U.S. patent application number 12/309305 was filed with the patent office on 2010-01-21 for combined electrochemical and laser micromaching process for creating ultri-thin surfaces.
Invention is credited to Jan Phuklin Prichystal.
Application Number | 20100012506 12/309305 |
Document ID | / |
Family ID | 38543867 |
Filed Date | 2010-01-21 |
United States Patent
Application |
20100012506 |
Kind Code |
A1 |
Prichystal; Jan Phuklin |
January 21, 2010 |
COMBINED ELECTROCHEMICAL AND LASER MICROMACHING PROCESS FOR
CREATING ULTRI-THIN SURFACES
Abstract
Ultra-thin sections in an electrically conducting material are
formed by electrochemically removing material to a thickness of
approximately 5 to 150 micrometers and removing further material by
laser micromachining to a material thickness of 1 to 30
micrometers. The electrochemical process quickly removes
substantial material but is not as precise and accurate as laser
machining to create the ultra-thin sections or translucent
sections. Removing material by an electrochemical process may be
controlled down to a thickness of approx. 10-12 micrometres so that
enough margin of a material thickness is left at the bottom of this
first cavity. The laser micromachining process removes remaining
material down to a predetermined level, e.g. 1-5 micrometres,
relatively rapidly, so that a relatively quick process for the
manufacture of ultra-thin sections in an electrically conducting
material is achieved. A metal structure manufactured by the novel
and inventive process is disclosed.
Inventors: |
Prichystal; Jan Phuklin;
(Struer, DK) |
Correspondence
Address: |
JAMES C. WRAY
1493 CHAIN BRIDGE ROAD, SUITE 300
MCLEAN
VA
22101
US
|
Family ID: |
38543867 |
Appl. No.: |
12/309305 |
Filed: |
July 12, 2007 |
PCT Filed: |
July 12, 2007 |
PCT NO: |
PCT/DK2007/000354 |
371 Date: |
August 28, 2009 |
Current U.S.
Class: |
205/655 |
Current CPC
Class: |
B23K 26/40 20130101;
B23K 2101/35 20180801; B23K 2103/50 20180801; B23K 26/60 20151001;
B23H 5/06 20130101 |
Class at
Publication: |
205/655 |
International
Class: |
C25F 3/02 20060101
C25F003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 13, 2006 |
DK |
PA 2006 00971 |
Claims
1. Process for the manufacture of ultra thin sections in an
electrically conducting material, comprising: firstly removing
material in an electrochemical process to a material thickness of
approximately 5-150 micrometers; secondly removing further material
by a laser micromachining process to a material thickness of 1 to
30 micrometers.
2. Process according to claim 1 wherein the electrochemical process
removes material down to a material thickness of 10 to 20
micrometers, and further that the laser micromachining process
removes further material down to a material thickness of 1 to 5
micrometers.
3. Process according to claim 1 wherein the electrochemical process
is a controlled anodic dissolution process, where the material is
the anode and a tool having a distal end acting as cathode so that
a reaction cell is created between the anode and cathode, and that
a salt containing electrolyte is led to the reaction cell through a
conduit in the tool.
4. Process according to claim 3 wherein the electrolyte is forced
through the conduit to the reaction cell, and where the distance
between the anode and cathode during the dissolving process is
maintained substantially constant.
5. Process according to claim 3 wherein the tool has a
cross-section substantially corresponding to the area of the
resulting ultra thin section, and where said tool is substantially
cylindrical, and the cylindrical section on the outside is provided
with a non-conductive coating.
6. Process according to claim 1 wherein the laser micromachining
process is performed by a high power femtosecond laser device
emitting laser light pulses, where the pulse length is between 150
femtoseconds and 15 picoseconds, preferably between 150
femtoseconds and 10 picoseconds and more preferably 1
picosecond.
7. Process according to claim 6 wherein the laser is controlled in
a scanning mode and scans the desired area of the ultra thin
section in a predetermined pattern.
8. Process according to claim 6 wherein the laser beam is passed
through beam shaping optics in order to create a homogeneous laser
beam shape or an Excimer type laser is used.
