PCB layout and soldering nozzle design in selective soldering processes
PCB layout and soldering
nozzle design in selective
soldering processes
by Reiner Zoch, SEHO Systems GmbH, Kreuzwertheim, Germany
initial situation
an assembly, however, are processed simulta-
The ability to reduce produc- Most frequently a selective soldering process
neously, multi-nozzle dip soldering processes
tion costs while maintaining
cannot be realized because of missing clear-
are featured with a short cycle time that
a consistent high quality
ance between the solder joint and neighbor-
ranges between 20 seconds and 30 seconds.
is essential. Densely popu-
ing components, such as
Most machine systems do not feature solder-
lated multilayer boards and
• SMDs which might be washed off
ing with an angle.
miniaturized, high-pin-count, during the process or
Both processes, at least partially, de-
fine-pitch devices cannot
• housings of other leaded compo-
mand different design rules.
be efficiently repaired with
nents which could be touched and
high quality. Manual repair
damaged by the solder nozzle.
pcB design rules
soldering processes can cause
In many other cases, solder bridges and poor
To avoid problems during selective solder-
enormous thermal problems
hole fill are the main reasons for faults. In
ing processes, PCB design rules are mainly
with lead-free applications.
addition, solder balls can cause difficulties.
related to clearance areas around the solder
‘Hidden costs,’ such as
The solder’s pull-off behavior, which is in-
joints. Measures also can be taken to im-
productivity rates, opera-
fluenced by several factors, is what is mainly
prove hole fill, such as correct component
responsible for reliable soldering results in
tor training and damaged
lead length, a proper ratio between the pin
the selective soldering process.
assembly costs, have to be
diameter and the via, thermal decoupling,
In general, one has to distinguish be-
taken into consideration as
etc.
tween the different selective wave soldering
well—the target, therefore, is
To reduce the risk of solder bridging,
processes.
a zero-fault selective soldering
the pitch between the component leads and
Selective soldering as a single miniwave
process.
length of the leads need to be considered,
process (Figure 1) can be performed in either
but a special soldering nozzle design can
Appropriate printed
a drag or a dip soldering mode and allows
help to minimize solder bridges.
circuit board design is
soldering with an angle. This offers a high
Another issue is solder balling, which can
important: pad shapes, their
flexibility and fewer restrictions with regard
also be reduced by proper board design or a
distance in relation to each
to board design; however, depending on
special soldering nozzle design.
other, the distance between a
the number of joints to be soldered, single
miniwave processes show a longer cycle time.
pad to be soldered and an ad-
clearance around the solder joints
Typical cycle times range between one and
joining one that is not to be
To perform a reliable soldering process, the
ten minutes.
wetted, the distance between
minimum allowed inner diameter of a single
Multi-nozzle dip soldering processes
individual pins, the length
miniwave soldering nozzle is 3 mm, which
(Figure 2), on the other hand, use product-
of these pins—all need to be
corresponds to an outer diameter of 4 mm.
specific solder nozzle tools, which results in
Minimum external dimensions for a solder-
taken into account. a certain inflexibility. As all solder joints of
Choosing the correct
soldering nozzle is the other
half of the equation.
Keywords: Selective
Soldering, PCB Design,
Solder Nozzles, Hole Fill,
Solder Bridging
This paper was originally presented
Figure 1. Single nozzle miniwave process. Figure 2. Multi-mozzle dip process.
at CEMCONEX 2008.
16 – Global SMT & Packaging – January 2009 www.globalsmt.net
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