WO2004053185A1

WO2004053185A1 - Method for the conservation of metal surfaces

Info

Publication number: WO2004053185A1
Application number: PCT/DE2003/003991
Authority: WO
Inventors: Uwe Landau
Original assignee: OTB Oberflächentechnik in Berlin GmbH & Co.
Priority date: 2002-12-06
Filing date: 2003-12-03
Publication date: 2004-06-24
Also published as: DE10257344A1; EP1570100A1; AU2003296518A1

Abstract

Disclosed is a method for the conservation of metal surfaces (10a) by means of plasma treatment in a CO2 containing and/or N2- containing reactive gas atmosphere, wherein the metal surfaces (10a) are preferably exposed to a dielectric barrier discharge (DBE) at atmospheric pressure. Ignition occurs with a high-frequency alternating current of typically approximately 1-10 kV between a discharge electrode (14) and a counter electrode (10), whereby at least one thereof is insulated dielectrically in relation to the discharge chamber (16) formed therebetween by means of a suitable dielectric (14a) such as, for instance glass or ceramic material. Preferably, the metal surface (10a) to be treated is earthed and used as a counter electrode (10) for at least one discharge electrode (14) which is embodied as a form electrode which reproduces the surface contours in a plane-parallel manner. The dielectric barrier discharge cannot, however, also be performed between plane-parallel electrodes whereby at least one of which is electrically insulated. According to the invention, an indirect dielectric barrier discharge can also be used, whereby the discharges (20) are carried out in an adjacent position in relation to the metal surface (10a) and whereby the respectively used inflowing reactive gas, is brought into contact therewith by means of plasma jets, for example. The above-mentioned method is particulary suitable for continuous or quasi-continuous conservation of metal strips (10), cut strips, circuit boards or succesively arranged individual parts.

Description

Process for the preservation of metal surfaces

description

The present invention relates to a method for the preservation of metal surfaces and objects or workpieces with correspondingly preserved surfaces.

High-quality metal surfaces play a major role in numerous technical fields of application. In microelectronics in particular, the progressive miniaturization of electronic components leads to ever higher demands on the surface quality, as an indispensable prerequisite for achieving the necessary high yields in the microelectronic machining processes. In this context, not only the finest impurities, e.g. by oils or greases, but also very thin oxide layers, which almost inevitably form on the surface during the storage and transport of workpieces. In the case of copper alloy strips for the production of electronic components, for example, light oxide layers are immediately noticeable due to a reddish discoloration and have a negative effect on the adhesive strength when the soldering, bonding or adhesive work is required. These oxide layers represent a major problem, particularly in the case of long transport and storage times, which in industrial practice necessitates the otherwise unnecessary subsequent cleaning of the strips in a pickle.

The object of the present invention is therefore to provide a method for the preservation of metal surfaces, by means of which in particular oxidation or tarnishing of the surfaces is reliably prevented or at least greatly weakened or reduced without the surface being attacked or in terms of its desired application properties is changed. The method sought is intended in particular to enable simple and inexpensive preservation of metal surfaces comprising copper, nickel, silver or their alloys, so that it is also suitable for electronic, in particular microelectronic, applications in which the provision and processing of corresponding surfaces with a very high surface quality is of great importance for numerous areas of application. In order to ensure sufficiently high yields, it should also enable continuous or at least quasi-continuous processing in one pass. This object is achieved according to the invention in that the metal surfaces are subjected to a plasma treatment in a reactive gas atmosphere containing CO ₂ and / or N ₂ . The gases mentioned can be used either individually or in any mixing ratio. However, mixtures with other gases, such as argon, are also possible. Conveniently, gases from standard gas cylinders can be used.

This plasma treatment of the metal surfaces according to the invention brings about a lasting suppression of the oxidation reactions which otherwise normally take place on the surface and thus leads to a preservation of the surfaces without these being attacked or their application properties being adversely changed. This not only leads to reliable oxidation protection of the surfaces under normal ambient conditions, but also prevents or delays tarnishing, at least even at higher temperatures, i.e. Oxidize the surfaces. For example, nickel silver and copper surfaces preserved according to the invention are resistant to tarnishing, for example at 200 ° C. for at least 1 hour and at 250 ° C. for at least 5 minutes.