9. Process according to claim 1 wherein a light detector is
arranged on the opposite side of the material from which the laser
process is being performed, where said light detector is
preprogrammed to switch off the laser device when a certain
predefined luminance is detected.
10. Process according to claim 1 wherein a light beam, for example
a laser beam, is directed into the ultra thin section, and where a
light detector is arranged on the opposite side of the material
from which the laser process is being performed, where said light
detector is pre-programmed to switch off the laser device when a
certain predetermined luminance is detected.
11. Process according to claim 1 wherein the electrochemical
process creates a first cavity, inside which first cavity the laser
micromachining process creates a number of second cavities, through
which second cavities light may shine through, where the number of
second cavities is in the range of 20 to 200 pr first cavity, more
preferred 50 to 150 pr first cavity and most preferred 90 to 110 pr
first cavity.
12. Metal structure having a front side and a back side, wherein
said front and back sides define a material thickness between them,
and where in said back side of the structure ultra thin sections
manufactured according to claim 1 are present, such that when a
source of light is present behind one or more of the ultra thin
sections in said metal structure, the ultra thin sections are
emitting light, and when no light is present, the front side
appears undisturbed.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a process for the
manufacture of ultra-thin sections in an electrically conducting
material.
BACKGROUND OF THE INVENTION
[0002] In the art it has been suggested and in particular by the
same applicants prior patent application published under WO
2004/077388 to create a plate where one surface, i.e. the user's
interface appears to be without markings whereas on the backside
apertures (blind holes) are provided so that it is possible to
shine light through these apertures whereby the front side of the
panel will indicate symbols or areas where interaction with the
display unit may be carried out. The prior art document further
describes a process for the manufacture wherein a UV-excimer
femtosecond laser was used in order to create a number of dots
approximately one millimetre by one millimetre in area where the
translucency in the bottom of the cavities, i.e. in each thin
section was 0.1 percent.
[0003] This process, however, was very efficient in creating the
grids of dots which together formed the symbols on the front side
of panels produced by this method, but the production method was
extremely time-consuming in that the laser process, although being
very precise, is extremely time-consuming.
OBJECT OF THE INVENTION
[0004] It is therefore an object of the present invention to
provide a process for the manufacture of ultra-thin sections in
metals in general, but especially in any conductive material in a
faster and more rational and thereby more economic manner than what
is known from WO 2004/077388.
DESCRIPTION OF THE INVENTION
[0005] The invention addresses this problem by providing a process
for the manufacture of ultra-thin sections in an electrically
conducting material, comprising: [0006] firstly removing material
in an electrochemical process to a material thickness of
approximately 10 to 20 micrometers; [0007] secondly removing
further material by a laser micromachining process to a material
thickness of 1 to 5 micrometers.
[0008] By combining the two methods it is possible by the
electrochemical process quickly to remove a substantial amount of
material. The electrochemical process is not as precise and
accurate so that it may be possible to solely rely on and use this
method in order to create the ultra-thin sections or translucent
sections. However, by removing material by an electrochemical
process down to a thickness of approx. 10-12 micrometres, enough
margin is provided, so that the electrochemical process may be
controlled in a manner so that it is satisfied that there is a
material thickness left at the bottom of this first cavity. By
thereafter applying the laser technique, in a laser micromachining
process, the remaining material down to a predetermined level, e.g.
1-5 micrometres, may be achieved relatively rapidly, so that a
relatively quick process for the manufacture of these ultra-thin
sections in an electrically conducting material is achieved.
[0009] In a further advantageous embodiment of the invention the
electrochemical process is a controlled anodic dissolution process
where the material is the anode and a tool having a distal end
acting as cathode, so that a reaction cell is created between the
anode and cathode, and that a salt containing electrolyte is led to
the reaction cell through a conduit in the tool.
[0010] The control of the electrochemical process may be carried
out by controlling the feed of the tool, i.e. the cathode. The
electrolyte is selected according to the electrically conducting
material. Examples of electrolytes in combination with materials
will be listed below.
