DE102004030726A1 - Process to etch manufacture printed circuit board by regulation of electrolytic cell voltage transverse to the direction of travel - Google Patents

Abstract

In a continual horizontal or vertical process to etch a printed circuit board, there is a voltage drop in the copper surface of one side of the board. The drop reaches a maximum per unit length in the vicinity of the contact interface. This voltage drop reduces the local electrolytic cell voltage transverse to the direction of travel, compensated by the conical anodes. Only the first part of the laminate incorporates a compensation agent. The current density is regulated in accordance with the laminate thickness to produce uniform electrolytic treatment.

Description

The This invention relates to electroplating and electrolytic etching of thin Layers on level material to be treated in continuous systems with horizontal or vertical transport of the goods. The preferred application is the treatment of printed circuit boards and conductor foils. The progressive Miniaturization of the. Electronics increasingly requires circuit boards and conductor foils, which are implemented in fine conductor technology. The structures on this material reach the smallest conductor widths and conductor distances of 20 μm and under. For Such dimensions of the electrolytically and etchable produced Structures must Base materials of printed circuit boards are used, which are a very thin metallic Have lamination. As a rule, it is the lamination of printed circuit boards and conductor foils around a Kupferkaschierung. The Thickness of this lamination goes down to 1 μm. The dimensions amount of the surfaces to be treated up to 660 mm square. In electrolytic treatment, the treatment stream in the thin one Lamination of the treated material over this comparatively long Routes flow. The occurring electrical voltage drop in the lamination affects very disturbing on the uniformity the electrolytic treatment. The voltage drop is locally different, because the current flows to the contact side of the material to be treated and in this direction, i. increases transversely to the transport direction.

This has locally different cell voltages U _Z result and thus uneven electrolytic treatment of the surface and the holes of the material to be treated. This applies to electroplating as well as for the electrolytic etching of material to be treated with thin metallic layers. As an example of the electrolytic etching here is called the differential etching of fine conductors. First, the conductor tracks are galvanized on a very thin copper surface layer by means of phototechnically applied, electrically non-conductive resist structures. The thickness of these conductors is z. B. 20 microns. After removal of the resist, the traces are etched together without etch resist and the original copper clad. This etching process, called differential etching, is complete when the gaps between the circuit traces are completely etched out. For this purpose, chemical etching is suitable in a spray-etching process. Because of the above-mentioned increasing precision of the structures, the electrolytic etching is becoming increasingly important for this difference etching, because in principle a higher etching accuracy and uniformity can be achieved. Only a very thin residual layer must be chemically etched after the electrolytic etching.

On the uniformity over the entire surface of the electrolytically etched circuit board, however, a very thin copper base layer has a disturbing effect. The electrical voltage drop in the still thinner during etching layer has the said different cell voltages U _Z result. Thus, the same disturbing influences of thin layers occur, as in galvanizing. During electrolytic etching, the material to be treated is predominantly poled anodically and the electrodes are negative. When galvanizing, the polarity is reversed. In this case, the electrodes are called anodes. The invention applies in both cases for the application of direct current and pulse current. In bipolar pulse current, the respective polarity is reversed for a short time. However, the predominant polarity is as mentioned above. To shorten the following description of the invention, this will be described only by the example of electroplating. However, it also fully relates to the electrolytic etching.

To reduce the disturbing influence of thin layers in the electrolytic treatment is in the document DE 101 41 056 C2 described method and the associated device known. The electrolytic treatment stream is fed by means of contact means as brackets laterally in the transport direction in the treated. At the contact side, the locally effective cell voltage U _{Z is} about as high as the applied rectifier voltage. With increasing distance from the feed side of the voltage drop takes .DELTA.U resulted in the copper layer the locally effective cell voltage U _Z from. It is proposed to divide the entire electrolytic cell into several electrolytic cells transversely to the transport direction. In the example shown, there are four electrolytic sub-cells. For the uniformity of the effective cell voltage then only the electrical voltage drop .DELTA.U in the copper layer is decisive, which is located in the region of the respective partial anode. Because of the increasing current in the direction of the contact means, different lengths of voltage drop occur per unit length transversely to the transport direction. Therefore, the electrodes of different length must be equipped in this direction. With a very thin copper cladding and the application of high current densities, four thicker layer areas and four thinner layer areas will occur transversely to the transport direction. As a particular disadvantage, however, is the very large technical effort for four times the cost of anodes, bath power sources and control and regulating agents to call.