In addition, the plasma treatment also causes (known per se) the desired cleaning of the surfaces from organic impurities and thus also leads to a noticeable improvement in the surface quality for subsequent machining or processing processes, so that additional cleaning steps to remove these undesirable impurities are eliminated. With regard to more detailed information on these cleaning effects by means of a plasma treatment, reference is made here, by way of example, to DE 43 32 866 A1, the information content of which is hereby fully incorporated into the present documents.

The preservation method according to the invention is particularly suitable for metal surfaces comprising copper, nickel, silver or their alloys, so that it is suitable for numerous electronic and microelectronic applications, such as, for example, the preservation of copper alloy carrier tapes for the production of electronic components (diodes, ICs, switches) , etc.) or PCBs. However, it can also be used for other metals or metal alloys. If necessary, these can also be applied to a non-metallic base, such as a plastic (endless) belt. In order to increase the surface reactions, the reactive gas is preferably allowed to flow relative to the surface in order to remove the reaction products formed and to bring new gas to the surface. Here, a flow rate between about 0.05 and 1 m / s has proven itself.

In principle, all conventional plasma processes such as e.g. a plasma treatment in a vacuum plasma system can be used. For economic reasons, however, a dielectric barrier discharge (DBE) is preferably used, which can be carried out under atmospheric pressure and at ambient temperature without great technical outlay and thus economically very cheaply. In such a dielectric barrier discharge, which is also called dielectric barrier discharge or silent discharge, the workpiece with the surface to be preserved is exposed to a corona discharge, which takes place between a discharge electrode and a counter electrode, at least one of which is dieelective with respect to the one between them formed discharge space is isolated.

In one embodiment of the invention, the metal surface to be treated is grounded and used as a counter electrode for at least one discharge electrode which is dielectrically insulated from the discharge gap for a direct dielectric barrier discharge between the two electrodes. This ensures that no voltage potential builds up on the metal surface, so that it can be easily touched during the preservation process. In particular, a discharge electrode is used as the discharge electrode, which reproduces the surface contours of the surface to be treated in a plane-parallel manner.

In a further embodiment according to the invention, however, the plasma treatment can also be carried out by a direct dielectric barrier discharge in a discharge space or discharge gap between plane-parallel electrodes, at least one of which is electrically insulated. This can be a glass electrode, for example, which is provided with a conductive layer on one side.

However, the plasma treatment can also be carried out according to the invention by means of an indirect dielectric barrier discharge, in which the discharges take place adjacent to the surface to be treated and are brought into contact with the surface by the inflowing reactive gas used, for example by means of so-called plasma nozzles. In addition to the glass already mentioned, ceramic is also usually used as the dielectric.

A voltage between approximately 1 and 10 kV, in particular, however, approximately 5 kV, with a frequency between approximately 20 and 200 kHz, in particular approximately 30 kHz, is typically used to generate the dielectric barrier discharges. Instead of the high frequency, however, a correspondingly lower frequency between approximately 50 and 60 Hz can also be used in a corresponding device.

For economic reasons, the surfaces to be treated are preferably preserved continuously or quasi-continuously in a single pass.

The method according to the invention is particularly suitable for the preservation of metallic tapes, in particular metallic lead frames as tape material (contacts, lead frames or carrier tapes, wires) for the production of electronic components (semiconductor components, switches or switch contacts bonded to lead frames) in the processing forms customary today , These belts can simply be fed continuously as an endless belt under ambient conditions through a suitable plasma treatment device filled with a reactive gas of the type mentioned and can be preserved there against oxidation influences in a simple and very inexpensive manner. However, the method according to the invention also enables a very economical preservation of tape strips (cut strips) of typically about 100-300 mm in length and a quasi-continuous processing of individual parts, such as PCBs or electronic shield housings arranged one behind the other, in continuous operation. These can be applied, for example, on a suitable plastic tape.

The plasma treatment method according to the invention makes it possible to produce workpieces with correspondingly preserved metal surfaces in a simple and inexpensive manner for numerous fields of application. The surfaces here preferably comprise copper, nickel, silver or their alloys, such as e.g. German silver.