[0011] In order to control the electrochemical process as many
parameters as possible should be maintained constant. Therefore, in
a further advantageous embodiment the electrolyte is forced through
the conduit to the reaction cell, and that the distance between the
anode and cathode during the dissolving process is maintained
substantially constant.
[0012] In this manner and in particular when the voltage, current
and current density are maintained substantially constant, the feed
of the tool into the cavity, created by the electrochemical process
and the flow of electrolyte will determine the speed with which the
hole is created by the tool.
[0013] The tool, i.e. the anode, in an example has a distal end
with a diameter of approx. 1 millimetre. This in turn creates holes
in the electrically conducting material in the range from 1.5
millimetres to 2.5 millimetres in diameter, where the variation is
caused by the voltage of the current, the current density and the
electrolyte. Therefore, by keeping the distance between the anode
and the cathode constant, i.e. having a continuous feed of anode
into the hole in the material, a substantially continuous and
relatively fast process is achieved.
[0014] In a further advantageous embodiment the tool has a cross
section substantially corresponding to the area of the resulting
ultra-thin section, and where said tool is substantially
cylindrical, and that the cylindrical section on the outside is
provided with a non-conductive coating.
[0015] As discussed above with reference to the diameter of the
distal end of the cathode and the resulting aperture, the range of
this aperture/holes may be minimized by further coating the anode
on its outside with an electrically non-conducting coating so that
the electrochemical process only will take place at the very distal
end of the tool. The non-conducting coating will isolate the anode
from the cathode where the coating is present, whereas without the
coating, electrochemical processes may occur on the sides of the
tool whereby holes are made which holes do not have a well-defined
cross-section and/or a non-homogenous cross-section due to
inhomogenities in the materials.
[0016] Once the electrochemical process has reduced the material
thickness to approx. 20 or 10 micrometers, the material is prepared
for further workings and in order to create the translucent
ultra-thin sections, a laser micromachining process is performed by
a high-power laser device emitting ultrashort laser light pulses,
where the pulse length is between 150 femtoseconds and 15
picoseconds, preferably 1 picosecond.
[0017] The pulse length, i.e. whether devices emitting 150
femtoseconds or 15 picoseconds pulse lengths are used or pulse
length in between, depends on the type of laser device, the
intensity of the laser, the laser-light repetition rate as well as
the mode in which the laser is operated.
[0018] In a further advantageous embodiment the laser is controlled
in a scanning mode, and scans the desired area of the ultra thin
section in a predetermined pattern.
[0019] In scanning-mode it is possible to have the laser move back
and forth, in a hatch pattern, or in circles inside the area where
it is desired to make the cavity down to the ultra-thin section.
Typically the diameter of the cavity will be 100 .mu.m to 120 .mu.m
which size roughly corresponds to the size of one pixel in an
LCD-screen.
[0020] Typically a laser-beam will have a Gaussian shape energy
profile so that if the cross section of the energy profile was
enlarged, it would have a shape so that the width of the profile
would include a tip substantially arranged in the middle of the
width section whereby a cavity will be created having slanted
sides. In order to compensate for this, the laser beam may be
treated in order to give it a so-called top-hat shape where the
laser-beam is passed through beam shaping optics in order to create
a homogeneous laser beam shape or alternatively an Excimer type
laser is used.
[0021] The advantages of using beam-shaping optics is the fact that
by transforming the laser-beam from the Gaussian profile to a
substantially top-hat profile, a larger area of the laser-beam will
be at the same level, so that a more even treatment of the surface
will be achieved. The principle of reshaping a laser-beam may be
carried out as described in "Aspheric laser-beam re-shaper
applications guide" by C. Michael Jefferson and John A. Hoffnagel
of IBM Almaden Research Center.
[0022] When using laser-beams and in particular when the
laser-beams have been reshaped, a trepanning or percussion mode of
the laser-beam has been found to be advantageous in that it is
well-defined how much material is removed by each pulse of laser
and thereby it becomes possible to very accurately guide and
control the laser beam in order to create the cavity having an
ultra-thin section left at the bottom of the hole.
