U.S. patent application number 11/333009 was filed with the patent office on 2006-06-22 for method and apparatus for forming a metallic feature on a substrate.
This patent application is currently assigned to Agency for Science, Technology and Research, Agency for Science, Technology and Research. Invention is credited to William T. Chen, Peter M. Moran.
Application Number | 20060134338 11/333009 |
Document ID | / |
Family ID | 34568069 |
Filed Date | 2006-06-22 |
United States Patent
Application |
20060134338 |
Kind Code |
A1 |
Chen; William T. ; et
al. |
June 22, 2006 |
Method and apparatus for forming a metallic feature on a
substrate
Abstract
A method of forming a metallic feature on a substrate,
comprising the steps of: providing a stamp having a raised region;
depositing catalytic particles on a selected area of the stamp,
including the raised region thereof; providing a substrate;
applying the stamp to the substrate, such that the raised region of
the stamp causes a corresponding indented region in the substrate
and at least some of the catalytic particles are transferred to a
selected area of the substrate; and plating the selected area of
the substrate.
Inventors: |
Chen; William T.; (Endicott,
NY) ; Moran; Peter M.; (West Coast Crescent,
SG) |
Correspondence
Address: |
WORKMAN NYDEGGER;(F/K/A WORKMAN NYDEGGER & SEELEY)
60 EAST SOUTH TEMPLE
1000 EAGLE GATE TOWER
SALT LAKE CITY
UT
84111
US
|
Assignee: |
Agency for Science, Technology and
Research
Singapore
SG
|
Family ID: |
34568069 |
Appl. No.: |
11/333009 |
Filed: |
January 17, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10081768 |
Feb 22, 2002 |
7026012 |
|
|
11333009 |
Jan 17, 2006 |
|
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|
Current U.S.
Class: |
427/402 |
Current CPC
Class: |
C23C 18/1608 20130101;
H05K 3/107 20130101; C25D 5/56 20130101; C25D 5/02 20130101; C23C
18/2033 20130101; H05K 2203/0108 20130101; H05K 2203/0709 20130101;
H01L 2251/105 20130101; C23C 18/30 20130101; H05K 3/182 20130101;
H05K 2201/09118 20130101 |
Class at
Publication: |
427/402 |
International
Class: |
B05D 1/36 20060101
B05D001/36 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 23, 2001 |
SG |
200101072-7 |
Claims
1. A method of forming a metallic feature on a substrate,
comprising the steps of: providing a mould, an inner surface
thereof having a raised region, depositing catalytic particles on a
selected area of the inner surface of the mould, including the
raised region thereof; providing a substrate material; moulding the
substrate material within the mould, such that a resulting
substrate has an indented region corresponding to the raised region
of the inner surface of the mould and at least some of the
catalytic particles are transferred to a selected area of the
substrate; and plating the selected area of the substrate.
2. A method according to claim 1, wherein the step of depositing
catalytic particles on the selected area of the inner surface of
the mould comprises the step of immersing at least the selected
area of the inner surface of the mould in a suspension comprising
the catalytic particles.
3. A method according to claim 2, wherein the step of immersing at
least the selected area of the inner surface of the mould in a
suspension comprising the catalytic particles comprises the step of
immersing at least the selected area of the inner surface of the
mould in an aqueous suspension comprising the catalytic
particles.
4. A method according to claim 2, further comprising the step of
drying at least the selected area of the mould, after immersion
thereof in the suspension.
5. A method according to claim 4, wherein the step of drying at
least the selected area of the mould comprises the step of blow
drying at least the selected area of the mould with a gas.
6. A method according to claim 5, wherein the step of blow drying
the selected area with a gas comprises the step of blow drying the
selected area with nitrogen, helium or air.
7. A method according to claim 4, wherein the step of depositing
catalytic particles on the selected area of the inner surface of
the mould comprises the step of depositing polymer-stabilised
catalytic particles on the selected area of the inner surface of
the mould.
8. A method according to claim 7, wherein the step of depositing
polymer-stabilised catalytic particles on the selected area of the
inner surface of the mould comprises the step of depositing
catalytic particles stabilised by polyvinylpyrrolidone,
poly-2-vinylpyridine or polyvinyl alcohol on the selected area of
the inner surface of the mould.
