U.S. patent application number 12/446096 was filed with the patent office on 2010-12-23 for paste patterns formation method and transfer film used therein.
This patent application is currently assigned to E. I. DU PONT DE MENOURS AND COMPANY. Invention is credited to Hideki Akimoto.
Application Number | 20100323123 12/446096 |
Document ID | / |
Family ID | 39333079 |
Filed Date | 2010-12-23 |
United States Patent
Application |
20100323123 |
Kind Code |
A1 |
Akimoto; Hideki |
December 23, 2010 |
PASTE PATTERNS FORMATION METHOD AND TRANSFER FILM USED THEREIN
Abstract
Disclosed is a paste pattern formation method comprising the
steps of: forming a transfer pattern material on a film base
material to prepare a transfer film; sticking the transfer film on
a substrate on which a transfer pattern is formed so that the
transfer pattern material contacts the substrate; separating the
film base material from the transfer pattern material; filling a
paste into the transfer pattern depression; solidifying the paste;
and removing the transfer pattern material.
Inventors: |
Akimoto; Hideki;
(Tochigi-Ken, JP) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY;LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1122B, 4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Assignee: |
E. I. DU PONT DE MENOURS AND
COMPANY
Wilmington
DE
|
Family ID: |
39333079 |
Appl. No.: |
12/446096 |
Filed: |
November 19, 2007 |
PCT Filed: |
November 19, 2007 |
PCT NO: |
PCT/US2007/024191 |
371 Date: |
April 17, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11602080 |
Nov 20, 2006 |
7744714 |
|
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12446096 |
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Current U.S.
Class: |
427/561 ;
257/E31.001; 427/256; 427/58; 427/98.4; 428/156 |
Current CPC
Class: |
C09K 2323/05 20200801;
H01L 31/022425 20130101; C09K 2323/02 20200801; Y10T 428/24479
20150115; H05K 3/1258 20130101; H01J 9/02 20130101; H05K 2203/0537
20130101; H05K 2203/0568 20130101; Y10T 428/24802 20150115; H01J
2211/36 20130101; Y02E 10/50 20130101; C09K 2323/00 20200801; H01J
9/24 20130101; C09K 2323/055 20200801 |
Class at
Publication: |
427/561 ;
427/256; 427/58; 427/98.4; 428/156; 257/E31.001 |
International
Class: |
H01L 31/18 20060101
H01L031/18; B05D 5/00 20060101 B05D005/00; H05K 3/00 20060101
H05K003/00; B32B 3/00 20060101 B32B003/00 |
Claims
1. A paste pattern formation method comprising the steps of:
applying a transfer pattern on a film base material, wherein said
transfer pattern comprises a transfer pattern material and transfer
pattern depressions, thus forming a transfer film; transferring the
transfer film onto a substrate so that the transfer pattern
material contacts the substrate; separating the film base material
from the transfer pattern material; applying a paste into the
transfer pattern depressions, resulting in a paste pattern;
solidifying the paste; and removing the transfer pattern
material.
2. A paste pattern formation method comprising the steps of:
applying a transfer pattern material on a film base material;
forming a transfer pattern depression(s) in the transfer pattern
material, thus forming a transfer film; transferring the transfer
film onto a substrate so that the transfer pattern material
contacts the substrate; separating the film base material from the
transfer pattern material; applying a paste into the transfer
pattern depression(s), resulting in a paste pattern; solidifying
the paste; and removing the transfer pattern material.
3. The paste pattern formation method according to claim 2, wherein
the transfer pattern depression(s) are patterned with a laser.
4. The paste pattern formation method according to claim 2, wherein
the transfer pattern depression(s) are patterned by
photoetching.
5. The paste pattern formation method according to claim 2, wherein
the transfer pattern depression(s) are patterned by press
stamping.
6. The paste pattern formation method according to claim 1 or 2,
wherein the transfer film is adhered by pressure onto the substrate
onto . which the paste pattern is formed.
7. The paste pattern formation method according to claim 1 or 2,
wherein the transfer film is adhered with an adhesive onto the
substrate onto which a paste pattern is formed.
8. The paste pattern formation method according to claim 1 or 2,
further comprising a step of, after applying the paste into the
transfer pattern depression(s), removing the paste remaining on the
transfer pattern material.
9. The paste pattern formation method according to claim 1 or 2,
wherein the step of applying the paste into the transfer pattern
depression(s) and the step of solidifying the paste are repeated
two times or more until a predetermined paste pattern height is
obtained.
10. The paste pattern formation method according to claim 1 or 2,
wherein the transfer pattern material is removed by dissolving with
water.
11. The paste pattern formation method according to claim 10,
wherein the transfer pattern material comprises a water-soluble
resin.
12. The paste pattern formation method according to claim 1 or 2,
wherein the transfer pattern material is removed by dissolving with
an organic solvent.
