Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

Here is a article on printing photo resist. Why would they deposit
photo resist instead of a direct resist.

R¨¦sum¨¦ / Abstract
This article presents a technique for resist deposition using a
novel fluid ejection method. An ejector has been developed to
deposit photoresist no silicon wafers without spinning. Drop-on-
demand coating of the wafer reduces waste and the cost of coating
wafers. The novel piezoelectric fluid ejector is based on a
variation of the design of a flextensional transducer that excites
axisymmetric resonant modes in a damped circular membrane. The
ejector is made by bonding a thin piezoelectric ring to a thin,
fully supported, circular membrane. The ejector design is optimized
for maximum flexure at the lowest order resonant frequency using
finite element modeling. The resist, is placed behind one face of
the membrane which has small orifice (50-150 ¦Ìm diameter) in its
center. By applying an ac signal across the piezoelectric element,
continuous or drop-on-demand ejection of the resist is achieved.
Shipley 1400-21, 1400-27, 1805, and 1813 resists were used to coat
sample 3 wafers. Later, these wafers were exposed and developed. The
deposited resist film was 3.5 ¦Ìm thick and had a surface roughness
of about 0.2 ¦Ìm. The ultimate goal is to deposit resist films with a
thickness of the order of 0.5 ¦Ìm, and a surface roughness of the
order of 30 A¡ã. Such goals can be attained by using micromachined
multiple ejectors presently under development, or with better
control liver the deposition environment. In the micromachined
configuration, thousands of ejectors will be made into a silicon die
and thus allow for full coating of a wafer in a few seconds. Coating
in a clean environment will allow the lithography of circuits for
microelectronic applications