[0023] In a further advantageous embodiment a light detector is
arranged on the opposite side of the material from which the laser
process is being performed, where said light detector is
pre-programmed to switch off the laser device (the laser removing
material) when a certain predetermined luminance is detected.
[0024] In a further advantageous embodiment a light-beam, e.g. a
laser-beam is directed into the ultra thin section, and that a
light detector is arranged on the opposite side of the material
from which the laser process is being performed, where said light
detector is pre-programmed to switch off the laser device (the
laser removing material) when a certain predetermined luminance is
detected. The light beam may be another second laser device having
different characteristics from the working laser or may be the
working laser.
[0025] The object of creating the ultra-thin sections is to provide
translucent sections in an otherwise homogenous surface, so that
when the material in which the ultra-thin sections are processed
from the backside, the front side of said material will appear not
to have undergone any changes. As a light source is arranged behind
the ultra-thin sections, and light is emitted from said light
source, the ultra-thin sections which are translucent will indicate
to a user whatever desired input is needed or wanted. Therefore, in
order to control the thickness of the ultra-thin section, a light
source, e.g. a laser-beam, may be directed together with the
working laser-beam into the cavity from the backside which light
source is arranged in conjunction with a light detector on the
front side of the material so that a as a certain luminance is
detected by the light detector, a sufficiently thin, ultra-thin
section is created and the working laser-beam may be switched off.
By controlling the light detector and adjusting its sensitivity, it
is possible in this manner to efficiently control the material
thickness in the ultra-thin sections. Typically, as stated above,
the average material thickness in the ultra-thin section will be
1-5 micrometers. This, of course, depends on the material on which
the process is applied, but for most metallic materials this will
be sufficient in order to visibly preserve the integrity of the
surface from the front side of the material. Additionally, in case
of Aluminium, an anodized layer will be formed on the surface, so
that the combined thickness in the ultra-thin sections will be
approx. 1-20 micrometers. It is, however, important that the
material thickness of the remaining metal is less than 20
nanometers in the translucent regions.
[0026] In a further advantageous embodiment of the invention the
electrochemical process creates a first cavity, inside which first
cavity the laser micromachining process creates a number of second
cavities, through which second cavities light may shine through,
where the number of second cavities are in the range of 20 to 200
pr first cavity, more preferred 50 to 150 pr first cavity and most
preferred 90 to 110 pr first cavity.
[0027] As already mentioned above, the cavities created by the
laser beam have a diameter of approx. 100-120 .mu.m roughly
equivalent to the size of a pixel on an LCD-display. In order to be
able to create a dot or a symbol when a light source shines through
the ultra-thin section an array of second cavities is necessary so
that a user watching the processed material from the front side
will be able to distinguish a substantial illuminated dot or
symbol, in that one single tiny pixel would not be enough.
[0028] The electrochemical process as explained above is able to
create a substantially larger first cavity, i.e. the majority of
the material is removed by the electrochemical process down to a
safe depth of the cavity as already explained above. Within this
cavity it is possible to create an array of second cavities by use
of the laser beam in order to create the desired pattern of
ultra-thin surfaces be it a dot, a symbol, a letter or any other
desired pattern. By selecting an anode having the desired
cross-section the desired cross-section of the first cavity may be
created in one continuous process whereupon the laser beam creates
the resulting ultra-thin surfaces. The anode may also be moved in
order to create a longer first cavity.
[0029] As an example ultra-thin sections are created in
aluminium-based materials where the material thickness is approx.
0.5-1 millimetre or 2 millimetres. The electrochemical process is
commenced as described above where the electrolyte might be a
sodium nitrate (NaNO.sub.3) water solution having a concentration
of 100 g per litre. The voltage is selected at 8 Volts whereby the
current density will be in the interval 1-1.3 A/mm.sup.2.
