Patent Application
20070264475
1. Field of the Invention
This invention relates generally to the field of micron-scale three dimensional (3D) surface feature manufacturing and more particularly to a method and apparatus for obtaining reduced size features by casting on an elastic membrane.
2. Description of the Related Art
Arbitrary millimeter-scale 3D surface features can be produced by direct-write additive or subtractive automated manufacturing processes. Presently, direct-write additive or subtractive mechanical methods fail at producing micron-scale 3D surface features because microscale mechanical tools have insufficient stiffness or strength to machine at the required resolution, and surface tension limits the resolution of liquid-phase additive techniques. Indirect methods, such as grayscale photolithography, and direct optical methods, such as UV laser ablation, and two-photon polymerization can produce submicron 3D surface features at substantially increased cost. Diffraction limits the resolution of the optical methods, and introducing shorter wavelengths to the optical methods increases costs again.
It is therefore desirable to introduce a low-cost technique which can extend each of these patterning methods to finer scales.
It is further desirable to provide a micron scale manufacturing technique which reduces the size of the features biaxially while maintaining the desired relief of the manufactured features.
A system and method incorporating the present invention provides for stretching an elastomeric sheet isotropically, coating it with a curable elastomer precursor, impressing a surface pattern into the precursor coating with a mold, curing the precursor coating to form a patterned elastomeric coating on the substrate elastomeric sheet, removing the pattern mold, and then allowing the substrate elastomeric sheet to relax to its original size. The cured patterned coating is forced to contract isotropically by the relaxing elastomeric sheet, creating a new surface pattern whose features will be reduced in size, while retaining the relief of the features.
In a first embodiment, stretching of the elastomeric sheet is accomplished with a stretcher having a frame with attachment manipulators extending radially inward and attaching to the membrane with clamps. Retracting the manipulators stretches the membrane to receive the elastomeric coating. An alternative embodiment employs a biaxial stretcher to engage and stretch the elastomeric sheet biaxially.
The features and advantages of the present invention will be better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
The present invention provides a method and apparatus for micron-scale feature manufacturing. As shown in
The membrane substrate is then coated 204 with a curable elastomer precursor on each side using an applicator brush, or by pumping the precursor out of a syringe. Double sided coating is employed such that the cured patterned substrate will relax symmetrically after the molds are removed and the tension is released as described below. A surface pattern is imprinted 206 into the precursor coating with a mold. In exemplary embodiments, molds are applied to each side of the stretched and coated substrate and clamped into place. Excess precursor which squeezes out from under the molds is wiped away. The substrate is then cured 208.
Multiple curing approaches are available for use in the present invention. In certain embodiments, the molds are transparent and a UV-curing precursor is used, the coating is then cured in a UV curing chamber. Alternatively a room temperature curing precursor is used and no exposure to UV or heat is required. A heat-curing precursor is used for other embodiments with heated platens attached to the molds, or radiation from heat lamps directed at the outer surface of the molds, or the whole assembly placed in a convection oven. Typical heating ramp rates are from 1 to 5° C./minute. Typical heating times at temperature range from 4 hours at 65° C. to 1 hour at 100° C.
The precursor coating, when cured, forms a patterned elastomeric coating on the substrate elastomeric membrane. The pattern molds are then removed 210 from each side of the stretched substrate. The attachment manipulators are extended 212 by de-tensioning the adjustment nuts and the substrate elastomeric membrane is allowed to relax to approximately its original size. The cured patterned coating contracts with the membrane creating a new surface pattern with features reduced in size. The relief of the features in the cured pattern is maintained or increased based on volume expansion in the unconstrained dimension during relaxation of the membrane.
In exemplary embodiments, the elastomeric membrane is Silicone ⅛″ to ¼″ thick with a Shore A hardness of 40-50 and elongation greater than 100% and preferably greater than 300%. In alternative embodiments, a Polyurethane membrane is employed.
An exemplary silicone precursor for the pattern coating is Dragon Skin Q produced by Smooth-On, Inc. The Properties of this precursor are shown in Table 1.
The alternative polyurethane membrane requires a silicone primer, such as Nusil SP-270, to enhance adherence of the silicone coating to the membrane.
The embodiment shown in
Exemplary patterns on which the present inventive combination is employed include pyramids, prisms, grooves, lenses and arbitrary relief patterns with pitch of 0.01 micron to 100 microns and relief of 0.01 micron to 50 microns. Exemplary starting substrate sizes are 1″ to 6″ diameter. A typical mold is about 0.5″ less in diameter than the stretched substrate to allow space for the tensioning clamps. The substrate is typically stretched from 20% to 100% in diameter. A typical mold pattern would have 50 micron features 20 microns in height. Materials for the pattern mold used for imprinting the precursor surface pattern are metals such as electroformed nickel, machined aluminum, electrochemically-etched aluminum or titanium or silicon, hard polymers such as epoxy, acrylic, polyurethane, polypropylene, nylon or ceramics such as fused silica and glass.
In an extended embodiment of the method of the present invention shown in
The production system for the replica casting product of the present invention is shown in
Having now described the invention in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present invention as defined in the following claims.