9. A method according to claim 1, wherein the step of depositing
catalytic particles on the selected area of the inner surface of
the mould comprises the step of depositing palladium-based
catalytic particles on the inner surface of the mould.
10. A method according to claim 9, wherein the step of depositing
catalytic particles on the selected area of the inner surface of
the mould comprises the step of depositing polymer-stabilised
catalytic particles on the selected area of the inner surface of
the mould.
11. A method according to claim 10, wherein the step of depositing
polymer-stabilised catalytic particles on the selected area of the
inner surface of the mould comprises the step of depositing
catalytic particles stabilised by polyvinylpyrrolidone,
poly-2-vinylpyridine or polyvinyl alcohol on the selected area of
the inner surface of the mould.
12. A method according to claim 1, wherein the step of providing a
substrate material comprises the step of providing a polymeric
substrate material.
13. A method according to claim 12, wherein the step of depositing
catalytic particles on the selected area of the inner surface of
the mould comprises the step of immersing at least the selected
area of the inner surface of the mould in a suspension comprising
the catalytic particles.
14. A method according to claim 13, further comprising the step of
drying at least the selected area of the mould, after immersion
thereof in the suspension.
15. A method according to claim 12, wherein the step of providing a
polymeric substrate material comprises the step of providing a
thermoset substrate material, and wherein the step of moulding the
substrate material comprises the steps of: moulding the substrate
material in an uncured or partially cured state; and curing the
substrate material in the mould.
16. A method according to claim 12, wherein the step of providing a
polymeric substrate material comprises the step of providing a
thermoplastic substrate material, and wherein the step of moulding
the substrate material comprises the step of heating the substrate
material to around or above the glass transition temperature
thereof.
17. A method according to claim 12, wherein the step of providing a
polymeric substrate material comprises the step of providing a
substrate formed from a polystyrene, a polyimide, an acrylic or an
epoxy.
18. A method according to claim 17, wherein the step of providing a
polymeric substrate material comprises the step of providing a
thermoset substrate material, and wherein the step of moulding the
substrate material comprises the steps of: moulding the substrate
material in an uncured or partially cured state; and curing the
substrate material in the mould.
19. A method according to claim 17, wherein the step of providing a
polymeric substrate material comprises the step of providing a
thermoplastic substrate material, and wherein the step of moulding
the substrate material comprises the step of heating the substrate
material to around or above the glass transition temperature
thereof.
20. A method according to claim 1, further comprising the step of
removing some of the catalytic particles from the inner surface of
the mould.
21. A method according to claim 20, wherein the step of removing
some of the catalytic particles from the inner surface of the mould
comprises the steps of: applying an adhesive surface to the inner
surface of the mould, and subsequently removing the adhesive
surface from the inner surface of the mould.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS This is a divisional
application of U.S. application Ser. No. 10/081,768, filed on Feb.
22, 2002, which is incorporated herein by reference.
THE FIELD OF THE INVENTION
[0001] This invention relates to a method and apparatus for forming
a metallic feature on a substrate, and in particular to a method
and apparatus for forming fine metallic features in close proximity
to one another on a substrate.
BACKGROUND OF THE INVENTION
[0002] The formation of fine metallic features in close proximity
to one another is of great commercial interest in several
industries, most notably the printed circuit board (PCB), flexible
circuit and packaging industries. The formation of smaller, more
densely arranged components on the surface of a substrate allows
the manufacture of PCB's that are cheap and operate quickly (due to
the proximity of the components), and for flip chip applications
the packaging industry requires the accurate patterning of solder
bumps onto PCB's for connection to chips.
[0003] Many conventional methods of forming metallic features on
substrates involve the use of photolithography to define a pattern
on the substrate. However, this technique is cumbersome and
expensive, and the size the of metallic features that can be
produced thereby on, for example, PCB's is limited to around 30
.mu.m and above. Moreover, the controlled formation of
three-dimensional features (i.e. those which are raised above the
surface of the substrate) is difficult using such conventional
methods.
[0004] More recent techniques comprise the application of catalytic
particles to the surface of a substrate by a soft stamp, the
particles being applied in a pattern which corresponds to the
metallic features that are to be created on the surface of the
substrate. Prior stamping, the substrate must first be activated by
oxidation and/or silanization in order to ensure the particles will
adhere to it. During subsequent electroless plating of the
substrate, metal will only plate to the substrate where catalytic
particles have been deposited. In this manner, small-scale metallic
surface features can be created.
