U.S. patent application number 10/712458 was filed with the patent office on 2004-05-20 for graphite metal coating.
This patent application is currently assigned to Franz Oberflachentechnik GmbH & Co KG. Invention is credited to Franz, Wolf-Dieter.
Application Number | 20040094424 10/712458 |
Document ID | / |
Family ID | 8177428 |
Filed Date | 2004-05-20 |
United States Patent
Application |
20040094424 |
Kind Code |
A1 |
Franz, Wolf-Dieter |
May 20, 2004 |
Graphite metal coating
Abstract
A method for applying a metal coating to graphite structural
members, in which a galvanic metal layer is deposited after said
graphite structural members have been anodically etched in an
alkaline etchant. The metal coating can serve as a basis for solder
connections and can be employed for creating electrical contacts or
for mechanically fixing the graphite structural member or it can
fulfil other demands on the surface (e.g. abrasion resistance).
Inventors: |
Franz, Wolf-Dieter;
(Geretsried, DE) |
Correspondence
Address: |
COHEN, PONTANI, LIEBERMAN & PAVANE
551 FIFTH AVENUE
SUITE 1210
NEW YORK
NY
10176
US
|
Assignee: |
Franz Oberflachentechnik GmbH &
Co KG
Geretsried
DE
|
Family ID: |
8177428 |
Appl. No.: |
10/712458 |
Filed: |
November 13, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10712458 |
Nov 13, 2003 |
|
|
|
PCT/EP02/03116 |
Mar 20, 2002 |
|
|
|
Current U.S.
Class: |
205/159 ;
205/171; 205/187 |
Current CPC
Class: |
C25D 5/54 20130101; C23C
18/1879 20130101; C23C 18/1896 20130101 |
Class at
Publication: |
205/159 ;
205/171; 205/187 |
International
Class: |
C25D 005/54 |
Foreign Application Data
Date |
Code |
Application Number |
May 14, 2001 |
EP |
01111708.2 |
Claims
I claim:
1. A method of applying a metal coating to graphite comprising:
anodic etching said graphite in an alkaline etchant, and then
electroplating said graphite.
2. The method as set forth in claim 1, comprising the following
step between said anodic etching and said electroplating: Pd
seeding said graphite.
3. The method as set forth in claim 2, comprising the following
step between said Pd seeding and said electroplating: electroless
plating to reinforce said Pd coating.
4. The method as set forth in claim 3, wherein at least Ni or Cu is
deposited in said electroless plating step.
5. The method as set forth in claim 1, comprising the following
step between said anodic etching and a subsequent step: directly
transferring said graphite, obtained with said anodic etching step,
into water or a weak aqueous solution.
6. The method as set forth in claim 5, wherein between said anodic
etching and said electroplating no ultrasound treatment is
implemented.
7. The method as set forth in claim 1, wherein said electroplating
involves at least one of the following group: Ag, Cu, Ni and
Sn.
8. The method as set forth in claim 1, wherein said electroplating
utilizes a current density in the range 0.1 to 10 A/dm.sup.2.
9. The method as set forth in claim 1, wherein the current duration
in said electroplating is in the range of 5 to 90 minutes.
10. The method as set forth in claim 1, wherein said anodic etching
is done in a solution of NaOH and/or KOH having a concentration in
the range 10 to 70% by weight.
11. The method as set forth in claim 10, wherein said anodic
etching is done at a temperature in the range 20.degree. C. to
70.degree. C.
12. The method as set forth in claim 1, wherein said graphite
comprises graphite particles bound by plastics.
13. A method of fabricating a solder connection to a graphite
component wherein, by a method as set forth in claim 1, a metal
coating is deposited on said graphite component, after which a
solder pad is applied to said metal coating as thus produced.
14. A method as set forth in claim 1, wherein said anodic etching
is performed with an applied electrical potential in the range of
4V to 20V.
15. A method as set forth in claim 14, wherein said anodic etching
has a duration in the range of 5 to 90 minutes, with the actual
duration being inversely proportional to the applied electrical
potential.
Description
[0001] This application is a Continuation-in-Part of
PCT/EP02/03116, filed on 20 Mar. 2002.
FIELD OF THE INVENTION
[0002] The present invention involves a method for applying a metal
coating to graphite.