A reduction of the voltage drop ΔU in the copper cladding is also achieved if the material to be treated is not only electrically contacted on one side but lying on both sides. Such a contact is the document DE 36 24 481 C2 refer to. However, this invention does not address the uneven electrolytic treatment of thin laminations. The longest distances for the currents in the lamination to the contact means halve compared to the one-sided contact. Again, a high technical effort for the two contact devices is required. With a thin lamination, however, a weakened layer thickness decrease occurs again towards the middle. However, only one width of the printed circuit boards can be produced transversely to the transport direction with double-sided contacting. The technical effort for a width-adjustable contact device would be even larger and therefore uneconomical.

It was already trying to solve the problem of thin lamination, by high-impedance anodes and with a feed of the treatment current in the anodes on the side opposite the contact means. As well a skew the anodes with the largest anode / cathode distance at the contact page. Both methods are too one-sided. They cover only a small area of the thickness of Kupferkaschierung. Therefore have they are not enforced in practice.

task It is the object of the present invention to provide a method and an apparatus for the electrolytic treatment of flat items such as e.g. Circuit boards indicate that the above technical disadvantages do not have. In particular, the task should be solved very inexpensively, wherein the electrolytic treatment uniformly across the transport direction over the entire material to be treated should take place.

Is solved the object by the method according to claims 1 to 8 and by the device according to the claims 9 to 16th

The invention is described below with reference to the schematic and not to scale 1 to 5 described in detail. Shown are examples with sections of electrolytic continuous systems with horizontal transport of the material to be treated.

1 shows in cross-section an electrolytic continuous system according to the prior art.

2 shows a typical current density diagram of an electrolytic cell for the treatment of printed circuit boards.

3 shows in plan view an electrolytic cell with conically cut anodes.

4 shows in plan view and in cross-section conical cut aperture between the anodes and the treated.

5 shows in plan view different lengths passive regions of the anodes in the transport direction.

According to the 1 the electrolytic continuous system consists of at least one upper electrolytic cell 2 and a lower electrolytic cell 3 for the simultaneous treatment of the material to be treated 1 , The treated material laminated on both sides 1 is the cathode with the upper electrically conductive lining 7 and the lower lamination 8th , These form together with the upper anodes 5 the upper electrolytic cells 2 and with the lower anodes 6 the lower electrolytic cells 3 , The influence of the thickness of these laminations on the Galvanisierergebnis should be influenced according to the invention.

The material to be treated is in 1 transported by non-illustrated means of transport continuously in the plane of the drawing. As a contact agent 4 Here are contact wheels at the top and at the bottom of the material to be treated 1 shown. They can also serve as a means of transport. It may be with the contact agents 4 also act on segmented contact wheels or brackets.

In the edge region of the printed circuit boards, in particular with a larger anode / cathode distance, a field line concentration occurs when the anodes 5 . 6 wider than the circuit board 1 , In this case, it is common edge trim 9 between the anodes and the material to be treated 1 install. This avoids a layer thickness increase in the edge region of the printed circuit boards. This increase is also called bone effect. The edge panels 9 extend through the entire flow system in the illustrated area.

The upper treatment current I _A5 flows from the upper anodes 5 the upper electrolytic cell 2 through the electrolyte 12 to the upper lamination 7 , The same applies to the lower electrolytic cell 3 for the lower treatment current I _A6 . Analogously, the cathode currents I _K flow.

The Anodes are in practice transverse to the transport direction electrically very good conducting, so that by the flow of current an insignificant electrical Voltage drop occurs in this direction.

