U.S. patent application number 10/492499 was filed with the patent office on 2004-12-09 for production of a surface area with metallic conductivity on oxidised al-mg alloys.
Invention is credited to Franz, Wolf-Dieter.
Application Number | 20040244880 10/492499 |
Document ID | / |
Family ID | 8178945 |
Filed Date | 2004-12-09 |
United States Patent
Application |
20040244880 |
Kind Code |
A1 |
Franz, Wolf-Dieter |
December 9, 2004 |
Production of a surface area with metallic conductivity on oxidised
al-mg alloys
Abstract
The invention relates to a method for the remetallisation of
surface areas on Al-- and/or Mg alloys by means of laser
bombardment and then by sealing using a free-flowing and
electroconductive substance.
Inventors: |
Franz, Wolf-Dieter;
(Geretsried, DE) |
Correspondence
Address: |
COHEN, PONTANI, LIEBERMAN & PAVANE
551 FIFTH AVENUE
SUITE 1210
NEW YORK
NY
10176
US
|
Family ID: |
8178945 |
Appl. No.: |
10/492499 |
Filed: |
April 9, 2004 |
PCT Filed: |
October 9, 2002 |
PCT NO: |
PCT/EP02/11298 |
Current U.S.
Class: |
148/525 |
Current CPC
Class: |
C25D 13/20 20130101;
C25D 5/42 20130101; B05D 1/007 20130101; C25D 11/20 20130101; C23C
22/82 20130101; C25D 13/22 20130101; B05D 5/067 20130101 |
Class at
Publication: |
148/525 |
International
Class: |
C22F 003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 11, 2001 |
EP |
01124437.3 |
Claims
1. A method for producing a metallically conductive surface portion
(2, 3) in a surface (1) of an alloy being oxidized and/or
phosphatized by anodisation, said alloy comprising Al and/or Mg, in
which method said surface portion (2, 3) is bombarded with a laser
in order to remove the oxide/phosphate layer and said surface
portion is covered thereafter with a metallically conductive fluid
substance being so fluid during application on said surface portion
that it can well adapt to the surface contour of said surface
portion.
2. (Cancelled)
3. (Cancelled)
4. A method according to claim 1, in which said surface (1)
comprises both oxides and phosphates.
5. A method according to claim 1, in which said alloy comprises at
least 2% Mg.
6. A method according to claim 5, in which said alloy is AZ 91 or
AM 50.
7. A method according to claim 1, in which said fluid substance is
a hardening substance on synthetic resin basis comprising
metallically conductive particles.
8. A method according to claim 7, in which said hardening substance
is a silicone adhesive.
9. A method according to claim 7, in which said metallically
conductive particles are silver particles or silver-covered metal
particles.
10. A method according to claim 1, in which at least a part of said
surface (1) corresponding to the border of said surface portion (2,
3) is covered with a lacquer before said laser bombardment.
11. A method according to claim 10, in which said lacquer is a
water lacquer.
12. A method according to claim 11, in which said lacquer has an
acrylic resin basis.
13. A method according to claim 10, in which said lacquer is
applied electrophoretically.
14. A method according to claim 10, in which said applied lacquer
layer is coloured or is treated with a colorization process.
15. A method according to claim 1, in which said surface portion
(2, 3) is successively bombarded at least twice.
16. A method according to claim 1, in which said laser bombardment
is performed in air atmosphere.
17. A method according to claim 1, in which a Q-switched Nd: YAG
laser is used for said laser bombardment.
18. A method according to claim 1, in which a power density on said
surface (1) in the region from 8 W/mm.sup.2 up to 70 W/mM.sup.2 is
used for said laser bombardment.
19. A method according to claim 1, in which said surface is the
surface or a surface portion (1) of a casing of an electric or
electronic device, especially a mobile phone.
20. A method according to claim 19, in which a plurality of casing
parts is connected and/or sealed against each other in an
electrically conductive manner with that metallically conductive
substance.
Description
[0001] The present invention relates to remetallization of oxidized
and/or phosphatized surfaces on Al and Mg alloys. Since Al and Mg
never occur as pure elements in technical reality, the present
invention generally speaks of alloys. This is meant to include also
alloys in which one of both metals appears almost exclusively.
