Background
[0001] The.present invention relates generally to the art of electroplating, and more particularly
to the art of electroforming on a patterned mandrel.
[0002] Electroforming of precision patterns, such as those used in optical systems, has
been accomplished by several methods. For example, precision mesh patterns have been
produced by electroplating onto a master pattern of lines formed by etching or ruling
lines into a glass substrate and depositing a conductive material into the etched
or ruled lines to form a conductive master pattern for electroplating. A major disadvantage
of this method is the limitation on the fineness and precision of etching glass.
[0003] Photolithographic techniques have also been used to produce patterned electroforming
mandrels. For example, a conductive substrate, such as a polished metal plate, is
coated with a layer of photoresist. 'A patterned photomask is placed over the photoresist,
which is then exposed to actinic radiation through the mask, thereby creating a pattern
of exposed and unexposed photoresist which is further developed. Either the exposed
or the unexposed portions of the photoresist are removed, depending on whether a positive
or negative pattern is desired, resulting in a conductive pattern on the substrate.
An electroplating process is then carried out to form a replica of the conductive
pattern which can thereafter be removed from the substrate. This method is also restricted
in the uniformity and precision of lines which can be formed, as well as requiring
reprocessing of the master pattern after limited-usage.
[0004] U.S. Patent No. 3,703,450 to Bakewell discloses a method of fabricating precision
conductive mesh patterns on a repetitively reusable master plate comprising a conductive
pattern formed on a nonconductive substrate and a nonconductive pattern formed in
the interstices of the conductive pattern. A reproduction of the master pattern is
formed by plating of a conductive pattern onto the master pattern within a matrix
defined by the nonconductive pattern. The conductive metal master pattern is typically
deposited onto a glass plate by evaporation of a metal such as chromium through a
ruled pattern formed on a stencil material. The nonconductive pattern is formed by
depositing a layer of photoresist over the conductive pattern coted side of the glass
plate. By exposing the photoresist to actinic radiation through the conductive pattern
coated substrate, exact registration of the conductive and nonconductive patterns
is achieved. The photoresist layer is developed and the exposed portions are remoyed,
leaving a pattern of photoresist over the conductive pattern. A silicon monoxide layer
is then deposited over the entire surface of the glass plate, covering both the photoresist/conductive
pattern coated portions and the exposed glass portions. Finally, the photoresist overlying
the conductive pattern and the silicon monoxide overlying the residual photoresist
material are removed, leaving the glass plate coated with a conductive metal pattern
and an array of silicon monoxide deposits in the interstitial spaces in the conductive
pattern. Replicas of the conductive pattern are then formed by electroplating.
Summary of the Invention
[0005] The present invention provides an alternative process for producing an electroforming
mandrel. A substrate transparent to actinic radiation is provided with a desired pattern
for electroforming an article. The surface of the substrate is then coated with a
continuous conductive film. A continuous layer of photoresist is deposited over the
conductive film. The photoresist is exposed to actinic radiation through the substrate,
the pattern acting to mask portions of the photoresist from exposure. The photoresist
is then developed, and the unexposed portions removed to yield a conductive pattern
of the underlying conductive film corresponding to the pattern on the substrate. Alternatively,
the exposed portions of the photoresist may be removed to yield a conductive pattern
which is a negative image of the pattern on the substrate. In other embodiments, either
the exposed or unexposed photoresist may be removed and the conductive film in the
areas underlying the removed photoresist may be etched away. Removing the remaining
photoresist exposes a pattern of the conductive film on the glass surface in either
a positive or negative image of the pattern on the substrate. The resultant article
is employed as a mandrel for the electroforming of metallic parts. The present invention
provides an alternative process for producing a heater element grid. A substrate transparent
to-actinic radiation is provided with a desired pattern for the heater element grid
to form a photomask. A substrate to be used as the electroforming mandrel is coated
with a continuous conductive film. A continuous layer of photoresist is deposited
over the conductive film. The photoresist is exposed to actinic radiation through
the photomask, the pattern acting to mask portions of the photoresist from exposure.
The photoresist is then developed, and the unexposed portions removed to yield a conductive
pattern of the underlying conductive film corresponding to the pattern of the photomask.
Alternatively, the exposed portions of the photoresist may be removed to yield a conductive
pattern which is a negative image of the pattern of the photomask. The resultant article
is employed as a mandrel for the electroforming of a metallic heater element grid.
