KR20020021629A - Process for electroplating a work piece coated with an electrically conducting polymer - Google Patents

Abstract

It is an object of the present invention to provide an electroplating process of a workpiece 1 coated with an electroconductive or modified polymer, which can simultaneously reduce current density and shorten electroplating time, independently from the workpiece to be electroplated. The invention is a first step, in which the workpiece is connected to the power source 8 with a complex adjacent contact element 5 and covered with a thin metal coat except for the point covered by the contact element, and then the contact element is removed in the second step. Thereby forming an uninterrupted metal coat 10.

Description

PROCESS FOR ELECTROPLATING A WORK PIECE COATED WITH AN ELECTRICALLY CONDUCTING POLYMER}

For the desired changes in the surface or surface structure of secondary and tertiary workpieces, electroplating is a process that corresponds to the art and is often used in practice, even when it is a non-metallic surface. Thus, for example in the manufacture of circuit boards, metallization and complete contact of the base material is achieved by electroplating. Generally, the base material consists of an insulator, most of the surface to be electroplated, coated with an electroplatable or modified polymer.

However, the deposition of metal coatings by electroplating on large areas of insulators coated with electrically conductive polymers is typically only possible with considerable effort. Since modified polymers also have a large intrinsic electrical resistance compared to metallic materials, the current density of the workpiece surface to be electroplated is unevenly distributed and does not develop a uniformly strong electric field. To achieve a continuous metal coat, the current density must be increased or the electroplating time must be extended.

In order to avoid the drawbacks associated with extending electroplating time, it is now known in the art to increase the current density. However, excessive current density in the contact region results in the destruction of the electrically conductive polymer coating. Electroplated metal deposition can then no longer occur due to reduced conductivity. To avoid breaking such polymer coatings, approximately small current densities should be chosen which lead to prolongation of electroplating time and ancillary disadvantages.

Therefore, electroplating of a workpiece coated with an electroconductive polymer needs to determine and balance the appropriate current density and electroplating time for the workpiece. In order to obtain a void-free coating, it is necessary to re-determine the work-related parameters, taking into account the balance between excessive current density on the one hand and extended electroplating time on the other. Therefore, large scale applications of processes currently known in the art are not satisfactory because very time-consuming adjustments have to be made or high failure rates are caused if such adjustments are not made.

It is therefore an object of the present invention to describe a method of electroplating a workpiece coated with an electroconductive polymer which is independent of the workpiece to be electroplated and at the same time reduces the current density while reducing the electroplating time in order to avoid the disadvantages mentioned.

According to the invention this problem is solved in the first step of the process by connecting the workpiece with the power supply with a complex adjacent contact element and coating it with a continuous thin metal film except for the contact position covered by the contact element. The contact element is removed in the second process step and an uninterrupted continuous coat is formed.

It is further proposed by the present invention that a plurality of current-carrying connections between the power source and the surface to be electroplated is covered by covering the workpiece to be electroplated with a plurality of adjacent contact elements. This has the advantage that the electric field is generated uniformly with only a small current density sufficient to electroplate the surface. An electroconductive polymer coating is produced in connection with the power source, with a nearly uniform electric field covering the entire surface of the workpiece to be electroplated.

In the first step of the process described by the present invention, after connecting the contact element to a power source, a thin metal film is formed on the electrically conductive polymer coating of the workpiece to be electroplated. This metal film is not interrupted except for the point of contact covered by the contact element. The contact element is disposed on the surface to be electroplated in such a way that the metal film deposited in the first step of the process extends over the entire surface and forms a continuous metal coat. Because of the large number of contact elements used, build-up of the metal coat only requires a relatively short electroplating time. It is advantageous that the current density is reduced but the electroplating time is not extended. On the contrary, the process described by the present invention also offers the possibility of shortening the electroplating time even if the current density is reduced. Disadvantages of the processes currently known in the art which result in breakage of the polymer coating due to excessive current density or extended electroplating time can be completely avoided with the use of the process described herein.

After the deposition of the continuous metal coat except for the points covered by the contact elements, they are removed in the second process step and the surface area to be electroplated is charged with current through the metal coat formed in the first process step. Metal deposits are now also formed at the contact points covered by the contact elements during the first process step, such that an uninterrupted metal coat is formed over the entire surface of the workpiece to be electroplated. In addition, during this second electroplating step, since the metal coat formed in the first process step covers the surface area, only a relatively small current density and a shorter electroplating time are required, so that a uniform electric field generally develops into a smaller current density. do. In addition, unlike polymer coats, metal coats exhibit good electrical conductors with low resistivity.