Further details, features and advantages of the present invention result not only from the associated claims - individually and / or in combination - but also from the following description of three preferred exemplary embodiments according to the invention in conjunction with the associated drawings. The drawings show: 1 shows a schematic representation of a first surface preservation according to the invention by means of a direct dielectric barrier discharge;

2 shows a schematic representation of a second surface preservation according to the invention by means of a direct dielectric barrier discharge; and

Fig. 3 is a schematic representation of a surface preservation according to the invention by means of an indirect dielectric barrier discharge.

1 shows a copper alloy strip 10 as a workpiece, which is moved in the form of an endless strip at ambient temperature and pressure at about 1 m / min in the direction of arrow 12 from right to left. The copper alloy strip 10 is grounded, so that no voltage potential builds up on the metal surface 10a during the preservation process and an operator can easily touch it in order to intervene in the processing process if necessary.

Opposite to the copper alloy strip 10 there is a discharge electrode 14 arranged parallel to it, which forms with the copper alloy strip 10 a narrow dielectric discharge space or discharge gap 16 of approximately 2 mm in height.

In the discharge gap 16, pure CO _{2 flows} from a reactive gas supply device (not shown), such as a commercially available gas bottle, in the direction of arrow 18 from left to right through the discharge gap 16 in order to discharge reaction products formed from the discharge gap 16 and to supply fresh carbon dioxide to bring up the surface 10a to be preserved. The flow rate is about 0.1 m / s. Depending on the application, this value can vary in certain areas. For example, in some applications, lower flow velocities of up to about 0.05 m / s and less or higher flow velocities of up to about 1 m / s and more can be set. Instead of carbon dioxide, nitrogen from commercially available gas bottles or a CO ₂ / N ₂ mixture with any mixing ratio can also be used. It is also possible to add other gases, such as Ar.

The discharge electrode 14 comprises an approximately 5 mm thick glass pane 14a (although a ceramic pane can optionally also be used as a dielectric) with a conductive layer 14b applied on the back, to which a high-frequency AC voltage of typically approximately 5 kV and a frequency of typically approximately 30 kHz is applied , At this high-frequency voltage, electrical discharges are made in the discharge gap 16 between the glass pane 14a and the surface 10a of the copper alloy strip 10 Discharges ignited, which are shown as discharge filaments 20. These discharge filaments 20 constantly re-ignite due to the alternating voltage present, so that a spatially homogeneous plasma is present in the discharge gap 16 on average over time. This plasma interacts with the surface 10a of the copper alloy strip 10 and reliably preserves it even at higher ambient temperatures against the formation of an undesired oxidation layer or against tarnishing, without the surface 10a being attacked or disadvantageous in terms of its desired application properties for subsequent microelectronic treatment or processing processes would be changed. This eliminates the need for prior cleaning of the metal surface 10a, which has been formed in the interim, from oxide layers that have formed in the meantime.

As already mentioned, the plasma treatment also brings about a very desirable additional cleaning of the metal surface 10a from any adhering organic contaminants, such as e.g. Oils or greases, and not only leads to a corresponding improvement in the surface quality, but also makes additional cleaning steps for removing these organic contaminants superfluous.

2 shows an exemplary, two-sided surface preservation according to the invention of a copper alloy strip 10, which is again wound onto a winding reel 26 at a speed of approximately 1 m / s from a decoiler 22 via two counter-rotating deflection reels 24a, 24b. Three dielectrically insulated discharge electrodes 14 are arranged at a distance from the two deflection reels 24a, 24b, the three discharge electrodes 14 assigned to the deflection reel 24a being located above the deflection reel 24a and the three discharge electrodes 14 assigned to the deflection reel 24b being located below the deflection reel 24b.