The mandrel is immersed in an electroforming solution, and current is applied to effect
the electrodeposition of metal onto the conductive pattern area on the mandrel. When
a sufficiently thick deposit is obtained, the remaining photoresist is removed, and
the electroformed heating grid is separated from the mandrel.
Detailed Description of the Preferred Embodiments
[0006] In a preferred embodiment of the present invention, a glass plate is provided with
a pattern representing the configuration of the article to be produced by electroforming.
While the pattern may be formed by a coating, a most preferred embodiment of the present
invention utilizes a glass photomask to provide the pattern, preferably a glass photomask
having a pattern formed by stain producing metal infused into the glass. Preferred
techniques for producing stained glass photomasks are described in detail in U.S.
Patents 4,144,066 and 4,155,735 to Ernsberger, the disclosures of which are incorporated
herein by reference.
[0007] A continuous conductive film is deposited on the surface of a substrate to be used
as the electroforming mandrel. The conductive film may be a metal or an electroconductive
metal oxide such as tin oxide or indium oxide. The conductive film may be deposited
by any conventional coating technique such as vacuum deposition, cathode sputtering,
chemical vapor deposition or pyrolytic coating techniques. In a most preferred embodiment
of the present invention, a conductive film comprising indium oxide is deposited by
magnetron sputtering. The conductive film is preferably deposited on a glass substrate.
In a most preferred embodiment of the present invention, a conductive film is sputtered
from a cathode comprising 80 to 90 percent indium and 10 to 20 percent tin.
[0008] Preferably, a continuous, transparent conductive film is deposited on the stained
surface of a stained glass photomask. The conductive film is preferably an electroconductive
metal oxide such as tin oxide or indium oxide. The conductive film may be deposited
by any conventional coating technique such as vacuum deposition, cathode sputtering,
chemical vapor deposition or pyrolytic coating techniques. In a most preferred embodiment
of the present invention, a conductive film comprising indium oxide is deposited by
magnetron sputtering. The conductive film is preferably deposited on the stained surface
of the photomask in order to optimize resolution of the pattern.
[0009] A continuous layer of photoresist is applied over the conductive film. Any conventional
photoresist with sufficient resolution is acceptable. In a preferred embodiment of
the present invention, photoresist in sheet form is laminated to the conductive film.
The photoresist is exposed to actinic radiation through the glass plate and conductive
film, which transmit sufficient radiation to cure the exposed portions of the photoresist.
The photomask pattern masks portions of the photoresist from exposure, and these portions
remain uncured. Following exposure of the photoresist, and a post-curing cycle if
necessary, the photoresist is developed. Preferably, the photoresist is contacted
with a chemical solution which dissolves and removes the unexposed-, uncured portions
of the photoresist, thereby providing a pattern of the underlying conductive film
which is a positive image of the pattern in the glass photomask. The remaining exposed,
cured portions-of the photoresist surrounding the conductive pattern form walls within
which the electroformed part is subsequently formed. In an alternative embodiment
of the present invention a positive working photoresist may be employed to form a
conductive film pattern which is a negative image of the photomask pattern.
[0010] The resulting article is employed as a mandrel for the electroforming of metallic
parts replicating the pattern on the conductive film. In accordance with the present
invention, the glass photomask substrate bearing a conductive film having a pattern
defined by the photoresist is contacted with a conventional metal-containing electrodeposition
solution. An electrical circuit is established, using the conductive film as the cathode
and an electrode of the metal to be deposited as the anode. An electrical potential
is applied, and metal is deposited on the conductive film in the pattern defined by
the photoresist. Electrodeposition is continued until the desired thickness is obtained
for the electroformed part. The substrate bearing the conductive film, photoresist,
and electroformed part is removed from the electrodeposition solution. Separation
of the electroformed part from the photomask mandrel may be effected by various means
such as alternately heating and chilling. If the part is thick enough, it may be stripped
from the mandrel with the photoresist intact. In this embodiment, the mandrel is immediately
reusable. However, in applications wherein the electroformed part is very thin and/or
comprises very fine lines, the remaining photoresist is first removed, preferably
by dissolution. Then the electroformed part is lifted off the photomask mandrel. If
the electroformed part is strong enough, it may be simply stripped from the conductive
film. However, in most preferred embodiments of the present invention wherein the
electroformed part comprises very fine lines, a preferred method for separating the
electroformed part from the photomask mandrel is to contact the electroformed part
with a tacky tape to which the part adheres, and to remove the part with the tape.
