DE4204193A1 - Electrolytic capacitor prodn. - by coating capacitor foil and/or anode body using sputtering process - Google Patents

Abstract

Prodn. of an electrolytic capacitor comprises coating the capacitor foil and/or the anode body, produced by pressing, before processing to capacitors, in which the material is deposited by sputtering. The appts. comprises a vessel (2); a high voltage prodn. appts. (3); and two high voltage electrodes (4,5) opposite each other in (2). In the vessel (2) of the appts. (1), strip-like carriers (7) are arranged for a foil and a number of capacitor bodies. The drive (12) moves the material (5) to be coated or the carrier with the capacitor body under the plasma zone (11) across the direction of the electric field produced between the electrodes. A capacitor foil made of Al or Ta or a Ta body produced by sintering is used as subtrate (5). Highly pure Al, Ta or Ti is used as target (4). ADVANTAGE - The capacitor has high capacity.

Description

The invention relates to a method in the preamble of claim 1 specified type and a device for Execution of the procedure.

The capacitance C of a plate capacitor is calculated using the formula
C = ε ε _oA / d,
where ε _{o is} the electrical field constant, ε is the dielectric constant of the capacitor, A is the effective area of the opposing electrodes and d is the distance between them. Strictly speaking, this formula only applies to large capacitors, but is also a good approximation for wound capacitors. While the minimum size of d is usually determined by the dielectric strength of the dielectric, the other sizes can be determined by physical means Possibilities are freely available.

A parameter for the when manufacturing a condenser The technical standard achieved is set by the spe specific capacity - that is, based on the component volume capacity - represents. In the pursuit of miniaturization It is of particular importance today that the construction size size of capacitors of specified capacitance (and nominal voltage solution) if possible to reduce it further.

High capacitance capacitors are commonly known as elec trolytic capacitors. Here is the one Plus pole-forming film made of aluminum or tantalum stands, an oxide layer applied electrolytically, wherein the electrolyte forms the cathode. The electrolyte is located with aluminum capacitors in an absorbent Pa pier, sintered is used for tantalum capacitors Tantalum powder and manganese dioxide. Here is a first Base body sintered from tantalum powder, then oxi dated (formed) and then covered with manganese dioxide.  

The manganese dioxide serves as the electrolyte and the tan Talode powder forms the anode.

Because of the given materials the dielectric number is also given, remains as an option to increase capacity essentially only the enlargement area A. A direct enlargement of the area che of the film material used would in turn an undesirable enlargement of the component bring. However, it is known the specific capacity by roughening the film surface. At Tantalum capacitors are used to sinter the tantalum powder also the surface enlargement.

Here is from DE-OS 31 27 161 a method for Her provision of electrode foils for electrolytic capacitors known, in the hard-rolled aluminum foil after pickling process is electrolytically roughened in an etching solution. The etching bath contains an electrolyte with a mixture from different chloride ions that as solutions like Hydrochloric acid or aluminum, sodium, potassium, magnesium or calcium chloride are present. The etching is at a bath temperature in the range of 60 to 100 ° C below Exposure to direct current with low ripple guided.

Furthermore, from DE-OS 39 14 000 a method for Production of roughened aluminum foils for low voltage Electrolytic capacitors known, which is also an elec trolytic etching bath required. At essentially the same The aluminum fo  In contrast to the previously mentioned method, the Etching bath treated with a pulse current.

Both known methods have the disadvantage that the technological process parameters, such as bath composition temperature, bath temperature, residence time of the aluminum foil in the Etching bath and ripple or frequency of the current, of which the surface roughness and thus the desired capacity increase in capacitors made from these foils is crucially dependent, only with a significant increase wall on measuring and control equipment can be held. Add to that the electrolytic roughened capacitor foils after removal from the etch also a technologically complex dishwashing and Cleaning process must be subjected. The essential However, the disadvantage of the etching process is that despite of the considerable technological expenditure only one Surface roughness of the capacitor foil can be achieved, which leads to a maximum capacity increase of 33%.

Based on the shortcomings of the prior art the invention has for its object a method of to specify the genus mentioned, with the less technological effort to treat the capacitor fo lines or bodies a significantly higher degree of surface Enlargement compared to the known etching process ren is reachable. In addition, a device for Perform the procedure.