The second process step for the formation of an uninterrupted continuous metal coat provides a metal coating at the point of contact which is not yet covered after completion of the first step so that the point of contact which is still open in this way is "closed" and is not interrupted. Metal coat may be performed in a manner that is formed in a second process step. The second process step may also be performed in such a way that the metal coat formed in the first process step continues to grow to form an uninterrupted metal coat that also covers the contact point. The second process step can also be performed using different electrolyte compositions, for example. When carrying out this process, it is important that the workpieces to be coated are connected by multiple adjacent contact elements so that a generally uniform electric field develops over the entire surface. The contact points covered by the contact elements of the surface to be coated can then be closed with the formation of a metal coating which is not interrupted in the second process step.

The process described in the present invention allows for the first time to provide a metal coating by electroplating on an electrically conductive polymer coated secondary or tertiary workpiece, requiring only relatively short electroplating time even with reduced current density. Thus, the disadvantages of processes currently known in the art that result in the destruction of the polymer coat due to excessive current density and extended electroplating time can be avoided. The electroplating process carried out as described herein allows for mass production of electroplated workpieces, because in terms of the current density to be set and the electroplating time to be selected, maximum independence from the workpiece to be electroplated is achieved, In addition, costly reconditioning of these process parameters is rarely needed prior to starting each new electroplating process.

According to one feature of the invention, each contact element of the surface to be electroplated is located grid-shaped next to each other. In this way, in both the first process step in which the surface to be coated is connected to the power source via a contact element and also in the second process step in which the current supply takes place via the metal coating formed in the first process step, a widely uniformly formed electric field is Extending over the entire surface area to be plated is achieved. It is also achieved that the metal coat itself to be formed in the first process step constitutes a continuous electrical conductor. Thus, it has been explained that it is particularly advantageous if neighboring contact elements are arranged equidistantly.

According to another feature of the invention, a contact element carrier comprising a plurality of contact elements is used for contact element placement. On the one hand, rapid placement of the contact element on the surface to be electroplated is achieved in this way, and on the other hand, the use of the contact element carrier allows large scale automation of the process described herein. The contact element carriers are preferably designed in such a way that the adjustment of the contact elements with respect to each other and to the contact element carrier itself is possible, including complex adjacent contact elements that can move from their relative positions for adjustment. Depending on the workpiece to be electroplated, the contact elements can be adjusted to ensure that all elements that will be placed on the surface of the workpiece to be electroplated actually establish an electrical connection between the workpiece to be electroplated and the power source. In this way, the appearance of voids in the metal coating to be formed can be avoided.

According to a first alternative, a frame in which the contact element is fixed is used as the contact element carrier. Such frame-shaped contact element carriers are particularly suitable for the electroplating of secondary workpieces, for example circuit boards. As explained by the present invention, such a frame is rectangular in shape while other shapes may be considered, depending on the type of application. The complex contact element is secured to all the components forming the frame or to the frame located at each component. For connection with a power source of the surface to be electroplated, it is contacted by an element of the frame-shaped contact element carrier. In this connection, according to a further feature of the invention, for a large coverage area, multiple frames can be located next to each other or on the side of the workpiece to be electroplated. This is particularly attractive in the case of circuit boards, in which the basic thermal circuit board is metal-coated on both sides in the course of the first process step.

According to a further feature of the invention, fixtures with complex contact elements are used as contact element carriers. This type of fixture is especially useful for the connection of tertiary workpieces. It is inserted into a fixture designed for this purpose and connected to the power source via a contact element attached to the fixture. In this way, uniform electroplating is possible without interruption of formally complex workpieces in one process step. Of course, other forms besides the design of the contact element carrier as a frame or fixture are also contemplated. The determining factor is that the surface of the workpiece to be electroplated can be widely covered by a contact element carrier having a complex contact element.

According to a further feature of the invention, the contact elements are designed to be movable on the one hand relative to each other and on the other hand relative to the contact element carrier and they are electroplated for connection with a power source, depending on the workpiece type. It can be adjusted for contact with the workpiece to be made. Thus, the process described by the present invention ensures that the workpiece surface of the regular shape and the complex shape of the irregular shape can be covered by the contact element over the whole area, and that the workpiece to be electroplated can be connected to the power source. Can be.