13. The paste pattern formation method according to claim 1 or 2,
wherein the transfer pattern material is removed by baking.
14. The paste pattern formation method according to claim 1 or 2,
wherein the paste pattern is an electrode pattern of a solar
cell.
15. The paste pattern formation method according to claim 1 or 2,
wherein the paste pattern is a wiring pattern of a wiring
board.
16. The paste pattern formation method according to claim 1 or 2,
wherein the paste pattern is a barrier rib of a plasma display
panel.
17. A transfer film used in the paste pattern formation method
according to claim 1, in which a transfer pattern depression is
formed on a film base material.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a paste pattern formation
method. More particularly, the present invention relates to a paste
pattern formation method for forming a paste pattern having a, high
aspect ratio. The present invention also relates to a transfer film
used in this paste pattern formation method.
[0003] 2. Description of the Related Art
[0004] Various types of patterns are formed in electrical devices.
For example, predetermined electrode patterns are formed on the top
and bottom surfaces in solar cells. In addition, predetermined
wiring patterns are formed on a substrate in wiring boards.
Moreover, patterns of barrier ribs for separating each dot, address
wires, electrodes and so on are formed in plasma display panels
(PDP).
[0005] The ability to easily produce patterns having a high aspect
ratio is an important issue common to these applications.
[0006] With respect to the electrode patterns of solar cells, it is
preferable to reduce the surface area occupied by the electrode
pattern on the light-receiving surface in order to increase the
light receiving surface area of the solar cell. However, reduction
in the cross-sectional area of the electrode pattern causes a
decrease in electrical conductivity of the electrode pattern.
Consequently, it is desirable to enhance the electrical
conductivity of the electrode pattern by forming an electrode
pattern that has adequate thickness in the perpendicular direction.
In other words, an electrode pattern having a high aspect ratio is
preferred.
[0007] In a wiring board, the use of a fine wiring pattern is
desirable to achieve high density, and in this case as well, a
wiring pattern having a high aspect ratio is desirable.
[0008] In PDP, if the barrier ribs are too wide, the dot pitch
becomes large and it is not possible to achieve high resolution.
Consequently, it is desirable to narrow the barrier ribs and in
this case as well, barrier ribs having a high aspect ratio are
desirable.
[0009] An example of a method for forming a desired pattern having
a high aspect ratio in these applications consists of repeatedly
carrying out screen printing. In the case of screen printing,
however, since there are limits on the amount of paste that can be
coated in a single coating, in order to form a pattern of adequate
thickness; it is necessary to repeatedly print the paste many
times. In addition, in the case a printing several times, it is
difficult to position the coating paste with high precision each
time.
[0010] Therefore, a technique is known in which patterning is
carried out using a photosensitive paste as a means of forming a
thick film pattern without using screen printing (see, for example,
Japanese Patent Application Laid-open No. 2003-107698). However,
processes using photosensitive paste require an expensive
investment with respect to the mask, developing apparatus and so
on, and production costs tend to be high. In addition, since the
electrically conductive or insulating fine powder contained in the
paste is optically opaque, random reflection occurs within the
paste composition during exposure when the coating thickness is
increased, thereby preventing light from adequately reaching deep
portions of the paste. Consequently, it is difficult to obtain a
pattern of high aspect ratio simply by using a photosensitive paste
and developing directly. Moreover, since photosensitive paste has
poor storage stability, control and transport of materials is
bothersome.
[0011] In consideration of these circumstances, a technique is used
in which a thick film pattern is formed which does not require a
photosensitive paste (see, for example, Japanese Patent Application
Laid-open No. 2002-290017). This document discloses a technology in
which, after forming a pattern by injecting a metallized paste into
a groove pattern, and transferring the metallized paste to a
ceramic substrate. In the case of forming a pattern and then
transferring it to a substrate in this manner, an adhesion means is
required to suitably transfer the pattern to the substrate.
Examples of such adhesion means include an adhesive layer or
blending-in a pressure-sensitive adhesive component into the
pattern. However, in the case of using an adhesive layer, not only
is there the added step of forming the adhesive layer, there is
also the risk of the adhesive layer components diffusing into the
pattern, as well as a decrease in electrical conductivity or other
predetermined pattern properties. In addition, in the case of
blending a pressure-sensitive adhesive component into the pattern,
it is difficult to select a preferable pressure-sensitive adhesive
component so that the required properties of the pattern do not
decrease due to the addition of the pressure-sensitive adhesive
component. Moreover, as is described in this document, in the case
of transferring to a substrate following pattern formation, there
is the risk of the pattern itself being deformed or the desired
aspect ratio being unable to be obtained due to pressure applied to
the pattern during transfer.
SUMMARY OF THE INVENTION
[0012] An object of the present invention is to provide an
inexpensive method for forming a paste pattern having a high aspect
ratio that enables production to be carried out easily, and does
not cause a decrease in paste pattern properties.
