Establishing a precision stencil printing process for miniaturized electronics assembly
Establishing a precision
stencil printing process for
miniaturized electronics
assembly
by Chris Anglin, Indium Corporation, Clinton, New York, USA
introduction to know the 0.3 mm pitch process through
It is widely accepted that One of the most important approaches to insight and experience. The rapid pace of
about 65% of all end-of-the-
characterize a stencil printing process is this latest technology change will now cre-
line defects occur in the stencil
measuring the level of variation in transfer
ate another new fashion for miniaturized
printing process. It is therefore
efficiency. Even a small deposit of solder
electronics assembly. With transcendence
critical that a precision stencil
paste can form a solder joint. However,
to 01005 and 0.3 mm pitch assembly will
printing process be developed
variation in the amount of adjacent depos-
come much renewed emphasis on further
to support miniaturized
its for a single component will inevitably
perfecting one’s stencil printing process.
alter uniform shapes and sizes of adjacent
electronic assembly.
solder joints. Assembly line defects occur
Discussion of methodology
This paper is a summary
with such excessive variation in solder paste
This paper provides a summary of
of a significant amount of
deposits.
projected process development demands
experimental data and process As we look back on a global electronics
for examining a precision ultra fine pitch
optimization techniques that industry trend to increase circuit density,
stencil printing process. We will examine
were employed to establish
major improvement factors for solder paste
stencil printing by considering various
a precision SMT printing
transfer efficiency have come from tooling
paste print trial measurement results. The
process. Our results indicate
and process control. These improvement
measurement data are actual results of ap-
that the industry standard
factors can be recognized in SMT PCB
plication experiments done as case studies
assembly transitions during the 1990s, and for solder paste customers. In most case
stencil aperture area ratio
most significantly since 2000. For ex- studies there are several considerations, but
requirement of > 0.66 is
amples, we can cite technology transitions always there is the desired goal for achiev-
an excellent rule of thumb. such as fine pitch, ultra fine pitch, no-clean ing a low level of variation in the transfer
However, by optimizing
paste, BGA assembly, lead-free, 0.5 mm efficiency. Typically there are at least two
printer setup, we have been
pitches CSP, etc. During each transition,
paste products to be compared, a paste
able to obtain acceptable
new assembly line practices fashioned im-
product used in current production, and
stencil printing results with
provement through better tooling and in-
candidate (experimental) paste products.
creased process control. Consequently, suc-
area ratios of 0.5 with Type
A strategy for experimental paste product
cess with 0.3 mm pitch assembly necessarily
III solder pastes. The work
print trials begins by first understanding
should be expected to include innovative
a current paste product’s level of variation
that was performed to achieve DFM for tooling (stencils/squeegees) and
in transfer efficiency and then following
these results will be discussed re-training for process control
1
. As OEM
a plan to systematically examine various
in detail in the paper.
management guides pad design changes for
experimental paste product prints until the
new printed circuit board designs, the as-
set goal (low variation) is reached.
sembly process engineers must observe key
The data from paste print trial ex-
elements about specifically how assembly
periments will provide the opportunity to
Keywords: Miniaturized tooling and process control will be chal-
quantitatively observe factors that con-
Electronics, 01005, CSP, Stencil
lenged by the 0.3 mm pitch design.
tribute to the final yield of the assembly
Printing, Process Optimization
Importantly, circuit board assembly
process. Among these factors is the stencil
management should expect a demand for
selection. There is a subtle assumption
tooling and process control change. In the
that the reader of this paper is cognizant of
transcendence to 0.3 mm pitch assembly,
This paper was originally presented at IPC
the importance of an area ratio sensitivity
there will be a need to throw off many com-
APEX Expo 2009.
analysis in improving print performance
2
.
mon process control freedoms and come
While a case study focused on miniaturiza-
10 – Global SMT & Packaging – August 2009 www.globalsmt.net
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