[0005] However, one drawback of this process is that the depth of
the metallic features is limited by the amount of metal that can be
deposited on a region of a substrate containing catalytic particles
before lateral spreading of the metal takes place. This clearly
places an upper limit both on the density of surface features that
can be created using this technique and on the minimum distance
between any two features.
[0006] A further drawback of this technique is that the oxidation
and silanization steps are lengthy. Furthermore, since these
surface treatments form a very thin (nanometer-sized) active layer
on the surface, any moulding or deformation of the substrate during
the stamping process is not practical. This precludes using the
existing method for moulding non-planar circuitry during the
stamping process. The stamping process using the previously
described technique is also slow.
BRIEF SUMMARY OF THE INVENTION
[0007] It is an object of the present invention to seek to provide
a method and apparatus for forming metallic features on a substrate
that alleviate some or all of the above drawbacks.
[0008] Accordingly, one aspect of the present invention provides a
method of forming a metallic feature on a substrate, comprising the
steps of: providing a stamp having a raised region; depositing
catalytic particles on a selected area of the stamp, including the
raised region thereof; providing a substrate; applying the stamp to
the substrate, such that the raised region of the stamp causes a
corresponding indented region in the substrate and at least some of
the catalytic particles are transferred to a selected area of the
substrate; and plating the selected area of the substrate.
[0009] Advantageously, the step of depositing catalytic particles
on the selected area of the stamp comprises the step of immersing
at least the selected area of the stamp in a suspension comprising
the catalytic particles.
[0010] Preferably, the step of immersing at least the selected area
of the stamp in a suspension comprising the catalytic particles
comprises the step of immersing at least the selected area of the
stamp in an aqueous suspension comprising the catalytic
particles.
[0011] Conveniently, the method further comprises the step of
drying at least the selected area of the stamp, after immersion
thereof in the suspension.
[0012] Advantageously, the step of drying at least the selected
area of the stamp comprises the step of blow drying at least the
selected area of the stamp with a gas.
[0013] Preferably, the step of blow drying at least the selected
area with a gas comprises the step of blow drying the selected area
with nitrogen, helium or air.
[0014] Conveniently, the step of depositing catalytic particles on
the selected area of the stamp comprises the step of depositing
polymer-stabilised catalytic particles on the selected area of the
stamp.
[0015] Advantageously, the step of depositing polymer-stabilised
catalytic particles on the selected area of the stamp comprises the
step of depositing catalytic particles stabilised by
polyvinylpyrrolidone, poly-2-vinylpyridine or polyvinyl alcohol on
the selected area of the stamp
[0016] Preferably, the step of providing a substrate comprises the
step of providing a substrate formed from a glass or a metal.
[0017] Conveniently, the step of providing a substrate comprises
the step of providing a polymeric substrate.
[0018] Advantageously, the step of providing a polymeric substrate
comprises the step of providing a substrate formed from a
polystyrene, a polyimide, an acrylic or an epoxy.
[0019] Preferably, the step of applying the stamp to the substrate
further comprises the step of heating at least one of the stamp or
the substrate.
[0020] Conveniently, the step of heating at least one of the stamp
or the substrate comprises the step of heating one of the stamp or
the substrate to around or above the glass transition temperature
of the substrate.
[0021] Advantageously, the method further comprises the step of
modifying at least the selected area of the substrate to facilitate
the deposition of the catalytic particles thereon.
[0022] Preferably, the step of modifying at least the selected area
of the substrate comprises the step of chemically modifying the
selected area of the substrate.
[0023] Conveniently, the step of chemically modifying at least the
selected area of the substrate comprises the step of silanising at
least the selected area of the substrate.
[0024] Advantageously, the method further comprises the step of
removing some of the catalytic particles from the stamp.
[0025] Preferably, the step of removing some of the catalytic
particles from the stamp comprises the steps of: applying an
adhesive surface to the stamp; and subsequently removing the
adhesive surface from the stamp.
[0026] Conveniently, the step of depositing catalytic particles on
the selected area of the stamp comprises the step of depositing
palladium-based catalytic particles on the selected area of the
stamp.
