DE4225961C2 - Device for electroplating, in particular copper plating, flat plate-like or arc-shaped objects - Google Patents

Description

The invention relates to a device for electroplating, in particular copper plating, flat, plate or bogenför shaped objects, especially th printed circuit boards with

• a) a machine housing which one with a liquid has space that can be filled with electrolytes;
• b) a conveyor, which the objects in we considerably horizontal, parallel to their main extent direction, continuously from one entrance to egg transported through the machine housing at the outlet;
• c) at least one anode, which is parallel to the movement path of the objects extends and with a first Pole of a voltage source is connected;
• d) a contacting device, which an electrical Makes contact with the objects and with a two ten pole of the voltage source is connected.

Such devices with different funding directions are in DE-OS 36 24 481 and DE-OS 32 36 545 described. You work consistently with a con constant DC voltage, so that the galvanize the objects on the way through the machine housing through the device essentially always in the same  electrical field. The plating speed speed, i.e. the speed with which the galvanic based metal layer on the objects is there at relatively low; this means that with a predetermined movement speed of the objects The length of the devices must be very large. Hereby who the known devices extremely expensive.

In the magazine article "Pulse Plating of Copper for Printed Board Technology ", Metal Finishing, April 1991, pages 21 to 27 is from scientific sub Searches for the galvanic deposition of copper with pulsating current when manufacturing printed circuit boards reports, taking into account rectangular pulse shapes were.

The object of the present invention is a Vorrich tion of the type mentioned so that height Here plating speeds are achievable and diesel ben layer thicknesses can be achieved with shorter devices that can.

This object is achieved in that the Voltage source at least one adjustable pulse genes rator includes, the output signals to the anode and the Contacting device placed and rectangular pulses with dial bar repetition frequency, clock ratio, amplitude and Po are larity, with the anode being averaged over time is positive with respect to the contacting device.

Surprisingly, it has been found that the plat animal speed can then be increased many times over can, if instead of a constant DC voltage to the Electrolysis electrodes, d. that is, at the anode on the one hand and the objects to be electroplated, on the other hand pulsating DC voltage is present. The currentless times that lie between the individual impulses compensates for the amplitude of the pulses accordingly is increased. The Abschei is with the same power consumption application rate in a device according to the invention and thus the current yield is considerably higher than in the state of the technique. The physical processes on which this is have not yet been researched in detail. It seems however, to be certain  that here concentration and polarization ef effects in the area of the anodes and the counter to be plated would play a role, which in pulsed operation be influenced favorably. In particular, the higher voltages in the inventive method can be used to penetrate the metal ions through the charge double layer in the area of the plattie objects to be favored, so that the Abschei metal is facilitated. The exact parameters of the output signals generated by the pulse generator, in particular So the repetition frequency, the clock ratio and the Amplitude, can be optimized through trials and thus the opposite geometrical relationships as well as each existing electrolytes can be adjusted. Different Electrolytes, in particular different types of Metal ions and different additives can be different make looking impulses necessary.

In a particularly preferred embodiment of the Invention comprises the voltage source at least two independent dependently operated pulse generators, their added output signals to the anode or the contact device and their relative phase position is adjustable. By overlaying the multiple, in particular two, from the independent pulse generators generated rectangular pulses, their characteristic parameters can be selected independently of each other, can be very Put together differentiated total impulses that are favorable Lead results.

Particularly fast electroplating speeds will be achieved with an embodiment of the invention, at wel cher the or the pulse generators such output signals generate that effectively at the anode or the contact voltage during part of the  Time has the reverse polarity at which the Anode is negative with respect to the contacting device. The temporary reversal of the polarity of the operating voltage appears in particular disadvantageous concentration effects close. It may also work again a small part of the layer previously plated back in solution what the surface of adhering ver cleansing free.

The repetition frequency of the output signals of the Impulsge nerators can be between 10 and 10,000 Hz.