[0013] The present invention relates to paste pattern formation
method comprising the steps of: applying a transfer pattern on a
film base material, wherein said transfer pattern comprises a
transfer pattern material and transfer pattern depressions, thus
forming a transfer film; transferring the transfer film onto a
substrate so that the transfer pattern material contacts the
substrate; separating the film base material from the transfer
pattern material; applying a paste into the transfer pattern
depressions, resulting in a paste pattern; solidifying the paste;
and removing the transfer pattern material.
[0014] The invention further concerns a paste pattern formation
method comprising the steps of: applying a transfer pattern
material on a film base material; forming a transfer pattern
depression(s) in the transfer pattern material, thus forming a
transfer film; transferring the transfer film onto a substrate so
that the transfer pattern material contacts the substrate;
separating the film base material from the transfer pattern
material; applying a paste into the transfer pattern depression(s),
resulting in a paste pattern; solidifying the paste; and removing
the transfer pattern material.
[0015] Patterning the transfer pattern may be done by laser,
photoetching, press stamping or other known methods.
[0016] In addition, the present invention includes a transfer film
used in this paste pattern formation method in which a transfer
pattern depression is formed on a film base material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a flow chart of the entire paste pattern formation
method of the present invention;
[0018] FIGS. 2A-2E are lateral cross-sectional views using
constituent elements of each step shown in FIG. 1;
[0019] FIGS. 3A-3H are lateral cross-sectional views of steps in
which a transfer pattern is formed on a film base material to
prepare a transfer film;
[0020] FIGS. 4A and 4B are lateral cross-sectional views of steps
in which a transfer film is stuck on a substrate on which a paste
pattern is formed, so that the transfer pattern material contacts
the substrate on which the paste pattern is formed;
[0021] FIGS. 5A and 5B are lateral cross-sectional views of a step
in which a film base material is separated from a transfer pattern
material;
[0022] FIGS. 6A-6D are lateral cross-sectional views of steps in
which a paste is applied into a transfer pattern depression, and a
step in which a paste is solidified; and
[0023] FIGS. 7A-7D is a lateral cross-sectional view of a step in
which a transfer pattern material is removed.
DETAILED DESCRIPTION
[0024] The paste pattern formation method of the present invention
forms a paste pattern by preliminarily transferring only a transfer
pattern material to a substrate and then filling a paste into the
pattern depression. Consequently, a paste pattern having a desired
aspect ratio can be obtained by suitably altering the height of the
transfer pattern material and thus, the pattern depression. In the
case of forming a paste pattern having a high aspect ratio in
particular, a paste pattern having a high aspect ratio can be
realized easily by overlapping several indentations.
[0025] In addition, since the paste pattern formation method of the
present invention does not necessarily require large-scale
production apparatus, (such as an exposure apparatus) during paste
pattern formation, and does not require control and transport costs
for photosensitive materials as in the case of using a
photosensitive paste for the pattern material, paste patterns can
be formed inexpensively.
[0026] Moreover, the paste pattern formation method of the present
invention does not involve the transfer of a dry paste to a
substrate after having preliminary formed a pattern by injecting a
paste into a groove pattern, but rather realizes paste pattern
formation by transferring only a transfer pattern material to a
substrate followed by applying a paste directly into the transfer
pattern depression and solidifying said paste. Consequently, paste
pattern formation can be carried out easily without interposing an
adhesive layer between the substrate and paste nor blending
adhesive components into the paste. However, this method does not
prevent the use of an adhesive layer or adhesive components. In the
case that components of a layer other than the paste pattern layer,
such as an adhesive layer, are not used, there is no diffusion of
components from other layers into the paste pattern layer.
[0027] In addition, there is no pressure during the application of
the paste other than the pressure required due to the application
method, for example, squeegee pressure. Consequently, there is
minimal risk of deformation of the paste pattern itself during
production. Thus, the desired paste pattern properties can be
reliably obtained.
[0028] As used herein, "paste pattern" refers to the pattern of the
paste on the substrate. Both paste pattern before solidifying and
after solidifying are included in the definition. As used herein,
"transfer pattern" refers to the pattern on the film base material,
which is transferred to the substrate. The transfer pattern
comprises a "transfer pattern material", which refers to the
material itself, and "transfer pattern depressions", which refers
to the space in the pattern in which there is not material.
[0029] In the present invention, a pattern (or paste pattern)
having a high aspect ratio refers to a pattern (or paste pattern)
in which the ratio of the pattern surface area to the surface in
which the pattern is formed, and particularly the width thereof, is
comparatively small, and which has a comparatively large thickness
in the direction perpendicular to the above-mentioned surface in
which the pattern is formed.
[0030] FIG. 1 is a flow chart of the entire paste pattern formation
method of the present invention, while FIG. 2 is a lateral
cross-sectional view using constituent elements of each step shown
in FIG. 1.