According to a further feature of the invention, metal grates are used as contact element carriers. Metal grates are particularly suitable for horizontal applications in continuous process equipment. This metal grate constitutes a complete electrical conductor so that its location on the surface to be electroplated leads to a build-up of an electric field which is common and uniform. Thus, within a relatively short time, a metal coat can be formed that uses only a low current density and basically constitutes the cathode of the grid. In other words, the area of the surface to be electroplated, which is not covered by the grid, is covered with a metal film. In the second step of the process, the grid can then be removed and a closed metal coating is formed on the surface. According to an advantageous feature, the surface to be electroplated is contacted by a grid, with which the workpiece is fed through the electrolyte. Thus, the grid is also used simultaneously with the conveyor. In this way, with a short circulation speed and ease of automation, it can be electroplated according to the process described by the invention on all reproducible surfaces of the workpiece. In order to ensure that the metal grate located in the workpiece to be electroplated can be removed without the destruction of the underlying polymer coat after deposition of the first metal coating, it is provided that the metal deposited from the metal grid is loosened from the workpiece. It is another feature of the present invention.

According to a further feature of the invention, the thickness of the metal coat produced by the process, which is the subject of the invention, can be specified. This can be adjusted on the one hand by the residence time in the electrolyte of the workpiece and on the other hand by the connected current density. In any case, it is possible to develop a metal coat of the required thickness suitable for the later demands of the finished workpiece.

The present invention relates to an electroplating process of a workpiece, coated with an electrically conductive or modified polymer. The present invention also shows an apparatus for carrying out this process.

Additional details, features and advantages of the invention are set forth in the following description of the accompanying drawings:

1 is a schematic diagram of the first stage of the process described by the present invention for the manufacture of a circuit board in a vertical process.

2 is a schematic diagram of a second step of the process described by the present invention for the manufacture of a circuit board in a vertical process.

3 is a schematic view of a grate serving as a contact element carrier.

4 is a schematic diagram of the first stage of the process described by the present invention for the manufacture of a circuit board in a horizontal process.

5 is a schematic cross-sectional view of a contact element according to a first application design.

6 is a schematic cross-sectional view of a contact element according to a second application design.

1 shows the manufacture of a circuit board 1 according to the process described herein. Here, the first step of the process is shown. In the electrolyte 2, which is generally perpendicular to the electrolyte surface 3, a base 4 composed of an insulator and coated with an electrically conductive or modified polymer layer is inserted. Since the base body 4 generally moves vertically with respect to the electrolyte surface 3, this process may also be referred to as a vertical process.

The base body 4 is connected to the power source 8 via a composite contact element 5. This is achieved by the branch wires 9. As can be shown schematically in FIG. 1, all contact elements 5 are electroplated and placed on a base 4 which is in electrical contact with the power source 8 by means of a contact element carrier 7. For example, the figure shows a three frame-shaped contact element carrier 7 with five contact elements 5 attached to each. The contact elements 5 are movable with respect to each other and with respect to the contact element carrier 7 so that each adjustment of the contact element 5 can be made according to the size or shape of the base 4 to be electroplated. Is fixed to each contact element carrier in a manner. Through the complex contact elements 5 used, after application of an electric current, an almost uniform electric field is developed that extends over the entire surface of the base 4 to be electroplated. As a result of the build-up of a uniform electric field extending over a large area, a short period of time with a relatively small current density except for the contact point 6, covered by a contact element 5, covered by a non-interrupting thin metal coat 10 It is formed within. The use of the composite contact element 5 allows electroplating to occur within a shorter electroplating time even at low current densities.

2 shows a second process step as described in the present invention. After the build-up of the metal coat 10 except for the contact point 6 covered by the contact element 5, a metal coat is formed in which the contact element is removed and not interrupted. For this purpose, the metal coat produced in the first process step is connected with the power source 8 by an electric wire 9. In this way, also an almost uniform electric field is developed in which the voids of the metal coat 10 are closed by metal deposition and an uninterrupted metal coat is produced. After build-up of the metal coat of the specified layer thickness, the base body 4 is again removed from the electrolyte 2.