[0002] Al, Mg, and in general also their alloys, are easily
oxidized materials on which oxide layers appear rapidly. The term
"oxidation" in its chemical sense shall include each reaction in
which the oxidation state or number is increased by a loss of
valence electrons, especially a reaction with oxygen. This can
appear on oxidized surfaces that have been produced accidentally by
contact to air or other oxidizing substances. The invention,
however, is also related to the remetallization of surfaces
oxidized and/or phosphatized intentionally for technical reasons,
which are known to the skilled person from various
applications.
[0003] It is often intended to produce electrically conductive
portions on such surfaces after oxidation/phosphatizing, especially
for producing an electrical contact to a bulk alloy thereunder. The
invention relates also to the case in which the oxide/phosphate
layer is removed down to the metal alloy thereunder for other
reasons than electrical reasons, in which, however, an actually
metallically conductive surface is produced.
[0004] The invention has the object to produce metallically well
conductive surface portions on oxidized and/or phosphatized
surfaces of Al and/or Mg alloys.
[0005] According to the invention, this object is achieved by a
method for producing a metallically conductive surface portion in a
surface of an alloy being oxidized and/or phosphatized by
anodisation, said alloy comprising Al and/or Mg, in which method
said surface portion is bombarded with a laser in order to remove
the oxide/phosphate layer and said surface portion is covered
thereafter with a metallically conductive fluid substance.
[0006] The terms "oxidized surface" and "phosphatized surface" do
not only refer to surfaces having a coverage of pure oxides or
phosphates of the respective alloy. Also other substances can be
included that have been produced in preceding intentional or
accidental reactions. Further, the surface can be covered with
other layers, additionally, that have to be removed also.
Especially, the invention refers to surfaces on which mixtures of
oxides and phosphates are present, e. g. to surfaces with phosphate
layers having incorporated oxides.
[0007] First it has been concluded that it is a prerequisite for a
metallically conductive surface with correspondingly good
electrical contact resistance to provide a residual-free removal of
the oxides and phosphates and possible further substances without a
concurrent new production of oxides or other non-conductive
substances. In this context, methods in which the work piece
treated has been heated substantially, have been considered as not
very promising.
[0008] A chemical dissolving of layers covering the surface has the
disadvantage that the corresponding processes usually are very
specific and that problems occur frequently in case of a mixture or
coverage of the surface layer with different other substances.
Thus, different procedures, in part in several steps, must be
developed for different applications.
[0009] A good possibility has been found in a mechanical removal by
milling, grinding, bombarding with particles and the like. Also,
these methods can be localized in a manner sufficient for
electrical contacts if adequately fine tools are used. Since the
layers to be removed are relatively thin, these methods are careful
processes not heating the work piece too strongly.
[0010] Surprisingly, it has been found in experiments that,
however, the best results could be achieved by a laser bombardment
of the surface in which the substances covering the surface
evaporate, are taken away by evaporation of other substances, or
are taken away by the extremely rapid local heating due to thermal
expansion. Therein, also other layers lying above the
oxide/phosphate layers can be taken away and be removed in the same
working process. Astonishingly, parameters can be found with which
on the one hand the residual-free removal of the surface layers is
possible, on the other hand the energy input is that small that the
work piece immediately cools the respective place so that even in
an oxygen containing environment, e. g. air atmosphere, substantial
new oxide layers are not produced. In any case, this applies for
the moment of laser bombardment as such. It is, however, important
to cover the treated surface portion with a layer closing the
remetallized surface again in order to avoid a slow new
oxidation.
[0011] Hereto, the invention proposes a fluid substance being
applied in a fluid condition in order to adapt to the surface
contour to enable a complete contact and a corresponding
protection. A substance can be chosen that hardens after
application or at least becomes more viscous. At least in the
final, i. e. in case of a hardening substance hardened condition,
the substance itself must show a metallic conductivity since it
takes the role of the metallically conductive surface instead of
the original alloy surface.
[0012] In conclusion, the method according to the invention
produces astonishingly good contact resistance values of e. g.
0.5-2.5 m.OMEGA./mm.sup.2 being completely sufficient for practical
applications. The laser method has the advantage to be able to run
along even complicated surface forms or tracks in short term. Also
surfaces of a complicated three dimensional shape can be treated
adequately. Especially it has been found that due to the short
working time and the thus high throughput in case of large numbers,
much more cost effective working processes can be achieved as with
mechanically removing methods.
