General Design Guidelines For Polymer-Based Microfluidic Devices

The manufacturability of a device depends on the individual design and the interaction between its
various design elements. In this respect, the following design guidelines for polymer-based microfluidic
devices give the user a better understanding of possible limitations in the design of a specific structure.
For the microfluidic design, two aspects besides the functionality have to be considered right at the start
of the design process: It must firstly be checked whether the design can be realized by replicative
technologies – allowing for low-cost mass-manufacturing – like injection molding, and secondly
whether the back-end processes, in particular the assembly (usually the secure sealing of the fluid with a
cover lid), can be ensured.
Besides the purely technical constraints, cost considerations can also have an influence on the chosen
manufacturing route, as different methods for mold insert fabrication have different technical constraints
(minimum feature size, maximum height, surface roughness, etc.) as well as different cost ranges.
a) Feature density
In order to allow for a good bond between a structured part and a cover foil, two adjacent channels or
similar features should be separated by at least twice their width, but not less than 200 µm.
Not more than 50% of the overall surface area should be covered with structural elements.
b) Distance to device edges
In order to allow for a good bond, features should have a minimum distance from the edge of the device
of 2 mm. The larger the device and the feature size, the larger this distance should be.
c) Minimum feature depth
Structures should have a minimum depth of 5 µm for features < 100 µm. For features between 100 and
1000 µm, the minimum depth is 15 µm.
d) Minimum residual thickness of the device
The minimum residual thickness of the device in structured areas (see Fig. 409) is 500 µm for areas
> 1 cm2. For smaller areas, a lower residual thickness might be possible, depending on the overall
device layout.
e) Maximum feature width
There is no practical limit to the feature width, however in the case of features wider than 4 mm, support
structures to prevent the cover lid from sagging might have to be included in the design.
f) Aspect ratio
For injection molded parts, the aspect ratio for microstructured elements should be less than 2.
g) Through-holes
The minimum diameter of through-holes realized by standard core pins is 500 µm. Smaller holes can be
realized with additional means upon request.
h) Open areas
Open areas are possible.