Online proceedings - EDA Publishing Association

and the dry film resist PerMX3020 (DFR), were used as
channel layers. These polymers hold similar chemical
compositions and can be structured via photolithography.
Either SU-8 or DFR also served as adhesive layer for
closing of the channel systems.
B. Channel Layer Fabrication
The PMMA substrate plate was rinsed with isopropyl
alcohol (IPA) and nitrogen. After that, all channel structures
were defined using photolithography. Therefore, two
optional methods and materials were used, either spin
coating of SU-8 or lamination of DFR.
SU-8 was chosen as channel layer material when the
fabrication of very narrow structures with aspect ratios
higher than 2:1 was intended. As it was found out earlier
that structured SU-8 features a stronger adhesion to another
SU-8 layer than to PMMA [5], a thin layer of SU-8 served
as an adhesion layer for the channel SU-8 layer. For this
purpose, a thin layer of SU-8 was spun onto the substrate.
After a pre-exposure bake, the SU-8 was fully exposed to
UV-light and post-baked to achieve an entire
polymerization. Then, the second SU-8 layer was spincoated
on top of the first one and pre-baked. The fluidic
systems were defined during exposure to UV-light using a
11-13
May 2011, Aix-en-Provence, France
1. Spin-coating of SU-8 or
lamination of DFR (adhesive
layer) on PMMA substrate
2. UV- Exposure
photo mask which contains the channel structures.
Thereafter, a post-exposure bake took place followed by a
development in a PGMEA developer solution.
For channel dimensions with aspect ratios lower than 2:1,
DFR was opted for the active structure. By means of a
desktop laminator, DFR was laminated on the substrate and
pre-baked. Like in the case of SU-8, the first DFR was fully
exposed for complete cross-linking to form an adhesive
layer. The second layer was exposed using a mask which
contains the channel systems. This layer was post-baked
and also developed in PGMEA. The process flow for the
channel layer fabrication including the fluidic interfaces is
pictured in Fig. 1.
C. Fluidic Interfaces
In contrast to Ref. [5], fluidic interfaces were realized by
CNC-assisted mechanical drilling of the structured PMMAepoxy-stack.
In order to protect the fluidic structures from
contaminations and mechanical damage, they were covered
by a protective foil (V-8-T, Nitto) which can easily be
drawn off after drilling (see Fig. 1).
D. Closing of Channels
Three different techniques of adhesive bonding were
applied and tested for the closure of channels with different
dimensions. The bonding options are shown in Fig. 2.
The first option was to use an additional DFR layer that
was laminated on top of the channel layer, like it was
presented before for moderately large channels with 220 µm
width [6]. This last DFR was fully exposed to serve as the
lid or bottom, respectively.
3. Spin coating of SU-8 or
lamination of DFR
(channel layer)
First bonding approach
1. Lamination of DFR on
top of the channel layer
4. UV-Exposure through
photo mask
2. UV-Exposure of
DFR
5. Development of SU-8/
DFR in devmr600
6. Covering with
protective foil
7. Mechanical drilling of
fluidic interfaces
Second and third bonding approaches
1. Spin-coating of SU-8
or lamination of DFR on
second PMMA substrate
2. Bonding partners are
pressed together
8. Removal of protective
foil
Fig. 1. Process flow of the channel layer fabrication including the fluidic
interfaces.
3. UV-Exposure of
SU-8 / DFR through
PMMA lid
Fig. 2. Process flows of the bonding techniques.
274