BACKGROUND OF THE INVENTION
[0003] Graphite is used as a material in a huge variety of
applications. In many cases, graphite members have to be used for
electrically conductive connections, where one often only uses
clamp connections or creates a contact by pressing on other
electrically conductive parts (in particular by pressing on metal
contacts). In order to address many technical problems, however, a
connection created by soldering or other connecting techniques is
required, thus making a metallic surface of the graphite member
mandatory.
SUMMARY OF THE INVENTION
[0004] One object of the invention is to provide an improved method
for applying a metal coating to graphite.
[0005] Another object of the invention is to ensure a good adhesion
between the applied metal layers and the graphite surface
itself.
[0006] These and other objects are attained in accordance with one
aspect of the invention directed to a method for applying a metal
coating to graphite that includes the steps of anodic etching the
graphite in an alkaline etchant, and then electroplating the
graphite.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0007] One aim of the invention is to ensure a good adhesion
between the metal layers to be applied and the graphite surface
itself. The inventor has discovered, that a good adhesion can be
accomplished when the graphite structural member is first
pretreated and activated by anodic etching in an alkaline etchant,
and is subsequently electroplated. Anodic etching is done with an
applied electrical potential, the grapite being the anode. By means
of the anodic etching in the alkaline etchant, the graphite surface
is not only thoroughly cleansed but also slightly etched, whereby
the subsequent electroplating is accomplished on a surface which is
mainly free of foreign impurities and graphite dust, and which is
slightly roughened. Accordingly, the metal layer can effectively
interlock with the graphite surface, thereby providing significant
adhesive properties. The alkaline etchant thus creates the
condition for such metal coatings to have a high adhesive strength
and temperature stability.
[0008] Optionally, the graphite surface can be Pd seeded prior to
electroplating. In addition, subsequently to this Pd seeding one
may deposit a so-called chemical metal layer. This refers to a
metal deposition by means of a reducing agent without applying
current (electroless plating). This electroless plating is
optional, but is preferably based on the Pd seeding. The
electroless plating preferably deposits Ni or Cu. These two metals
may also be present together or in a combination with other
metals.
[0009] The cleansing effect of the alkaline etchant may
additionally be enhanced by an ultrasound treatment. This helps to
detach particles adhering to the surface and, furthermore, it is
effective to mix thoroughly and to equalise the concentrations in
the surface surroundings. This ultrasound treatment, however, has
several disadvantages. In some structural members it is undesirable
due to the mechanical stress exerted on sensitive parts.
Furthermore, it requires the incorporation of the members into a
device suitable for the ultrasound treatment. In order to optimise
the uniformity of the ultrasound treatment, one can select in
particular annular configurations of the batches of structural
members to be treated, which however is rather complicated with
respect to the machinery.
[0010] According to a particularly preferred feature of the
invention, the described ultrasound treatment is completely omitted
and the temporal and technical effort is, thus, significantly
reduced. Instead of this, the treated graphite members taken out of
the alkaline etchant are directly (i.e. in a direct succession
without any further intermediate treatment) dipped into a weak
aqueous solution or into water. Thereby, at the surfaces of the
members, strong gradients of concentration are produced due to the
residual portions of the solution employed for the etchant. These
residual parts of the etchant show a short and rather intensive
reaction with the water or the weak aqueous solution, which becomes
obvious by the temporary sparkling in the water or in the aqueous
solution near the surface. This sparkling effect, according to the
inventor's observation, has a cleansing effect similar to the
ultrasound bath, and effectively and easily removes from the
surface those impurities already being etched off or being loosened
by the etchant.
[0011] The process just being described is thus preferably to be
used to completely omit an ultrasound treatment at least in this
field of the method.
[0012] The described electroplating of graphite may be accomplished
on a mounting apparatus and, in case of a specific geometry or
shape of the members, in drums. The electroplating can preferably
employ Ag, Cu, Ni or Sn, or a mixture of these metals, or a mixture
of one or several of these metals with other metals. In particular
Sn and Sn-alloys have good soldering characteristics, so that the
galvanic layer provides a good basis for a subsequent (optional)
soldering step.