The two deflection reels 24a and 24b, together with the three discharge electrodes 14 assigned to them, each form a discharge space 16a, 16b, through which nitrogen can be flowed in from a gas supply device (not shown) in the direction of the arrows 18 in order to produce reaction products from the two discharge spaces 16a , 16b and to bring fresh nitrogen to the surfaces 10a to be preserved. The flow rate is again about 0.1 m / s. Instead of nitrogen, carbon dioxide from standard gas cylinders can also be used. If necessary, mixtures of both gases can also be used. The copper alloy strip 10 is now guided over the first and under the second deflection reel 24a or 24b through the first and second discharge space 16a or 16b in such a way that in the first discharge space 16a its top side and then in the second discharge space 16b its bottom side with the interacts electrical discharges 20, which are generated by applying a suitable high-frequency voltage to the discharge electrodes 14 in the two discharge spaces 16a, 16b. As a result, the copper alloy strip 10 is provided on both sides with a surface protection according to the invention against oxidation or tarnishing.

However, according to the invention, the plasma treatment of a workpiece surface to be preserved can also be carried out by a direct dielectric barrier discharge between plane-parallel electrodes, of which in turn at least one is electrically insulated with respect to a dielectric discharge space formed between them. Glass or ceramic panes, which are provided with a conductive layer on their respective opposite side, can in turn serve as electrodes. The workpiece to be preserved is simply inserted into the discharge space between the two discharge electrodes.

However, three-dimensional workpieces can, for example, also be arranged in a formula electrode which reproduces the contours of the workpiece in a plane-parallel manner.

3 exemplarily illustrates the surface preservation of a workpiece 10 with a metal surface 10a according to the invention by means of an indirect dielectric barrier discharge. A discharge electrode 14 with an associated counter electrode 14 'is arranged adjacent to the metal surface 10a to be preserved, the discharge electrode 14 being electrically insulated by a dielectric 14a with respect to an electrical discharge space 16 formed between the electrodes 14, 14'. A high-frequency voltage of the type mentioned is in turn applied to the discharge electrode 14, so that electrical discharges are continuously ignited in the discharge space 16. These discharges are brought into contact with the metal surface 10a by means of carbon dioxide, which flows in the direction of the arrow 18 through the discharge space 16 against the metal surface 10a, with which they in turn interact in the known manner and thereby effect the desired surface preservation.

Claims

claims

1. A method for the preservation of metal surfaces (10a), characterized in that the metal surfaces (10a) are subjected to a plasma treatment in a reactive gas atmosphere containing CO ₂ and / or N ₂ .

2. The method according to claim 1, characterized in that metal surfaces (10a) are preserved, which comprise copper, nickel, silver or their alloys.

3. The method according to claim 1 or 2, characterized in that the reactive gas is allowed to flow relative to the metal surface (10a).

4. The method according to claim 3, characterized in that a flow rate between 0.05 and 1 m / s is set.

5. The method according to any one of the preceding claims, characterized in that a dielectric barrier discharge under atmospheric pressure is used for the plasma treatment.

6. The method according to claim 5, characterized in that the metal surface to be treated (10a) is grounded and used in the dielectric barrier discharge as a counter electrode (10) for at least one discharge electrode (14).

7. The method according to claim 6, characterized in that a formula electrode is used as the discharge electrode (14), which reproduces the surface contours plane-parallel.

8. The method according to claim 5, characterized in that the plasma treatment is carried out by a direct dielectric barrier discharge between plane-parallel electrodes (14, 14 ').

9. The method according to claim 5, characterized in that the plasma treatment is carried out by an indirect dielectric barrier discharge, in which the discharges are brought into contact with the surface (10a) by the reactive gas.

10. The method according to any one of claims 5-9, characterized in that glass or ceramic is used as the dielectric (14a).

11. The method according to any one of claims 5-10, characterized in that a high voltage between 1 and 10 kV with a frequency between 20 and 200 kHz is used.

12. The method according to any one of the preceding claims, characterized in that the preservation is carried out continuously or quasi-continuously in one pass.

13. The method according to claim 12, characterized in that metallic strips (10), strip strips (cut strips), printed circuit boards or individual parts arranged one behind the other are processed.

14. Workpiece (10) with a metal surface (10a) preserved by a plasma treatment method according to one of the preceding claims.

15. Workpiece according to claim 14, characterized in that the metal surface (10a) comprises copper, nickel, silver or their alloys.