The plate or arch-shaped counter to be galvanized stands, especially the circuit boards, often show Through holes, the lateral surfaces of which are also closed are galvanized. In many cases this is just ahead drawn or exclusive galvanization of the lateral surfaces of these through holes desired. Surprisingly has been found in devices according to the invention, that a preferred deposition of metal on the jacket through holes is done when the electrical lyt is cooled. A temperature sensor is particularly useful range between 10 and 30 ° C, preferably between 18 and 24 ° C. Therefore, in a preferred embodiment the invention provided a device with which the Electrolyte is coolable.

A favorable embodiment looks such that a sump is provided for the electrolyte, from which the electrolyte is continuously brought into the space of the machine housing that can be filled with electrolyte, and into which the electrolyte is returned from there, and that the cooling device comprises:

• a) a main cooler with which the one located in the sump  Electrolyte below a first preselectable Temperature is maintained;
• b) at least one auxiliary cooler with which the sump removed electrolyte on the way to that with electrolyte fillable space of the machine housing is coolable and of this electrolyte on a second preselectable Temperature that is lower than the first.

By dividing the total cooling effect into one Main and an auxiliary cooler can be a particularly pre rapid and rapid regulation of the electrolyte temperature "on site", d. H. near the objects to be plated, bewerk digits. The "main cooling" on the first preselectable Temperature takes place through a relatively large aggregate already in the swamp. This first preselectable temperature lies just a little above the temperature that the electrolyte should reach "on site". The final second temperature which is below the first temperature value is then changed from the fast working auxiliary cooler with lower power which acts on the electrolyte only on its way to the anode.

In most devices of the type mentioned the objects are plated on both sides. Therefore extends on both sides to the path of movement of the objects one electrode each. In such devices expediently according to a further feature of the invention sen provided that two operate independently Bare auxiliary coolers are provided, the first Auxiliary cooler electrolyte flowing through the objects on the side facing the anode and the other auxiliary cooler flowing electrolyte the counter would be on the side facing the other anode to be led.  

In an embodiment of this type of the invention The device is a nearby object to each auxiliary cooler arranged on the side facing the corresponding anode Neter temperature sensor assigned, which the local monitors the local temperature of the electrolyte and then the controls associated auxiliary cooler. Are multiple anodes available, it may well be useful for comparison reduction of the order on the opposite sides the local temperature of the objects to be electroplated to choose the electrolyte differently, so different geometrical conditions, also in the flow movement of the electrolyte to be able to take into account.

The anode is expediently an inert dimension bile electrode; then there is a separate facility seen with which the electrolyte used in electroplating removed metal ions can be fed again. The Known devices mentioned at the outset use consuming anodes, d. H. Anode baskets made with the metal are filled, which is to be electroplated. This Metal then goes into the electrical system during electrolysis lyte over and thus replaces those metal ions that the Electrolytes through the deposition on the to galvanize objects are lost. Inert electrodes like they are proposed according to the invention, however, lead at more reproducible conditions and thus enable more favorable results when plating. Also read such inert electrodes are easier on under adapt different working widths of the machines than that known anode baskets filled with metal.

The inert anodes can, for example, be made of platinized Expanded metal or material coated with conductive oxide or carbon.  

If the device according to the invention is used for copper electroplating, the device with which the copper ions removed during the electroplating can be fed back to the electrolyte can comprise:

• a) a supply of metallic copper;
• b) a device with which part of the electrolyte enrichable with oxygen and the metallic copper is feedable.

Metallic copper is commonly used in sulfuric acid copper sulfate solutions not soluble. This än changes when the electrolyte is additionally oxygenated is enriched. The dosed oxygenation can so be used to a very specific amount to chemically dissolve metallic copper, so chosen is that the concentration of copper ions in the electrolyte remains essentially constant.

In particular, a pump can be featured in this context be seen which takes electrolyte from the swamp and over one or more air injectors from the supply of metalli chemical copper. In this case the oxygen which is required to loosen the metallic copper, taken from the ambient air and at the passage of the air injectors added to the electrolyte.

