U.S. patent application number 09/959105 was filed with the patent office on 2002-10-31 for process for electroplating a work piece coated with an electrically conducting polymer.
Invention is credited to Hupe, Jurgen, Kronenberg, Walter.
Application Number | 20020157959 09/959105 |
Document ID | / |
Family ID | 7631430 |
Filed Date | 2002-10-31 |
United States Patent
Application |
20020157959 |
Kind Code |
A1 |
Kronenberg, Walter ; et
al. |
October 31, 2002 |
Process for electroplating a work piece coated with an electrically
conducting polymer
Abstract
The object of the invention is to provide a process for
electroplating a work piece (1) which is coated with an
electrically conducting or modified polymer, wherein, independently
of the work piece to be electroplated, it is possible to
simultaneously reduce the current density and shorten the
electroplating time. The invention includes, as a first step, that
the work piece is connected to a current source (8) by multiple
adjoining contact elements (5) and covered with a thin metallic
coat, except at the points covered by the contact elements and that
subsequently, in a second step, the contact elements are removed
and an unbroken metal coat (10) is formed.
Inventors: |
Kronenberg, Walter; (Koln,
DE) ; Hupe, Jurgen; (Langenfeld, DE) |
Correspondence
Address: |
SENNIGER POWERS LEAVITT AND ROEDEL
ONE METROPOLITAN SQUARE
16TH FLOOR
ST LOUIS
MO
63102
US
|
Family ID: |
7631430 |
Appl. No.: |
09/959105 |
Filed: |
December 19, 2001 |
PCT Filed: |
February 20, 2001 |
PCT NO: |
PCT/US01/01235 |
Current U.S.
Class: |
205/136 ;
205/118; 205/128 |
Current CPC
Class: |
C25D 7/0614 20130101;
H05K 3/241 20130101; C25D 5/56 20130101 |
Class at
Publication: |
205/136 ;
205/118; 205/128 |
International
Class: |
C25D 005/02 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 18, 2000 |
DE |
100074359 |
Claims
1. A process for electroplating a work piece coated with an
electrically conducting or modified polymer characterized by the
work piece, in a first process step, being connected by multiple
adjoining contact elements to a current source and coated with a
thin metal layer, except at the contact points covered by the
contact elements and subsequently, in a second process step, the
contact elements being removed an unbroken metal coat is
formed.
2. A process in accordance with claim 1, characterized by the
individual contact elements being arranged next to each other,
lattice-like on the surface of the work piece to be
electroplated.
3. A process in accordance with claims 1 and 2, characterized by
adjoining contact elements being located equidistant to each
other.
4. A process in accordance with claim 1 to 3, characterized by a
contact element carrier with multiple contact elements for the
arrangement of the contact elements being used.
5. A process in accordance with claim 4, characterized by a frame
with contact elements attached being used as the contact element
carrier.
6. A process in accordance with claim 5, characterized by several
frames being used next to each other and/or on both sides of the
work piece to be electroplated for large area coverage of the
surface to be electroplated.
7. A process in accordance with claim 4, characterized by a rack
with several contact elements attached being used as a contact
element carrier.
8. A process in accordance with claim 1 to 7, characterized by the
contact elements being adjustable in their relative position to the
contact element carrier and located for connecting the work piece
to be electroplated to the current source, depending on the work
piece geometry.
9. A process in accordance with claim 4, characterized by a
metallic grate being used as the contact element carrier.
10. A process in accordance with claim 9, characterized by the
grate being placed on the surface of the work piece to be
electroplated, and that the work piece is guided through the
electrolyte together with the grate.
11. A process in accordance with claim 10, characterized by the
metal deposited on the metallic contact points being dissolved by
means of counter anodes.
12. A process in accordance with one of the foregoing claims,
characterized by the metal coat being formed in a thickness, which
can be selected.
13. A fixture for carrying out the process in accordance with one
of the claims 1 to 12, characterized by at least one contact
clement carrier with multiple adjoining contact elements being
provided for connection of the work piece to be galvanized with a
current source.
14. A fixture in accordance with claim 13, characterized by the
individual contact elements being installed on the contact element
carrier in such a manner that their position on the contact element
carrier is adjustable.
15. A fixture in accordance with claim 13 and 14, characterized by
the contact element carrier being designed as a frame or a
rack.