[0031] As shown in FIGS. 1 and 2, the paste pattern formation
method of the present invention comprises first to sixth steps
(S202 to S212). In the first step (S202 in FIGS. 1 and 2A), a
transfer pattern, comprising a transfer pattern material 304 and a
transfer pattern depression 305 is formed on a film base material
302 to prepare a transfer film 306. In the second step (S204 in
FIGS. 1 and 2B), transfer film 306 is transferred to a substrate
308 so that the pattern material 304 contacts substrate 308. In the
third step (S206 in FIGS. 1 and 2C), film base material 302 is
separated from transfer pattern material 304. In the fourth step
(S208 in FIGS. 1 and 2D), a paste 310 is applied into the transfer
pattern. depression 305. In the fifth step (S210 in FIGS. 1 and
2D), paste 310 is solidified. In the sixth step (S212 in FIGS. 1
and 2E), the transfer pattern material (not shown) is removed from
substrate 308 to obtain a desired pattern 312.
[0032] The paste pattern formation method of the present invention
is suitable for forming a paste pattern having a high aspect ratio.
For example, the paste pattern formation method of the present
invention is suitable for forming a paste pattern having a high
aspect ratio, as defined by "pattern thickness/pattern width" on a
surface on which a paste pattern is formed, of 1/5 or more. There
are no particular limitations on the upper limit of the aspect
ratio, but 10/1 is a preferred upper limit in terms of
productivity. In one embodiment, the aspect ratio may range from
1/5 to 10/1.
[0033] The following provides a detailed explanation of each of the
above-mentioned first though sixth steps.
[0034] (First Step)
[0035] FIG. 3 is a detailed lateral cross-sectional view of the
first step in FIG. 2. In this step, a film base material 402 is
first prepared (FIG. 3A. A smooth film-like material which has
separability with respect to the transfer pattern material, and
which is stable at a drying temperature, can be used for film base
material 402. Examples of film base materials may comprise metal,
paper and polymer materials. Typical examples of polymer materials
which can be used include polyethylene, polypropylene, polystyrene,
polyvinyl chloride, polyvinylidene chloride, polyamide,
polyethylene terephthalate, polybutylene terephthalate, polyacetal,
polycarbonate, polyphenylene oxide, polyethylene naphthate,
polyphenylene sulfide, polysulfone, polyether sulfone, polyether
imide, polyether ether ketone, polyamide imide, crystalline
polymer, polyimide resin and fluororesin. The film base material
surface can be subjected to releasing treatment in the form of
silicon treatment and so on, as necessary. Next, a transfer pattern
material 404 is formed on film base material 402 (FIG. 38). The
type of transfer pattern material 404 differs according to the
processing mode of transfer pattern material 404 to be described
later. Transfer pattern material 404 can be formed by, for example,
coating a paste-like resin or resin solution and drying. Examples
of preferable methods for applying the transfer pattern material at
a uniform thickness include coating with a blade coater, reverse
coater, bar coater, gravure coater, knife coater, spray coater, die
coater or comma coater followed by drying to obtain a predetermined
thickness.
[0036] After having formed transfer pattern material 404 on film
base material 402 in this manner, transfer pattern material 404 is
processed to a predetermined shape to form a transfer pattern
depression 405. There are no particular limitations on the method
for forming the transfer pattern depression, and examples of
methods that can be used include those that use a laser (FIGS. 3C
to 3E) and those that use press stamping (FIGS. 3F to 3H).
[0037] In the case of adopting a method that uses a laser, transfer
pattern material 404 is removed at the site irradiated with the
laser 406. In the case the polymer itself used in transfer pattern
material 404 lacks the ability to absorb the laser, transfer
pattern material 404 can be processed with a laser by preliminarily
dispersing a laser-absorbing pigment or dye in the paste. Carbon
powder or graphite powder is preferable, since these powders
exhibit superior laser absorption. Therefore, one embodiment of the
transfer pattern material comprises material selected from carbon
powder, graphite powder, and combinations thereof. There are no
particular limitations on the materials that constitute the
transfer pattern material provided it can be formed into the form
of a film and can stick to a substrate 502 to be described later
and ultimately be removed. Examples of these materials include
polyethylene, polypropylene, polybutadiene, polyvinyl chloride,
polystyrene, polyvinyl alcohol, polyvinyl acetate, ethylene-vinyl
alcohol copolymer, polyvinyl pyrrolidone, ethyl cellulose, ABS
plastic, acrylic resin, epoxy resin, urethane resin and photoresist
resins. The material to be used may be suitably selected
corresponding to the patterning method. For example, in the case of
patterning using a laser, a resin that is easily decomposed by heat
is used, examples of which include polyvinyl alcohol, ethyl
cellulose and polybutadiene. In addition, if attempting to remove
by dissolving with water, a water-soluble resin is preferable,
examples of which include polyvinyl alcohol, polyvinyl pyrrolidone
and carboxymethyl cellulose.