To get good electroplating results are cheap ones Flow conditions of the electrolyte within the machine of importance. In this regard, one proves Embodiment of the invention as advantageous, in which in the machine housing several perpendicular to the direction of motion walls of the objects are provided,  which reach close to the objects and one Include a plurality of holes through which the electrolyte Objects can be fed or removed from the objects is. In this embodiment of the invention, the Electrolyte in a variety of locations within the Machine housing fed and in the same way on one Many places removed. The confluence points and the tapping points are relatively close to the Objects, so that they are well defined in their area Form flow paths.

If the direction of flow of the electrolyte changes in Direction of movement of the objects successive walls the alternates, influences of the flow direction on the galvanization result when passing through the ge Entire device mutually compensated.

An embodiment of the invention will follow hand of the drawing explained in more detail; Show it

Figure 1 is a vertical section through an apparatus for electroplating printed circuit boards.

FIG. 2 schematically shows the device for treating the electrolyte used in the device of FIG. 1;

Fig. 3 is a block diagram of the circuit arrangement with which the operating voltage for the device shown in Fig. 1 is generated.

Fig. 1 shows a vertical section through an on device for electroplating printed circuit boards, the section plane in the left half of the figure is offset compared to the section plane in the right half of the figure. This is explained in more detail below.

The circuit boards to be electroplated are conveyed by a conveyor device, which comprises a plurality of driven rollers 2 , in the direction of arrow 3 through the machine housing 1 of the device. Immediately above and below the path of movement of the printed circuit boards, an anode 4 or 5 made of inert material, for example made of platinized expanded metal, extends parallel to this. The anodes 4 , 5 are connected via a line 6 to a power supply device, which is shown in FIG. 3 and is described in more detail below. The edge rollers of the conveyor system are designed as contact rollers 7 which are connected to a line 8 via a brush device known per se. Line 8 also leads to the power supply device already mentioned above.

The anodes 4 , 5 are except at their ends over distance holder 9 attached to the machine housing 1 . The attachment takes place indirectly in the illustrated embodiment via sheets 10 , which in turn are screwed sealed to the machine housing 1 . A plurality of distribution spaces 12 , 13 is formed between the sheets 10 and white sheets 11 , which extend above and below over the entire machine width and length. The distribution spaces 12 are used for the supply of electrolyte, the distribution spaces 13 for the removal of electrolyte from the interior of the machine housing 1 . The distribution spaces 12 , 13 alternate in the direction of movement (arrow 3 ); perpendicular to this there is a distribution space 12 opposite a distribution space 13 .

The inside of the machine housing 1 comprises a plurality of distributor walls 14 which are perpendicular to the direction of movement. A plurality of angled bores 15 , perpendicular to the plane of the drawing, are guided through each of these distributor walls 14 and connect the space between the anodes 4 , 5 to a respective distributor space 12 , 13 .

On the top and bottom of the machine housing 1 he stretch, perpendicular to the plane of Fig. 1 offset against each other, each an electrolyte feed channel 16 (right half of Fig. 1) or electrolyte discharge channel 17 (left half of Fig. 1). This makes it clear in what manner the cutting planes in the two halves of FIG. 1 are shifted from each other. The distribution spaces 12 are connected via openings 60 to the electrolyte supply channels 16 , the distribution spaces 13 via openings 61 to the electrolyte discharge channels 17 .

The upper electrolyte supply channel 16 has a connecting piece 18 which is connected to the line 19 of the device shown in FIG. 2 for processing the electrolyte. In a corresponding manner, the lower electrolyte feed channel 16 is seen with a connecting piece 20 which is connected to the line 21 of the device for processing the electrolyte of FIG. 2.

The two electrolyte discharge channels 17 each have a connecting piece 22 and 23 ; both are connected to line 24 in FIG. 2.

In the left side wall 25 in FIG. 1 of the machine housing 1 , an additional distribution space 12 a and an angled channel 14 a are incorporated; in a corresponding manner, 26 of the machine housing 1 is found in the right in Fig. 1 side wall, an additional distribution space 12 a, the through holes 14 a, 14 b with the adjacent manifold space 12 or the space between the anodes 4, 5 is connected. Fresh electrolyte is introduced into the immediate beginning or end region of the space between the anodes 4 , 5 via the distribution spaces 12 a and 12 b and the associated holes 14 a, 14 b, 14 c.