16. A fixture in accordance with claim 13 and 14, characterized by
the contact element carrier being a metallic grate onto which the
work piece to be electroplated may be placed.
17. A fixture in accordance with claim 16, characterized by the
metal grate forming and endless band.
18. A fixture in accordance with claim 17, characterized by the
grate simultaneously serving as a work piece conveyor.
19. A fixture in accordance with claim 16 to 18, characterized by
counter anodes being provided in order to avoid galvanizing of the
contact points.
Description
[0001] The invention refers to a process for electroplating a work
piece, which is coated with an electrically conducting or modified
polymer. In addition, the invention shows apparatus for carrying
out this process.
[0002] For the targeted change of the surface, or of the surface
structure, of two and three dimensional work pieces,
electroplating, even in the case of non-metallic surfaces, is a
process which corresponds to the state of the art and which often
is used in practice. Thus, for example in the manufacture of a
circuit board, metallizing and complete contact formation of the
base material is achieved by electroplating. Generally, the base
material consists of an insulator where a large portion of the
surface, which is to be electroplated, is coated with an
electrically conducting or modified, polymer.
[0003] However, the deposition of a metallic coating on the large
area of an insulator coated with an electrically conducting polymer
by electroplating is usually only possible with considerable
effort. Due to the fact that even a modified polymer has a high
specific electrical resistance compared to a metallic material, the
current density on the surface of the work piece to be
electroplated is distributed in an uneven manner so that an evenly
strong electrical field does not develop. In order to still achieve
a continuous metal coat either the current density must be
increased or the electroplating time must be extended.
[0004] In order to avoid the disadvantages connected with extending
the electroplating time, it is known from the current state of the
art to increase the current density. However, an excessive current
density in the contact area leads to the destruction of the
electrically conducting polymer coating. An electroplated metal
deposition can then no longer take place, due to the diminished
electrical conductivity. In order to avoid such a destruction of
the polymer coating, an appropriately low current density must be
selected which results in an extension of the electroplating time
and the attendant disadvantages.
[0005] It is therefore necessary for electroplating a work piece
coated with an electrically conducting polymer to determine and to
balance the current density and the electroplating time appropriate
to the work piece. In order to obtain a coating without voids it is
therefore necessary to consider the balance between excessive
current density on the one hand and an excessive electroplating
time on the other, whereby the work piece-related parameters are to
be determined again. Thus large-scale applications of the processes
known from the current state of the art are not satisfactory since
either very time-consuming adjustments must be made or a high
failure rate results if these adjustments are not made.
[0006] In order to avoid the disadvantages mentioned it is
therefore the intent of the invention to describe a method for
electroplating of a work piece which is coated with an electrically
conducting polymer which is independent of the work piece to be
electroplated and which permits a shortening of the electroplating
time while, at the same time, reducing the current density.
[0007] According to the invention this problem is solved by
connecting the work piece in the first step of the process to a
current source by multiple adjacent contact elements and coating
with a continuous, thin metal layer except at the contact locations
covered by the contact elements. The contact elements are removed
in a second process step, and an unbroken, continuous coat is
formed.
[0008] It is further proposed by the invention to cover the work
piece to be electroplated with a multitude of adjacent contact
elements so that a multitude of current-carrying connections
between the surface to be electroplated and the current source are
formed. This has the advantage that an electrical field is
generated even with only a low current density, which is sufficient
for electroplating the surface. The electrically conducting polymer
coating is connected to the current source so that an almost
uniform electrical field is generated covering the entire surface
of the work piece to be electroplated.
[0009] In the first step of the process described by the invention,
after connecting the contact elements to the current source, a thin
metal layer is formed on the electrically conducting polymer
coating of the work piece to be electroplated. This metal layer is
unbroken except for the contact points covered by the contact
elements. The contact elements are laid out on the surface to be
electroplated in such a manner that the metal layer deposited in
the first step of the process extends over the entire surface and
forms a continuous metal coat. Due to the multitude of the contact
elements used, the build-up of the metal coat requires only a
relatively short electroplating time. It is of advantage that
despite the reduction of the current density the electroplating
time does not increase. To the contrary, the process described by
the invention presents the possibility to also reduce the
electroplating time despite the reduced current density. The
disadvantages of the processes known from the current state of the
art represented by a destruction of the polymer coating, due to an
excess of current density or due to an excess of electroplating
time can be entirely avoided by the use of the process described by
the invention.
