Biomedical Engineering Reference
In-Depth Information
assembly system: as a method of arranging parts for assembly, as the fastening
mechanism, and as a method for fine positioning adjustments.
Several factors argue for using MEMS to manipulate the parts being as-
sembled. The starting point is that submicrometer dimensional control is readily
available through MEMS but is very difficult and expensive with conventional
machining. The excellent mechanical properties of silicon are an advantage. An-
other factor is the well-developed infrastructure that already exists for silicon
materials and processing. If there were any questions about the fundamental
reliability of MEMS devices, they should have been put to rest with the success
of Texas Instrument's (TI's) digital light projector chips (see the last section of
this chapter for the history of this product), which are by any reasonable measure
the most reliable mechanical devices ever created. Finally, there is a clear roadmap
for downscaling MEMS that has already been formulated by the IC industry.
Direct assembly is aimed at overcoming one of the principal limitations of MEMS
processing, its generation of essentially two-dimensional parts. Assembling
MEMS parts will enable multiple degrees of freedom of motion.
The key points of this assembly strategy include a movable tether approach
that allows parts to be arranged on silicon wafers and constrained in a known
position until they are captured. To achieve high throughput, the parts and fin-
ished goods are arranged in a periodic array to allow parallel assembly. The parts
consist of modular MEMS carriers that have either integrated MEMS devices or
preattached component parts. The carriers include silicon snap connectors that
make mechanical and, if needed, electrical connections with the assembly sub-
strate. An array of MEMS grippers is attached to the macroscale robotics used to
capture parts from the parts array and carry and attach them to the assembly
arrays in a highly parallel manner. Figure 4-7 shows an assembled MEMS grip-
per device, called a rotapod, used to capture and position parts. The rotapod is a
MEMS device assembled from two separate MEMS parts using snap connectors.
It has a gripper mechanism and is capable of rotating along two axes. This part
will be able to capture parts and rotate them into position for assembly, thus
breaking out of the dominant two-dimensional MEMS assembly paradigm.
The grippers and snap connectors are designed with self-centering mecha-
nisms that allow significant tolerance in the capture and attachment process. This
self-centering capability effectively discretizes the assembly process, allowing
high-precision assembly with relatively inexpensive robotics. The silicon snap
connectors place components more accurately than the robotics.
The main advantage of such a MEMS-based manufacturing technique over
current practices is parallel processing, analogous to the advantage that IC pro-
cessing enjoys over discrete electronics. Parallel processing should drive down
the cost of microsystem assembly.
This assembly manufacturing technology may find its first major application
and a large market share in manufacturing fiber-optic communication compo-
nents. This will allow demonstration of the technology at larger size scales and
Search WWH ::
Custom Search