[0027] Another aspect of the present invention provides a method of
forming a metallic feature on a substrate, comprising the steps of:
providing a mould, an inner surface thereof having a raised region,
depositing catalytic particles on a selected area of the inner
surface of the mould, including the raised region thereof;
providing a substrate material; moulding the substrate material
within the mould, such that a resulting substrate has an indented
region corresponding to the raised region of the inner surface of
the mould and at least some of the catalytic particles are
transferred to a selected area of the substrate; and plating the
selected area of the substrate.
[0028] Advantageously, the step of depositing catalytic particles
on the selected area of the inner surface of the mould comprises
the step of immersing at least the selected area of the inner
surface of the mould in a suspension comprising the catalytic
particles.
[0029] Preferably, the step of immersing at least the selected area
of the inner surface of the mould in a suspension comprising the
catalytic particles comprises the step of immersing at least the
selected area of the inner surface of the mould in an aqueous
suspension comprising the catalytic particles.
[0030] Conveniently, the method further comprises the step of
drying at least the selected area of the mould, after immersion
thereof in the suspension.
[0031] Advantageously, the step of drying at least the selected
area of the mould comprises the step of blow drying at least the
selected area of the mould with a gas.
[0032] Preferably, the step of blow drying the selected area with a
gas comprises the step of blow drying the selected area with
nitrogen, helium or air.
[0033] Conveniently, the step of depositing catalytic particles on
the selected area of the inner surface of the mould comprises the
step of depositing polymer-stabilised catalytic particles on the
selected area of the inner surface of the mould.
[0034] Advantageously, the step of depositing polymer-stabilised
catalytic particles on the selected area of the inner surface of
the mould comprises the step of depositing catalytic particles
stabilised by polyvinylpyrrolidone, poly-2-vinylpyridine or
polyvinyl alcohol on the selected area of the inner surface of the
mould.
[0035] Preferably, the step of providing a substrate material
comprises the step of providing a glass or metal substrate
material.
[0036] Conveniently, the step of providing a substrate material
comprises the step of providing a polymeric substrate material.
[0037] Advantageously, the step of providing a polymeric substrate
material comprises the step of providing a substrate formed from a
polystyrene, a polyimide, an acrylic or an epoxy.
[0038] Preferably, the step of providing a polymeric substrate
material comprises the step of providing a thermoset substrate
material, and wherein the step of moulding the substrate material
comprises the steps of: moulding the substrate material in an
uncured or partially cured state; and curing the substrate material
in the mould.
[0039] Conveniently, the step of providing a polymeric substrate
material comprises the step of providing a thermoplastic substrate
material, and wherein the step of moulding the substrate material
comprises the step of heating the substrate material to around or
above the glass transition temperature thereof.
[0040] Advantageously, the method further comprises the step of
removing some of the catalytic particles from the inner surface of
the mould.
[0041] Preferably, the step of removing some of the catalytic
particles from the inner surface of the mould comprises the steps
of: applying an adhesive surface to the inner surface of the mould,
and subsequently removing the adhesive surface from the inner
surface of the mould.
[0042] Conveniently, the step of depositing catalytic particles on
the selected area of the inner surface of the mould comprises the
step of depositing palladium-based catalytic particles on the inner
surface of the mould. further aspect of the present invention
provides a method of forming a metallic feature on a substrate,
comprising the steps of: providing a stamp; depositing
polymer-stabilised catalytic particles on a selected area of the
stamp; providing a substrate; applying the stamp to the substrate
such that at least some of the polymer-stabilised catalytic
particles are transferred to a selected area of the substrate; and
plating the selected area of the substrate.
[0043] Advantageously, the step of depositing polymer-stabilised
catalytic particles on the selected area of the stamp comprises the
step of depositing catalytic particles stabilised by
polyvinylpyrrolidone, poly-2-vinylpyridine or polyvinyl alcohol on
the selected area of the stamp
[0044] Preferably, the selected area of the stamp comprises a
raised region of the stamp.
[0045] Conveniently, the step of applying the stamp to the
substrate comprises the step of pressing the stamp and the
substrate against one another such that the raised region of the
stamp causes a corresponding indented region in the substrate.