Typically, the anode will advance 0.0125 millimetres per second
into the material. As the electrochemical machining reaches the
desired depth, i.e. where a material thickness at the bottom of the
cavity of 10-20 micrometers, the electrochemical machining is
interrupted, the electrolyte removed and the laser micromachining
process proceeds. Typically, the laser micromachining process from
10-20 micrometers and down to 1-5 micrometers, takes less than a
second per hole, and as the laser has to work sequentially, i.e.
one cavity at a time, and the laser beam needs to be repositioned
between each cavity, it may take some time in order to create the
number of cavities in an array. This, however, is much faster than
using laser alone, and more precise than the electrochemical
machining alone.
[0030] Typically, the laser in scanning mode is operated at an
intensity of 8 mW-200 mW where the pulse length was kept at 150
femtoseconds at 6 kHz, the wave length of 775 nm. Alternatively the
intensity was operated at 100 mW to 1 W with pulse lengths of 10
picoseconds at 30-100 kHz with a wave length of 1064 nm. In the
other modes, i.e. trepanning or percussion, the procedure was
carried out with an intensity of 1 W, where the pulse length was
150 femtoseconds at 6 kHz at the same wave length as used in the
scanning mode.
DESCRIPTION OF THE DRAWING
[0031] FIG. 1 illustrates the process of electrochemical
machining.
[0032] FIG. 2 illustrates the theoretical intensity distribution of
a Gaussian laser and a tophat laser.
[0033] FIG. 3 illustrates a schematic set-up for laser
micromachining.
[0034] FIG. 4 illustrates the finishes product by the combined
process.
DETAILED DESCRIPTION OF THE INVENTION
[0035] The combination of two processes as is the scope of the
present invention provides a number of advantages over the
processes seen alone and removes some of the disadvantages which
the single processes have. Electrochemical micromachining does as
explained with reference to FIG. 1 dissolve the material into which
the blind holes are to be made by a controlled anodic
electrochemical dissolution process where the work piece 1 is the
anode and the tool 2 is the cathode. The process further requires
an electrolyte 3 whereby an electrolytic cell is created, so that
an electrolysis process between the anode 1 and the cathode 2 may
take place. In this manner it is possible by further feeding the
cathode as indicated by the arrow 4 into the material 1 to dissolve
the material as indicated in the right hand side of FIG. 1. The
electrolyte 3 is typically fed through a conduit 5 provided inside
the tool. By further coating 6 the tool by non-conductive coating
layer it is assured that the electrolysis process occurs at the
distal end 10 of the tool.
[0036] The electrolyte is typically a salt solution in water.
Sodium chloride or sodium nitrate as well as potassium nitrate may
be used, but best results were found by using sodium nitrate
(NaNO.sub.3). The electrolysis process is driven by directing a
current having a relatively high current density at low voltage
between the work piece 1 and the tool 2. Thereby the anode-cathode
process will dissolve the metal into metallic ions in a deplating
reaction. The metallic ions will react with OH-- and will form
hydroxide reaction products. The electrolyte and the reaction
products will be removed as the electrolyte is continuously fed
through the conduit 5 in the work piece. In this manner the cross
section of the tool 2 will create an aperture 7 in the work piece
1.
[0037] The electrolyte further serves to remove the dissolved
metal, the gases produced by the electrolysis process as well as
removing heat from the working area. Therefore, the electrolyte is
continuously fed through the conduit 5 in the tool 2. As there is
no mechanical contact between the tool 2 and the work piece 1 and
further the material removing process is electrochemical and
therefore there is no contact between the two, there are no
specific requirements to the hardness, toughness and so forth of
the tool, and due to the nature of the process there is
substantially no wear on the tool as such. The coating 6 provides
for all electrochemical machining to take place at the distal end
10 of the tool. Therefore, it is possible to create substantially
cylindrical holes i.e. blind holes where the sides of the holes are
parallel in that any electrochemical processes along the tool's
shaft may be avoided due to the non-conductive coating 6.
[0038] The electrochemical machining continues down to a material
thickness of 10-20 .mu.m indicated by the zone 8.
[0039] Turning to the further process of machining the final layers
down to 1-5 .mu.m thickness, attention is directed to FIGS. 2 and
3.