The electrical resistance of typical copper laminations is only about 1 milliohm per dm ² . Usual electrical currents through these surfaces are up to 100 amperes at cell voltages U _Z in the order of 1 to 2 volts. With a printed circuit board width of 600 mm then occur about 0.3 volt differences in the local-acting cell voltages U _Z. The influence of the cell voltage U _Z on the local current density i is shown in FIG 2 for a copper bath containing an aqueous sulfuric acid electrolyte as a typical example of printed circuit board technology. This diagram is valid for a particular electrolytic cell. The characteristics of an electrolytic cell are influenced, inter alia, by the properties of the electrolyte, the anodes, the electrolyte flow and the geometry of the electrolytic cell, such as the anode / cathode distance. To record the cell voltage / current density curve, ie the U _Z / i diagram, an electrically highly conductive material to be treated is used, eg a printed circuit board with a thick copper cladding. For this purpose, several times electroplated circuit boards are suitable, as they occur in dummies. In this case, the electrical voltage drop .DELTA.U in the lamination is negligibly small. This has the consequence that in all areas of the electrolytic cell transverse to the transport direction an equal cell voltage U _{Z is} effective and thus the same large local current densities i. The prerequisite here is that a voltage drop across the transport direction in the anodes does not occur. This is the case in practice because the cross sections of the electrical conductors of the anodes can be selected to be correspondingly large. Thus, the very small voltage drops in the anodes are almost independent of the current density. Therefore, this voltage drop in the anodes is no longer considered in the following considerations.

According to the diagram in 2 is the local current density i at a local cell voltage U _Z of 1.5 volts about 2 A / dm ² and at 2.5 V about 10 A / dm ^second A change in the cell voltage U _Z of only 0.6 V already has a current density change from 2 A / dm ² to 6 A / dm ² result. At 6 A / dm ² , approximately three times as much copper is deposited as at 2 A / dm ² , if the same treatment time t is present. The deposited layer thickness d is substantially proportional to the current density i and the treatment time t. This gives the formula

d ~ i · t

With increasing current density i and increasing treatment time t, the layer thickness d becomes larger. The present invention combines the electrolytically given current density trace i as a function of the spatially acting tent voltage U _Z with the treatment time t according to the above formula. Transverse to the transport direction, the product of current density i and the treatment time t must always be the same size at each location, in order to deposit a uniform layer thickness d in this direction. According to the invention, at high current density i, which occurs in the vicinity of the contact means, the treatment time t is chosen to be small. In the far-range contact means, the current density i is smaller as a result of the voltage drop .DELTA.U in the copper cladding. Accordingly, the treatment time t must be set larger.

The current density differences transversely to the transport direction are dependent on the electrical conductivity of the copper cladding and thus the thickness of the same. With decreasing thickness, as occurs in the fine conductor technology, the current density differences across the transport direction are greater. For a certain eg average current density in the amount of eg 6 A / dm ² , a uniform electrolytic deposition can be set by means of different treatment times t. The different treatment times t are due to different lengths of anodes in the transport direction 11 the continuous flow system, just like the 3 for a section of the plant shows, set. Near the contact track 10 are the anodes 5 . 6 short and thus the treatment time t is small for a given transport speed. At the contact far side 17 the treatment time t is great. The diagonally cut anodes, which follow with upper layer thickness anodes 15 and lower layer thickness anodes 16 have the added advantage of lower anode material consumption compared to rectangular anodes over the entire area of the prior art electrolytic cell.

Prefers become insoluble Anodes used. These are usually made of titanium with an electric conductive and anodic resistant coating.

All in all These materials are very expensive. Therefore, the invention are conical Anodes running very economical, especially since they are a wearing part and renewed from time to time. Also shaped accordingly soluble Anodes are for the invention can be used.

In existing electrolytic continuous systems, the anodes are cut rectangular. If printed circuit boards with thinner copper laminations are to be produced in these systems, the invention in a second embodiment can also be advantageously used to achieve a planar electrolytic treatment. In this case, according to the 4 arranged conically extending diaphragms between the anodes and cathodes transversely to the transport direction, which again influence the local treatment times t and thus the locally deposited layer thicknesses d transversely to the transport direction. That's why these panels below layer thickness panels 13 called. In the field of contact agents 4 or the contact track 10 is the covered anode length in the transport direction 11 large and thus the treatment time t small. In contact far area 17 this is the other way around.

