Optimizing batch cleaning for removing lead-free flux residues on PCAs
Optimizing batch cleaning
for removing lead-free flux
residues on PCAs
by Steve Stach, Austin American Corporation, Bernet, TX, USA, and Mike Bixenman, DBA, Kyzen
Corporation, Nashville, TN, USA
introduction
mils that were fully filled with flux (Figures
Electronic assembly cleaning
High growth electronic products require
1 and 2). The core research of this paper
processes are becoming increas-
performance on demand, and miniaturiza-
focuses on this cleaning challenge because
ingly more complex because of
tion is accelerating the need for thinner
it is considered one of the most difficult
and highly dense circuitry. Miniaturization
global environmental mandates
cleaning challenges faced by manufacturing
is constantly imposing new criteria and
and customer-driven product
engineers when designing cleaning processes
challenges on the cleaning process. One
that achieve the demands of building today’s
performance requirements.
such challenge is the removal of all soldering
circuit designs.
Manufacturing strategies today residues adjacent to fine pitch components
Test boards were built and populated
require process equivalence. That and under Z-axis area array, leadless chip
with 1210 and 1825 chip cap resistors using
is to say, if a product is made or
carriers and chip cap components.
one eutectic and five lead-free solder pastes.
modified in different locations
Aqueous inline spray-in-air in combina-
The solder pastes represent leading low resi-
or processes around the world,
tion with engineered cleaning materials
due, and in some applications, eutectic and
the result should be the same.
create a path for removing surface and Z-axis
lead-free no-clean soldering materials. The
residues from the populated circuit assem-
If cleaning is a requirement,
research studied process variables needed to
bly. The problem is that not all manufactur-
will existing electronic assembly
remove flux residues under the Z-axis using
ing operations have the capacity, utilities
an aqueous batch dishwasher style cleaning
cleaning processes meet the chal-
or floor space to support an aqueous inline
equipment.
lenge? Innovative cleaning fluid cleaning process. ‘Process equivalence’
and cleaning equipment designs (the ability for spot cleaning, batch and
The research in practice—
provide improved functionality in
inline cleaning equivalence) is a core need
applying the data findings
both batch and continuous inline
within electronic assembly manufacturing
Inspection standards are designed around
cleaning processes. The purpose
operations. The focus of this research is
what we can see or what we can dissolve.
of this designed experiment is to
to develop process variables that provide
If the flux remains trapped under tightly
process equivalence between aqueous inline
spaced components, we probably will not
report optimized cleaning process
and batch cleaning processes for cleaning
see it, and we may not measure it on a clean-
parameters for removing lead-free
flux residues under the Z-axis.
liness test. In reality, an assembly could meet
flux residues on populated circuit
the IPC ‘ROSE’ cleanliness test and the
assemblies using innovative
The research in brief—the core research
visual inspection standards with significant
cleaning fluid and batch cleaning
With the advent of SMT in the 1980’s,
quantities of flux remaining under surface
a need arose to clean gaps of less than 5
equipment designs.
resistors, capacitors, transistors, LCCs, and
other tightly spaced ‘leadless’ components.
In this study, components were removed
both physically and with de-soldering tools
Keywords: Batch Cleaning,
to grade the flux remaining.
Inline Cleaning, Process
Equivalence, Process Cleaning
Rate
!
Figure 1. Heavily populated printed circuit assembly
Article originally published in the SMTA with leadless chip carriers (one removed to show flux Figure 2. Flux filling the gap under a chip cap
International 2008 conference proceedings. residue).
resistor.
12 – Global SMT & Packaging – September 2008 www.globalsmt.net
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