27 JP JP52324197A patent/JP4028892B2/ja not_active Expired - Fee Related
  • 1996-09-27 AT AT96934478T patent/ATE186081T1/de not_active IP Right Cessation
  • 1996-09-27 KR KR10-1998-0704072A patent/KR100465545B1/ko not_active Expired - Fee Related
  • 1996-09-27 WO PCT/EP1996/004232 patent/WO1997023665A1/de not_active Ceased
  • 1996-09-27 ES ES96934478T patent/ES2139388T3/es not_active Expired - Lifetime
  • 1996-09-27 DE DE59603510T patent/DE59603510D1/de not_active Expired - Fee Related
  • 1996-09-27 CA CA002241055A patent/CA2241055A1/en not_active Abandoned
  • 1996-09-27 US US09/091,136 patent/US6132584A/en not_active Expired - Fee Related
  • 1996-09-27 CN CN96199166A patent/CN1093337C/zh not_active Expired - Fee Related
  • 1996-09-27 EP EP96934478A patent/EP0868545B1/de not_active Expired - Lifetime
  • 1996-09-27 BR BR9612163A patent/BR9612163A/pt not_active Application Discontinuation

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