(355 nm), results in better quality PMMA channels [ 15 ]. Most organic materials
show an intense absorbtion in the ultraviolate region, for instance, excimer laser at
wavelengths of about 190–248 nm or third harmonic of Solid State Lasers of
355 nm; remain transparent at the most common semiconductor (800 nm) and
Nd-YAG (1064 nm) wavelengths [ 16 ]. In this chapter infrared laser fabrication is
considered, as it is universal for PMMA fabrication; however the other wavelength
can be utilized as well under certain conditions and ablation environments [ 14 ].
Among the merits of microfabrication with laser is the capability to engrave and
to cut designs on a wide variety of materials. The materials suitable for engraving/
cutting cover a wide range including: wood, acrylic, plastic, glass, leather, corian,
fabric, coated metals, annodized aluminum, ceramics, mylar, pressboard, and more.
Thermal plastics (e.g., PC, COC) are not suitable substrates for laser ablation
because they tend to degrade in the process. PVC brings another sort of difficulty
it melts and fills the cut groove. Therefore, we look mainly into PMMA. At 1200
dpi, the moving precision of CO 2 laser (e.g., Epilog Mini 18 Laser cutter) is about
0.02 mm (~20μm). Microdevices are easily made within minutes by engraving
channels in PMMA, or by moulding PDMS onto a PMMA master. It has been
demonstrated that ablation of mechanically stable material such as PEEK (poly-
PDMS replicaPDMS
replicaPDMS
replicaSaggingunprotected gold ~1 μmEtchingPDMS replicaStamp on goldgold, 38 nmEtch unprotected goldPDMSPDMS- Oxidize + Silanize
- Transfer structure
into PDMS replica
PDMSPDMSSi waferSi waferSi waferSi waferSi waferSpincoat polymer
and dyeLaser ablationTransfer structure
into PDMSSeparate and generate
PDMS stamp for μCP
>10 μm>5 μm
~3 μm~1 μm~1 μm~1 μmSi wafer ~10 μmFig. 3.7 Stamp preparation by laser ablation for microcontact printing. The pattern is transferred
from the PDMS stamp to the PDMS replica, which bears a positive image of the originally ablated
pattern that has been embossed on its surface. Then the replica is applied for stamping
hexadecanethiol onto a gold surface. This replica is used for stamping onto a gold surface, and
the unprotected gold is removed by etching to give features of sizes of 1μm. Reprinted by
permission from Analytical Chemistry: [Journal of Analytical Chemistry, 1998] [ 13 ]
3 Manufacturing Methods Overview for Rapid Prototyping 97