This task is carried out with the characteristic features of Claims 1 and 11 solved.  

The invention includes the knowledge that it is for the Enlargement of the effective surface of condensers metal electrodes serving metal electrodes compared to the known etching process is much more effective instead the roughening of the surface of the capacitor foils or -body on these foils by using the sputter- Technology to apply a layer with high porosity. The same applies to an additional enlargement the surface of sintered bodies for tantalum capacitors. Such a coating enables enlargement the effective surface by several orders of magnitude.

To carry out the coating process of foils or bodies for the production of electrolyte condensates satoren is a direct voltage diode sputtering system (DC cathode sputtering) particularly cheap because both the parallel arrangement of the electrodes and the relatively short distance between the electrodes of the Dio densystems for the arrangement of foil materials (elec trolytic capacitors) or smaller anode bodies (Tan valley capacitors) between them are favorable. The Electrodes are located within an inert gas filled recipients and are connected to a high voltage system connected. The body to be coated (substrate) carries a positive, preferably earth potential, whereas the sputter cathode (target) with the negative output of the High-voltage system is connected. After applying the high Voltage to the electrodes ignites the discharge in dependence the internal pressure of the recipient and the electrodes distance, with an ionization between the electrodes capable plasma is created. The ion impact from the  Target metal atoms diffuse through the Plasma and hit on the substrate as condensate low. The majority of the dust particles are electrically neutral and have a quintuple higher energy than particles from thermal sources can be evaporated. This results in a higher one Adhesive strength of sputtered versus vaporized Layers.

According to another advantageous development of the same voltage diode sputtering system it is favorable to the between an existing magnetic field in their electrodes table field overlay. This can result in reduction an increase in the working pressure in the recipient Collision path of the accelerated particles in the plasma area be enough.

In contrast to the known coating processes, the individual workpieces of various configurations ration are located after the before preferred embodiment of the invention two, each with equipped with a separate electric drive and Foil-carrying winding bodies in gas-loaded receptacles the cathode sputtering system. The foil material becomes essentially parallel to after the discharge is ignited the electrodes and perpendicular to the direction of the tw existing electrical field moves them. Here the film material is taken off a roll and onto the others wound up. The transport speed of the Aluminum or tan to be coated according to the invention Valley foil depends on the desired layer  thickness based on the possible dusting rate (0.66 µm / min for aluminum, 0.69 µm / min for tantalum and 0.36 µm / min for Titan at 10 kW power) and the length of the sputtering roughness appropriately regulated. The main characteristics of the metal layers that can be applied by sputtering (in particular Layer thickness and surface structure) are essentially chen by the type of inert gases in the recipient of the Katho atomization system, the associated internal pressure, of the distance between target and substrate as well as from the Substrate temperature in relation to the melting temperature of the Determined substrate.

According to a preferred embodiment of the invention, the recipient of the cathode sputtering system is filled with argon at a pressure in the range 1 ≦ p ≦ 30 µbar. According to a favorable development of the invention in terms of process costs, a protective gas atmosphere in the recipient of the system is generated by a mixture of argon and nitrogen. The formed as a film (for electrolytic capacitors) or as an anode body (for tantalum capacitors) has a temperature T _o during sputtering, which should be kept essentially constant by cooling, since the substrate - due to the thermal heating - during during the coating process. The temperature ratio T of substrate temperature T _o and melting temperature T _m can be varied according to the process in a range from T <0.2. A range of 0.3 ≦ T ≦ 0.8 appears favorable, with higher values of T leading to an increase in the layer density per sputtering process with a simultaneous increase in the surface roughness of the applied layer. After reaching a maximum of the roughness, a decrease in the temperature ratio T can occur again. The optimal value may have to be determined experimentally. For films or base bodies for the production of electrolytic capacitors, either aluminum, tantalum or titanium is used as the target. The higher substrate temperatures are more favorable in order to achieve a greater roughness of the coating, since in this temperature range there is essentially a porous column growth when the coating is formed.