The effect of the layer thickness diaphragms 13 on the local layer growth in the continuous plant is as well as in the first embodiment of the invention with the described conical layer thickness anodes 15 . 16 , In place of the conical anodes or diaphragms can also step-shaped versions occur. A continuous system in this case consists of many individual electrolytic cells or cell groups with individual anodes 5 . 6 and the associated individual rectifiers, not shown, or pulse current devices for Badstrom generation. The 5 shows stepped passive areas 14 the electrolytic cells. These passive areas 14 can be realized by appropriate apertures or by anodes, which are shortened in the contact area.

The treatment times t of the electrolytic cells in the continuous flow system add up to the total treatment time. It can be seen that the total time in the vicinity of the contact means is smallest and increases with increasing distance from the contact means. This compensates over the entire run-through the transversely to the transport direction decreasing current density i so that the product of i · t remains the same size. The passive areas 14 can be advantageously produced by different narrower, ie shortened anodes or by correspondingly large aperture. In both cases, the same electroplating result is achieved again.

With the measures according to the invention described above, a continuous system can be set very precisely for a product with a specific copper base layer thickness. In practice, however, it often happens that printed circuit boards are treated with different thicknesses of copper cladding and / or with different transport speeds for different thicknesses of deposits. In this case, the layer thickness diaphragms must 13 adapted to the respective item to be treated, ie exchanged or moved mechanically at the installation location transversely to the transport direction. This is associated with a corresponding amount of time to rebuild the system or with a corresponding design effort for the displacement device.

Therefore, according to the invention, it is also preferably proposed to use only the first part of the continuous flow system with the layer thickness anodes described in the transport direction 15 . 16 or the stationary layer thickness diaphragms 13 equip. For example, in a continuous flow system 42 Anodes the first 21 Anodes with layer thickness diaphragms 13 equipped at the top and bottom. By varying the current densities in both parts of the continuous system, it is possible to achieve a planar deposition, even if the above-mentioned parameters of the printed circuit boards are different. This is indicated by the following examples, which are to abbreviate the description only on Schichtdickenblenden 13 refer, clearly. Correspondingly cut anodes have the same effect.

With thin copper lamination, as described, more copper is deposited on the contact side without diaphragms than on the contact-far side. If, on the other hand, the initial area of the continuous system with layer thickness diaphragms 13 is equipped and galvanized with high current density i, then will be far away in contact 17 deposited more copper than in the other area of the circuit boards, which also has a much shorter treatment time t. Thus, an excess of layer thickness in the region of the printed circuit boards is generated transversely to the transport direction, in which then in the second part of the continuous system, not with Schichtdickenblenden 13 is equipped; less isolated. In total, it is thus possible to produce a flat layer in this continuous system for thin copper laminations.

If a thick copper cladding is to be galvanized in the same installation, then the described compensation of the deposits in the initial area and end area of the continuous installation is no longer required or only to a small extent. The layer thickness diaphragms 13 are not really necessary. However, they are present because they are needed for the thin laminations. In the initial area, therefore, with thick laminations, only a small excess of layer thickness in the contact area is far away 17 the circuit board generated. This is achieved by setting a small local effective current density i in the initial region of the continuous system. There is a total of only a small layer structure, in absolute terms, even a small shift rise to the contact far side 17 entails.

In the following part of the continuous system, which does not have layer thickness diaphragms 13 is then galvanized with higher current density i and thus realizes the essential layer structure up to the nominal layer thickness. In this area, the printed circuit boards are galvanized almost evenly with the thicker copper lamination. The layer waste to the contact far side 17 is small here. All in all, this results in a flat overall layer thickness again after the entire continuous system, which is always the goal of the electrolytic treatment.