[0038] After having suitably selected the material of transfer
pattern material 404 in this manner, transfer pattern material 404
is formed on film base material 402, and a predetermined transfer
pattern 408 (made of transfer pattern material 404 and transfer
pattern depression 405) is formed at a predetermined location of
transfer pattern material 404 by sequentially irradiating with a
laser 406 to obtain a transfer film 410 (FIGS. 3C to 3E). A laser
that is absorbed by transfer pattern material 404 and penetrates
film base material 402 is used for laser 406 used at this time. YAG
lasers are preferable since they penetrate Teflon films and
polyester films. Furthermore, the use of a laser normally results
in the risk of the laser reaching film base material 402 causing
damage thereto. In the present invention, however, since film base
material 402 is separated in a subsequent step and is not directly
involved in paste pattern formation, damage to film base material
402 does not present a problem even if it is damaged.
[0039] In the case of laser patterning, digital patterning
eliminates the need for expensive molds such as a die or exposure
mask in comparison with other patterning methods (such as press
stamping or photoetching to be described later), while also
enabling the pattern to be changed by simply modifying CAD data.
Since laser patterning involves the drawing of lines, although this
method tends to take considerable time if the pattern surface area
is large, patterning time does not present that much of a problem
in applications having small pattern surface areas. For example,
since the electrode pattern of a solar cell has an extremely small
surface area to secure a light receiving surface area with respect
to the substrate surface area, the time required for patterning is
short even if laser patterning is applied.
[0040] In contrast, in the case of adopting a technique using press
stamping, a thermoplastic film or thermosetting or photosetting
liquid resin is used for the composition of transfer pattern
material 404, a die 412 heated to a high temperature is pressed on
a predetermined location of the transfer pattern material 404
formed on the film base material 402, the die 412 is then removed
and a desired pattern formation depression 414 is formed to obtain
a transfer film 416 (FIGS. 3F to 3H). Glass, metal of silicon is
used for die 412, and in the case of a thermoplastic film, the film
is molded at a temperature equal to or higher than the softening
point, while in the case of a thermosetting resin, the resin is
cured with light or heat. A technique such as hot embossing can be
used as an example of press stamping in the case transfer pattern
material 404 is a thermoplastic resin.
[0041] Furthermore, patterning by press stamping offers the
advantage of being able to produce a transfer pattern in less time
than other patterning methods (such as laser processing and
photoetching).
[0042] Moreover, although not shown in FIG. 3, patterning can also
be carried out by photoetching on the condition of using a dry film
resist for transfer pattern material 404 after having formed
transfer pattern material 404 on film base material 402.
Furthermore, although patterning by photoetching requires exposure
and developing apparatuses, in the case the wiring pattern is fine
and complex, it offers the advantage of being able to form the
transfer pattern in less time than other patterning methods (such
as laser processing and press stamping).
[0043] (Second Step)
[0044] FIG. 4 is a detailed lateral cross-sectional view of the
second step S204 in FIG. 2.
[0045] In this step, a transfer film 508 comprised of a film base
material 504 and a transfer pattern material 506 is stuck on a
substrate 502 (FIG. 4A). There are no particular limitations on the
sticking means, and attachment may be carried out with a laminator
or press. in the case of producing transfer pattern depression 506
with a thermoplastic resin, attachment of substrate 502 and
transfer pattern depression 506 is carried out at a temperature
equal to or higher than the softening point of the resin. In the
case of producing transfer pattern material 506 with a
thermosetting resin, the thermosetting resin is molded in the B
stage (semi-cured state) and then adhered at a temperature equal to
or higher than the softening point. Substrate 502 can also be
adhered to the transfer pattern (a film comprising the transfer
pattern material, transfer pattern depression(s), and film base
material) 508 after having heated substrate 502 to the vicinity of
the softening point of the transfer pattern material.
[0046] In addition, in the case the transfer pattern material has
tackiness, this adhering can be carried out simply by applying
pressure without heating. Moreover, this adhering can also be
carried out by applying a silicon-based or acrylic-based removable
pressure-sensitive adhesive to the adhered portion of transfer film
508.
[0047] Furthermore, substrate 502 and transfer film 508 are
preferably pressed following attachment (FIG. 4B) to enhance
adhesive strength therebetween. For example, substrate 502 and
transfer film 508 can be pressed with a laminator or press.
[0048] Substrate 502 is cooled to room temperature in the case of
having been stuck by applying heat.
[0049] (Third Step)
[0050] FIG. 5 is a detailed lateral cross-sectional view of the
third step S206 in FIG. 2. In this step, only a film base material
604 is separated from a transfer film 608, comprised of a film base
material 604 and a transfer pattern material 606, stuck to a
substrate 602 (FIG. 5A). Separation can be carried out easily by
using, for example, a dicing tape separation apparatus used in
semiconductor production. This type of procedure allows the
obtaining of a laminate 610 in which transfer pattern material 606
is formed on substrate 602 (FIG. 5B).