The investigation of the surface quality fiction according to coated foils with a scanning electron microscope showed an essentially cauliflower-like Structure of the coating showing an increase in surface compared to the uncoated condition by several sizes results in regulations. With aluminum coated in this way nium or tantalum foils are advantageous Electrolytic capacitors can be produced at the same Size have a correspondingly increased capacity.

Advantageous developments of the invention are in the Un claims are identified below along with the description of the preferred embodiment the invention with reference to the figures. It demonstrate:

Fig. 1 a preferred embodiment of the DC clamping nungssputteranlage for coating condensate sator sheets in a schematic cross-sectional representation,

Fig. 2 is a development of the system shown in Fig. 1 in a schematic sectional illustration,

3 shows another advantageous further development of the system shown in FIG.

Fig. 4 shows another embodiment of the system shown in Fig. 1 as well

Fig. 5 is a scanning electron microscope through a portion taken on a coated film surface.

In Fig. 1 a suitable for coating capacitor foils DC diode sputtering system 1 is shown in cross section in schematic form. It essentially consists of a recipient 2 , which is evacuated via a vacuum pump 8 and then charged with a protective gas, preferably argon, via a line 10 controlled by a valve 9 . Inside the recipient 2 there are the electrodes 4 , which are designated as target 4 (cathode) and substrate 5 (anode), and are arranged opposite each other at a distance of a few centimeters. The electrodes 4 , 5 are polarized accordingly, connected to a high-voltage generating plant 3 .

The target 4 consists of aluminum, tantalum or titanium with a high degree of purity, whereas the substrate 5 is formed from the aluminum or tantalum foil to be coated, under which a guide plate 13 is arranged for mechanical stabilization. Since a certain temperature must be maintained for desired layer thicknesses with a defined porosity on the substrate, the excess amount of heat generated during sputtering on the substrate is dissipated via the guide plate 13 to a cooling system 6 . Elements of the same cooling system are arranged on the top of the target 4 and protect it from overheating. After the high voltage has been applied to the electrodes 4 , 5 , a discharge is ignited between them, a plasma 11 forming in the space between the electrodes 4 , 5 . Ionized plasma particles are accelerated to the target 4 by the electrical field existing between the electrodes 4 , 5 and trigger the emission of metal atoms there, which move to the substrate 5 with high specific energy and are deposited as a coating. The material to be coated is arranged so that it can be unwound on a film carrier 7 . From there it is unrolled, coated and then wound onto a second film carrier. The film carriers 7 are each set in rotation by a drive unit 12 whose speed can be controlled, the film 5 to be coated being transported below the plasma 11 transversely in the direction of the electrical field existing between the electrodes 4 , 5 .

The for a safe winding and unwinding of the film mat rials required leadership and leadership roles are out Not shown for reasons of clarity. Same thing applies to process control and monitoring systems that a fully automatic management of the film enable stratification.  

Are shown in Figs. 2, 3 and 4. Advantageous developments of the sputtering equipment 1 according to Fig. 1 in schemati lized form. For a simpler substrate structure, it is favorable to pass the film to be coated directly over the cooling system 6 ( FIG. 2). The required connection of the substrate 5 takes place via a sliding contact 14 which is suitably arranged on one of the film carriers 7 . In order to support the acceleration of the charge carriers of the plasma 11 by the electric field during the sputtering process, a magnet system 16 is additionally arranged on the rear of the target 4 ( FIG. 3). The superimposition of the existing electric field with a magnetic field leads to an effective extension of the ionization path by helically deflecting the electrons released during the impact processes in the plasma 11 , whereby more inert gas atoms can be ionized. At the same time it is achieved that the substrate 5 is mainly hit by atomized material and thus hen only relatively low substrate temperatures arise. For the implementation of the coating process by cathode sputtering, it is still advantageous to reduce the operating costs by realizing the protective gas atmosphere required in the recipient 2 by a mixture of argon and nitrogen. The recipient 2 therefore has an additional, valve-controlled line 15 , via which nitrogen can be supplied in a defined amount ( FIG. 4). It has proven to be favorable to produce the protective gas atmosphere in equal parts from argon and nitrogen.

In variants not shown of the previously shown Sputtering systems are the same as a power supply  voltage or high-frequency AC voltage source seen. Another advantageous embodiment exists in that the sputtering system is designed as a triode system at which the bias voltage is chosen to be very low and in particular is zero.

