Establishing a precision stencil printing process for miniaturized electronics assembly
conclusive if there no characteristic differ-
265µm aperture—35µm space 205µm aperture—95µm space
ence exists in the manufacturing tolerance
255µm aperture—45µm space 195µm aperture—105µm space
among test stencil apertures when com-
245µm aperture—55µm space 185µm aperture—115µm space
pared to manufacturing tolerance for actual
235µm aperture—65µm space 175µm aperture—125µm space
manufacturing introduction of new stencil
225µm aperture—75µm space 165µm aperture—135µm space
design technology. Omission of the compre-
215µm aperture—85µm space 155µm aperture—145µm space hensive mix of stencil features could cause
the test trial printing process (established
Figure 16. Design proposal alternatives for 0.3 mm pitch. using a test stencil with limited features)
to be bogus. Similarly, if there is a process
difference among test stencil apertures
pad size and pad space. The list of major the precision stencil printing process;
because of location of the aperture arrange-
attributes that pose significant opportunity conceivably, just one or two aperture pat-
ment, a newly established precision print
for variation in transfer efficiency should be terns get consideration for an alternative
process from a non-representative aperture
further considered. Figure 16 suggests theo- solder deposition during the miniaturized
arrangement (in the test stencil) could also
retical test design proposal alternatives for assembly. Among 40 aperture patterns, it
show bogus results. It’s not merely the pad
0.3 mm pitch. Note that the combined size could be determined certain aperture pat-
size, pad space, mask design, and aperture
and space measure 0.3 mm. The opportuni- terns can be eliminated from the stencil (in
manufacturing technology, but also the
ty for test vehicle attributes that contribute the actual manufacturing process strategy)
comprehensive arrangement of the aperture
to variation in the stencil printing process and these solder joints will be approached
layout could alter the print results.
would start with considerations about the by use of performs, paste dispense, or in-
pad design limitations. Clearly mask design novative jet printing processes. These one
references
tolerance may not be the same at both ends or two aperture patterns normally fit into a
1. Steudel, H. J., and Desruelle P.,
of the size range. The uniform size, shape stencil printing process but although they
“Product Design and Development,”
and locations of board pads may also be a are not the 0.3 mm pitch components, they
Manufacturing in the Nineties, 1992,
consideration. just can’t fit properly in the new product
Van Nostrand Reinhold, pp. 80-84.
The distribution of stencil aperture design. Frequently, alternate solder deposi-
2. Anglin, C., “Improving print perfor-
characteristics is not generally known, but tion processes may prefer alternate units of
mance using area ratio sensitivity analy-
is assumed to be within a tolerance level. measure. Consequently, alternate units and
sis,” Global SMT & Packaging, Vol. 8,
For 0.3 mm pitch arrays on a typical stencil alternate axis settings on box plots could
No. 5, May 2008, pp. 16-20.
design, uniform stencil aperture dimen- be useful. Venn diagrams
9
(for all solder
3. Juran, J.M., and Gyrna, F.M, Quality
sions could conceivably become the most deposition processes) can be devised includ-
Planning and Analysis, 1993 McGraw
significant source for variation in transfer ing the results from transfer efficiency, and
Hill.
efficiency for miniaturized electronics a comparison made from the data between
4. Speitel, K. F., “Measurement As-
assembly. There could be new challenges the variation in transfer efficiency in the
surance,” Handbook of Industrial
from stencil aperture tolerance consider- stencil printing process and other alterna-
Engineering, 1992, John Wiley & Sons,
ations, especially with respect to a variety of tive soldering methods. The point to be
Inc., pp. 2246-2250.
array locations within real product design made is that the preferred units of measure
5. Juran, J.M., and Gyrna, F.M, Quality
layouts. New alternative innovative manu- for axis settings should best convey the mes-
Planning and Analysis, 1993, McGraw
facturing technologies are being tried for sage of the transfer efficiency variation, and
Hill, pp. 193-194.
precision printing processes at new levels of then used to determine the comprehensive
6. IBM, “CBGA Surface Mount Assem-
miniaturization. The method shown in this solution for all soldering on the new prod-
bly and Rework,” User’s Guide, May
paper for reporting the variation in transfer uct design for the actual manufacturing
23, 2002, p. 17.
efficiency could become vitally important, strategy.
7. Steudel, H. J., and Desruelle, P., “Prob-
staggering product design considerations if The method for reporting variation
lem Identification,” Manufacturing
interaction is shown to occur between the in transfer efficiency can be impressively
in the Nineties, 1992, Van Nostrand
distribution of aperture dimensions for a detailed and complex, but can conve-
Reinhold, pp. 89-92.
0.3 mm pitch component array and nearby niently omit necessary attributes merely
8. Racz, L., and Szekely, J, “Estimation
01005 locations, QFNs, or open copper to encourage limited discussion of results
of Solder Volume,” Handbook of Fine
pads for shield attachment. shown. This is a potential concern if the
Pitch Surface Mount Technology, 1994,
Perfecting the stencil printing pro- unrecognized attributes possess character-
Van Nostrand Reinhold, pp. 267-307.
cess also requires perfecting use of visual istic features that contribute to variation.
9. Yeh, Y.-C., “Concepts of Probability,”
software tools. A conventional reporting For example, if a new product introduction
Handbook of Industrial Engineering,
approach that only presents data in a tradi- design is to include a 0.3 mm pitch array
1992, John Wiley & Sons, Inc., pp.
tional set of metric units may need change. closely surrounded by 01005 components,
2401-2406
The axis settings of the figures should be nearby QFNs with ground pads, and enor-
well labeled with clearly marked units, but mous open copper pad for shields, then a
Chris Anglin, a technical support engineer
preferred units of measure may alternatively test vehicle with a similar design has the
with Indium Corporation, has over 15 years of
be selected to better convey visual presenta- opportunity to indicate variation in transfer
experience in advanced process development, new
tion of transfer efficiency. For example, efficiency from print test trials. Print test
product introduction, and electronics assembly
slight variation of cubic micron units could trials using various innovative stencil
manufacturing. He has a master’s degree in
be a recognizable concern. But, variation manufacturing technologies could indicate
Industrial Engineering from the State University
expressed in cubic mils or nanoliters may their viability in the precision print process
of New York at Binghamton. He is trained in
allow for a more clear understanding. as measured by the variation in transfer
Six Sigma Black Belt programs and is also an
Consider 38-40 aperture patterns are in efficiency. However, this would only be
SMTA-certified process engineer.
18 – Global SMT & Packaging – August 2009
www.globalsmt.net
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