[0046] Advantageously, the step of depositing polymer-stabilised
catalytic particles on the selected area of the stamp comprises the
step of immersing at least the selected area of the stamp in a
suspension comprising the polymer-stabilised catalytic
particles.
[0047] Preferably, the step of immersing at least the selected area
of the stamp in a suspension comprising the polymer-stabilised
catalytic particles comprises the step of immersing at least the
selected area of the stamp in an aqueous suspension comprising the
polymer-stabilised catalytic particles.
[0048] Conveniently, the method further comprises the step of
drying at least the selected area of the stamp, after immersion
thereof in the suspension.
[0049] Advantageously, the step of drying at least the selected
area of the stamp comprises the step of blow drying at least the
selected area of the stamp with a gas.
[0050] Preferably, the step of blow drying at least the selected
area of the stamp with a gas comprises the step of blow drying the
selected area with nitrogen, helium or air.
[0051] Conveniently, the step of providing a substrate comprises
the step of providing a glass or metal substrate.
[0052] Advantageously, the step of providing a substrate comprises
the step of providing a polymeric substrate.
[0053] Preferably, the step of providing a polymeric substrate
comprises the step of providing a substrate formed from a
polystyrene, a polyimide, an acrylic or an epoxy.
[0054] Conveniently, the step of applying the stamp to the
substrate further comprises the step of heating at least one of the
stamp or the substrate. Advantageously, the step of heating at
least one of the stamp or the substrate comprises the step of
heating at least one of the stamp or the substrate to around or
above the glass transition temperature of the substrate.
[0055] Preferably, the method further comprises the step of
modifying at least the selected area of the substrate to facilitate
the position of the polymer-stabilised catalytic particles
thereon.
[0056] Conveniently, the step of modifying at least the selected
area of the substrate comprises the step of chemically modifying at
least the selected area of the substrate.
[0057] Advantageously, the step of chemically modifying at least
the selected area of the substrate comprises the step of silanising
at least the selected area of the substrate.
[0058] Preferably, the method further comprises the step of
removing some of the polymer-stabilised catalytic particles from
the stamp prior to the application thereof to the substrate.
[0059] Conveniently, the step of removing some of the
polymer-stabilised catalytic particles from the stamp comprises the
steps of: applying an adhesive surface to the stamp; and
subsequently removing the adhesive surface from the stamp.
[0060] Advantageously, the step of applying an adhesive surface to
the stamp comprises the step of applying a patterned adhesive
surface to the stamp.
[0061] Preferably, the step of depositing polymer-stabilised
catalytic particles on the selected area of the stamp comprises the
step of depositing palladium-based polymer-stabilised catalytic
particles on the selected area of the stamp.
[0062] Another aspect of the present invention provides a stamp for
application to a substrate, having a selected area comprising a
raised region on a surface thereof and at least the selected area
of the surface having catalytic particles deposited thereon.
[0063] Conveniently, the catalytic particles are polymer-stabilised
catalytic particles.
[0064] A further aspect of the present invention provides a stamp
for application to a substrate, comprising polymer-stabilised
catalytic particles deposited on a selected area of a surface
thereof.
[0065] Advantageously, the selected area of the surface of the
stamp comprises at least one raised region.
[0066] Another aspect of the present invention provides an
apparatus for preparing a substrate, comprising: a stamp according
to the above; and means to apply the stamp to a substrate.
[0067] Preferably, the apparatus further comprises means to
selectively remove some of the catalytic particles from the
stamp.
[0068] Conveniently, the apparatus further comprises means to plate
the substrate.
[0069] Advantageously, the means to plate the substrate comprise
means to electroless plate or immersion plate the substrate
BRIEF DESCRIPTION OF THE DRAWINGS
[0070] In order that the present invention may be more readily
understood, embodiments thereof will now be described, by way of
example, with reference to the accompanying drawings, in which:
[0071] FIG. 1 shows a cross-sectional view of a stamp;
[0072] FIG. 2 shows a cross-sectional view of the stamp of FIG. 1,
with catalytic particles deposited thereon, embodying the present
invention;
[0073] FIG. 3 shows a cross-sectional view of the stamp of FIG. 2
being applied to a substrate;
[0074] FIG. 4 shows a cross-sectional view of the substrate of FIG.