[0051] In this step, the adhesive strength between film base
material 604 and transfer pattern material 606 is required to be
less than the adhesive strength between transfer pattern material
606 and substrate 602. In the case the adhesive strength between
film base material 604 and transfer pattern material 606 is weak,
film base material 604 separates from transfer pattern material
606.
[0052] Adhesive strength can be controlled according to the
selection of the materials used and the adhesive. For example, the
adhesive strength between film base material 604 and transfer
pattern material 606 can be made to be extremely weak by using a
fluorine film such as a TEFLON.RTM. PFA film (commercially
available from E.I. du Pont de Nemours and Company) for film base
material 604. In addition, peel strength may also be controlled by
adhering transfer pattern material 606 and substrate 602 with a
powerful adhesive. Examples of adhesives useful in the present
invention include thermo elastic adhesive such as silicone, rubber,
elastomer and acrylic type adhesives.
[0053] (Fourth and Fifth Steps)
[0054] FIG. 6 is a detailed lateral cross-sectional view of the
fourth step S208 and the fifth step S210 in FIG. 2. First, in the
fourth step, a paste 706 is filled into a transfer pattern
depression stuck to substrate 702 (FIG. 6A). After filling the
paste, any residual paste remaining on transfer pattern material
704 (not shown) is either wiped off with a solvent or the substrate
surface is cleaned with a blasting apparatus or polisher. Residual
paste can cause the formation of undissolved portions during
removal of transfer pattern material 704 by dissolving to be
described later. In the case of removing using a peel-off method to
be described later, there is the risk of the paste being peeled off
or the substrate being contaminated. Paste may be removed each time
in the case of repeatedly filling and drying the paste.
[0055] The type of paste filled may be suitably selected
corresponding to the purpose of the formed pattern. For example, in
the case of forming an electrically conductive pattern, a paste
containing an electrically conductive powder may be filled.
Examples of electrically conductive powders which can be used
include, but are not limited to, gold, silver, copper, palladium,
platinum, nickel, tin and carbon powder and mixtures thereof. A
mixed type combining two or more types of materials may also be
used. Examples of mixed types include types in which the surface of
an electrically conductive powder is coated with a different metal
(e.g., silver-coated copper), alloy types in which two or more
types of electrically conductive powders are alloyed in combination
(e.g., silver-copper, silver-palladium and silver-tin powder), and
compound types (e.g., zinc oxide, tin oxide, ruthenium oxide and
lanthanum hexaboride).
[0056] Next, in the fifth step, dry paste pattern 708 (FIG. 6B) is
obtained by solidifying the paste. Methods used to solidify the
paste depend on the type of paste. For example, solidification by
drying, hardening by heat or hardening by light may be used. It is
preferable to determine the suitable solidification method based on
the paste properties.
[0057] However, in some embodiments, there are cases in which a dry
paste pattern of a desired height (and therefore, aspect ratio) is
unable to be obtained by evaporation of solvent components in the
paste with a single round of paste filling and drying. In such
cases, a dry paste pattern 712 of a desired height is obtained by
filling additional paste 710 onto dry paste pattern 708 (fourth
step) and then drying this additional paste (fifth step) (FIGS. 6C
and 6D).
[0058] Although paste filling and drying are carried two times each
in the above-mentioned explanation, there are no limitations on the
number of times these can be carried out, and may be carried out as
many times as is necessary to obtain a dry paste of the desired
height. Therefore, in some embodiments, multiple paste application
and drying steps are carried out.
[0059] In order to produce a paste pattern having a desired aspect
ratio in a single filling, transfer pattern material 704 may be
laminated several times in advance so as to be formed sufficiently
higher than a desired paste pattern height, and then paste 706 may
be filled while anticipating the evaporated amount of the solvent
component during drying thereof.
[0060] (Sixth Step)
[0061] FIG. 7 is a detailed lateral cross-sectional view of a sixth
step S212 in FIG. 2. In this step, the transfer pattern material
804 is removed (FIGS. 7B to 7D) from the substrate 802 and dry
paste pattern 806 applied and dried in transfer pattern depression
(FIG. 7A) to obtain a desired paste pattern 808 (FIG. 7E). Examples
of removal methods which can be used include, but are not limited
to, a method in which removal is carried out by dissolving (FIG.
7B), a method in which removal is carried out by separation
(peel-off) (FIG. 7C), and a method in which removal is carried out
by baking (FIG. 7D).