[0013] Thus, after the etching process, one can preferably apply
either
[0014] a Pd seeding+chemical Ni+Cu (or Ni)
[0015] or galvanic Ni directly after the rinsing
[0016] or galvanic Cu directly after the rinsing.
[0017] These layers are then used as a basis for the deposition of
further layers (Sn or other metals).
[0018] Preferred parameter ranges for the electroplating are a
current density in the range 0.1 to 10 A/dm.sup.2, and a duration
of treatment, i.e. bath and current duration, in the range 5 to 90
minutes.
[0019] The anodic etching can preferably be performed in a sodium
hydroxide solution (solution of NaOH) or in a potassium hydroxide
solution (solution of KOH) or in a mixture of both lyes, for
example in range of concentration of 10 to 70% by weight, with a
particularly preferred range of 20 to 50% by weight. For this aim,
temperatures of 20.degree. to 70.degree. C. have achieved good
results, with temperatures in the range of 30.degree. C. to
40.degree. C. being preferable.
[0020] The term "graphite" in this invention refers to all
materials in which graphite is contained in such a degree and is
present on the relevant surface, that applying a metal coating of
the graphite surfaces themselves is essential to attain the desired
technical result. This, of course, includes all pure graphite
materials as well as those containing minor additives. Preferably,
however, the invention is also directed to plastic-bound graphite
materials in which graphite particles are contained within a
plastic matrix. Such material serves various technical
applications, in which the method according to the invention can be
of great advantage.
[0021] Concretely, the invention can be realised according to the
following example, the characteristics of which, however, are not
to be regarded as limiting the scope of protection in any way.
[0022] A structural member of an electrical device, with such
member being formed of a graphite bound by plastics, is produced in
a conventional way so that it acquires its final shape. Then, a
batch including a large number of the structural members is
cleansed and etched by anodic etching in a commercially available
device for electrolytic etching in a solution of NaOH having a
concentration of 50% by weight and at a temperature of 30.degree.
to 40.degree. C., followed by a direct transfer to a simple water
bath at room temperature. There, the solution displays a transient
sparkling around the structural members in the batch. The batch is
then rinsed and Pd seeded in a known fashion. For this aim,
commercial ionogenic or colloidal Pd-solutions are available. The
Pd-seeds serve as a catalyst for the subsequent steps of
metallization.
[0023] The anodic etching is performed with an applied electrical
potential in the range of 4V to 20V. The preferred range is 9V to
10V. The duration of the anodic etching is between 5 and 90
minutes, with the actual time being inversely proportional to the
strength of the applied electrical potential. For example, for the
preferred range of 9V to 10V, 30 to 40 mins. are used. For the
resultant range of 200 to 500 V min, an approximate preferred range
is 300 to 400 V min.
[0024] A Ni-layer having a thickness of 0.1 to 2 .mu.m is
chemically deposited (by electroless plating) on the Pd-seeded
graphite members. Because the Ni layer is very thin, it may be
reinforced by chemical Ni, chemical Cu, galvanic Ni and/or galvanic
Cu.
[0025] An electrolytic Sn-alloy may then be applied to the
reinforced chemical metal layer to form a layer thickness between 5
and 10 .mu.m so that the solder pads can be directly placed
thereupon. A galvanic reinforcement is preferred to a chemical
reinforcement. The soldering process itself is completely
conventional, since only the surface of the Sn-alloy is essential
for it.
[0026] The solder pad offers not only excellent electrical contact
with the graphite structural member, but it has such a good
adhesion to the graphite structural member, that it may also be
employed for mechanical fixation. This avoids fixing the graphite
structural member by clamping or by screwing on via a tapped hole
or by other interlocking or frictional connections. One can simply
employ a suitable metal stripe as a mounting device.
[0027] The invention is advantageous in that by applying a metal
coating to graphite, i.e. the deposition of adhering, and not just
surface-mounted, metal layers, such metal layers will provide a
valuable contribution for creating electrical contacts on and/or
for mechanically fixing graphite structural members. On the one
hand, other metallic contact elements can be pressed on these
deposited metal layers, so that only comparatively low transition
resistances occur. On the other hand, the metal layers can be used
as a basis for solder connections or other methods for creating a
firm connection to the structural member, which require a metallic
surface.
* * * * *