[0013] Therein, it has also been surprising that the surface
portions for the electrical contacts can be covered in reasonable
time periods with laser technology, being specially developed for
microscopic processes, by arranging single shots side by side or by
using a continuous laser bombardment, namely because of the
relatively small necessary energy per surface unit, as explained
above.
[0014] As said above, the invention is directed to technical oxide
layers and/or phosphate layers on Al or Mg alloys. Especially
anodized surfaces are relevant.
[0015] Thus, the invention relates e. g. to the removal of anodic
oxidation layers on Al alloys. A special feature of the invention
is that also alloys with a relevant Mg ratio can be remetallized.
Thus, the invention preferably relates to alloys having a Mg ratio
of at least 2 weight %, preferably at least 10, 30 or even 40
weight % Mg. These are especially the alloys AZ91 and AM50 having
each around 90 weight % Mg.
[0016] As a metallically conductive flowable substance, preferably
hardening materials on synthetic resin basis are considered that
comprise metallically conductive particles, i. e. that are not
conductive in their matrix. These can be electrically conductive
adhesives, e. g. silicone adhesives. The metallic particles in the
fluid material can consist of Ag or Cu. A preferred choice is
silicone adhesive comprising Ag covered Cu particles. The Ag
coverage provides for a very good electrical conductivity wherein
the high costs of adhesives having a substantial Ag ratio can be
avoided.
[0017] A special aspect of the invention is an additional
application of a lacquer layer on the surface before laser
bombardment, possibly having interposed additional layers. It has
been assumed that especially with organic materials and lacquers
crack and polymerisation processes due to the thermal energy input
of the laser, which can lead to extremely resistant insulating
covers, can not be avoided. Actually, however, very good results
with low contact resistances can be realised.
[0018] On the other hand, the lacquer layer has the primary
advantage to stabilise the layers during laser bombardment and to
avoid or at least to cover cracks in the layers at the borders of
the remetallized portions which are unavoidable in some cases.
Therewith, together with the sealing by means of the flowable
material, it can be achieved that, finally, the Al or Mg alloys can
be encapsulated completely.
[0019] The term "lacquer" comprises each material having a
sufficient adhesion on the surface, and being somewhat elastic in
the applied condition, and which fulfils the above described
function. Especially appropriate are water lacquers, especially
water lacquers on acrylic resin basis.
[0020] However, also cathodic immersion lacquers (KTL lacquers) or
electrophoretic lacquer layers are possible.
[0021] Such lacquer layers can be applied directly and
two-dimensionally on the surface. In areas outside of the border
region of the remetallized portion, in which they are principally
not necessary according to the invention, they provide for an
additional protective layer for the alloy or are useful in a
colorization of the surface. Thus, technical limitations in a
colorization of layers on Al and Mg alloys can be bypassed by using
an adequately coloured lacquer.
[0022] According to another aspect of the invention, the surface
portions to be remetallized are bombarded with the laser twice or
multiple times successively wherein some time passes by there
between, during which e. g. other surface portions can be
bombarded. Thus, the energy input per shot can be limited and a too
large heating can be avoided while, on the other hand, a complete
removal of the layers is possible. Preferably, the surface portions
to be remetallized are bombarded twice.
[0023] A special advantage of the invention is that, despite the
energy input by the laser, it is not necessary (however also not
excluded) to work in an inert gas atmosphere. A laser device can be
used in normal room air atmosphere or in another working
environment under presence of oxidizing substances. Depending on
the oxidizing tendency of the environment, the maximum time period
until the coverage with the fluid conductive substance is to be
chosen. In air atmosphere, some hours or even days can pass between
the laser bombardment and the succeeding coverage depending on the
environmental temperature and air humidity.
[0024] Many different laser types can be used. Proven as useful are
infrared lasers, especially Nd activated yttrium-aluminium-garnet
lasers (Nd: YAG). Typical power densities of the laser bombardment
are in the region of 8 W/mm.sup.2 up to 20 W/mm.sup.2, preferably
between 8 W/mm.sup.2 and 40 W/mm.sup.2.