Immediately adjacent to the inlet slot 27 for the Lei terplatten in the left end wall 25 of the machine housing, nip roller pairs 28 are provided. Correspondingly, 1 pinch roller pairs 30 are located in the vicinity of the outlet slot 29 in the right end wall 26 of the machine housing 1 . The nip roller pairs 28 and 30 reduce the introduction or removal of treatment liquid into the machine housing 1 or from the machine housing 1 and also represent a type of dynamic seal which prevents electrolyte from flowing out of the machine housing 1 through the column 27 or 29 limited. The amount of electrolyte, which inevitably escapes through these leaks in the time unit, is small compared to the amount of electrolyte that is drawn off via the connecting pieces 22 and 23 , and can be made in time by means of the connecting pieces 18 and 20 supplied amount of electrolyte can be easily replaced.

In Fig. 2 that device is shown, which is used for the treatment of the electrolyte, which is introduced via the connection spigot 18 , 20 in the direction shown in Fig. 1 Before and is removed again via the connection piece 22 , 23 of this device. Since the Vorrich device works with inert anodes 4 , 5 , the copper, which is galvanized onto the circuit boards, must be supplied via the electrolyte. As will become clear later, the electrolyte also requires a certain temperature control. Both types of "preparation" take place in the device shown in FIG. 2.

This device comprises a serving as a sump for the electro lyte container 31 , which is filled to a certain level with electrolyte. A permeable basket 32 , in which copper scrap 33 is located, is immersed in this. The copper scrap 33 does not dissolve due to the electrolyte itself, which consists essentially of sulfuric acid copper sulfate. Copper ions are introduced into the electrolyte as follows:
A pump 34 removes electrolyte from the sump 31 and feeds it via a line 35 to a large number of air injectors 36 connected in parallel. In the air injectors 36 , the electrolyte is enriched with air-oxygen and thus directed onto the copper scrap 33 in the container 32 . With the help of atmospheric oxygen, the electrolyte can now dissolve the copper scrap 33 , so that additional copper ions get into the electrolyte.

The copper content in the electrolyte can be approximately between 2 and 240 g / l, preferably between 10 and fluctuate 200 g / l. A copper is particularly typical concentration of 100 g / l. Frequently about 10 g / l EDTA used as an additive.

In the line 35 is a solenoid valve 37 , which is controlled by a control device 38 for the copper content of the electrolyte. The control device 38 is connected via a line 39 to a sensor 40 arranged in the electrolyte. This monitors the concentration of copper ions in the electrolyte, for example by determining the density of the electrolyte, or in a photometric manner. If the copper ion concentration in the electrolyte drops below a certain value, the control device 38 opens the solenoid valve 37 . Now, via the air injectors 36 , electrolyte enriched with atmospheric oxygen can hit the copper scrap 33 and release copper ions therefrom until the copper ion concentration monitored by the sensor 40 has reached the desired value again. Then the control device 38 closes the magnetic valve 37 .

As already mentioned, the temperature control of the electrolyte can influence where the copper preferentially deposits on the printed circuit boards during the electrolysis in the device of FIG. 1. It has been found that cooling the electrolyte leads to the metal deposition preferably taking place on the lateral surfaces of the through-hole in the printed circuit boards. A temperature range between 10 and 30 ° C., preferably between 18 and 24 ° C., is particularly suitable. For this reason, the electrolyte is additionally cooled by the device shown in FIG. 2. For this purpose, a main cooling device 41 is initially provided, which supplies a cooling coil 42 arranged in the sump 31 with coolant. The cooling coil 42 keeps the electrolyte in the sump 31 at a certain basic temperature.