3 shows an alternative to the metal grate 11 which serves as the area contact element and is provided with an insulator except for the point of contact. The workpiece to be electroplated in the first process step is placed on the grate 11 so that the surface to be electroplated faces the grate and is fed in a horizontal process through the electrolyte 2. This is shown schematically in FIG. This can be regarded as a great 11 which simultaneously forms an endless band which serves as a conveyor. The great 11 is moved by the drive device 13 in the movement direction 14 by the reversing roll 12. The great 11 is connected to the power source 8 by, for example, a sliding contact 15. For example, for the manufacture of circuit boards, the base 4 is arranged on the grate 11 at the loading station 16. The loading station 6 is located outside of the electrolyte tank 17. The base 4 placed on the grate 11 moves in the direction 14 to be inserted into the electrolyte tank 17 and soaked in the electrolyte 2. This process is also referred to as a horizontal process, as opposed to the vertical process described above, since the grate 11 generally moves parallel to the electrolyte surface 3. As a result of the large coverage of the surface of the base 4 to be electroplated, only a relatively small current density and shortened electroplating time are required for the formation of the first metal coat. After build-up of this metal coat, the base body 4 is removed from the electrolyte tank 17 in the direction 14 and moves to the unloading station 18. Here, the base 4 is removed from the grate 11. In order to avoid permanent electroplating of the contact points, the deposited metal may be dissolved by the counter anode 19. After completion of the first process step and the build-up of the metal coat according to FIG. 4, a build-up of the metal sheath which does not stop in a manner similar to the vertical process already described above takes place.

5 and 6 show two alternatives of the contact element 5 respectively located in the contact element carrier 7. The contact elements shown in FIGS. 5 and 6 are different because of their relative mobility in the lifting direction 20. This is achieved by means of suitable spring elements. Respectively, the contact element is designed as follows: The current-carrying contact pin 21 moves radially relative to the base 4 (lifting direction 20). The contact pin 21 is surrounded by an insulator 22 and attached to the contact element carrier 7 by a threaded connector 23. This design also has the advantage of installing the contact element 5 on the non-level surface of the base body 4. In this way the composite contact element 5 is in contact with the base 4, ensuring that an electrical connection between the base 4 and the power source 6 is established.

Reference word list

1 circuit board

2 electrolyte

3 electrolyte surface

4 primitives

5 contact elements

6 contact points

7 contact element carrier

8 power

9 wires

10 metal coating

11 great

12 reversing rolls

13 drive unit

14 transport device

15 sliding contacts

16 loading stations

17 electrolyte tank

18 removal station

19 counter anode

20 stroke direction

21 contact pins

22 insulator

23 connecting devices

Claims (19)

In the first process step, the workpiece is connected to the power supply by a complex adjacent contact element and coated with a thin film of metal except for the contact points covered by the contact element, and then in the second process step the contact element is removed and uninterrupted Electroplating process of a workpiece coated with an electroconductive or modified polymer, characterized in that is formed. The process according to claim 1, wherein each contact element is arranged in a grid-shape next to each other on the surface of the workpiece to be electroplated. The process as claimed in claim 1 or 2, characterized in that adjacent contact elements are located equidistant from each other. 4. Process according to any one of the preceding claims, characterized in that a contact element carrier having a complex contact element is used for the arrangement of the contact elements. The process according to claim 4, wherein the frame to which the contact element is attached is used as the contact element carrier. 6. A process according to claim 5, wherein a plurality of frames are used next to each other and / or on both sides of the workpiece to be electroplated for a large coverage of the surface to be electroplated. The process according to claim 4, wherein a rack with a plurality of contact elements attached is used as the contact element carrier. 8. Process according to any one of the preceding claims, characterized in that the contact element is adjustable and positioned relative to the contact element carrier in accordance with the workpiece form for the connection of the workpiece and the power source to be electroplated. The process according to claim 4, wherein the metal grates are used as contact element carriers. 10. The process according to claim 9, wherein the great is located on the surface of the workpiece to be electroplated and the workpiece is guided through the electrolyte with the great. The process according to claim 10, wherein the metal deposited at the metal contact point is dissolved by the opposite anode. Process according to any of the preceding claims, characterized in that the metal coat is formed to a thickness that can be selected. A fixture for carrying out the process according to any one of claims 1 to 12, characterized in that at least one contact element carrier having complex adjacent contact elements is provided for the connection of the workpiece and the power source to be electroplated. 14. A fixture according to claim 13, wherein each contact element is fitted to the contact element carrier in such a way that their position in the contact element carrier is adjustable. The fixture of claim 13 or 14, wherein the contact element carrier is designed as a frame or rack. 15. The fixture of claim 13 and 14, wherein the contact element carrier is a metal grate on which the workpiece to be electroplated can be located. The fixture of claim 16 wherein the metal grates form an infinite band. 18. The fixture of claim 17 wherein the grate is simultaneously used as a workpiece conveyor. 19. The fixture of any one of claims 16-18, wherein an opposite anode is provided to avoid electroplating at the point of contact.