[0010] After the deposition of the continuous metallic coat, except
the points covered by the contact elements, these 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. A metal deposit now also forms at the contact points
covered by the contact elements during the first process step, so
that a unbroken metal coat forms over the entire surface of the
work piece to be electroplated. During this second electroplating
step also only relatively low current densities as well as short
electroplating times are required since the metal coat formed in
the first process step covers the surface area, and thus a
generally homogeneous electrical field is built also with low
current density. In addition, in contrast to a polymer coat, the
metallic coat represents a good electrical conductor with a low
specific resistance.
[0011] The second process step intended for the formation of an
unbrokenly continuous metal coat can be carried out in accordance
with the invention in such a manner that the contact points not yet
covered after the completion of the first step are provided with a
metal coating, so that in this manner the contact points still
remaining open are "closed", and an unbroken metal coat is formed
in the second process step. The second process step can also be
carried out in such a manner that the metal coat formed in the
first process step keeps growing so that an unbroken metal coat is
formed which also covers the contact points. The second process
step can also be carried out using a different electrolyte
composition, for example. When carrying out this process, it is
important that the connection of the work piece to be coated is by
multiple adjoining contact elements so that a generally homogeneous
electrical field is built over the entire surface. The contact
points covered up by the contact elements of the surface to be
coated can then be closed by the formation of an unbroken metal
coating in a second process step.
[0012] With the process described in the invention, it is possible
for the first time to provide a two or three dimensional work piece
with an electrically conducting polymer coat with a metal coating
by electroplating, whereby in spite of reduced current density only
a relatively short electroplating time is required. The
disadvantages of the known processes from the current state of the
art which result in the destruction of the polymer coat due to
excessive current density and due to excessive electroplating time
can therefore be avoided. An electroplating process conducted as
described in the invention permits the mass production of
electroplated work pieces since with regard to the current density
to be set and the electroplating time to be selected, the greatest
independence from the work piece to be electroplated is achieved,
and also a costly readjustment of these process parameters prior to
the beginning of each new electroplating process is not
required.
[0013] In accordance with one characteristic of the invention, the
individual contact elements on the surface to be electroplated are
placed lattice-like next to each other. In this manner it is
achieved that both in the first process step in which the surface
to be coated is connected to the current source over the contact
elements and also in the second process step when the current
supply takes place over the metal coating formed in the first
process step an extensive, evenly formed electrical field extends
over the entire surface area to be electroplated. In addition, it
is achieved that the metal coat to be formed in the first process
step by itself constitutes a continuous electrical conductor. It is
therefore suggested that it is especially advantageous if
neighboring contact elements are laid out equidistant.
[0014] In accordance with another characteristic of the invention,
a contact element carrier is used for the contact element layout,
which comprises several contact elements. On the one hand, a quick
placement of the contact elements on the surface to be
electroplated is achieved in this manner, on the other hand, the
use of a contact element carrier permits extensive automation of
the process described in the invention. The contact element carrier
preferably is designed in such a manner that it comprises multiple
adjoining contact elements which can be moved from their relative
position for adjustment purposes, whereby adjustment of the contact
elements relative to each other as well as to the contact element
carrier itself is possible. Depending on the work piece to be
electroplated, adjustment of the contact elements is possible so
that it can be ensured that all contact elements to be placed on
the surface of the work piece to be electroplated actually
establish an electrical connection between the work piece to be
electroplated and the current source. In this manner, it can be
avoided that voids appear in the metal coating to be formed.
[0015] In accordance with a first alternative, a frame with mounted
contact elements is used as a contact element carrier. Such a
frame-like contact element carrier is especially suitable for
electroplating of 2-dimensional work pieces such as, for example,
circuit boards. As suggested by the invention, such a frame is
rectangular in shape while other geometric shapes are conceivable,
depending on the type of application. Multiple contact elements are
mounted on the frame which are placed either on all or on
individual components forming the frame. For the connection of the
surface to be electroplated to the current source, this is
contacted by the elements of the frame-shaped contact element
carrier. In this connection, in accordance with a further
characteristic of the invention, for large area coverage, several
frames can be placed next to each other or on either side of the
work piece to be electroplated. It is especially attractive in the
case of circuit boards, to metal-coat the basic raw circuit board
on both sides in the course of one process step.