A pump 43 takes the precooled electrolyte from the sump 31 and feeds it via line 19 to the upper connection piece 18 of the machine shown in FIG. 1. In the line 19 is an auxiliary cooler 44 , the cooling coil 45 is supplied by an auxiliary cooling device 46 . The auxiliary cooling device 46 is connected via an elec trical line 47 to a temperature sensor 48 , which is arranged in the area of the objects to be electroplated on the side facing the upper inert anode 4 ( FIG. 1). The temperature sensor 47 measures the local temperature of the electrolyte there. If this rises above a certain value, the auxiliary cooling device 46 ensures by charging the cooling coil 45 in the auxiliary cooler 44 that the temperature in the area of the sensor 48 drops again in a corresponding manner.

Another pump 49 takes the sump 31 of the Einrich device of FIG. 2 electrolyte and leads this via line 21 to the lower connection piece 20 of the device shown in Fig. 1. A further auxiliary cooler 50 is located in line 21 , the cooling coil 51 of which is supplied by the auxiliary cooling device 46 independently of the cooling coil 45 . For this purpose, the auxiliary cooling device 46 is connected via an electrical line 52 to a temperature sensor 53 which is arranged in the area of the objects to be electroplated on the side facing the lower anode 5 and measures the local temperature there. With the help of the temperature sensor 53 , the auxiliary cooling device 46 and the auxiliary cooler 50 , this local temperature of the electrolyte is kept below a certain value, which may well differ from the target value of the temperature on the other side of the objects to be galvanized. Since the basic cooling of the electrolyte is already provided in the sump by the main cooling device 41 or its cooling coil 42 , the output of the auxiliary cooling device 46 need not be designed to be very large. The temperature of the electrolyte in the sump 31 is already quite close to the target values of the temperatures in the area of the upper and lower anode 4 , 5 , so that the auxiliary coolers 44 and 50 can regulate these target values very quickly and with slight control fluctuations.

The power supply device for the device of FIG. 1 is shown in FIG. 3. It comprises a schematically illustrated transformer 54 , which is connected on the primary side to the mains voltage and on the secondary side with two impulse generators 55 , 56 . The pulse generators 55 and 56 can each independently generate rectangular pulses, the frequency, clock ratio, amplitude, polarity and relative phase position are essentially freely selectable. The output signals of the two pulse generators 55 and 56 are superimposed and fed to the electrodes of the device of FIG. 1 via lines 6 and 8, respectively. At the electrodes (anodes 4 , 5 , contact wheels 7 and thus finally the circuit board itself) is therefore a pulsed DC voltage. Corresponding to the function of the device, a positive voltage is predominantly applied to the anodes 4 , 5 on average over time; during certain periods, however, a polarity reversal can take place in such a way that the anodes 4 , 5 are negative with respect to the contact rollers 7 and thus with respect to the printed circuit boards. During these time phases, the copper layer deposited on the printed circuit boards is briefly removed again. In addition, polarization and concentration effects in the vicinity of the electrodes of the device of FIG. 1 are largely eliminated. The delivered by the two pulse generators 55 and 56 in the pulse are optimized for the respective application and adapted to the given geometry of both the circuit board itself and the device as well as the chemical composition and temperature of the electrolyte. With optimal settings, which can be determined by means of targeted test series, very high deposition rates of a few µ per meter can be achieved with a movement speed of about one meter per minute of the printed circuit boards. This means that in a device, the total length of which does not exceed 5 meters, a layer with a thickness of 25 μ can be electroplated in one step. The safety layer with a thickness of 4-5 μ that was previously used in the electroplating of printed circuit boards and which was applied separately can be omitted.