With thin copper lamination is in An catchment area of the continuous system, with layer thickness diaphragms 13 equipped with high current density i galvanized and in the end, which has no layer thickness diaphragms, with low current density. With thick copper cladding, the reverse current density settings for the electrolytic cells are set along the transport path. This implies also all other thicknesses of copper lamination between thin and thick, ie from eg 1 μm to 18 μm. By dimensioning the size of the layer thickness diaphragms, their conical shape and number in a given pass line, and by choosing individual current densities i in each electrolytic cell or group of adjacent electrolytic cells, a large thickness range of the initial copper cladding can be plated in that a flat overall layer is created.

During the Electroplating grows the layer, i. the layer thickness decreases in the continuous flow system from electrolytic cell to the next continuously too. Change with it the electroplating conditions in the electrolytic cells along the transport track. Because for every electrolytic cell or Cell group the galvanizing currents by independent Rectifiers are individually adjustable, can be on the layer growth be reacted control technology and control technology. Especially at slow transport speed and thus a long treatment time t with significant increase in layer thickness per cell, can in each electrolytic cell another, for each instantaneous layer thickness optimal current density i can be adjusted. Such a continuous system allows, in practice PCBs with copper cladding from e.g. 1 μm up to 18 μm to produce, in all cases a flat layer is generated. To achieve the flat target layer thickness is at the thinnest Copper laminations, which are particularly critical, only with a smaller transport speed and / or lower current density to galvanize. In practice, an existing continuous flow system According to the invention with layer thickness diaphragms equipped and for Copper laminations of 1.5 μm up to 18 μm dimensioned. This is a previously unseen large area. With transport speeds between 1.5 m / min. and 2.5 m / min. planar layers were deposited, whereby the given tolerances the layer thicknesses of + -10 % were safely adhered to.

One greater Another advantage of the invention is that the precision of the copper deposition increased at the expense of production throughput almost arbitrarily can be. In the case of fine conductor technology, the permissible layer thickness tolerance becomes always smaller. An inventively equipped continuous flow system fulfills these requirements Claims. A little bit smaller meets this Claims. A little bit smaller production throughput will then be in favor of the necessary precision accepted. Overall, the invention requires comparatively the prior art very low cost, yet a great benefit is achieved. Not least because the throughput system equipped with it be adapted very flexibly to the requirements of the respective products can do without having to rebuild the plant.

Also in a two-sided feed of the material to be treated is at thin Laminations a layer thickness drop occur to the middle of the printed circuit boards, even if this is smaller than with the one-sided feed. In the case of two-sided feed, the layer thickness diaphragms according to the invention are used or layer thickness anodes mirror symmetrically in the flow system built-in. Again, by means of the current density adjustment, such as described, a uniform electrolytic Treatment achieved.

It may happen that the course of the cumulative layer thickness across the Transport direction is not linear, but a slight increase or Lowering in the middle region of the material to be treated has. The fine correction let yourself by non-linearly cut edges of the layer thickness anodes or Layer thickness panels reach transversely to the transport direction.

The Arrangement of the layer thickness diaphragms or the layer thickness anodes takes place essentially in the initial area of the continuous system. The first however, the first electrolytic cells may be made from others establish without these measures equipped be. For example, at first to electroplate a small initial layer throughout the board area and reinforce. something similar applies to the end area of the continuous system, which can be equipped with special screens.

1

treated, PCB, conductor foil,

2

Upper electrolytic cell

3

Lower electrolytic cell

4

contact means

5

Upper anode

6

Lower anode

7

Upper lamination

8th

Lower lamination

9

edge panel

10

Contact track, Contact

11

Transport direction, transport path

12

electrolyte

13

Coating Thickness panel

14

passive range

15

Upper Coating Thickness anode

16

Lower Coating Thickness anode

17

Contact distant area

d

layer thickness

t

treatment time

i

Current density, locally effective current density

I

treatment current

Claims (16)

