Vapor phase vs. convection reflow in RoHS-compliant assembly
Vapor phase vs. convection
reflow in RoHS-compliant
assembly
by Dan Coada, EPIC Technologies, Norwalk, OH USA
introduction
to consider in volume manufacturing.
The contract manufacturing in-
Vapor phase (VP) reflow technology has
Today’s VP reflow process makes use of
dustry is changing rapidly from
been in existence since the early 1970s as a
the heat produced by a boiling fluorinated
lead-based soldering to lead-free
reflow process for surface mount technol-
polymer or fluid. This boiling fluid pro-
soldering. There is no stopping
ogy (SMT) assemblies. While used for some
duces a uniform temperature zone (vapor
the transition or the reality that
defense applications and in smaller volume
blanket) in which the PCBA is exposed for
production settings, the disadvantages
lead-free components are going
solder purposes. Heat is transferred to the
associated with the initial processing tech-
to be introduced in lead-based
PCBA as it is immersed into the vapor area
nology limited its widespread acceptance.
processes. This challenge to
until the PCBA reaches temperature equi-
These disadvantages included environmen-
librium with the boiling point of the fluid.
engineering and quality is a
tal concerns about the fluids being used,
The primary soldering benefits of VP in
huge concern and one that needs throughput limitations, applicability only
comparison to infrared (IR) or convection
scrutiny and a watchful eye. to single-sided printed circuit board as-
include an oxygen free (inert) environment
EMS providers rely on compo-
semblies (PCBAs) and an inherent problem
without the need for nitrogen, fixed upper
nent suppliers to ensure that the
with tombstoning.
temperature exposure and superior heat
lead-free transition on the com-
Advances in VP technology have
transfer on thermally challenged PCBAs.
ponent terminations is seamless
addressed many of these shortcomings
VP also offers distinct advantages
to their soldering processes, but
through continued development of im-
in the realm of lead-free soldering. Key
that rarely happens. Termina-
proved machines, chemical selections and
benefits include a lower peak reflow
process controls. Doublesided PCBAs are
tion changes require additional
temperature, an inert environment without
easily processed in current equipment. As a
modification to solder profiles
nitrogen, improved solder wetting and flow
result, VP is becoming a viable alternative
and a reduction in profiling time
and flux chemistries in order to
ensure proper wetting of the sol-
der to the lead-free termination.
The need for nitrogen to be used
in convection reflow is becoming
a requirement more than an op-
tion, and nitrogen is costly.
This paper will look at the
advantages and disadvantages
of vapor phase (VP) and convec-
tion reflow in RoHS-compliant
processing and discuss associ-
ated design for manufacturing
(DFM) issues.
Keywords: Vapor Phase,
Convection Reflow, IR Reflow,
Lead-Free
This paper was originally published in the
proceedings of the SMTA International
Conference, Orlando, Florida, August 2008.
Figure 1. Vapor phase soldered, lead free, ENIG surface fnish (U26 partially removed in shear/tensile test).
20 – Global SMT & Packaging – March 2009
www.globalsmt.net
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