The part is preferably removed from the tape by dissolution of the adhesive.
[0011] In a most preferred embodiment of the present invention wherein the electroformed
part is a heating grid comprising very fine lines, a preferred method for separating
the electroformed heating element from the mandrel is to remove the photoresist, contact
the electroformed part with a polymeric material to which the part adheres, and remove
the heating grid element attached to the polymeric material. Preferably, the polymeric
material is an interlayer sheet to be laminated to a rigid sheet to form an aircraft
transparency. In a most preferred embodiment, the polymeric material is a sheet of
polyvinyl butyral, a surface of which is chemically treated to soften the surface.
The tacky surface is used to pick the heating grid off the mandrel. The polyvinyl
butyral sheet is then laminated to a second polymer sheet with the heating grid between
them. Various solvents may be used to soften the polyvinyl butyral; diethylene glycol
monobutyl ether is preferred.
[0012] The present invention will be further understood from the descriptions of specific
examples which follow.
EXMIPLE I
[0013] A glass photomask electroforming mandrel is prepared by coating a glass plate with
a photographic emulsion comprising silver nalide which is exposed to actinic radiation
through a master pattern which defines the shape of the part to be electroformed.
Exposed areas of the photographic emulsion form a latent image which is developed
by immersion in developing solutions which convert the silver halide to colloidal
silver. The coated glass plate is subjected to an electric field which induces migration
of the silver ions into the glass. The silver ions are reduced to elemental silver
which agglomerates into colloidal, microcrystalline color centers which form a stained
pattern within the glass which corresponds with the master pattern of the article
to be electroformed. The stained glass surface is then coated with a continuous conductive
film by magnetron sputtering of a cathode comprising 90 percent indium and 10 percent
tin. The preferred indium oxide film has a surface resistivity less than about 20
ohms per square. A continuous layer of photoresist is applied over the conductive
film by laminating a sheet of photoresist to the indium oxide at a temperature of
235°F. (about 113°C.). A photoresist layer having a thickness of 0.001 inch (about
0.025 millimeter) is available from Thiokol/Dynachem Corp. of Tustin, California.
The photoresist is exposed to actinic radiation (Colight M-218) through the glass
photomask for 20 seconds and cured. The photoresist is developed with a solvent which
removes the unexposed portions of the photoresist thereby providing a pattern of the
underlying indium oxide in the shape of the article to be electroformed. The resultant
article is used as an electroforming mandrel in the following process.
EXAMPLE II
[0014] The glass photomask electroforming mandrel of Example I is prepared for electroforming
by sequential dipping into a dilute solution of hydrochloric and nitric acids, and
isopropanol, each followed by a water rinse to clean and wet the electroforming surface.
The glass photomask is dipped into the electroforming solution several times to completely
wet the surface and remove air bubbles before the electroforming process commences.
The electroforming solution comprises nickel sulfamate, and is maintained at a temperature
of 110°F. (about 43°C.). A cathode contact is applied to the indium oxide film of
the glass photomask electroforming mandrel. An anode contact is applied to a depolarized
nickel plate. Both the mandrel and the plate are immersed into the nickel sulfamate
solution. At a current density of 10 amps per square foot, electroforming proceeds
at a rate of 0.001 inch (0.025 millimeter) per 100 minutes. When the electroformed
part reaches the desired thickness, the mandrel is removed from the solution, the
remaining photoresist is dissolved and removed with sodium hydroxide solution, and
the electro formed part is removed from the mandrel with tack tape.
EXAMPLE III
[0015] A glass photomask is prepared by coating a glass plate with a photographic emulsion
comprising silver halide which is exposed to actinic radiation through a master pattern
in the shape of the part to be electroformed. Exposed areas of the photographic emulsion
form a latent image which is developed by immersion in developing solutions which
convert the silver halide to colloidal silver. The coated glass plate is subjected
to an electric field which induces migration of the silver ions into the glass. The
silver ions are reduced to elemental silver which agglomerates into colloidal, microcrystalline
color centers which form a stained pattern within the glass which corresponds with
the master pattern of the article to be electroformed. An electroforming mandrel is
prepared by coating a glass substrate surface with a continuous conductive film by
magnetron sputtering of a cathode comprising 90 percent indium and 10 percent tin.
The preferred indium oxide film has a surface resistivity less than 20 ohms per square.