Claims (14)

1. Device for electroplating, in particular copper plating, flat, plate-shaped or arc-shaped objects, in particular printed circuit boards, with

• a) a machine housing which has a space which can be filled with a liquid electrolyte;
• b) a conveyor which conveys the objects substantially horizontally, parallel to their main direction of extension, continuously from an input to an output through the machine housing;
• c) at least one anode which extends parallel to the movement path of the objects and is connected to a first pole of a voltage source;
• d) a contacting device which makes electrical contact with the objects and is connected to a second pole of the voltage source;

characterized in that the voltage source comprises at least one adjustable pulse generator ( 55 , 56 ), the output signals of which are applied to the anodes ( 4 , 5 ) and the contacting device ( 7 ) and square-wave pulses with a selectable repetition frequency, clock ratio, amplitude and polarity, whereby on average the anode ( 4 , 5 ) is positive with respect to the contacting device ( 7 ). 2. Device according to claim 1, characterized in that the voltage source comprises at least two independently working pulse generators ( 55 , 56 ), the added output signals of which are applied to the anode ( 4 , 5 ) or the contacting device ( 7 ) and their relative phase position is adjustable. 3. Apparatus according to claim 1 or 2, characterized in that the one or more pulse generators ( 55 , 56 ) generate such output signals that the effective at the anode ( 4 , 5 ) or the contacting device ( 7 ) voltage during part the time has the opposite polarity, at which the anode ( 4 , 5 ) relative to the contacting device ( 7 ) is negative. 4. Device according to one of the preceding claims, characterized in that the repetition frequency of the output signals of the pulse generator ( 55 , 56 ) is between 10 and 10,000 Hz. 5. Device according to one of the preceding claims, that a device ( 42 , 44 , 50 ) is provided with which the electrolyte can be cooled. 6. The device according to claim 5, characterized in that a sump ( 31 ) is provided for the electrolyte, from which the electrolyte is continuously brought into the electrolyte-fillable space of the machine housing ( 1 ) and in which the electrolyte is returned from there and that the cooling device comprises:

• a) a main cooler ( 42 ) with which the electrolyte in the sump ( 31 ) is kept below a first selectable temperature;
• b) at least one auxiliary cooler ( 44 , 50 ) with which the electrolyte removed from the sump ( 31 ) can be cooled on the way to the space of the machine housing ( 1 ) which can be filled with electrolyte and which keeps this electrolyte at a second preselectable temperature which is lower than the first.

7. The device according to claim 6, in which both sides parallel to the path of movement of the objects each anode, characterized in that two independently operable auxiliary coolers ( 44 , 50 ) are provided, the electrolyte flowing through the first auxiliary cooler ( 44 ) the objects on the side facing one anode ( 4 ) and the electrolyte flowing through the other auxiliary cooler ( 50 ) are fed to the objects on the side facing the other anode ( 5 ). 8. The device according to claim 7, characterized in that each auxiliary cooler ( 44 , 50 ) in the vicinity of the objects on the corresponding anode ( 4 , 5 ) facing side arranged temperature sensor ( 48 , 53 ) is assigned, which the monitors the temperature of the electrolyte there and then controls the associated auxiliary cooler ( 44 , 50 ). 9. Device according to one of the preceding claims, characterized in that the anode ( 4 , 5 ) is a first dimensionally stable electrode and a separate device ( 34-40 ) is provided with which the electrolyte the metal ions removed during the galvanization again are feedable. 10. The device according to claim 9, characterized in that the anode ( 4 , 5 ) consists of platinized expanded metal or material coated with conductive oxide or carbon. 11. The device according to claim 9 for copper electroplating, characterized in that the device with which the electrolyte is removed from the copper ions withdrawn during the electroplating comprises:

• a) a supply ( 33 ) of metallic copper;
• b) a device ( 34-40 ) with which part of the electrolyte can be enriched with oxygen and the metallic copper can be supplied.

12. The apparatus according to claim 11, characterized in that a pump ( 34 ) is provided which takes the electrolyte from the sump ( 31 ) and injectors ( 36 ) to the supply ( 33 ) of metallic copper via one or more air injectors. 13. Device according to one of the preceding claims, characterized in that in the machine housing ( 1 ) a plurality of perpendicular to the direction of movement of the objects walls ( 14 ) are provided, which come up close to the objects and comprise a plurality of holes ( 15 ) , via which the electrolyte can be supplied to or removed from the objects. 14. The apparatus according to claim 13, characterized in that the flow direction of the electrolyte alternates with successive walls ( 14 ) in the direction of movement of the objects.