[0062] In the case of employing a dissolving method, transfer
pattern material 804 is removed by utilizing the difference in the
solubility of substrate 802 and dry paste pattern 806 and the
solubility of transfer pattern material 804 (FIG. 7B). A solvent
which dissolves the transfer pattern material 804 without also
dissolving substrate 802 and dry paste pattern 806 is suitable
selected for use as solvent 810. Dissolving can be carried out by
utilizing various materials including water, an alkaline aqueous
solution or an organic solvent.
[0063] In the case of dissolving with water, transfer pattern
material 804 is preferably formed from, for example, a
water-soluble resin such as polyvinyl alcohol PVA, while paste 806
is preferably formed from a non-water-soluble substance. Dissolving
with water is the most preferable from the viewpoint of safety and
environmental destruction caused by waste liquid.
[0064] In the case of employing a method of dissolving with an
alkaline aqueous solution, transfer pattern material 804 is
preferably formed with a resin that can be dissolved in an alkaline
aqueous solution, while paste 806 is preferably formed with a resin
which is insoluble in an alkaline aqueous solution. In the case of
employing a method of dissolving with an organic solvent, transfer
pattern material 804 is preferably formed from a material which is
soluble in the organic solvent used, while paste 806 is preferably
formed from a resin which is insoluble in the organic solvent
used.
[0065] In the case of employing a method using separation (peel-off
method), removal is carried out by, for example, using a dicing
tape separation apparatus used in semiconductor production (FIG.
7C). A method which uses separation enables production costs to be
further reduced as compared with the above case of dissolving with
water since special equipment is not required.
[0066] In the case of employing a method using baking, transfer
pattern material 804 is removed by utilizing the difference in the
content of impurities (or organic matter) in substrate 802 and dry
paste pattern 806 and the content of impurities (or organic matter)
of transfer pattern material 804 (FIG. 7D). Namely, since organic
matter volatilizes while inorganic matter remains as a result of
baking, by preliminarily making nearly all of substrate 802 and dry
paste pattern 806 to be composed of inorganic matter, and while
making nearly all of transfer pattern material 804 to be composed
of organic matter, the transfer pattern material 804 is eliminated
by baking, for example, in a convection oven. Baking conditions may
be suitably selected corresponding to the material used to form the
transfer pattern material. It is necessary to raise the baking
temperature in the case of using a resin resistant to thermal
decomposition. On the other hand, the transfer pattern material can
be removed at a comparatively low baking temperature in the case of
using a resin susceptible to thermal decomposition. Furthermore,
the desired paste pattern 808 in FIG. 7E may also be obtained
without using a baking oven by, for example, bringing a burner in
close proximity from the direction indicated with the thick arrows
shown in FIG. 7D and baking off transfer pattern material 804.
[0067] Although the above explanation has described a dissolving
method, peel-off method and baking method as examples of methods
for removing the transfer pattern material from a substrate, these
methods can be suitably selected according to various purposes.
[0068] Although the peel-off method requires several peeling
operations equal to the number of each portion of the transfer
pattern material if a plurality of transfer pattern material
transferred to the substrate are present separately, the dissolving
method realizes removal of the transfer pattern material by only
immersing in solution once regardless of the shape of the transfer
pattern material In other words, when it is desirable to remove the
transfer pattern material in a single operation (or step), the
dissolving method is advantageous. In addition, since there is no
generation of debris and so forth during separation of the
depression as when using the peel-off method, the dissolving method
allows the obtaining of a highly accurate paste pattern shape.
[0069] In addition, although the dissolving method requires an
apparatus and solution for immersing in solution, the peel-off
method does not require any such apparatuses and so on to be
provided, and simply requires that the transfer pattern material be
able to be peeled off mechanically, thereby making this method
advantageous. Moreover, in the peel-off method, the pattern paste
material is only required to be provided adhesiveness with the
substrate and non-adhesiveness with the transfer pattern material,
and since it is not required to be provided with solvent resistance
as in the case of pattern paste materials used in the dissolving
method, a wide range of materials can be selected.
[0070] Moreover, since the baking method requires a high
temperature for baking, it has the disadvantage of only being able
to be used with heat-resistant, organic substrates as compared with
the dissolving method and peel-off method. However, since this
method does not require that considerations be given to differences
in solubility or tackiness with the substrate with respect to the
characteristics of the transfer pattern material, there are more
choices available for the transfer pattern material, thereby
offering the advantage of facilitating removal thereof.
[0071] As has been explained above, the paste pattern formation
method of the present invention, which comprises the
above-mentioned first to sixth steps, offers the advantages of
reduced production costs, easy production and the formation of
patterns having a high aspect ratio without less desirable paste
pattern properties. In addition, paste patterns obtained by this
type of formation method are suitable for use as the electrode
patterns of solar cells, the wiring patterns of wiring boards, or
the barrier ribs of plasma display panels.
