Conquering SMT stencil printing challenges with today’s miniature components
Conquering SMT stencil
printing challenges with
today’s miniature components
Is electroform technology the right solution?
by Robert F. Dervaes, Fine Line Stencil, Inc.; Jeff Poulos, Alternative Solutions, Inc.; and Scott Williams, Ed
Fagan, Inc.
introduction
no smaller than 0.025”, and registration
This article discusses new de-
One of the challenges facing OEMs and
of the stencil apertures to the SMT pads
velopments in stencil laser and
CMs in building assemblies with minia-
was not precise enough as component sizes
material technology and shows
ture components is the stencil printing
decreased. These limitations would not
how these advancements, when
process. Many of today’s designs incorpo-
allow chemical etching to keep pace with
rate a mix of miniature and much larger
combined, provide comparable
the rapid advancements in component and
components. Manufacturing engineers
and cost-effective alternatives to
PCB design.
are faced with the dilemma of choosing a
In the early 1990s, lasers started being
traditional electroformed sten-
thinner stencil foil to ensure solder paste
used to produce solder paste stencils. This
cils. The results are improved
release for the miniature components or
new technology was a major improvement
yields, cycle time reductions and a thicker foil to ensure sufficient solder
over traditional silkscreen and chemical
significant cost savings. volume for the larger components. With a
etching in producing stencils quicker,
standard laser-cut stencil using 300 series
cheaper and with much smaller aperture
stainless steel, one would have to make that
sizes. The motion systems on the laser
difficult choice. An electroformed stencil
systems also provided a much higher po-
Keywords: Laser-Cut Stencils,
gives more options in balancing release
sitional accuracy for the stencil apertures,
Electroform Stencils, Single
for miniature components and volume for
leading to much better alignment between
Mode CW Ytterbium Fiber
larger ones due to its ability to successfully
the stencil and PCB. With these significant
print smaller components without reducing
Laser, Fine Grain Material
improvements, component pitches down to
the foil thickness. However, many have
0.016” could easily be cut.
difficulty justifying the 3X-4X cost increase
While these laser systems are capable
and added schedule delay for an electro-
of producing high-quality solder paste
formed stencil, especially with more and
stencils for the majority of assemblies,
more companies moving to a low-volume,
advancements in component and PCB
high-mix array of jobs. Faced with these
design continued. With the introduction
two options, is electroformed technology
of components like micro BGA (µBGA),
the right solution, or have technological
quad flat no-lead (QFN), and 0201s,
advancements allowed new developments
laser-cut stencils struggled to produce ac-
in stencil technology?
ceptable solder paste release for these very

small apertures without a reduction in the
Brief history of stencil technologies
thickness of the stencil foil. This was not
Before stencil lasers were developed, the
always an acceptable solution as the larger
only manufacturing methods for produc-
components would have insufficient solder
ing solder paste stencils were silk screening
volume. Enter electroformed technology.
and chemical etching. The etching process
Electroformed stencils are produced by
was time consuming and hazardous due
electroplating nickel on top of a stainless
to the powerful chemicals used to etch
steel substrate under various specialized
the metal. There also were limitations as
and challenging conditions. The plated
to how small a stencil aperture could be
nickel film is later removed from the
effectively produced during the etching
stainless steel substrate, resulting in the
This paper was originally presented at the IPC process. Chemically etched stencils typi-
nickel foil that is the electroformed stencil.
APEX Expo 2009 in Las Vegas, Nevada. cally were limited to component pitches
30 – Global SMT & Packaging – March 2009 www.globalsmt.net
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