A continuous layer of photoresist is applied over the conductive film by laminating
a sheet of photoresist to the indium oxide at a temperature of 235°F. (about 113°C.).
A photoresist layer having a thickness of 0.001 inch (about 0.025 millimeter) is available
from Thiokol/Dynachem Corp. of Tustin, California. The photoresist is exposed to actinic
radiation (Colight M-218) through the glass photomask for 20 seconds and cured. The
photoresist is developed with a solvent which removes the unexposed portions of the
photoresist thereby providing a pattern of the underlying indium oxide corresponding
with the pattern in the photomask which in turn corresponds with the master pattern
in the shape of the article to be electroformed. The resultant article is used as
an electroforming mandrel in the following process.
EXAMPLE IV
[0016] A glass mandrel 3 by 7 inches (about 7.6 by 17.8 centimeters) is prepared as in Example
I having a screen pattern comprising lines 0.0012 inch (about 0.03 millimeter) wide
spaced 0.022 inches (about 0.56 millimeters) apart. The mandrel is prepared for electroforming
by sequential dipping into a dilute solution of hydrochloric and nitric acids, and
isopropanol, each followed by a water rinse to clean and wet the electroforming surface.
The glass mandrel is dipped into the electroforming solution several times to completely
wet the surface and remove air bubbles before the electroforming process commences.
The electroforming solution comprises nickel sulfamate, and is maintained at a temperature
of 110°F. (about 43°C.). A cathode contact is applied to the indium oxide film of
the glass electroforming mandrel. An anode contact is applied to a depolarized nickel
plate. Both the mandrel and the plate are immersed into the nickel sulfamate solution.
At a current density of 10 amps per square foot, electroforming proceeds at a rate
of 0.001 inch (0.025 millimeter) per 100 minutes. When the electroformed part reaches
the desired thickness, 0.0005 inches (about 0.013. millimeters), the mandrel is removed
from the solution. The remaining photoresist is dissolved and removed with sodium
hydroxide solution at 150°F. (about 66°C.). The electroformed heating grid is removed
from i the mandrel by contacting the surface with a sheet of polyvinyl butyral, the
contacting surface of which has been treated with diethylene glycol monobutyl ether
to produce an adhesive surface. As the polyvinyl butyral sheet is pulled away from
the mandrel, the grid remains attached to the tacky surface of the polyvinyl butyral.
To form a heatable interlayer, the polyvinyl butyral sheet bearing the heating grid
is laminated to another polymeric sheet with the heating grid between the sheets.
EXAMPLE V
[0017] An optical grid is produced by electroforming as in Example II, except that the conductive
pattern on the mandrel comprises finer lines more closely spaced. An optical grid
is produced comprising lines 0.001 inch (about 0.025 millimeter) wide spaced 0.003
inch (about 0.076 millimeter) apart.
[0018] The above examples are offered to illustrate the present invention. Various modifications
are included within the scope of the present invention. For example, metallic substrates
may be used for the electroforming mandrel, and other metals may be deposited by electroforming,
such as copper, iron, lead, tin and zinc. The electroformed elements of the present
invention need not be grid patterns, but may be produced in any shape or configuration,
limited only by the artwork. The scope of the present invention is defined by the
following claims.
1. A method for producing an electroforming mandrel comprising the steps of:
a. providing a substrate which transmits actinic radiation with a pattern which masks
the transmission of actinic radiation;
b. depositing on a surface of the patterned substrate a continuous conductive film
which transmits actinic radiation;
c. depositing on the conductive film a continuous layer of a photoresist;
d. exposing said photoresist to actinic radiation through said masking substrate and
conductive film; and
e. developing said photoresist to selectively remove a portion thereof in order to
uncover a pattern of the underlying conductive film.
2. A method for producing an electroforming mandrel comprising the steps of:
a. providing a substrate which transmits actinic radiation with a pattern which masks
the transmission of actinic radiation to form a photomask;
b. depositing on a surface of a second substrate a continuous conductive film to form
an electroforming mandrel;
c. depositing on the conductive film a continuous layer of a photoresist;
d. exposing said photoresist to actinic radiation through said photomask; and
e. developing said photoresist to selectively remove a portion thereof in order to
uncover a pattern of the underlying conductive film which corresponds with the pattern
of the photomask.
3. A method according to claims1,2 wherein the substrate is glass.
4. A method according to claim 3, wherein the glass substrate is provided with a masking
pattern by means of a stain pattern within the glass.