3 after application thereto of the stamp of FIG. 2.
[0075] FIG. 5 shows a cross-sectional view of the substrate of FIG.
4 following metalisation thereof;
[0076] FIG. 6 shows a cross-sectional view of a further stamp
embodying the present invention;
[0077] FIG. 7 shows a cross-sectional view of the stamp of FIG. 6,
with a length of adhesive tape applied thereto;
[0078] FIG. 8 shows a cross-sectional view of the stamp of FIG. 7,
after removal of the adhesive tape;
[0079] FIG. 9 shows a cross-sectional view of a further substrate,
following application of the further stamp thereto and metalisation
thereof.
[0080] FIG. 10 shows a cross-sectional view of a third stamp
embodying the present invention;
[0081] FIG. 11 shows a cross-sectional view of the stamp of FIG. 10
after application of an adhesive surface thereto;
[0082] FIG. 12 shows a cross-sectional view of the stamp of FIG. 11
being applied to a third substrate; and
[0083] FIG. 13 shows the substrate of FIG. 13 following
metalisation thereof.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0084] Turning firstly to FIG. 1, a stamp 1 is shown. The stamp 1
may be formed from silicon, or may be formed from any other
suitable material such as glass, a metal or a polymer. A stamping
surface 2 of the stamp 1 is formed to have raised regions 3
thereon, there being sunken channels 4 between the raised regions
3. The pattern of raised regions 3 corresponds to a pattern of
metallic features that are to be formed on a substrate.
[0085] In a first step of a method embodying the present invention,
the stamping surface 2 of the stamp 1 is coated with a layer of
catalytic particles 5, as shown in FIG. 2. The stamp 1 now embodies
the present invention. In a preferred embodiment, the catalytic
particles 5 comprise nanometer-sized palladium particles.
Advantageously, the catalytic particles 5 are coated with molecules
of polyvinylpyrrolidone, poly-2-vinylpyridine or polyvinyl alcohol,
which coating confers the beneficial effect of stabilising the
colloidal suspension of the catalytic particles 5 against
agglomeration.
[0086] The layer of catalytic particles 5 is deposited on the
stamping surface 2 of the stamp 1 by immersion of the stamp 1 in a
suspension of the catalytic particles 5. The catalytic particles 5
are adsorbed weakly to the stamping surface 2 of the stamp 1. After
immersion in the suspension the stamp 1 is removed from the
suspension and blown dry with a gas, such as nitrogen, helium or
air. Immersion of the stamp 1 in the suspension may take place for
a few seconds, or longer (e.g., several minutes or tens of
minutes), as required. It may also be done repeatedly with a drying
step in between, if required.
[0087] In a subsequent step of the method of the present invention,
the stamp 1 is pressed against a surface of a substrate 6, the
stamping surface 2 of the stamp 1 being placed in contact with the
substrate 6. This step is shown in FIG. 3. The stamp 1 is pressed
against the substrate 6 sufficiently forcefully that the raised
regions 3 on the stamping surface 2 of the stamp 1 form
corresponding indented regions 7 in the surface of the substrate 6,
but not so forcefully that the sunken regions 4 of the stamping
surface 2 come into contact with the surface of the substrate
6.
[0088] Advantageously, the substrate 6 is a polymeric substrate. In
a preferred embodiment of the invention, the substrate 6 is formed
from a thermoplastic material, and the stamp 1 is heated to around
or above the glass transition temperature of the substrate material
before or during application of the stamp 1 to the substrate 6. The
material of the substrate 6 is selected to be sufficiently soft (or
to become sufficiently soft on heating) that formation of the
indented regions 7 by the raised regions 3 of the stamp 1 occurs
readily.
[0089] Alternatively, the substrate 6 is formed from a partially
cured thermoset polymer, and the substrate 6 is cured during or
after the stamping process.
[0090] During the application of the stamp 1 to the substrate 6,
the substrate 6 forms either direct or indirect bonds with the
catalytic particles 5 on the stamping surface 2 of the stamp 1.
These bonds are stronger than those between the catalytic particles
5 and the stamping surface 2 of the stamp 1. Hence, when the stamp
1 is removed from the substrate 6, many of the catalytic particles
5 remain in the indented regions 7 of the surface of the substrate
6, as shown in FIG. 4.
