36 DESIGN007 MAGAZINE I SEPTEMBER 2024
Welcome to the next step in the manufactur-
ing process—the one that gets the chemical
engineer in all of us excited. I am referring to
outer layer imaging, or how we convert digital
designs to physical products. On a recent epi-
sode of I-Connect007's On the Line with… pod-
cast, we explained how the outer layer imaging
process maps the design's unique features onto
the board.
At this point, the boards have gone through
the electroless copper process. ey are primed
and ready for us to apply the photo image to
the external layers, physically transferring
the digital copper image of the design to the
outer layer. Every component of the design
layout—from pads to through-hole pads, trace
routes, and ground fill—goes onto the manu-
facturing panel.
Designing for Reality:
Outer Layer Imaging
is transition from digital to physical is
where the designer's IP meets the board.
Dry Film vs. Liquid Photoimageable (LPI)
Once the surface is prepped, we apply the
photoresist to the board. It is the mechanism
that will accept the digital design and physically
create it on the panel. ere are two applica-
tion methods available: dry film, and imaging
using an LPI polymer that is like a solder mask.
Dry film is a thin layer of polymer, usually
blue or purple. It comes in rolls like Saran
wrap, and it's applied with heat and pressure.
When unwinding the roll, it physically lami-
nates on the surface of the panel. is results in
a uniform—usually a 2.3 mil—photoresist.
Dry film is more forgiving and more uniform
in thickness, but that thickness can limit some
Connect the Dots
by Matt Stevenson, ASC SUNSTONE CIRCUITS
