www.nicoform.com By Berl Stein, NiCoForm, Inc., Rochester, NY

www.aos-inc.com
www.nicoform.com
By Berl Stein, NiCoForm, Inc.,
Rochester, NY USA
Art Caneer, Advanced Optical Systems,
Huntsville, AL USA
Optifab 2005
Rochester, NY May 2005
Electroforming also called Galvanoplasty - making of duplicates by
electroplating metal onto a mold of an object, then
removing the mold (Encyclopedia Britannica)
Selected examples of electroforming applications in optics
' Direct use optics and related devices - reflectors,
mirrors, optical slits, screens, masks, CCD
housings, IR cold shields
' Inserts for molding of plastic optics - spheric,
aspheric, Fresnel lenses, diffraction gratings,
micropatterned antireflective (moth eye) and
illuminating (brightness enhancing) structures,
holographic optics
Common Mandrel Types
What can be replicated?
' Diamond-turned or polished metal masters: copper, brass,
electroless nickel, aluminum, stainless steel
' Photoresist or epoxy on glass masters - holograms, micro
arrays, diffraction gratings, micro- and mini-channels, etc.
' Plastic masters - etched, molded or machined
' Silicon or Glass masters - etched, machined and/or polished
Note: the last three mandrel types must be rendered conductive prior to
electroforming
Advantages of Electroforming
How you can benefit from this technology
' Multiple replicas from a single mandrel drastically reduce
manufacturing costs
' Rapid turnaround (an average form takes 1-2 days to electroform)
shortens time to market
' Exact replication of intricate surface finishes, geometries and
textures, excellent dimensional stability
' Mounting and alignment elements can be incorporated in the
electroform reducing or eliminating assembly cost
' Desired material properties - hardness, wear resistance, thermal
conductivity are assured
' Thin wall cross-sections lower components weight
' Many optical coatings (Au, Ag, Rh, Cu oxide, etc.) can be provided
as part of the electroforming cycle rather than a secondary operation
FAAME Project Goals
List of accomplished tasks
' Electroform spherical and aspheric mirrors from precision diamond
machined mandrels
' Develop a thorough understanding of critical control variables and
establish a process window assuring the highest degree of electroform
accuracy
' Understand factors influencing mandrel durability and establish
guidelines for extending useful mandrel life
' Electroform 3 generations of mirrors and track generational replication
fidelity
' Electroform gold faced mirrors for improved reflectivity
' Electroform a wildly aspheric mirror from a diamond machined Al
mandrel
Electroforming Basics
What takes place in the solution
Ni & Co Ions, ionic radii - 0.69 D, 0.72 D
Mandrel
Nickel and Cobalt ions are
attracted by the negatively
charged mandrel, travel to its
surface and, gaining two
electrons turn into atoms of
nickel and cobalt, forming a
metallic layer on the mandrel’s
surface. The electroformed
layer faithfully replicates the
microgeometry of the surface
Electroformed
Layer
Difficulties in Precision Replication
Stress-induced distortions
Mandrel
Zero stress electroform is
undistorted with true
angles
Compressive stress electroform expands,
angles become more
obtuse
Tensile stress -electroform
contracts, angles become
more acute
Generational Replication
DIRECT
PROCESS
Master
Mandrel
Replica
GRANDDAUGHTER
PROCESS
Master
Mandrel
Daughter Transfer
Mandrel
Granddaughter
Working Mandrel
Replica
Mirror Replication Tree
Granddaughter Process
Original Mandrel
(Master)
Daughter Mirrors
Granddaughter
Mirrors
Final Mirrors
Mandrel and Electroforms
Generational replication
Diamond machined mandrel (left) and 1st and 2d generation mirrors
electroformed from it (right)
FAAME Factors
Critical process variables
' Affecting replication fidelity
& Deposit internal stress based on plating bath
chemistry
& Solution agitation
& Shielding
& Fixturing
' Affecting mandrel durability
& Mandrel cleaning and passivation cycles
& Mandrel material
& Electroform separation technique
Quality Progression
•
Usually Interferometric Quality
Rarely Interferometric Quality
Totally W arped
Initial Mirror
•
Adjustments
Testing Methods
•
Current
density/
Stress level
bounding
•
Electric
field/Thickness
adjustments
Testing
enhancements
(Calipers)
•
•
•
•
•
Fine
stress level
targeting
Testing
enhancements
(Knife Edge)
Flow shield/
Flow rate
control
improvements
Testing
enhancements
(Profilometer)
Testing
enhancements
(Interferometer)
FPS Mirror Electroforming
Wildly aspheric mirror
Aluminum diamond turned mandrel (left) and electroformed NiColoy™ mirror (right)
Optical Coatings
High and low emissivity
Gold-coated FAAME mirror (above)
Gold and Cu oxide - coated shutters (right)
Reflective Optical Coatings
Reflectivity of Various Metals
Examples of Electroformed Microand Submicrostructures
' Micro- and Nanofluidic Devices
' Slit Apertures and Clear Optical
Paths
' Fiberoptic Components
' Subwavelength Structures
Microfluidic Electroform from an etched
Si wafer mandrel
Electroformed Moth-Eye
Microstructure
FAAME Project Results
What has been achieved
' Over 65 mirrors from 3 diamond turned spheric and
aspheric mandrels were electroformed and thoroughly
documented
' 3 generations of replicas created with high fidelity - 1-3
waves and < 0.1% deviation in Radius of Curvature
' Process variables and process window identified
' Gold coated replicas created from the same master
' Several wildly aspheric replicas from an Al diamond turned
mandrel were successfully electroformed with high
precision
When to Electroform?
Manufacturing cost comparison for a
4 - 5" OD mirror (per piece)
High-Precision Electroforming
In NiColoy®
' In-tank stress monitoring enables accurate control of
conditions in the bath, thus preventing electroform distortion
' NiCoForm has developed a family of proprietary low-stress,
high strength Ni-Co electroforming chemistries, NiColoy®,
while most known Ni-Co plating baths induce considerable
stress in the deposit
' Automatic controllers for Nickel and Cobalt concentrations
assure a stable alloy composition