[0016] In accordance with a further characteristic of the
invention, a fixture with multiple contact elements is used as
contract element carrier. A fixture of this type especially serves
the connection of a 3-dimensional work piece. This is inserted into
a fixture designed for this purpose and connected to the current
source over the contact elements attached to the fixture. In this
manner it is made possible to unbrokenly electroplate even a
geometrically complex work piece in one process step. It is
self-evident, of course, that in addition to the design of the
contact element carrier as a frame or as a fixture other forms are
conceivable. The deciding factor is that the surface of the work
piece to be electroplated can be covered area-wide by the contact
element carrier with multiple contact elements.
[0017] In accordance with a further characteristic of the
invention, the contact elements are designed to be movable in their
relative position on the one hand to each other, as well as to the
contact element carrier on the other hand; and that they can be
adjusted for contact with the work piece to be electroplated for
connection to the current source, depending on the work piece
geometry. Thus, it can be ensured that by means of the process
described by the invention not only regularly shaped work piece
surfaces but also irregularly shaped, complex geometric forms can
be covered over their entire area by contact elements, and the work
piece to be electroplated can be connected to the current
source.
[0018] In accordance with a further characteristic of the
invention, a metallic grate is used as the contact element carrier.
The metallic grate is especially suited to horizontal applications
in continuous processing facilities. This metallic grate
constitutes a complete electrical conductor so that its placement
on the surface to be electroplated leads to the build-up of a
general, homogeneous electrical field. Thus, within a relatively
short time, and using only a low current density, a metallic coat
can be formed which basically constitutes a negative of the grid.
In other words, the areas of the surface to be electroplated not
covered by the grid are covered with a metal layer. In a second
step of the process, the grid can then be removed and a closed
metal coating formed on the surface. In accordance with an
advantageous characteristic, the surface to be electroplated is
contacted by the grid, and the work piece together with the grid is
fed through the electrolyte. Thus, the grid simultaneously also
serves as a conveyor. In this manner, given short cycle rates and
ease to automate, and above all reproducible, surfaces of work
pieces can be electroplated in accordance with the process
described by the invention. In order to ensure that the metal grate
placed on the work piece to be electroplated can be removed without
destroying the underlying polymer coat after the deposition of the
first metal coating, it is another characteristic of the invention
that counter anodes are supplied by which the metal deposited from
the metallic grid is loosened from the work piece.
[0019] In accordance with a further characteristic 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 dwell time of the work piece in
the electrolyte, and by the connected current density on the other.
In any case, it is possible to build a metal coat of the required
thickness adapted to the later demands on the finished work
piece.
[0020] Additional details, characteristics and advantages of the
invention are discussed in the following descriptions of the
enclosed drawings:
[0021] FIG. 1 is a schematic of the first step of the process
described by the invention for the manufacture of a circuit board
in the vertical process.
[0022] FIG. 2 is a schematic of the second step of the process
described by the invention for the manufacture of a circuit board
in the vertical process.
[0023] FIG. 3 is a schematic of a grate serving as a contact
element carrier.
[0024] FIG. 4 is a schematic of the first step of the process
described by the invention for the manufacture of a circuit board
in the horizontal process.
[0025] FIG. 5 is a schematic section of a contact element in
accordance with a first application design.
[0026] FIG. 6 is a schematic section of a contact element in
accordance with a second application design.
[0027] FIG. 1 shows the manufacture of a circuit board 1 in
accordance with the process described in the invention. Here, the
first step of the process is shown. In electrolyte 2, generally
perpendicular to the electrolyte surface 3, a base body 4 made of
an insulator and coated with an electrically conducting or modified
polymer layer is inserted. Due to the fact that the base body 4 is
moved generally perpendicular to the electrolyte surface 3, this
process may also be referred to as a vertical process.
[0028] The base body 4 is connected to the current source 8 over
multiple contact elements 5. This is achieved by a branching
electric wire 9. As can be seen in FIG. 1 schematically, all
contact elements 5 are placed onto the base body 4 which is to be
electroplated and make electrical contact with the current source 8
by means of the contact element carriers 7. For example, the figure
shows three frame-shaped contact element carriers 7 with five
contact elements 5 attached to each. The contact elements 5 are
fixed to each of the contact element carriers in such a manner that
they are movable both relative to each other and relative to the
contact element carrier 7, so that individual adjustment of the
contact elements 5 can be made with reference to the size or
geometric shape of the base body 4 which is to be electroplated.