5. A method according to claims1,2, wherein the conductive film is selected from the
group consisting of indium oxide, tin oxide and mixtures thereof.
6. A method according to claims1,2, wherein the conductive film is deposited by magnetron
sputtering.
7. A method according to claims1,2, wherein the photoresist is applied by laminating
a sheet of photoresist to the conductive film.
8. A method according to claims1-7 wherein the photoresist is developed by contacting
it with a solvent which removes the uncured portions of the photoresist.
9. An article of manufacture for use as a mandrel in a process for electroforming
a metallic part comprising:
a. a substrate which transmits actinic radiation;
b. applied to said substrate a pattern which masks the transmission of actinic radiation;
c. on a surface of the patterned substrate, a continuous conductive film which transmits
actinic radiation; and
d. over the conductive film, a discontinuous layer of photoresist defining a pattern
corresponding with the pattern applied to said substrate.
40 . An article of manufacture for use as a mandrel in a process for electroforming
a metallic part comprising:
a. a substrate;
b. on a surface of the substrate, a continuous conductive film; and
c. over the conductive film, a discontinuous layer of photoresist defining a pattern
for an article to be produced by electroforming.
11. An article according to claims9,10, wherein the substrate is glass.
12. An article according to claim 9, wherein the pattern applied to said substrate
comprises stain producing metal within the glass surface.
12. An article according to claims 12, wherein the pattern comprises silver.
14. An article according to claims9,10, wherein the conductive film is selected from
the group consisting of indium oxide, tin oxide and mixtures thereof.
15. An article according to claims9,10, wherein the photoresist defines a pattern
of conductive metal which is a positive image of the pattern applied to the substrate.
16. A method of electroforming a metallic part comprising the steps of:
a. preparing an electroforming mandrel which comprises a photomask substrate, a continuous
transparent conductive film on a surface of the substrate, and a discontinuous layer
of photoresist which defines a pattern on the surface of the conductive film;
b. attaching a cathodic connector to the conductive film of said electroforming mandrel;
c. attaching an anodic connector to an electrode comprising metal to be deposited
on the mandrel;
d. immersing the mandrel and the metal electrode into an electroforming solution;
e. establishing an electric current through said electrodes and solution in order
to deposit metal from the anode onto the cathodic surface of the conductive film;
and
f. carrying out electrodeposition of the metal to the desired thickness to electroform
the metallic part on the mandrel.
17. A method of electroforming a metallic article comprising the steps of:
a. preparing an electroforming mandrel by depositing on a surface of a substrate a
first continuous layer of a conductive film, and a second continuous layer of photoresist;
b. exposing said photoresist to actinic radiation through a photomask having a pattern
corresponding to the configuration of an article to be electroformed;
c. developing the photoresist by removing portions of the photoresist to uncover a
pattern of the conductive film corresponding to the configuration of the article to
be electroformed;
d. attaching a cathodic connector to the conductive film;
e. attaching an anodic connector to an electrode comprising metal to be deposited
on the conductive film;
f. immersing the mandrel and the metal electrode into an electroforming solution;
g. establishing an electric current through said electrodes and solution in order
to deposit metal from the anode onto the cathodic surface of the conductive film;
and
h. carrying out electrodeposition of the metal to the desired thickness to electroform
the metallic article on the mandrel.
18. A method according to claim 17, wherein the substrate is glass.
19. A method according to claim 16., wherein the substrate is a stained glass photomask.
2-0. A method according to claim 19, wherein the substrate is a glass photomask stained
with silver.
21. A method according to claims16,17 wherein the conductive film is selected from
the group consisting of indium oxide, tin oxide and mixtures thereof.
22. A method according to claim 21, wherein said conductive film is produced by the
process of magnetron sputtering.
23. A method according to claim 22, wherein said photoresist is developed to produce
a pattern of the underlying conductive film which is a positive image of the photomask
pattern.
24. A method according to claims16,17 which further comprises the step of removing
the photoresist after the electroforming of the metallic part in order to facilitate
separation of the part from the mandrel.
25. A method according to claims16,17 wherein said electroforming solution comprises
nickel sulfamate, and said metal electrode comprises nickel.
26. A method according to claim 17, wherein the metallic article is removed from the
mandrel by contacting the article with a polymeric material to which the article adheres.
27. A method according to claim 26, wherein said polymeric material is a sheet of
polyvinyl butyral.