01005 assembly process—from the board design to reflow
01005 assembly process—
from the board design to
reflow
by Norbert Heilmann, Siemens AG, Munich, Germany
introduction
The trend towards ever
01005 components challenge all processes
smaller components and more
in the assembly sequence because of their
function density continues
size: 0.2 mm by 0.4 mm. They are almost
invisible, at least for the naked eye, and
unabated in the SMT field.
extremely lightweight (0.04 mg). With those
Manufacturers and users
facts in mind it is easy to understand that
must increasingly coordinate
the whole assembly process, but even more
their activities to develop
importantly, the materials and the layout of
usable and cost-effective the PCBs, must be designed for the use of
solutions. these components.
Now, which process steps or topics need
Figure 2. NSMD pad, SMD pad and semi-SMD pad,
to be looked at closer? Of course, the first
respectively.
question to ask is if 01005s should be used
Keywords: 01005, PCB or not. And, if so, what benefit do they
Design, Pad Layout, Solder offer? When these questions are answered,
and reflow?
Paste Printing, Component
design and layout should begin.
Looking into these processes, we
Once the PCB is created, the solder
found out that all three types do not show
Placement, Reflow
paste application is the next crucial step.
a significant difference in how close two
Since this step contributes significantly to
adjacent components (gap) can be arranged
the quality of the finished (reflowed) board,
on a PCB without creating any electrical or
any effort to be successful here is worth it.
manufacturing problems. Relative to the
For the placement of these ‘dust-particle-
PCB-manufacturing, the solder paste print-
like’ components, correct and reliable
ing, or component placement we discovered
pickup is the key to a smooth placement
the following:
process. Reflowing 01005s, however, is not
• For all three types the minimum
really different from soldering bigger passive
gap should not be less than 150
components.
µm.
• The limiting factor for the board
pcB design and pad layout
is the registration tolerance of
In surface mount technology (SMT) typically
the solder mask, which today is
non-solder-mask-defined (NSMD) pads are
around +/- 50 µm.
used. However, when it comes to small pas-
• For solder paste printing it is
sive components, some people tend to use
important that the remaining
solder-mask-defined (SMD) pads. In Figure 2
stencil material between two
the different appearance of both pad types
openings has enough mechani-
can be seen. On the left, the NSMD pad
cal strength so that no damage
with the typical opening of the solder mask
occurs.
is shown, and on the right the SMD pad,
• The SMD or the semi-SMD pad
where the copper extends underneath the
has the advantage that the sten-
solder mask, can be seen.
cil sits on top of the solder mask
Recently a combination of the two pad
and therefore seals securely.
types, a so-called semi-solder-mask-defined
• The solder mask is also stabi-
pad has been invented, and it seems to have
lizing the bottom layer of the
some advantages compared to the other two.
solder balls of the printed solder
When comparing the three pad types,
paste layer. This results in a
Figure 1. 01005 capacitors and resistors
the question is do they behave any different-
better-defined print.
ly during solder paste printing, placement
12 – Global SMT & Packaging – September 2008
www.globalsmt.net
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