After applying the current, based on the multiple contact elements
5 used, a nearly homogeneous electrical field is built up which
extends over the entire surface of the base body 4 to be
electroplated. As a result of the build-up of the even electric
field extending over a wide area, an unbroken, thin metal coat 10
forms within a short time at a relatively low current density
except at the contact points 6, covered by the contact elements 5.
By the use of multiple contact elements 5 electroplating can occur
within a short electroplating time, despite a low current
density.
[0029] FIG. 2 shows the second process step as described in the
invention. After the build-up of the metal coat 10 with the
exception of the contact points 6 covered by the contact elements
5, the contact elements are removed and an unbroken metal coat is
formed. For this, the metal coat produced in the first process step
is connected to the current source 8 by means of the electric wire
9. In this manner, an also nearly homogeneous electrical field is
built up which leads to the still void spots in the metal coat 10
being closed by metal deposition, and an unbroken metal coat is
created. After the build-up of the specified layer thickness of the
metal coat, the base body 4 is again removed from the electrolyte
2.
[0030] FIG. 3 shows an alternative version of a metallic grate 11
which serves as an area contact element and which is provided with
insulation except for the contact points. In the first process step
the work piece to be electroplated is laid onto the grate 11 with
the surface to be electroplated toward the grate and fed through
the electrolyte 2 in the horizontal process. This is shown
schematically in FIG. 4. This can be viewed as grate 11 forming an
endless band which, at the same time, serves as the conveyor. By
means of reversing rolls 12 the grate 11 is moved by a drive unit
13 in the transport direction 14. The grate 11 is connected to a
current source 8 by sliding contacts 15, for example. For the
manufacture, for example of circuit boards, the base bodies 4 are
laid on the grate 11 at the loading station 16. The loading station
16 is located outside the electrolyte tank 17. The base bodies 4
laying on the grate 11 are transported in direction 14 and inserted
into electrolyte tank 17 and immersed in the electrolyte 2. Due to
the fact that the grate 11 generally runs parallel to the
electrolyte surface 3 this process is also referred to as the
horizontal process, in contrast to the previously mentioned
vertical process. As a result of the wide area coverage of the
surface of the base body 4 to be electroplated, only a relatively
weak current density and a short electroplating time are required
for the formation of a first metallic coat. After the build-up of
this metal coat, the base bodies 4 are removed from the electrolyte
tank 17 in the direction 14 and transported to the unloading
station 18. There, the base bodies 4 are removed from the grate 11.
In order to avoid permanent electroplating of the contact points,
the metal deposited there can be dissolved by means of the counter
anode 19. Subsequent to the completion of the first process step
and the build-up of metal coats in accordance with FIG. 4, there
follows in a manner similar to the vertical process already
described above, the build-up of the unbroken metal covering.
[0031] FIGS. 5 and 6 each show two alternatives of a contact
element 5 located on a contact element carrier 7. The contact
elements shown in FIGS. 5 and 6 differ due to their relative
movability in the lifting direction 20. This is achieved by a
suitable spring element. Individually, the contact elements are
designed as follows: The current-carrying contact pin 21 is movable
radially relative to the base body 4 (lifting direction 20). The
contact pin 21 is surrounded by insulation 22 and attached to the
contact element carrier 7 by a threaded connector 23. This design
has the advantage of fitting the contact element 5 also to a
non-level surface of the base body 4. By this method it is ensured
that multiple contact elements 5 contact the base body 4, and thus
an electrical connection is established between the base body 4 and
the current source 6.
[0032] Reference Key List
[0033] 1 Circuit board
[0034] 2 Electrolyte
[0035] 3 Electrolyte surface
[0036] 4 Base body
[0037] 5 Contact element
[0038] 6 Contact point
[0039] 7 Contact element carrier
[0040] 8 Current source
[0041] 9 Electric wire
[0042] 10 Metal coating
[0043] 11 Grate
[0044] 12 Reversing rolls
[0045] 13 Drive unit
[0046] 14 Transport device
[0047] 15 Sliding contact
[0048] 16 Loading station
[0049] 17 Electrolyte tank
[0050] 18 removal station
[0051] 19 Counter anode
[0052] 20 Stroke direction
[0053] 21 Contact pin
[0054] 22 Insulation
[0055] 23 Connecting unit
* * * * *