[0091] In a preferred embodiment of the present invention, the
surface of the substrate 6 is modified to facilitate the deposition
of the catalytic particles 5 thereon. Such modification may be
chemical (for instance, silanising of the substrate surface), and a
skilled person will appreciate that there are several ways in which
the substrate surface may be advantageously modified.
[0092] The substrate 6 is now ready for plating. The plating may be
electroless plating, or may be performed by any other suitable
method, for example immersion plating. The catalytic particles 5
perform as activators for the plating. Consequently, when the
substrate 6 is plated, plating occurs only where the catalytic
particles 5 are present on the surface of the substrate 6. It will
be clear that, since the catalytic particles 5 are present only in
the indented regions 7 of the surface of the substrate 6,
metalisation of the surface of the substrate 6 during the plating
process will only occur in the indented regions 7 thereof.
[0093] This means that, as metalisation of the surface of the
substrate 6 progresses, the deposited metal will be contained
within the walls formed by the non-indented regions of the surface
of the substrate 6, and no lateral progress of the deposited metal
across the surface of the substrate 6 will be possible. FIG. 5
shows the substrate 6 after metalisation thereof, and it can be
seen that the deposited metal 8 is restricted to the indented
regions 7 of the surface of the substrate 6.
[0094] It will be appreciated that the above method allows the
formation of metallic features on the surface of a substrate very
close to one another, with very little possibility of the metallic
features interfering with one another, due to the presence of the
walls of substance material therebetween.
[0095] In addition, the metallic features can be of relatively
great depth, and the width of the features is independent of this
depth, allowing greater control over the exact dimensions of the
metallic features.
[0096] In another embodiment of the present invention, the
catalytic particles 5 may be selectively removed from the surface
of a stamp prior to the application of the stamp to the substrate.
An example of this is shown in FIGS. 6 to 9.
[0097] FIG. 6 shows a further stamp 9, which has a stamping surface
10 which is patterned to have raised regions 11 with sunken regions
12 therebetween. The stamping surface 10 of the further stamp 9 is
coated with catalytic particles 5, as described above.
[0098] Prior to the application of the further stamp 9 to a
substrate, a layer of adhesive tape 13 is placed over the stamping
surface 10 of the further stamp 9, as shown in FIG. 7. The
catalytic particles 5 deposited on the raised regions 11 of the
stamping surface 10 of the further stamp 9 will come into contact
with the adhesive tape 13. However, the catalytic particles in the
sunken regions 12 of the stamping surface 10 of the further stamp 9
do not come into contact with the adhesive tape 13.
[0099] The adhesive tape 13 is subsequently removed from the
stamping surface 10 of the further stamp 9, and the catalytic
particles 5 with which the adhesive tape 13 was in contact are also
removed. Hence, as shown in FIG. 8, the raised regions 11 of the
further stamp 9 have no catalytic particles 5 thereon, but the
sunken regions 12 of the further stamp 9 have catalytic particles 5
adhered thereto.
[0100] The further stamp 9 is then applied to a further substrate
14. However, in contrast to the above-described application of the
stamp 1 to the substrate 6, the further stamp 9 is pressed against
the further substrate 14 with sufficient force for the entirety of
the stamping surface 10 of the further stamp 9, including the
sunken regions 12 thereof, to come into contact with the surface of
the further substrate 14. Once the further stamp 9 is removed from
the further substrate 14, catalytic particles 5 are only bonded to
the further substrate 14 in regions thereof corresponding to the
sunken regions 12 of the further stamp 9, as shown in FIG. 9.
[0101] It will be appreciated that the selective removal of
catalytic particles 5 from the surface of a stamp prior to
application thereof to a substrate allows corresponding selective
metalisation of the substrate during subsequent electroplating.
[0102] The above example also illustrates how the method of the
present invention may be employed to create metallic features that
protrude above the surface of a substrate. After application of the
further stamp 9 to the further substrate 14, the surface of the
further substrate 14 will comprise peaks (corresponding to the
sunken regions 12 of the further stamp 9) and troughs
(corresponding to the raised regions 11 of the further stamp 9).
The peaks will be metallised. Hence, metallic features that
protrude above the surface of the further substrate 14 may be
created. The finely-controlled formation of such features as
provided by embodiments of the present invention is useful in, for
example, the provision of bumps on a PCB for connection to a
chip.
