SGIA Journal Graphic November/December 2016 - 26

Development. MEMS forms their piezo
actuator, ink channels and nozzle plates
using semiconductor wafer level micromachining techniques. Ricoh, Konica
Minolta, HP Scitex (X2), Panasonic and
Fujifilm Dimatix employ silicon micromachining for making parts for models
of their printheads, such as the piezo
actuators, nozzle plates and ink channels.
MEMS fabricates the different layers
that are subsequently assembled into
inkjet printheads. MEMS printhead
manufacture first requires a MEMS
foundry where printhead layers, actuators,
nozzle plates and other parts are micromachined. Following foundry processing,
the printhead manufacturer aligns and
adheres the layers and connectors. MEMS
foundries include ST Microelectronics,
Rohm Semiconductor, Silicon Sensing
(SSS), Silex Microsystems in addition
to Canon, Ricoh, Konica Minolta and
Epson that operate their own foundries.
SPGPrints's sister compa ny, Stork
Veco B.V. reportedly is "the world's
leading manufacturing company of
two-dimensional, high accuracy Metal
Precision Products"13 offering spin coating
of photo resists and electro forming,
photo etching and laser cutting for micromachining of inkjet nozzle plates among
other MEMS applications.
MEMS fabrication of inkjet printheads
requires the removal of all contamination
from the surfaces to receive the masking
and photo resists. Typically, a hydrogen
peroxide or similar type liquid cleanses
the surface. The surface material is heated
to about 150oC to evaporate any residual
moisture. The photolithographic process
then deposits a photo resist coating on the
silicon or metal plate using spin coating
or other coating methods. After the photo
resist is baked, it is photographically or
projection masked while exposed to UV
light. The process develops the photo resist,
etches the surface and removes the residual
photo resist. This photolithographic
process forms precise geometric patterns
that have enabled the production of nozzle
plates and printhead layer components.
A met hod Stock Veco employs
features a base metal support (mandrel)
to receive the photo resist pattern for its
nickel (Ni) electroforming process. The
electroplating process deposits Ni on the
mandrel where the photo resist has not
covered it. As it builds above the height of
the resist layer, the Ni can overflow onto
the top of the resist.
For a l l it s adva nta ge s, M E MS
fabrication techniques also have a few
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November/December 2016

disadvantages. They require flat substrate
surfaces to begin. They are not useful for
creating shapes that are not flat. They
also require clean room environments
free of dust and dirt in order to achieve
the yield rates for acceptable performance
printheads. A minimum clean room
standard of Class 10 FED STD 209E
is generally recommended. Class 10
is equivalent to the ISO 4 clean room
standard. It requires that no more than
352 particles equal to or greater than
0.5µm in the largest dimension can be in
any cubed meter of the clean room.
HP

Since 1977-1978, HP has lead the
development of Thin Film and MEMS
technology for the manufacture of inkjet
printheads. HP uses the TIJ printheads
it developed in its print solutions for
consumer desktop, office, graphic arts and
industrial production applications. HP
continues to invest in and advance its TIJ,
as well as its HP Scitex X2 PIJ, printhead
technologies, resulting in higher resolution,
greater durability and printer reliability. In
February 2015, HP introduced its MEMS
built High Definition Nozzle Architecture
(HDNA), which features, according to
HP, "a 2,400 dot-per-inch, dual channel,
thermal inkjet (TIJ) print head capable of
speeds up to 800 feet per minute. This top
speed is 33 percent higher than the 600
fpm of the previous HP TIJ heads, and the
resolution is twice the previous 1,200 dpi.
This fourth generation of print heads is made
using MEMS (Micro-Electro-Mechanical
Systems) technology that is widely used in
silicon-based electronics manufacturing.
MEMS has gained acceptance in print
head manufacturing because it allows
for increased nozzle density (i.e., higher
resolution) and permits the creation of
integrated print head circuitry."14
The HDNA heads are a first step toward
addressing the inability of TIJ to print
grayscale as many PIJ heads can. HP
incorporated two nozzle sizes into these
heads to produce two drop sizes and three
gray levels for higher apparent resolution
and perceived print quality. The head's
dual parallel channel configuration enables
higher print speeds or nozzle redundancy
at half speed. Each channel can also print a
different ink color from the other channel.
HP is beginning to use its HDNA heads in
single-pass print systems for applications
from office CAD to production corrugated
packaging printing.
HP is using its HDNA printheads on
its new Inkjet Web Press T series systems,
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