Parallel print & inspection processes to achieve 100% post-print inspection
Parallel print & inspection
processes to achieve 100%
post-print inspection
by Wolfram Hübsch, ERSA GmbH, Wertheim, Germany
Today’s PCB manufacturing facilities are • Solder joint inspection
As the first process step in increasingly under pressure to guarantee • Electronic final testing.
an SMT production line,
and document process quality. This As the first process step, the solder
applies in particular to the most difficult paste printing process must be assigned a
solder paste printing is of
SMT production task; the solder paste key importance for the quality of an SMT
key importance. Errors here
printing process. production line. Errors that occur here
can lead to costly repairs if
In order to secure the competitiveness can affect the product in all other process
of SMT production, it is necessary to steps, making a correction more expensive
they’re not caught before the
establish processes and procedures in as you move down the line, because the
product moves up the line. Yet
an economical manner. Highly efficient cost of repairing the component increases
according to current studies,
‘slim’ production is necessary in order to with each additional process step.
counteract the global increase in price Due to the vast number of factors that
only 20% of SMT production pressure and remain profitable in the influence the printing process, there is a
lines have implemented 100%
long term. Unfortunately, however, the very high share of potential problems that
increasing demands on the production are directly related to this task. According
post-print inspection. However,
processes due to miniaturisation (0201, to an analysis by C.H. Mangin (Figure 2),
100% post-print inspection 01005, CSP, etc.), new processes (COB) the printing process represents the highest
with traditional methods comes
and increasing quality requirements risk of error with a 64% share of all possible
(3 and 6 Sigma) can adversely affect the causes for defects in the total SMT process.
with high time and labour
economic efficiency of a production line. It therefore makes the most sense to
costs. New technologies are
The European and American markets monitor and correct problems here at the
needed to make 100% post-
in particular are continually looking printing step. 100% post-print inspection
to reduce associated labour costs. This is the only correct way to decrease and/or
print inspection viable for the
results in fewer operators having to take completely avoid printer-related defects.
average manufacturer in order
on ever more complex tasks throughout Current studies have shown, however, that
to keep competitive in a highly
the production line. The usual tasks such only 20% of SMT production lines have
as feeding process materials (solder paste, implemented 100% post-print inspection.
competitive industry. components etc.) can be handled by even The logic here is elusive.
less qualified personnel. Faults can occur
continuously as a result of an unstable
Keywords: Stencil Printing,
process step or a high share of pseudo-
Solder Paste Printing,
errors in a post-print inspection test, for
Post-Print Inspection, Quality
example. These process line problems must
also be handled by operators. Whenever
an operator is required, operator training is
Loader Printer Pick & Place Reflow Unloader
required, and subjectivity is thus brought
into the total quality equation.
In the past, an SMT line used to be
comprised of three core processes: paste
printing, component placement and
reflow soldering.
Today, the SMT line also involves
AOI
AOI
Pick & Place
Solder joint
more demanding monitoring processes to
AOI
ensure quality (Figure 1):
Paste inspection
Electronic final test
• Solder paste inspection
• Traceability (data matrix code
Figure 1. Additional process steps in today’s
& barcode)
SMT line.
• Placement inspection & control
42 – Global SMT & Packaging - August 2008 www.globalsmt.net
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