EXAMPLES
Example 1
Production of Black Paste for Transfer Film
[0072] 35 parts of polyvinyl alcohol resin PVA #500 (Kanto
Chemical) were added to 65 parts of ion exchange water heated to
90.degree. C. in a stainless steel container, and then dissolved by
stirring for 2 hours. Next, after cooling the solution to room
temperature, 15 parts of glycerin (Kanto Chemical) were added and
stirred for 5 minutes. Next, 20 parts of a commercially available
Indian ink (Kuretake, BA7-18) were added followed by stirring for 5
minutes to obtain a black paste-like PVA solution. Finally, this
PVA solution was transferred to a plastic container and allowed to
stand overnight to obtain a black paste for a transfer film.
[0073] (Production of Transfer Film)
[0074] Using a TEFLON (registered trademark) 500 PFA film
(available from E.I. du Pont de Nemours and Co.) for the film base
material (film thickness: 125 .mu.m), the black paste was coated
thereon using a doctor blade method. Next, the coated paste was
dried for 10 minutes in an oven at 85.degree. C. Moreover, the PFA
film coated with the black paste was removed from the oven and
allowed to stand to cool to room temperature to obtain a glossy
black film. Subsequently, when the thickness of the black film was
measured with a micrometer, the film thickness was found to be 70
.mu.m. This black film was then patterned to the shape of a pattern
produced by CAD using a YAG laser marker (COMMAX, YAG-5W,
wavelength: 1064 nm). The shape of the pattern of the resulting
transfer pattern depression was 70 .mu.m wide and 70 .mu.m
deep.
[0075] (Transfer of Transform Film Having Transfer Pattern Formed
Thereon to a Substrate)
[0076] A glass substrate was preheated for 1 minute on a hot plate
at 100.degree. C. Next, a transfer film on which a transfer pattern
was formed was arranged on the preheated glass substrate so that
the transfer pattern side contacted the glass substrate, and after
allowing to stand for 10 seconds, the transfer film was pressed
onto the glass substrate. Moreover, the glass substrate with
transfer film was removed from the hot plate and allowed to stand
until it returned to room temperature. When the film base material
in the form of PFA film was slowly peeled from the glass substrate
with transfer film stuck in this manner, the transfer pattern
material was stuck on the glass substrate. The shape of the
resulting transfer pattern depression was 70 .mu.m wide and 70
.mu.m deep.
[0077] (Filling of Paste)
[0078] A silver paste (available from du Pont de Nemours and Co. as
Product No. CB700) was applied to the transfer pattern depression
by squeegee. Next, the glass substrate having the transfer pattern
depression filled with silver paste was placed on a hot plate at
80.degree. C. for 5 minutes to pre-dry the coated silver paste. The
glass substrate was removed from the hot plate and allowed to stand
until it returned to room temperature. After drying, since a slight
indentation was observed where the silver paste was embedded in the
transfer pattern depression, silver paste was applied again by
squeegeeing to fill in the indentation. Subsequently, the glass
substrate in which the transfer pattern depression had been
re-filled with silver paste was placed on a hot plate at 80.degree.
C. for 10 minutes to pre-dry the coated silver paste. The substrate
was removed from the hot plate and allowed to stand until it
returned to room temperature. There was minimal indentation
observed where the silver paste was embedded in the depression
after drying. Finally, paste remaining on the transfer pattern
material was wiped off using a solvent (available from du Pont de
Nemours and Co., Axerel.RTM. 2000).
[0079] (Separation of Transfer Film: Peel-Off Method)
[0080] After drying the substrate having a transfer pattern
depression filled with paste by heating for 15 minutes on a hot
plate at 130.degree. C., the substrate was allowed to stand until
it returned to room temperature. Next, the transfer pattern
material was slowly peeled off by hand. As a result, only the paste
pattern of the embedded silver paste remained on the substrate. The
shape of the resulting paste pattern was 70 .mu.m wide and 60 .mu.m
deep.
[0081] As described above, a paste pattern having a high aspect
ratio (6/7) was able to be formed easily using the peel-off
method.
Example 2
Separation of Transfer Film: Hot Water Dissolving Method
[0082] A substrate having a transfer pattern depression filled with
paste produced using the same method as Example 1 was heated for 10
minutes on a hot plate at 130.degree. C. followed by removing from
the hot plate and allowing to stand until it returned to room
temperature. Next, the substrate with transfer pattern material was
immersed for 10 minutes in hot water at 80.degree. C. followed by
ultrasonic treatment for 30 seconds using an ultrasonic cleaner.
Subsequently, the substrate was removed from the hot water and
washed with running water at 40.degree. C. As a result, only the
paste pattern of the embedded silver paste remained on the
substrate. The shape of the resulting paste pattern was 70 .mu.m
wide and 60 .mu.m deep. As noted previously, the aspect ratio has
no upper limit, however in this example the aspect ratio was
6/7.
[0083] As has been described above, a paste pattern having a high
aspect ratio (6/7) was also able to be formed easily using a hot
water dissolving method.
* * * * *