For the production of electrolytic capacitors, which are gesin Have tantalum shaped bodies, this form body on a film-shaped means of transport, which in place of the capacitor foil shown above occurs in a continuous cycle through the previously represented asked device performed, the residence time in Area of influence is chosen so that the droplet-shaped elements with a corresponding one by sputtering worn layer.

In FIG. 5 the image of a, cutout recorded by means of scanning electron microscope of a coated surface by sputtering is Darge provides. The coating has a cauliflower-like structure. This can be described with the help of a fractal structure, which consists of a large number of hemispheres in a layered layer. In the next layer layer, the existing hemispheres are attached to other hemispheres or parts of hemispheres etc. Depending on the coating time, the cauliflower-like surface structures can be produced on the film forming the substrate, which are necessary for a desired increase in capacity. More than five layers are favorable. The desired layer thickness can be applied in one coating process.

In practical investigations, layers emerged wear, where an increase in their active surface che was ascertainable by more than three orders of magnitude. These results exceed those with the usual etching process driving or sintering methods achievable surface roughness skills considerably. With those coated by sputtering Aluminum or tantalum foils or pressed moldings can be capacitors with very high capacities produce extremely low volume of the components.

The invention is not restricted in its implementation to the preferred embodiment given above game. Rather, a number of variants are conceivable which of the solution shown also in principle makes use of different types.

Claims (15)

1. A method for producing an electrolytic capacitor, characterized in that the capacitor foil or the anode body produced by compression molding is subjected to a coating process prior to further processing into capacitors, with the aim of increasing the effective foil or body surface, in which the material application done by a sputtering process. 2. A method for producing a capacitor according to claim 1, characterized in that a capacitor foil made of aluminum or tantalum or a, in particular by sintering, molded body made of tantalum is used as the substrate ( 5 ). 3. A method for producing a capacitor according to claim 1, characterized in that high-purity aluminum, tantalum or titanium is used as the target ( 4 ). 4. A method for producing a capacitor according to one of the preceding claims, characterized in that a DC sputtering system ( 1 ) is used for the coating process. 5. A method for producing a capacitor according to claim 4, characterized in that the DC sputtering system ( 1 ) has a diode system. 6. Method for producing a capacitor according to egg nem of the preceding claims, thereby ge indicates that the sputtering process in one Shielding gas atmosphere at a pressure in the range of 1 ≦ p ≦ 30 µbar is carried out. 7. A method of manufacturing a capacitor according to An saying 6, characterized, that as a protective gas, a mixture of argon and nitrogen is used. 8. A method of manufacturing a capacitor according to An saying 7, characterized, that the protective gas mixture is made in a ratio of 1: 1 becomes. 9. A method for producing a capacitor according to one of the preceding claims, characterized in that the temperature ratio T of substrate temperature T _o and melt repair of the substrate T _{m is} in a range from 0.3 ≦ T ≦ 0.8. 10. Sputtering system for coating capacitors according to one of the preceding claims, comprising

• - a recipient ( 2 ),
• - A high-voltage generating plant ( 3 ) and
• - two high-voltage electrodes ( 4 , 5 ), which face each other at a short distance within the recipient,

characterized in that in the recipient ( 2 ) of the sputtering system ( 1 ) band-shaped carrier ( 7 ) for a film or a number of condenser bodies are provided, the drive units ( 12 ) the film material to be coated ( 5 ) or the Move the carrier having the capacitor body below the plasma zone ( 11 ) essentially transversely to the direction of the electrical field present between the electrodes. 11. Sputtering system according to claim 10, characterized in that the drive units ( 12 ) are designed to be adjustable in their speed. 12. Sputtering system according to claim 11, characterized in that the high-voltage generation system for ( 3 ) voltage supply of the substrate has a sliding contact ( 14 ) which is arranged on the foil carrier ( 7 ). 13. Sputtering system according to one of claims 10 to 12, characterized in that as Power supply a DC voltage or high frequency te AC voltage source is provided. 14. Sputtering system according to one of claims 10 to 13, characterized in that this is designed as a triode system in which the bias chip voltage is chosen to be very low and is in particular zero.