[0040] In FIG. 2 are illustrated theoretical beam shapes of a laser
beam. The laser beam indicated by 11 has a distribution
corresponding to a Gaussian shape which will be the untreated shape
of a laser beam. Therefore, when an untreated laser beam is used,
the energy at the tip 12 will be very high so that the major part
of material removal will occur at the tip and lessen towards the
sides of the laser beam. This in turn indicates that was the laser
cap stationary and pulsing, a hole having a shape as indicated by
the curve 11 will be the result. By scanning such a beam in a
predetermined pattern, the tip of the beam 12 will level the bottom
of the hole so that a substantially even bottom may be created.
[0041] However, by applying reshaping techniques to the laser beam,
e.g. by passing the laser beam through a pair of aspheric lenses
with adapted focusing lens, it is possible to reshape the Gaussian
curve into a so-called top-hat configuration as illustrated with
reference to 13. An example of such a pair of beam shaping lenses
is a pair of lenses where one is plano-convex and the other
plano-concave. The characteristics of the beam 13 is the fact that
the energy level is substantially constant and covers a much larger
area of the tip of the beam so that it is possible to work larger
surfaces at the same time. The energy needed in order to create the
beam 12 or the beam 13 is equal. By further increasing the power
for the output of the top-hat 13 configuration, it becomes possible
to remove more and more material. These techniques are adapted to
the process according to the present invention depending on the
desired mode of work for the laser beam.
[0042] The ultra-thin section is created firstly by the
electrochemical machining process and thereafter by a laser
micromachining process, using ultra-short laser pulses. For this
purpose a schematic set-up as indicated in FIG. 3 is used. The
working laser beam 14 is directed into mirrors 15 arranged in a
scanner head 16. The scanner head will there-after move the working
laser beam in a predetermined pattern in order to create an
ultra-thin section with the desired area and cross-section.
[0043] In order to determine when to interrupt the laser
micromachining it is necessary to monitor the proceedings very
carefully. This is in practice done by placing a light detector 18
on the opposite side of the material to be worked. As the light
detector detects a predetermined amount of light passing the
ultra-thin section 20, the working laser beam 14 is cut off,
whereby further micromachining is halted. Better results were
obtained by directing a further laser detection beam 17 into the
working laser beam 14 and placing a light detector 18 on the
opposite side of the material to be worked. In order to distinguish
the two laser beams from each other they may be operated at
different wavelengths and the light detector arranged accordingly.
Alternatively, the further laser detection beam is continuous,
while the working beam is pulsed. The detection system is
synchronized with the working beam and the light is measured only
between the pulses of the working beam, e.g. when the working laser
beam is off.
[0044] A focusing lens 19 may be provided in order to concentrate
the laser beam in specific points as explained above.
[0045] The result of the combined process is firstly processing the
work piece 1 by an electro-chemical process as explained with
reference to FIG. 1 and thereafter switching to a laser
micromachining process as explained with reference to FIG. 3 which
creates a material as roughly illustrated with reference to FIG.
4.
[0046] Firstly, a blind hole 21 has been created by means of the
electrochemical machining after which the work piece 1 has been
cleaned from electrolyte and other pollutants and thereafter
exposed to the laser beam micromachining. The micromachining
creates the blind holes 22. By creating an array of blind holes
with the laser micro machining and only leaving an ultra-thin
section 20, it is possible to place a light source adjacent the
cavity 21 and shine light through the array of holes 22 so that on
the undisturbed surface 23 of the work piece illumination will be
provided through the ultra-thin sections 20. When no light is
directed into the cavities the front surface appears
undisturbed.
[0047] The ultra-thin section 20 may in fact be covered by a
transparent oxide layer prior to the electrochemical micro
machining step as is normal when aluminium is the base
material.
[0048] In order to stabilize the structure the cavity 21 may be
filled up with a transparent stabilizing material such as clear
epoxy or the like. The only requirement for this filler is that it
is possible to transmit light through the material so that the
translucent regions created by the array of apertures 22 is not
hampered by the stabilizing material filled into the cavity.
[0049] Above reference is made to high power laser devices emitting
ultra short laser light pulses. Non limiting examples of such
devices are generally referred to as femtosecond lasers or
picosecond lasers
* * * * *