Biomedical Engineering Reference
In-Depth Information
potential increases, which make the nickel harder to deposit,
thus, requiring more energy. When gas is released from the
electrodes, a wetting agent is often added to speed up the gas
discharge. Adding a wetting agent reduces the surface tension
between the gas and plating solution, thus allowing the gas
bubble to grow larger. A structure modiier is used to improve
the structure of metal coatings, and may change the lattice
type and orientation. Coatings are also used to adjust stress.
A lattening agent can reduce the rugged surface of the plated
layer and smooth the coating surface. Many brighteners also
have a leveling effect. Brightening and leveling agents can be
combined under a wide range of current density for smoother
coatings. The frequency and amount of luid injections depends
on the roughness of the substrate and the requirements for
thickness, gloss, and smoothness. The ingredients in the bath
should remain the consistent to maintain the coating quality.
Nickel is the electroforming solution based on nickel sulfamate
used to make the electroforming mold.
(c) Post-processing: To complete the formation of micro-
structures, the coating layer usually has high electrical
resistance, so galvanic grinding is done after the completion
of excess coating removal. After grinding the photo-resistant
layer, the plate is then placed in a heated alkali solution and
then water to avoid shedding. After cleaning, moisture is
removed with dry nitrogen, allowing the mother mold to set.
6.2.3
Micro Molding: Hot-Embossing
and Micro-Injection
Micro-molding technique generally shapes polymer plastic materials
with techniques including hot embossing, injection molding [8-9].
Using polymer plastic material as a biological sensor chip substrate
provides ive major advantages: (1) low-cost and high-scalability
can increase market competitiveness; (2) transparency — compared
to non-transparent silicon substrate, transparent plastic chips are
useful for observing micro-low channels in laboratory or clinical
tests; (3) good biocompatibility; (4) they can be discarded after
use and will not cause cross-contamination between samples; (5)
better mechanical strength relative to high silicon and glass chips
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