[0025] E. g. the laser can be a commercial Nd: YAG laser of the
type Baasel "Star Mark". Typical conveying speeds are between 100
and 500 mm/s, preferably between 200 and 400 mm/s. Therein,
repetition frequencies of the flash lamp and thus of the laser
pulse of 1-5 kHz, preferably 2-4 kHz, can be reached. A flash lamp
current of 10-30 A with 380 V can be adequate.
[0026] An especially important application field of the invention
is in casings and casing parts of electric or electronic apparatus
which are produced increasingly from Al and also from Mg alloys for
weight reasons, recently. Such casings must be electrically
contacted or electrically connected to other parts due to a
shielding of electromagnetic interference radiation and/or for
grounding due to safety aspects. Hereto, also this conductive
substance, e. g. the above mentioned silicone adhesive with Ag
coated Cu particles, can be used as an adhesive or sealing. Such
problems occur especially for mobile electronic apparatus because
for weight reasons the alloys treated here are very frequently used
here. The most important example are mobile phones.
[0027] A preferred embodiment is a die-casting part of the Mg alloy
AZ91 shown in the enclosed figure. Shown is a chassis part 1 of a
mobile phone casing. This chassis part 1 shall be glued to other
metallic or metallically coated casing parts along lines 2 shown in
the figure. It is essential on the one hand that the Mg die-casting
chassis part 1 has a good surface stability and a high-grade
appearance. Due to frequent hand contacts and the thus given
concurrent influence of salts, weak acids and humidity as well as
due to climate influences and other circumstances during a use for
years, the outer surface can look improper in case of an
insufficient coating. The inner surface, however, can produce
particles in case of corrosion and thus cause defects of electronic
parts.
[0028] It is further important for the glueing that the parts glued
are connected in an electrically well conductive manner in order to
produce an electromagnetic shielding of the mobile phone. In
conclusion, a stable coating of Mg die-casting part 1 must
concurrently enable a good electrical conductivity of the surface
portions 2 used for glueing. This applies also for surface parts of
contact domes 3 for a circuit board of a mobile phone which also
become conductive because of the necessary grounding. Further
details of chassis part 1 are not necessary for understanding the
invention.
[0029] Chassis part 1 is coated with a commercial "Anomag" layer,
namely an anodic oxidation/phosphatizing layer of about 3-5 .mu.m
thickness which is commercially offered by Magnesium Technology
Licensing Ltd. (Auckland, New Zealand) and their contract partners.
To be precise, this is a phosphate layer with incorporated oxides
on the Mg alloy substrate.
[0030] The Anomag layer is covered with a acrylic water lacquer
before laser bombardment in order to encapsulate the surface and
improve their appearance. The laser bombardment is done in normal
atmosphere and room temperature.
[0031] The surface is thereafter treated with a commercial Nd: YAG
laser at chassis 2 and contact domes 3 as shown. This laser is
Q-switched. Lines 2 and areas 3 shown in the figure are tracked
twice, wherein one shot is set beside the other, to be precise. The
distance, size, and energy per shot can be found empirically in
order to provide for a continuous track having a sufficient width.
The track width should be not too small in order to optimize the
electrical contact resistance to the other casing part. On the
other hand, the track width should be not too large and should be
covered by the later applied adhesive bead completely. Here, it is
about 1 mm. Therein, the energy input per shot should not be
unnecessarily high in order to avoid a substantial heating in
larger depths. Due to the double bombardment, the energy per shot
can be decreased further. Here, 20 W/mm.sup.2 are used per
shot.
[0032] The laser used is a "Baasel StarMark" set to a pulse
repetition frequency of 3 kHz. The conveying speed is about 300
mm/s and thus enables a very rapid work.
[0033] After metallizing, the metallized portions are brush-coated
with a silicone adhesive with Ag coated Cu particles. This should
be done as soon as possible after the laser bombardment in order to
optimize the contact resistance. This adhesive can also be used for
sealing and connecting during glueing the chassis part shown with
other casing parts of the mobile phone.
[0034] Such other casing parts are also metallic or metallically
coated and are glued such that an electric contact to the adhesive
is given. In this way, a sealed and electrically shielded casing
can be produced, finally.
* * * * *