Enabling Manufacturing Technologies - Implications of Emerging Micro-and Nanotechnologies - page 144

MOTHER
SUBSTRATES

HOST SUBSTRATE

A A

DNA polymers
with different
sequences

} } }

lifted off
devices

B B

FIGURE 4-9 DNA-assisted microassembly. SOURCE: Esener, S. 2001. Emerging Ap-
plications of Micro and Nanophotonic Components and Their Interface with Biology.
Briefing by Sadik Esener, Electrical and Computer Engineering Department, University
of California San Diego, to the Committee on Implications of Emerging Micro and Nano
Technology, National Academy of Sciences, Irvine, Calif., December 19.

devices and the host using small solder balls under the devices. After the hybrid-
ization process, the substrate is removed from the fluid and dried and the system
is heat treated. Contacts are then formed in a manner similar to flip-chip bonding.
Remaining DNA strands do not harm the quality of the ohmic contact. Although
solder balls have been used in the initial demonstrations, many of the existing
techniques for forming electrical contacts can in principle be used with DNA-
assisted assembly.
This DNA-assisted assembly method is best suited to very small devices, on
the order of 100 micrometers or less (all the way down to tens of nanometers),
that can flow freely and find the correct position without blocking other devices.
In addition to DNA-assisted assembly, several other chemical and biological
molecules can be used advantageously for device-forming pick-and-place as well
as for micro- and nanoactuation. These techniques include, for example, the use
of patterned hydrophobic films on hydrophilic substrates to form devices such as
microfluidics and microlenses 53,54 (see Figure 4-10) and proteins for transport
and actuation functions.

PACKAGING

The packaging of integrated circuits involves many complex but well devel-
oped technologies. 55,56 The packaging field has evolved in response to two major
influences—cost and the need to put chips ever closer together on printed circuit
boards. Dual-inline packages first gave way to surface mount packages, and these
are now being superseded by chip-scale packages. Flip-chip attachment of ICs to
boards essentially mates the chip to the package. Hermetic sealing of ICs from
the outside environment has been a standard requirement. With the exception of