[0103] In an alternative embodiment of the present invention, the
stamp 1 or the further stamp 9 is provided as part of a mould, to
be used in an injection or compression moulding process. Liquid
substrate material is placed in the mould, and upon hardening of
the substrate material a substrate having a surface with indented
regions 7 corresponding to the raised regions 3, 11 on the stamping
surface 2, 10 of the stamp 1 or the further stamp 9 is formed.
[0104] It will be appreciated that this method of forming a
substrate may be employed with a wide variety of substrate
materials. For instance, if the substrate material is a thermoset
polymer, the substrate material is preferably moulded in an uncured
or partially cured state and cured whilst in the mould. In
contrast, if the substrate material is a thermoplastic polymer, the
substrate material is preferably heated to above the glass
transition temperature thereof and cooled in the mould as known in
the art.
[0105] In another aspect, the present invention involves the use of
polymer-stabilised catalytic particles. Known methods employ
catalytic particles that are stabilised by surfactants, for example
tetraoctadecylammonium bromide in toluene.
[0106] The use of polymer-stabilised catalytic particles, however,
allows stamping to be done without any surface treatment of the
substrate being necessary. This is important as it allows the
substrate to be significantly deformed during stamping or moulding.
Consequently, non-planar surfaces and conformal circuitry can be
formed during the stamping process. In addition, the present method
and apparatus allow the particles to weakly adhere to a stamp
within seconds, thus expediting the preparation of the stamp and
reducing manufacturing time. Examples of suitable polymers that may
be used to stabilise catalytic particles include
polyvinylpyrrolidone, poly-2-vinylpyridine and polyvinyl alcohol.
However, the present invention is not limited to these specific
polymers.
[0107] This aspect of the present invention is not limited to use
with a stamp having raised regions on a stamping surface thereof,
and may be used with planar stamps. FIG. 10 shows a planar third
stamp 15 with a layer of polymer-stabilised catalytic particles 16
deposited on a stamping surface 17 thereof.
[0108] An adhesive surface 18, having raised regions 19 thereon, is
pressed against the stamping surface 17 of the third stamp 15 to
selectively remove some of the polymer-stabilised catalytic
particles 16 therefrom. In this embodiment of the invention, as
will be seen below, the raised regions 19 of the adhesive surface
18 correspond to the gaps between metallic features that it is
desired to form on a substrate. The adhesive surface 18 is removed
from the stamping surface 16 of the third stamp 15, leaving
polymer-stabilised catalytic particles 16 only on those regions of
the stamping surface 17 of the third stamp that did not come into
contact with the adhesive surface 18, i.e. those corresponding to
the gaps between the raised regions 19 of the adhesive surface 18
as shown in FIG. 11.
[0109] The third stamp 15 is then applied to a planar third
substrate 20, as shown in FIG. 12. In contrast to the above
described embodiments, the pressing of third stamp 15 against the
third substrate 20 does not create any significant indentations
therein, as the stamping surface 17 of the third stamp 15 is
substantially planar. As described above, the polymer-stabilised
catalytic particles 16 will be transferred from the third stamp 15
to the third substrate 20.
[0110] Following removal of the third stamp 15 from the third
substrate 20, the third substrate 20 is electroless plated with a
metal 21 resulting in metalisation of the third substrate 20 only
in the regions thereof on which polymer-stabilised catalytic
particles 16 have been deposited. (as shown in FIG. 13).
[0111] The above invention is not limited to use in the PCB,
flexible circuit and packaging industries, and it is envisaged that
the present invention could also be used to pattern magnetic
features (such as nickel/cobalt alloys) onto disks to form
patterned media disk drives. Alternatively, fine metal lines
produced using the present invention could be used for optical or
other gratings.
[0112] In the present specification "comprises" means "includes or
consists of" and "comprising" means "including or consisting
of".
[0113] The features disclosed in the foregoing description, or the
following claims, or the accompanying drawings, expressed in their
specific forms or in terms of a means for performing the disclosed
function, or a method or process for attaining the disclosed
result, as appropriate, may, separately, or in any combination of
such features, be utilised for realising the invention in diverse
forms thereof.
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