Process for the electrolytic treatment of good, in particular of printed circuit boards and conductor foils on the top and / or bottom in continuous systems with horizontal or vertical continuous transport of the treated material in the transport direction successively arranged electrolytic cells or groups of cells, each with individual bath current sources characterized in that the uniform electrolytic treatment of the material to be treated transversely to the transport direction, the electrolytic cells are essentially equipped in the beginning of the continuous system on the contact side with layer thickness or in the surface at least partially reduced anodes as layer thickness anodes, in this initial region with thin lamination of the treated material with high current density and in the end of the Continuous flow system, which is essentially not equipped with layer thickness diaphragms or layer thickness anodes, with low current density galvanis Conversely, in the case of thick lamination, conversely in the initial low current density region and in the end region of the high current density continuous flux system, the transitions can be from thin to thick lamination and thus from high to low current density and vice versa. Method according to claim 1, characterized that by conical or stepped extending layer thickness apertures or layer thickness anodes a preferred electrolytic treatment of the material in the contact area This avoids that in this area, the active treatment area smallest is and is largest in contact with remote area. Process according to Claims 1 and 2, characterized that by different sized ones Layer thickness diaphragms or layer thickness anodes along the transport path, and by the number of electrolytic cells equipped therewith Layer growth from one electrolytic cell to the next individually influenced becomes. Process according to claims 1 to 3, characterized that along the transport path through different sized current densities in the electrolytic cells or in groups of electrolytic Cells the layer growth of electrolytic cell or group is influenced individually by cells to the subsequent ones. Process according to claims 1 to 4, characterized that a layer thickness increase in the edge region of the material to be treated is avoided by using edge stops. Process according to claims 1 to 5, characterized that the layer growth transverse to the transport direction by mechanical slidable layer thickness diaphragms is affected. Process according to claims 1 to 6, characterized that by a non-linear course of the edges of the layer thickness diaphragm and / or the layer thickness anodes the layer growth transverse to the transport direction individually influenced becomes. Process according to claims 1 to 7, characterized that in two-sided contacting the material to be treated, the means for influencing the local Current densities are arranged mirror-inverted on both sides and that from the two sides along the transport path the material to be treated with different current densities in the electrolytic cells is treated. Device for the electrolytic treatment of good, in particular of printed circuit boards and conductor foils on the top and / or bottom in continuous systems with horizontal or vertical continuous transport of the material to be treated with in the transport direction successively arranged electrolytic cells or groups of Cells each with individual bath power sources for performing the Process according to the claims 1 to 8, characterized by electrolytic cells in the continuous system, along the transport path substantially in the initial area with means for differently influencing the electrolytic treatment are equipped transversely to the transport direction and by electrolytic Cells in the end of the flow system, which is essentially not equipped with these means are. Apparatus according to claim 9, characterized by means for influencing the electrolytic treatment transversely to the transport direction than in the contact area ( 10 ) shortened rectangular layer thickness anodes, wherein in the transport direction the reduction decreases from one electrolytic cell to the subsequent cell or cell group or as conically cut layer thickness anodes with the largest dimension in the transport direction at the contact far side ( 17 ) of the material to be treated. Apparatus according to claim 9, characterized by means for influencing the electrolyti treatment transverse to the transport direction as rectangular layer thickness diaphragm on the contact side, which are shorter from electrolytic cell to the subsequent cell or cell group transverse to the transport direction or by conically cut layer thickness diaphragm, which at the contact side ( 10 ) have seen the largest dimension in the transport direction. Device according to claims 9 to 11, characterized by arranging layer thickness anodes of different sizes or Layer thickness diaphragms in the electrolytic cells or groups of cells in the transport direction of the material to be treated. Device according to claims 9 to 12, characterized by edge diaphragms ( 9 ) along the transport path ( 11 ). Device according to claims 9 and 13, characterized by means for influencing the electrolytic treatment transversely to the transport direction through layer thickness diaphragms or layer thickness anodes, the transversely to the transport direction at their edges a non-linear Course have. Device according to claims 9 to 14, characterized layer thickness diaphragms which can be displaced transversely to the transport direction. Device according to claims 9 to 15, characterized by a mirror image arrangement of the devices in a Infeed of the treatment stream into the material to be treated by means of contacts from the two sides transverse to the transport direction.